Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/mscorlib/system/text/basecodepageencoding.cs

@@ -0,0 +1,355 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+#if FEATURE_CODEPAGES_FILE
+namespace System.Text
+{
+    using System;
+    using System.Diagnostics.Contracts;
+    using System.Globalization;
+    using System.Runtime.InteropServices;
+    using System.Security;
+    using System.Collections;
+    using System.Runtime.CompilerServices;
+    using System.Runtime.Serialization;
+    using System.Runtime.Versioning;
+    using System.Security.Permissions;
+    using Microsoft.Win32.SafeHandles;
+
+    // Our input file data structures look like:
+    //
+    // Header Structure Looks Like:
+    //   struct NLSPlusHeader
+    //   {
+    //       WORD[16]    filename;       // 32 bytes
+    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3, 2, 0, 0
+    //       WORD        count;          // 2 bytes = 42     // Number of code page index's that'll follow
+    //   }
+    //
+    // Each code page section looks like:
+    //   struct NLSCodePageIndex
+    //   {
+    //       WORD[16]    codePageName;   // 32 bytes
+    //       WORD        codePage;       // +2 bytes = 34
+    //       WORD        byteCount;      // +2 bytes = 36
+    //       DWORD       offset;         // +4 bytes = 40    // Bytes from beginning of FILE.
+    //   }
+    //
+    // Each code page then has its own header
+    //   struct NLSCodePage
+    //   {
+    //       WORD[16]    codePageName;   // 32 bytes
+    //       WORD[4]     version;        // 8 bytes = 40     // I.e: 3.2.0.0
+    //       WORD        codePage;       // 2 bytes = 42
+    //       WORD        byteCount;      // 2 bytes = 44     // 1 or 2 byte code page (SBCS or DBCS)
+    //       WORD        unicodeReplace; // 2 bytes = 46     // default replacement unicode character
+    //       WORD        byteReplace;    // 2 bytes = 48     // default replacement byte(s)
+    //       BYTE[]      data;           // data section
+    //   }
+
+    [Serializable]
+    internal abstract class BaseCodePageEncoding : EncodingNLS, ISerializable
+    {
+        // Static & Const stuff
+        internal const String CODE_PAGE_DATA_FILE_NAME = "codepages.nlp";
+        [NonSerialized]
+        protected int dataTableCodePage;
+
+        // Variables to help us allocate/mark our memory section correctly
+        [NonSerialized]
+        protected bool bFlagDataTable = true;
+        [NonSerialized]
+        protected int iExtraBytes = 0;
+
+        // Our private unicode to bytes best fit array and visa versa.
+        [NonSerialized]
+        protected char[] arrayUnicodeBestFit = null;
+        [NonSerialized]
+        protected char[] arrayBytesBestFit = null;
+
+        // This is used to help ISCII, EUCJP and ISO2022 figure out they're MlangEncodings
+        [NonSerialized]
+        protected bool m_bUseMlangTypeForSerialization = false;
+
+        [System.Security.SecuritySafeCritical] // static constructors should be safe to call
+        static BaseCodePageEncoding()
+        {
+        }
+
+        //
+        // This is the header for the native data table that we load from CODE_PAGE_DATA_FILE_NAME.
+        //
+        // Explicit layout is used here since a syntax like char[16] can not be used in sequential layout.
+        [StructLayout(LayoutKind.Explicit)]
+        internal unsafe struct CodePageDataFileHeader
+        {
+            [FieldOffset(0)]
+            internal char TableName;            // WORD[16]
+            [FieldOffset(0x20)]
+            internal ushort Version;            // WORD[4]
+            [FieldOffset(0x28)]
+            internal short CodePageCount;       // WORD
+            [FieldOffset(0x2A)]
+            internal short unused1;             // Add a unused WORD so that CodePages is aligned with DWORD boundary.
+                                                // Otherwise, 64-bit version will fail.
+            [FieldOffset(0x2C)]
+            internal CodePageIndex CodePages;   // Start of code page index
+        }
+
+        [StructLayout(LayoutKind.Explicit, Pack=2)]
+        internal unsafe struct CodePageIndex
+        {
+            [FieldOffset(0)]
+            internal char CodePageName;     // WORD[16]
+            [FieldOffset(0x20)]
+            internal short CodePage;        // WORD
+            [FieldOffset(0x22)]
+            internal short ByteCount;       // WORD
+            [FieldOffset(0x24)]
+            internal int Offset;            // DWORD
+        }
+
+        [StructLayout(LayoutKind.Explicit)]
+        internal unsafe struct CodePageHeader
+        {
+            [FieldOffset(0)]
+            internal char CodePageName;     // WORD[16]
+            [FieldOffset(0x20)]
+            internal ushort VersionMajor;   // WORD
+            [FieldOffset(0x22)]
+            internal ushort VersionMinor;   // WORD
+            [FieldOffset(0x24)]
+            internal ushort VersionRevision;// WORD
+            [FieldOffset(0x26)]
+            internal ushort VersionBuild;   // WORD
+            [FieldOffset(0x28)]
+            internal short CodePage;        // WORD
+            [FieldOffset(0x2a)]
+            internal short ByteCount;       // WORD     // 1 or 2 byte code page (SBCS or DBCS)
+            [FieldOffset(0x2c)]
+            internal char UnicodeReplace;   // WORD     // default replacement unicode character
+            [FieldOffset(0x2e)]
+            internal ushort ByteReplace;    // WORD     // default replacement bytes
+            [FieldOffset(0x30)]
+            internal short FirstDataWord;   // WORD[]
+        }
+
+        // Initialize our global stuff
+        [SecurityCritical]
+        unsafe static CodePageDataFileHeader* m_pCodePageFileHeader = 
+            (CodePageDataFileHeader*)GlobalizationAssembly.GetGlobalizationResourceBytePtr(
+                typeof(CharUnicodeInfo).Assembly, CODE_PAGE_DATA_FILE_NAME);
+
+        // Real variables
+        [NonSerialized]
+        [SecurityCritical]
+        unsafe protected CodePageHeader* pCodePage = null;
+
+        // Safe handle wrapper around section map view
+        [System.Security.SecurityCritical] // auto-generated
+        [NonSerialized]
+        protected SafeViewOfFileHandle safeMemorySectionHandle = null;
+
+        // Safe handle wrapper around mapped file handle
+        [System.Security.SecurityCritical] // auto-generated
+        [NonSerialized]
+        protected SafeFileMappingHandle safeFileMappingHandle = null;
+
+        [System.Security.SecurityCritical]  // auto-generated
+        internal BaseCodePageEncoding(int codepage) : this(codepage, codepage)
+        {
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        internal BaseCodePageEncoding(int codepage, int dataCodePage) :
+            base(codepage == 0? Microsoft.Win32.Win32Native.GetACP(): codepage)
+        {
+            // Remember number of code page that we'll be using the table for.
+            dataTableCodePage = dataCodePage;
+            LoadCodePageTables();
+        }
+
+        // Constructor called by serialization.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal BaseCodePageEncoding(SerializationInfo info, StreamingContext context) : base(0)
+        {
+            // We cannot ever call this, we've proxied ourselved to CodePageEncoding
+            throw new ArgumentNullException("this");
+        }
+
+        // ISerializable implementation
+#if FEATURE_SERIALIZATION
+        [System.Security.SecurityCritical]  // auto-generated_required
+        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            // Make sure to get teh base stuff too This throws if info is null
+            SerializeEncoding(info, context);
+            Contract.Assert(info!=null, "[BaseCodePageEncoding.GetObjectData] Expected null info to throw");
+
+            // Just need Everett maxCharSize (BaseCodePageEncoding) or m_maxByteSize (MLangBaseCodePageEncoding)
+            info.AddValue(m_bUseMlangTypeForSerialization ? "m_maxByteSize" : "maxCharSize",
+                          this.IsSingleByte ? 1 : 2);
+
+            // Use this class or MLangBaseCodePageEncoding as our deserializer.
+            info.SetType(m_bUseMlangTypeForSerialization ? typeof(MLangCodePageEncoding) :
+                                                           typeof(CodePageEncoding));
+        }
+#endif
+
+        // We need to load tables for our code page
+        [System.Security.SecurityCritical]  // auto-generated
+        private unsafe void LoadCodePageTables()
+        {
+            CodePageHeader* pCodePage = FindCodePage(dataTableCodePage);
+
+            // Make sure we have one
+            if (pCodePage == null)
+            {
+                // Didn't have one
+                throw new NotSupportedException(
+                    Environment.GetResourceString("NotSupported_NoCodepageData", CodePage));
+            }
+
+            // Remember our code page
+            this.pCodePage = pCodePage;
+
+            // We had it, so load it
+            LoadManagedCodePage();
+        }
+
+        // Look up the code page pointer
+        [System.Security.SecurityCritical]  // auto-generated
+        private static unsafe CodePageHeader* FindCodePage(int codePage)
+        {
+            // We'll have to loop through all of the m_pCodePageIndex[] items to find our code page, this isn't
+            // binary or anything so its not monsterously fast.
+            for (int i = 0; i < m_pCodePageFileHeader->CodePageCount; i++)
+            {
+                CodePageIndex* pCodePageIndex = (&(m_pCodePageFileHeader->CodePages)) + i;
+
+                if (pCodePageIndex->CodePage == codePage)
+                {
+                    // Found it!
+                    CodePageHeader* pCodePage =
+                        (CodePageHeader*)((byte*)m_pCodePageFileHeader + pCodePageIndex->Offset);
+                    return pCodePage;
+                }
+            }
+
+            // Couldn't find it
+            return null;
+        }
+
+        // Get our code page byte count
+        [System.Security.SecurityCritical]  // auto-generated
+        internal static unsafe int GetCodePageByteSize(int codePage)
+        {
+            // Get our code page info
+            CodePageHeader* pCodePage = FindCodePage(codePage);
+
+            // If null return 0
+            if (pCodePage == null)
+                return 0;
+
+            Contract.Assert(pCodePage->ByteCount == 1 || pCodePage->ByteCount == 2,
+                "[BaseCodePageEncoding] Code page (" + codePage + ") has invalid byte size (" + pCodePage->ByteCount + ") in table");
+            // Return what it says for byte count
+            return pCodePage->ByteCount;
+        }
+
+        // We have a managed code page entry, so load our tables
+        [System.Security.SecurityCritical]
+        protected abstract unsafe void LoadManagedCodePage();
+
+        // Allocate memory to load our code page
+        [System.Security.SecurityCritical]  // auto-generated
+        [ResourceExposure(ResourceScope.None)]
+        [ResourceConsumption(ResourceScope.Machine, ResourceScope.Machine)]
+        protected unsafe byte* GetSharedMemory(int iSize)
+        {
+            // Build our name
+            String strName = GetMemorySectionName();
+
+            IntPtr mappedFileHandle;
+
+            // This gets shared memory for our map.  If its can't, it gives us clean memory.
+            Byte *pMemorySection = EncodingTable.nativeCreateOpenFileMapping(strName, iSize, out mappedFileHandle);
+            Contract.Assert(pMemorySection != null,
+                "[BaseCodePageEncoding.GetSharedMemory] Expected non-null memory section to be opened");
+
+            // If that failed, we have to die.
+            if (pMemorySection == null)
+                throw new OutOfMemoryException(
+                    Environment.GetResourceString("Arg_OutOfMemoryException"));
+
+            // if we have null file handle. this means memory was allocated after 
+            // failing to open the mapped file.
+            
+            if (mappedFileHandle != IntPtr.Zero)
+            {
+                safeMemorySectionHandle = new SafeViewOfFileHandle((IntPtr) pMemorySection, true);
+                safeFileMappingHandle = new SafeFileMappingHandle(mappedFileHandle, true);
+            }
+
+            return pMemorySection;
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        protected unsafe virtual String GetMemorySectionName()
+        {
+            int iUseCodePage = this.bFlagDataTable ? dataTableCodePage : CodePage;
+
+            String strName = String.Format(CultureInfo.InvariantCulture, "NLS_CodePage_{0}_{1}_{2}_{3}_{4}",
+                iUseCodePage, this.pCodePage->VersionMajor, this.pCodePage->VersionMinor,
+                this.pCodePage->VersionRevision, this.pCodePage->VersionBuild);
+
+            return strName;
+        }
+
+        [System.Security.SecurityCritical]
+        protected abstract unsafe void ReadBestFitTable();
+
+        [System.Security.SecuritySafeCritical] // 
+        internal override char[] GetBestFitUnicodeToBytesData()
+        {
+            // Read in our best fit table if necessary
+            if (arrayUnicodeBestFit == null) ReadBestFitTable();
+
+            Contract.Assert(arrayUnicodeBestFit != null,
+                "[BaseCodePageEncoding.GetBestFitUnicodeToBytesData]Expected non-null arrayUnicodeBestFit");
+
+            // Normally we don't have any best fit data.
+            return arrayUnicodeBestFit;
+        }
+
+        [System.Security.SecuritySafeCritical] // 
+        internal override char[] GetBestFitBytesToUnicodeData()
+        {
+            // Read in our best fit table if necessary
+            if (arrayBytesBestFit == null) ReadBestFitTable();
+
+            Contract.Assert(arrayBytesBestFit != null,
+                "[BaseCodePageEncoding.GetBestFitBytesToUnicodeData]Expected non-null arrayBytesBestFit");
+
+            // Normally we don't have any best fit data.
+            return arrayBytesBestFit;
+        }
+
+        // During the AppDomain shutdown the Encoding class may already finalized and the memory section 
+        // is invalid. so we detect that by validating the memory section handle then re-initialize the memory 
+        // section by calling LoadManagedCodePage() method and eventually the mapped file handle and
+        // the memory section pointer will get finalized one more time.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe void CheckMemorySection()
+        {
+            if (safeMemorySectionHandle != null && safeMemorySectionHandle.DangerousGetHandle() == IntPtr.Zero)
+            {
+                LoadManagedCodePage();
+            }
+        }
+    }
+}
+
+#endif // FEATURE_CODEPAGES_FILE

mcs/class/referencesource/mscorlib/system/text/codepageencoding.cs

@@ -0,0 +1,144 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+
+// WARNING:
+//
+// This is just an IObjectReference proxy for the Code Page Encodings.
+namespace System.Text
+{
+    using System;
+    using System.Runtime.Serialization;
+    using System.Security.Permissions;
+    using System.Diagnostics.Contracts;
+
+    /*=================================CodePageEncoding==================================
+    ** This class is here only to deserialize the Code Page classes from Everett (V1.1) into
+    ** Appropriate Whidbey (V2.0) objects.  We also serialize the Whidbey classes
+    ** using this proxy since we pretty much need one anyway and that solves Whidbey
+    ** to Everett compatibility as well.
+    ==============================================================================*/
+
+    [Serializable]
+    internal sealed class CodePageEncoding : ISerializable, IObjectReference
+    {
+        // Temp stuff
+        [NonSerialized]
+        private int m_codePage;
+        [NonSerialized]
+        private bool m_isReadOnly;
+        [NonSerialized]
+        private bool m_deserializedFromEverett = false;
+
+        [NonSerialized]
+        private EncoderFallback encoderFallback = null;
+        [NonSerialized]
+        private DecoderFallback decoderFallback = null;
+
+        // Might need this when GetRealObjecting
+        [NonSerialized]
+        private Encoding realEncoding = null;
+
+        // Constructor called by serialization.
+        internal CodePageEncoding(SerializationInfo info, StreamingContext context)
+        {
+            // Any info?
+            if (info==null) throw new ArgumentNullException("info");
+            Contract.EndContractBlock();
+
+            // All versions have a code page
+            this.m_codePage = (int)info.GetValue("m_codePage", typeof(int));
+
+            // See if we have a code page
+            try
+            {
+                //
+                // Try Whidbey V2.0 Fields
+                //
+                this.m_isReadOnly = (bool)info.GetValue("m_isReadOnly", typeof(bool));
+
+                this.encoderFallback = (EncoderFallback)info.GetValue("encoderFallback", typeof(EncoderFallback));
+                this.decoderFallback = (DecoderFallback)info.GetValue("decoderFallback", typeof(DecoderFallback));
+            }
+            catch (SerializationException)
+            {
+                //
+                // Didn't have Whidbey things, must be Everett
+                //
+                this.m_deserializedFromEverett = true;
+
+                // May as well be read only
+                this.m_isReadOnly = true;
+            }
+        }
+
+        // Just get it from GetEncoding
+        [System.Security.SecurityCritical]  // auto-generated
+        public Object GetRealObject(StreamingContext context)
+        {
+            // Get our encoding (Note: This has default fallbacks for readonly and everett cases)
+            this.realEncoding = Encoding.GetEncoding(this.m_codePage);
+
+            // If its read only then it uses default fallbacks, otherwise pick up the new ones
+            // Otherwise we want to leave the new one read only
+            if (!this.m_deserializedFromEverett && !this.m_isReadOnly)
+            {
+                this.realEncoding = (Encoding)this.realEncoding.Clone();
+                this.realEncoding.EncoderFallback = this.encoderFallback;
+                this.realEncoding.DecoderFallback = this.decoderFallback;
+            }
+
+            return this.realEncoding;
+        }
+
+#if FEATURE_SERIALIZATION
+        // ISerializable implementation
+        [System.Security.SecurityCritical]  // auto-generated_required
+        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            // We cannot ever call this.
+            Contract.Assert(false, "Didn't expect to make it to CodePageEncoding ISerializable.GetObjectData");
+            throw new ArgumentException(Environment.GetResourceString("Arg_ExecutionEngineException"));
+        }
+#endif
+
+        // Same problem with the Decoder, this only happens with Everett Decoders
+        [Serializable]
+        internal sealed class Decoder : ISerializable, IObjectReference
+        {
+            // Might need this when GetRealObjecting
+            [NonSerialized]
+            private Encoding realEncoding = null;
+
+            // Constructor called by serialization, have to handle deserializing from Everett
+            internal Decoder(SerializationInfo info, StreamingContext context)
+            {
+                // Any info?
+                if (info==null) throw new ArgumentNullException("info");
+                Contract.EndContractBlock();
+
+                this.realEncoding = (Encoding)info.GetValue("encoding", typeof(Encoding));
+            }
+
+            // Just get it from GetDecider
+            [System.Security.SecurityCritical]  // auto-generated
+            public Object GetRealObject(StreamingContext context)
+            {
+                return this.realEncoding.GetDecoder();
+            }
+
+#if FEATURE_SERIALIZATION
+            // ISerializable implementation, get data for this object
+            [System.Security.SecurityCritical]  // auto-generated_required
+            void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+            {
+                // We cannot ever call this.
+                Contract.Assert(false, "Didn't expect to make it to CodePageEncoding.Decoder.GetObjectData");
+                throw new ArgumentException(Environment.GetResourceString("Arg_ExecutionEngineException"));
+            }
+#endif
+        }
+    }
+}

mcs/class/referencesource/mscorlib/system/text/decoder.cs

@@ -0,0 +1,351 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System.Runtime.Serialization;
+    using System.Text;
+    using System;
+    using System.Diagnostics.Contracts;
+    // A Decoder is used to decode a sequence of blocks of bytes into a
+    // sequence of blocks of characters. Following instantiation of a decoder,
+    // sequential blocks of bytes are converted into blocks of characters through
+    // calls to the GetChars method. The decoder maintains state between the
+    // conversions, allowing it to correctly decode byte sequences that span
+    // adjacent blocks.
+    //
+    // Instances of specific implementations of the Decoder abstract base
+    // class are typically obtained through calls to the GetDecoder method
+    // of Encoding objects.
+    //
+    [System.Runtime.InteropServices.ComVisible(true)]
+    [Serializable]
+    public abstract class Decoder
+    {
+        internal DecoderFallback         m_fallback = null;
+
+        [NonSerialized]
+        internal DecoderFallbackBuffer   m_fallbackBuffer = null;
+
+        internal void SerializeDecoder(SerializationInfo info)
+        {
+            info.AddValue("m_fallback", this.m_fallback);
+        }
+
+        protected Decoder( )
+        {
+            // We don't call default reset because default reset probably isn't good if we aren't initialized.
+        }
+
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public DecoderFallback Fallback
+        {
+            get
+            {
+                return m_fallback;
+            }
+
+            set
+            {
+                if (value == null)
+                    throw new ArgumentNullException("value");
+                Contract.EndContractBlock();
+
+                // Can't change fallback if buffer is wrong
+                if (m_fallbackBuffer != null && m_fallbackBuffer.Remaining > 0)
+                    throw new ArgumentException(
+                      Environment.GetResourceString("Argument_FallbackBufferNotEmpty"), "value");
+
+                m_fallback = value;
+                m_fallbackBuffer = null;
+            }
+        }
+
+        // Note: we don't test for threading here because async access to Encoders and Decoders
+        // doesn't work anyway.
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public DecoderFallbackBuffer FallbackBuffer
+        {
+            get
+            {
+                if (m_fallbackBuffer == null)
+                {
+                    if (m_fallback != null)
+                        m_fallbackBuffer = m_fallback.CreateFallbackBuffer();
+                    else
+                        m_fallbackBuffer = DecoderFallback.ReplacementFallback.CreateFallbackBuffer();
+                }
+
+                return m_fallbackBuffer;
+            }
+        }
+
+        internal bool InternalHasFallbackBuffer
+        {
+            get
+            {
+                return m_fallbackBuffer != null;
+            }
+        }
+
+        // Reset the Decoder
+        //
+        // Normally if we call GetChars() and an error is thrown we don't change the state of the Decoder.  This
+        // would allow the caller to correct the error condition and try again (such as if they need a bigger buffer.)
+        //
+        // If the caller doesn't want to try again after GetChars() throws an error, then they need to call Reset().
+        //
+        // Virtual implimentation has to call GetChars with flush and a big enough buffer to clear a 0 byte string
+        // We avoid GetMaxCharCount() because a) we can't call the base encoder and b) it might be really big.
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual void Reset()
+        {
+            byte[] byteTemp = {};
+            char[] charTemp = new char[GetCharCount(byteTemp, 0, 0, true)];
+            GetChars(byteTemp, 0, 0, charTemp, 0, true);
+            if (m_fallbackBuffer != null)
+                m_fallbackBuffer.Reset();
+        }
+
+        // Returns the number of characters the next call to GetChars will
+        // produce if presented with the given range of bytes. The returned value
+        // takes into account the state in which the decoder was left following the
+        // last call to GetChars. The state of the decoder is not affected
+        // by a call to this method.
+        //
+        public abstract int GetCharCount(byte[] bytes, int index, int count);
+
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual int GetCharCount(byte[] bytes, int index, int count, bool flush)
+        {
+            return GetCharCount(bytes, index, count);
+        }
+
+        // We expect this to be the workhorse for NLS Encodings, but for existing
+        // ones we need a working (if slow) default implimentation)
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe int GetCharCount(byte* bytes, int count, bool flush)
+        {
+            // Validate input parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes",
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count",
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            byte[] arrbyte = new byte[count];
+            int index;
+
+            for (index = 0; index < count; index++)
+                arrbyte[index] = bytes[index];
+
+            return GetCharCount(arrbyte, 0, count);
+        }
+
+        // Decodes a range of bytes in a byte array into a range of characters
+        // in a character array. The method decodes byteCount bytes from
+        // bytes starting at index byteIndex, storing the resulting
+        // characters in chars starting at index charIndex. The
+        // decoding takes into account the state in which the decoder was left
+        // following the last call to this method.
+        //
+        // An exception occurs if the character array is not large enough to
+        // hold the complete decoding of the bytes. The GetCharCount method
+        // can be used to determine the exact number of characters that will be
+        // produced for a given range of bytes. Alternatively, the
+        // GetMaxCharCount method of the Encoding that produced this
+        // decoder can be used to determine the maximum number of characters that
+        // will be produced for a given number of bytes, regardless of the actual
+        // byte values.
+        //
+        public abstract int GetChars(byte[] bytes, int byteIndex, int byteCount,
+                                        char[] chars, int charIndex);
+
+        public virtual int GetChars(byte[] bytes, int byteIndex, int byteCount,
+                                       char[] chars, int charIndex, bool flush)
+        {
+            return GetChars(bytes, byteIndex, byteCount, chars, charIndex);
+        }
+
+        // We expect this to be the workhorse for NLS Encodings, but for existing
+        // ones we need a working (if slow) default implimentation)
+        //
+        // WARNING WARNING WARNING
+        //
+        // WARNING: If this breaks it could be a security threat.  Obviously we
+        // call this internally, so you need to make sure that your pointers, counts
+        // and indexes are correct when you call this method.
+        //
+        // In addition, we have internal code, which will be marked as "safe" calling
+        // this code.  However this code is dependent upon the implimentation of an
+        // external GetChars() method, which could be overridden by a third party and
+        // the results of which cannot be guaranteed.  We use that result to copy
+        // the char[] to our char* output buffer.  If the result count was wrong, we
+        // could easily overflow our output buffer.  Therefore we do an extra test
+        // when we copy the buffer so that we don't overflow charCount either.
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe int GetChars(byte* bytes, int byteCount,
+                                              char* chars, int charCount, bool flush)
+        {
+            // Validate input parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException(chars == null ? "chars" : "bytes",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteCount < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((byteCount<0 ? "byteCount" : "charCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // Get the byte array to convert
+            byte[] arrByte = new byte[byteCount];
+
+            int index;
+            for (index = 0; index < byteCount; index++)
+                arrByte[index] = bytes[index];
+
+            // Get the char array to fill
+            char[] arrChar = new char[charCount];
+
+            // Do the work
+            int result = GetChars(arrByte, 0, byteCount, arrChar, 0, flush);
+
+            // The only way this could fail is a bug in GetChars
+            Contract.Assert(result <= charCount, "Returned more chars than we have space for");
+
+            // Copy the char array
+            // WARNING: We MUST make sure that we don't copy too many chars.  We can't
+            // rely on result because it could be a 3rd party implimentation.  We need
+            // to make sure we never copy more than charCount chars no matter the value
+            // of result
+            if (result < charCount)
+                charCount = result;
+
+            // We check both result and charCount so that we don't accidentally overrun
+            // our pointer buffer just because of any GetChars bug.
+            for (index = 0; index < charCount; index++)
+                chars[index] = arrChar[index];
+
+            return charCount;
+        }
+
+        // This method is used when the output buffer might not be large enough.
+        // It will decode until it runs out of bytes, and then it will return
+        // true if it the entire input was converted.  In either case it
+        // will also return the number of converted bytes and output characters used.
+        // It will only throw a buffer overflow exception if the entire lenght of chars[] is
+        // too small to store the next char. (like 0 or maybe 1 or 4 for some encodings)
+        // We're done processing this buffer only if completed returns true.
+        //
+        // Might consider checking Max...Count to avoid the extra counting step.
+        //
+        // Note that if all of the input bytes are not consumed, then we'll do a /2, which means
+        // that its likely that we didn't consume as many bytes as we could have.  For some
+        // applications this could be slow.  (Like trying to exactly fill an output buffer from a bigger stream)
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual void Convert(byte[] bytes, int byteIndex, int byteCount,
+                                      char[] chars, int charIndex, int charCount, bool flush,
+                                      out int bytesUsed, out int charsUsed, out bool completed)
+        {
+            // Validate parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException((bytes == null ? "bytes" : "chars"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            bytesUsed = byteCount;
+
+            // Its easy to do if it won't overrun our buffer.
+            while (bytesUsed > 0)
+            {
+                if (GetCharCount(bytes, byteIndex, bytesUsed, flush) <= charCount)
+                {
+                    charsUsed = GetChars(bytes, byteIndex, bytesUsed, chars, charIndex, flush);
+                    completed = (bytesUsed == byteCount &&
+                        (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0));
+                    return;
+                }
+
+                // Try again with 1/2 the count, won't flush then 'cause won't read it all
+                flush = false;
+                bytesUsed /= 2;
+            }
+
+            // Oops, we didn't have anything, we'll have to throw an overflow
+            throw new ArgumentException(Environment.GetResourceString("Argument_ConversionOverflow"));
+        }
+
+        // This is the version that uses *.
+        // We're done processing this buffer only if completed returns true.
+        //
+        // Might consider checking Max...Count to avoid the extra counting step.
+        //
+        // Note that if all of the input bytes are not consumed, then we'll do a /2, which means
+        // that its likely that we didn't consume as many bytes as we could have.  For some
+        // applications this could be slow.  (Like trying to exactly fill an output buffer from a bigger stream)
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe void Convert(byte* bytes, int byteCount,
+                                             char* chars, int charCount, bool flush,
+                                             out int bytesUsed, out int charsUsed, out bool completed)
+        {
+            // Validate input parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException(chars == null ? "chars" : "bytes",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteCount < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((byteCount<0 ? "byteCount" : "charCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // Get ready to do it
+            bytesUsed = byteCount;
+
+            // Its easy to do if it won't overrun our buffer.
+            while (bytesUsed > 0)
+            {
+                if (GetCharCount(bytes, bytesUsed, flush) <= charCount)
+                {
+                    charsUsed = GetChars(bytes, bytesUsed, chars, charCount, flush);
+                    completed = (bytesUsed == byteCount &&
+                        (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0));
+                    return;
+                }
+
+                // Try again with 1/2 the count, won't flush then 'cause won't read it all
+                flush = false;
+                bytesUsed /= 2;
+            }
+
+            // Oops, we didn't have anything, we'll have to throw an overflow
+            throw new ArgumentException(Environment.GetResourceString("Argument_ConversionOverflow"));
+        }
+    }
+}

mcs/class/referencesource/mscorlib/system/text/decoderbestfitfallback.cs

@@ -0,0 +1,249 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// DecoderBestFitFallback.cs
+//
+// This is used internally to create best fit behavior as per the original windows best fit behavior.
+//
+namespace System.Text
+{
+    using System;
+    using System.Text;
+    using System.Threading;
+    using System.Diagnostics.Contracts;
+
+    [Serializable]
+    internal sealed class InternalDecoderBestFitFallback : DecoderFallback
+    {
+        // Our variables
+        internal Encoding encoding = null;
+        internal char[]   arrayBestFit = null;
+        internal char     cReplacement = '?';
+
+        internal InternalDecoderBestFitFallback(Encoding encoding)
+        {
+            // Need to load our replacement characters table.
+            this.encoding = encoding;
+            this.bIsMicrosoftBestFitFallback = true;
+        }
+
+        public override DecoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new InternalDecoderBestFitFallbackBuffer(this);
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return 1;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            InternalDecoderBestFitFallback that = value as InternalDecoderBestFitFallback;
+            if (that != null)
+            {
+                return (this.encoding.CodePage == that.encoding.CodePage);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return this.encoding.CodePage;
+        }
+    }
+
+    internal sealed class InternalDecoderBestFitFallbackBuffer : DecoderFallbackBuffer
+    {
+        // Our variables
+        internal char                   cBestFit = '\0';
+        internal int                    iCount = -1;
+        internal int                    iSize;
+        private InternalDecoderBestFitFallback  oFallback;
+
+        // Private object for locking instead of locking on a public type for SQL reliability work.
+        private static Object s_InternalSyncObject;
+        private static Object InternalSyncObject
+        {
+            get
+            {
+                if (s_InternalSyncObject == null)
+                {
+                    Object o = new Object();
+                    Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
+                }
+                return s_InternalSyncObject;
+            }
+        }
+
+        // Constructor
+        public InternalDecoderBestFitFallbackBuffer(InternalDecoderBestFitFallback fallback)
+        {
+            this.oFallback = fallback;
+
+            if (oFallback.arrayBestFit == null)
+            {
+                // Lock so we don't confuse ourselves.
+                lock(InternalSyncObject)
+                {
+                    // Double check before we do it again.
+                    if (oFallback.arrayBestFit == null)
+                        oFallback.arrayBestFit = fallback.encoding.GetBestFitBytesToUnicodeData();
+                }
+            }
+        }
+
+        // Fallback methods
+        public override bool Fallback(byte[] bytesUnknown, int index)
+        {
+            // We expect no previous fallback in our buffer
+            Contract.Assert(iCount < 1, "[DecoderReplacementFallbackBuffer.Fallback] Calling fallback without a previously empty buffer");
+
+            cBestFit = TryBestFit(bytesUnknown);
+            if (cBestFit == '\0')
+                cBestFit = oFallback.cReplacement;
+
+            iCount = iSize = 1;
+
+            return true;
+        }
+
+        // Default version is overridden in DecoderReplacementFallback.cs
+        public override char GetNextChar()
+        {
+            // We want it to get < 0 because == 0 means that the current/last character is a fallback
+            // and we need to detect recursion.  We could have a flag but we already have this counter.
+            iCount--;
+            
+            // Do we have anything left? 0 is now last fallback char, negative is nothing left
+            if (iCount < 0)
+                return '\0';
+
+            // Need to get it out of the buffer.
+            // Make sure it didn't wrap from the fast count-- path
+            if (iCount == int.MaxValue)
+            {
+                iCount = -1;
+                return '\0';
+            }
+
+            // Return the best fit character
+            return cBestFit;
+        }
+
+        public override bool MovePrevious()
+        {
+            // Exception fallback doesn't have anywhere to back up to.
+            if (iCount >= 0)
+                iCount++;
+
+            // Return true if we could do it.
+            return (iCount >= 0 && iCount <= iSize);
+        }
+
+        // How many characters left to output?
+        public override int Remaining
+        {
+            get
+            {
+                return (iCount > 0) ? iCount : 0;
+            }
+        }
+
+        // Clear the buffer
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe void Reset()
+        {
+            iCount = -1;
+            byteStart = null;
+        }
+
+        // This version just counts the fallback and doesn't actually copy anything.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe override int InternalFallback(byte[] bytes, byte* pBytes)
+        // Right now this has both bytes and bytes[], since we might have extra bytes, hence the
+        // array, and we might need the index, hence the byte*
+        {
+            // return our replacement string Length (always 1 for InternalDecoderBestFitFallback, either
+            // a best fit char or ?
+            return 1;
+        }
+
+        // private helper methods
+        private char TryBestFit(byte[] bytesCheck)
+        {
+            // Need to figure out our best fit character, low is beginning of array, high is 1 AFTER end of array
+            int lowBound = 0;
+            int highBound = oFallback.arrayBestFit.Length;
+            int index;
+            char cCheck;
+
+            // Check trivial case first (no best fit)
+            if (highBound == 0)
+                return '\0';
+
+            // If our array is too small or too big we can't check
+            if (bytesCheck.Length == 0 || bytesCheck.Length > 2)
+                return '\0';
+
+            if (bytesCheck.Length == 1)
+                cCheck = unchecked((char)bytesCheck[0]);
+            else
+                cCheck = unchecked((char)((bytesCheck[0] << 8) + bytesCheck[1]));
+
+            // Check trivial out of range case
+            if (cCheck < oFallback.arrayBestFit[0] || cCheck > oFallback.arrayBestFit[highBound - 2])
+                return '\0';
+
+            // Binary search the array
+            int iDiff;
+            while ((iDiff = (highBound - lowBound)) > 6)
+            {
+                // Look in the middle, which is complicated by the fact that we have 2 #s for each pair,
+                // so we don't want index to be odd because it must be word aligned.
+                // Also note that index can never == highBound (because diff is rounded down)
+                index = ((iDiff / 2) + lowBound) & 0xFFFE;
+
+                char cTest = oFallback.arrayBestFit[index];
+                if (cTest == cCheck)
+                {
+                    // We found it
+                    Contract.Assert(index + 1 < oFallback.arrayBestFit.Length,
+                        "[InternalDecoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array");
+                    return oFallback.arrayBestFit[index + 1];
+                }
+                else if (cTest < cCheck)
+                {
+                    // We weren't high enough
+                    lowBound = index;
+                }
+                else
+                {
+                    // We weren't low enough
+                    highBound = index;
+                }
+            }
+
+            for (index = lowBound; index < highBound; index += 2)
+            {               
+                if (oFallback.arrayBestFit[index] == cCheck)
+                {
+                    // We found it
+                    Contract.Assert(index + 1 < oFallback.arrayBestFit.Length,
+                        "[InternalDecoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array");
+                    return oFallback.arrayBestFit[index + 1];
+                }
+            }
+
+            // Char wasn't in our table            
+            return '\0';
+        }
+    }
+}
+

mcs/class/referencesource/mscorlib/system/text/decoderexceptionfallback.cs

@@ -0,0 +1,158 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// DecoderExceptionFallback.cs
+//
+namespace System.Text
+{
+    using System;
+    using System.Runtime.Serialization;
+    using System.Globalization;
+
+    [Serializable]
+    public sealed class DecoderExceptionFallback : DecoderFallback
+    {
+        // Construction
+        public DecoderExceptionFallback()
+        {
+        }
+
+        public override DecoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new DecoderExceptionFallbackBuffer();
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return 0;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            DecoderExceptionFallback that = value as DecoderExceptionFallback;
+            if (that != null)
+            {
+                return (true);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return 879;
+        }
+    }
+
+
+    public sealed class DecoderExceptionFallbackBuffer : DecoderFallbackBuffer
+    {
+        public override bool Fallback(byte[] bytesUnknown, int index)
+        {
+            Throw(bytesUnknown, index);
+            return true;
+        }
+
+        public override char GetNextChar()
+        {
+            return (char)0;
+        }
+
+        public override bool MovePrevious()
+        {
+            // Exception fallback doesn't have anywhere to back up to.
+            return false;
+        }
+
+        // Exceptions are always empty
+        public override int Remaining
+        {
+            get
+            {
+                return 0;
+            }
+        }
+
+        private void Throw(byte[] bytesUnknown, int index)
+        {
+            // Create a string representation of our bytes.            
+            StringBuilder strBytes = new StringBuilder(bytesUnknown.Length * 3);
+
+            int i;
+            for (i = 0; i < bytesUnknown.Length && i < 20; i++)
+            {
+                strBytes.Append("[");
+                strBytes.Append(bytesUnknown[i].ToString("X2", CultureInfo.InvariantCulture));
+                strBytes.Append("]");
+            }
+            
+            // In case the string's really long
+            if (i == 20)
+                strBytes.Append(" ...");
+
+            // Known index
+            throw new DecoderFallbackException(
+                Environment.GetResourceString("Argument_InvalidCodePageBytesIndex",
+                   strBytes, index), bytesUnknown, index);           
+        }
+
+    }
+
+    // Exception for decoding unknown byte sequences.
+    [Serializable]
+    public sealed class DecoderFallbackException : ArgumentException
+    {
+        byte[]    bytesUnknown = null;
+        int       index = 0;
+
+        public DecoderFallbackException()
+            : base(Environment.GetResourceString("Arg_ArgumentException"))
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        public DecoderFallbackException(String message)
+            : base(message)
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        public DecoderFallbackException(String message, Exception innerException)
+            : base(message, innerException)
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        internal DecoderFallbackException(SerializationInfo info, StreamingContext context) : base(info, context)
+        {
+        }
+
+        public DecoderFallbackException(
+            String message, byte[] bytesUnknown, int index) : base(message)
+        {
+            this.bytesUnknown = bytesUnknown;
+            this.index = index;
+        }
+
+        public byte[] BytesUnknown
+        {
+            get
+            {
+                return (bytesUnknown);
+            }
+        }
+
+        public int Index
+        {
+            get
+            {
+                return this.index;
+            }
+        }
+    }
+}

mcs/class/referencesource/mscorlib/system/text/decoderfallback.cs

@@ -0,0 +1,285 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+//
+using System;
+using System.Security;
+using System.Threading;
+using System.Globalization;
+using System.Diagnostics.Contracts;
+
+namespace System.Text
+{
+    [Serializable]
+    public abstract class DecoderFallback
+    {
+        internal bool                  bIsMicrosoftBestFitFallback = false;
+
+        private static volatile DecoderFallback replacementFallback; // Default fallback, uses no best fit & "?"
+        private static volatile DecoderFallback exceptionFallback;
+
+        // Private object for locking instead of locking on a internal type for SQL reliability work.
+        private static Object s_InternalSyncObject;
+        private static Object InternalSyncObject
+        {
+            get
+            {
+                if (s_InternalSyncObject == null)
+                {
+                    Object o = new Object();
+                    Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
+                }
+                return s_InternalSyncObject;
+            }
+        }
+
+        // Get each of our generic fallbacks.
+
+        public static DecoderFallback ReplacementFallback
+        {
+            get
+            {
+                if (replacementFallback == null)
+                    lock(InternalSyncObject)
+                        if (replacementFallback == null)
+                            replacementFallback = new DecoderReplacementFallback();
+
+                return replacementFallback;
+            }
+        }
+
+
+        public static DecoderFallback ExceptionFallback
+        {
+            get
+            {
+                if (exceptionFallback == null)
+                    lock(InternalSyncObject)
+                        if (exceptionFallback == null)
+                            exceptionFallback = new DecoderExceptionFallback();
+
+                return exceptionFallback;
+            }
+        }
+
+        // Fallback
+        //
+        // Return the appropriate unicode string alternative to the character that need to fall back.
+        // Most implimentations will be:
+        //      return new MyCustomDecoderFallbackBuffer(this);
+
+        public abstract DecoderFallbackBuffer CreateFallbackBuffer();
+
+        // Maximum number of characters that this instance of this fallback could return
+
+        public abstract int MaxCharCount { get; }
+
+        internal bool IsMicrosoftBestFitFallback
+        {
+            get
+            {
+                return bIsMicrosoftBestFitFallback;
+            }
+        }
+    }
+
+
+    public abstract class DecoderFallbackBuffer
+    {
+        // Most implimentations will probably need an implimenation-specific constructor
+
+        // internal methods that cannot be overriden that let us do our fallback thing
+        // These wrap the internal methods so that we can check for people doing stuff that's incorrect
+
+        public abstract bool Fallback(byte[] bytesUnknown, int index);
+
+        // Get next character
+
+        public abstract char GetNextChar();
+
+        // Back up a character
+
+        public abstract bool MovePrevious();
+
+        // How many chars left in this fallback?
+
+        public abstract int Remaining { get; }
+
+        // Clear the buffer
+
+        public virtual void Reset()
+        {
+            while (GetNextChar() != (char)0);
+        }
+
+        // Internal items to help us figure out what we're doing as far as error messages, etc.
+        // These help us with our performance and messages internally
+        [SecurityCritical]
+        internal     unsafe byte*    byteStart;
+        [SecurityCritical]
+        internal     unsafe char*    charEnd;
+
+        // Internal Reset
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe void InternalReset()
+        {
+            byteStart = null;
+            Reset();
+        }
+
+        // Set the above values
+        // This can't be part of the constructor because DecoderFallbacks would have to know how to impliment these.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe void InternalInitialize(byte* byteStart, char* charEnd)
+        {
+            this.byteStart = byteStart;
+            this.charEnd = charEnd;
+        }
+
+        // Fallback the current byte by sticking it into the remaining char buffer.
+        // This can only be called by our encodings (other have to use the public fallback methods), so
+        // we can use our DecoderNLS here too (except we don't).
+        // Returns true if we are successful, false if we can't fallback the character (no buffer space)
+        // So caller needs to throw buffer space if return false.
+        // Right now this has both bytes and bytes[], since we might have extra bytes, hence the
+        // array, and we might need the index, hence the byte*
+        // Don't touch ref chars unless we succeed
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe virtual bool InternalFallback(byte[] bytes, byte* pBytes, ref char* chars)
+        {
+            // Copy bytes to array (slow, but right now that's what we get to do.
+          //  byte[] bytesUnknown = new byte[count];
+//            for (int i = 0; i < count; i++)
+//                bytesUnknown[i] = *(bytes++);
+
+            Contract.Assert(byteStart != null, "[DecoderFallback.InternalFallback]Used InternalFallback without calling InternalInitialize");
+
+            // See if there's a fallback character and we have an output buffer then copy our string.
+            if (this.Fallback(bytes, (int)(pBytes - byteStart - bytes.Length)))
+            {
+                // Copy the chars to our output
+                char ch;
+                char* charTemp = chars;
+                bool bHighSurrogate = false;
+                while ((ch = GetNextChar()) != 0)
+                {
+                    // Make sure no mixed up surrogates
+                    if (Char.IsSurrogate(ch))
+                    {
+                        if (Char.IsHighSurrogate(ch))
+                        {
+                            // High Surrogate
+                            if (bHighSurrogate)
+                                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+                            bHighSurrogate = true;
+                        }
+                        else
+                        {
+                            // Low surrogate
+                            if (bHighSurrogate == false)
+                                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+                            bHighSurrogate = false;
+                        }
+                    }
+
+                    if (charTemp >= charEnd)
+                    {
+                        // No buffer space
+                        return false;
+                    }
+
+                    *(charTemp++) = ch;
+                }
+
+                // Need to make sure that bHighSurrogate isn't true
+                if (bHighSurrogate)
+                    throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+
+                // Now we aren't going to be false, so its OK to update chars
+                chars = charTemp;
+            }
+
+            return true;
+        }
+
+        // This version just counts the fallback and doesn't actually copy anything.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe virtual int InternalFallback(byte[] bytes, byte* pBytes)
+        // Right now this has both bytes and bytes[], since we might have extra bytes, hence the
+        // array, and we might need the index, hence the byte*
+        {
+            // Copy bytes to array (slow, but right now that's what we get to do.
+//            byte[] bytesUnknown = new byte[count];
+//            for (int i = 0; i < count; i++)
+  //              bytesUnknown[i] = *(bytes++);
+
+            Contract.Assert(byteStart != null, "[DecoderFallback.InternalFallback]Used InternalFallback without calling InternalInitialize");
+
+            // See if there's a fallback character and we have an output buffer then copy our string.
+            if (this.Fallback(bytes, (int)(pBytes - byteStart - bytes.Length)))
+            {
+                int count = 0;
+
+                char ch;
+                bool bHighSurrogate = false;
+                while ((ch = GetNextChar()) != 0)
+                {
+                    // Make sure no mixed up surrogates
+                    if (Char.IsSurrogate(ch))
+                    {
+                        if (Char.IsHighSurrogate(ch))
+                        {
+                            // High Surrogate
+                            if (bHighSurrogate)
+                                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+                            bHighSurrogate = true;
+                        }
+                        else
+                        {
+                            // Low surrogate
+                            if (bHighSurrogate == false)
+                                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+                            bHighSurrogate = false;
+                        }
+                    }
+
+                    count++;
+                }
+
+                // Need to make sure that bHighSurrogate isn't true
+                if (bHighSurrogate)
+                    throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex"));
+
+                return count;
+            }
+
+            // If no fallback return 0
+            return 0;
+        }
+
+        // private helper methods
+        internal void ThrowLastBytesRecursive(byte[] bytesUnknown)
+        {
+            // Create a string representation of our bytes.
+            StringBuilder strBytes = new StringBuilder(bytesUnknown.Length * 3);
+            int i;
+            for (i = 0; i < bytesUnknown.Length && i < 20; i++)
+            {
+                if (strBytes.Length > 0)
+                    strBytes.Append(" ");
+                strBytes.Append(String.Format(CultureInfo.InvariantCulture, "\\x{0:X2}", bytesUnknown[i]));
+            }
+            // In case the string's really long
+            if (i == 20)
+                strBytes.Append(" ...");
+
+            // Throw it, using our complete bytes
+            throw new ArgumentException(
+                Environment.GetResourceString("Argument_RecursiveFallbackBytes",
+                    strBytes.ToString()), "bytesUnknown");
+        }
+
+    }
+}

mcs/class/referencesource/mscorlib/system/text/decodernls.cs

@@ -0,0 +1,301 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System.Runtime.Serialization;
+    using System.Security.Permissions;
+    using System.Text;
+    using System;
+    using System.Diagnostics.Contracts;
+    // A Decoder is used to decode a sequence of blocks of bytes into a
+    // sequence of blocks of characters. Following instantiation of a decoder,
+    // sequential blocks of bytes are converted into blocks of characters through
+    // calls to the GetChars method. The decoder maintains state between the
+    // conversions, allowing it to correctly decode byte sequences that span
+    // adjacent blocks.
+    //
+    // Instances of specific implementations of the Decoder abstract base
+    // class are typically obtained through calls to the GetDecoder method
+    // of Encoding objects.
+    //
+
+    [Serializable]
+    internal class DecoderNLS : Decoder, ISerializable
+    {
+        // Remember our encoding
+                        protected   Encoding m_encoding;
+        [NonSerialized] protected   bool     m_mustFlush;
+        [NonSerialized] internal    bool     m_throwOnOverflow;
+        [NonSerialized] internal    int      m_bytesUsed;
+
+#region Serialization
+
+        // Constructor called by serialization. called during deserialization.
+        internal DecoderNLS(SerializationInfo info, StreamingContext context)
+        {
+            throw new NotSupportedException(
+                        String.Format(
+                            System.Globalization.CultureInfo.CurrentCulture, 
+                            Environment.GetResourceString("NotSupported_TypeCannotDeserialized"), this.GetType()));
+        }
+
+#if FEATURE_SERIALIZATION
+        // ISerializable implementation. called during serialization.
+        [System.Security.SecurityCritical]  // auto-generated_required
+        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            SerializeDecoder(info);
+            info.AddValue("encoding", this.m_encoding);
+            info.SetType(typeof(Encoding.DefaultDecoder));
+        }
+#endif
+
+#endregion Serialization 
+
+        internal DecoderNLS( Encoding encoding )
+        {
+            this.m_encoding = encoding;
+            this.m_fallback = this.m_encoding.DecoderFallback;
+            this.Reset();
+        }
+
+        // This is used by our child deserializers
+        internal DecoderNLS( )
+        {
+            this.m_encoding = null;
+            this.Reset();
+        }
+
+        public override void Reset()
+        {
+            if (m_fallbackBuffer != null)
+                m_fallbackBuffer.Reset();
+        }
+
+        public override unsafe int GetCharCount(byte[] bytes, int index, int count)
+        {
+            return GetCharCount(bytes, index, count, false);
+        }
+
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe int GetCharCount(byte[] bytes, int index, int count, bool flush)
+        {
+            // Validate Parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (index < 0 || count < 0)
+                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (bytes.Length - index < count)
+                throw new ArgumentOutOfRangeException("bytes",
+                    Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            Contract.EndContractBlock();
+
+            // Avoid null fixed problem
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            // Just call pointer version
+            fixed (byte* pBytes = bytes)
+                return GetCharCount(pBytes + index, count, flush);
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override int GetCharCount(byte* bytes, int count, bool flush)
+        {
+            // Validate parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes",
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count",
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // Remember the flush
+            this.m_mustFlush = flush;
+            this.m_throwOnOverflow = true;
+
+            // By default just call the encoding version, no flush by default
+            return m_encoding.GetCharCount(bytes, count, this);
+        }
+
+        public override unsafe int GetChars(byte[] bytes, int byteIndex, int byteCount,
+                                             char[] chars, int charIndex)
+        {
+            return GetChars(bytes, byteIndex, byteCount, chars, charIndex, false);
+        }
+
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe int GetChars(byte[] bytes, int byteIndex, int byteCount,
+                                             char[] chars, int charIndex, bool flush)
+        {
+            // Validate Parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if ( bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                    Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (charIndex < 0 || charIndex > chars.Length)
+                throw new ArgumentOutOfRangeException("charIndex",
+                    Environment.GetResourceString("ArgumentOutOfRange_Index"));
+
+            Contract.EndContractBlock();
+
+            // Avoid empty input fixed problem
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            int charCount = chars.Length - charIndex;
+            if (chars.Length == 0)
+                chars = new char[1];
+
+            // Just call pointer version
+            fixed (byte* pBytes = bytes)
+                fixed (char* pChars = chars)
+                    // Remember that charCount is # to decode, not size of array
+                    return GetChars(pBytes + byteIndex, byteCount,
+                                    pChars + charIndex, charCount, flush);
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override int GetChars(byte* bytes, int byteCount,
+                                              char* chars, int charCount, bool flush)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteCount < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((byteCount<0 ? "byteCount" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // Remember our flush
+            m_mustFlush = flush;
+            m_throwOnOverflow = true;
+
+            // By default just call the encoding's version
+            return m_encoding.GetChars(bytes, byteCount, chars, charCount, this);
+        }
+
+        // This method is used when the output buffer might not be big enough.
+        // Just call the pointer version.  (This gets chars)
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe void Convert(byte[] bytes, int byteIndex, int byteCount,
+                                              char[] chars, int charIndex, int charCount, bool flush,
+                                              out int bytesUsed, out int charsUsed, out bool completed)
+        {
+            // Validate parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException((bytes == null ? "bytes" : "chars"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            Contract.EndContractBlock();
+
+            // Avoid empty input problem
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+            if (chars.Length == 0)
+                chars = new char[1];
+
+            // Just call the pointer version (public overrides can't do this)
+            fixed (byte* pBytes = bytes)
+            {
+                fixed (char* pChars = chars)
+                {
+                    Convert(pBytes + byteIndex, byteCount, pChars + charIndex, charCount, flush,
+                        out bytesUsed, out charsUsed, out completed);
+                }
+            }
+        }
+
+        // This is the version that used pointers.  We call the base encoding worker function
+        // after setting our appropriate internal variables.  This is getting chars
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override void Convert(byte* bytes, int byteCount,
+                                              char* chars, int charCount, bool flush,
+                                              out int bytesUsed, out int charsUsed, out bool completed)
+        {
+            // Validate input parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException(chars == null ? "chars" : "bytes",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteCount < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((byteCount<0 ? "byteCount" : "charCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // We don't want to throw
+            this.m_mustFlush = flush;
+            this.m_throwOnOverflow = false;
+            this.m_bytesUsed = 0;
+
+            // Do conversion
+            charsUsed = this.m_encoding.GetChars(bytes, byteCount, chars, charCount, this);
+            bytesUsed = this.m_bytesUsed;
+
+            // Its completed if they've used what they wanted AND if they didn't want flush or if we are flushed
+            completed = (bytesUsed == byteCount) && (!flush || !this.HasState) &&
+                               (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0);
+
+            // Our data thingys are now full, we can return
+        }
+
+        public bool MustFlush
+        {
+            get
+            {
+                return m_mustFlush;
+            }
+        }
+
+        // Anything left in our decoder?
+        internal virtual bool HasState
+        {
+            get
+            {
+                return false;
+            }
+        }
+
+        // Allow encoding to clear our must flush instead of throwing (in ThrowCharsOverflow)
+        internal void ClearMustFlush()
+        {
+            m_mustFlush = false;
+        }
+    }
+}

mcs/class/referencesource/mscorlib/system/text/decoderreplacementfallback.cs

@@ -0,0 +1,212 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// DecoderReplacementFallback.cs
+//
+namespace System.Text
+{
+    using System;
+    using System.Diagnostics.Contracts;
+
+    [Serializable]
+    public sealed class DecoderReplacementFallback : DecoderFallback
+    {
+        // Our variables
+        private String strDefault;
+
+        // Construction.  Default replacement fallback uses no best fit and ? replacement string
+        public DecoderReplacementFallback() : this("?")
+        {
+        }
+
+        public DecoderReplacementFallback(String replacement)
+        {
+            if (replacement == null)
+                throw new ArgumentNullException("replacement");
+            Contract.EndContractBlock();
+
+            // Make sure it doesn't have bad surrogate pairs
+            bool bFoundHigh=false;
+            for (int i = 0; i < replacement.Length; i++)
+            {
+                // Found a surrogate?
+                if (Char.IsSurrogate(replacement,i))
+                {
+                    // High or Low?
+                    if (Char.IsHighSurrogate(replacement, i))
+                    {
+                        // if already had a high one, stop
+                        if (bFoundHigh)
+                            break;  // break & throw at the bFoundHIgh below
+                        bFoundHigh = true;
+                    }
+                    else
+                    {
+                        // Low, did we have a high?
+                        if (!bFoundHigh)
+                        {
+                            // Didn't have one, make if fail when we stop
+                            bFoundHigh = true;
+                            break;
+                        }
+
+                        // Clear flag
+                        bFoundHigh = false;
+                    }
+                }
+                // If last was high we're in trouble (not surrogate so not low surrogate, so break)
+                else if (bFoundHigh)
+                    break;
+            }
+            if (bFoundHigh)
+                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex", "replacement"));
+
+            strDefault = replacement;
+        }
+
+        public String DefaultString
+        {
+             get
+             {
+                return strDefault;
+             }
+        }
+
+        public override DecoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new DecoderReplacementFallbackBuffer(this);
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return strDefault.Length;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            DecoderReplacementFallback that = value as DecoderReplacementFallback;
+            if (that != null)
+            {
+                return (this.strDefault == that.strDefault);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return strDefault.GetHashCode();
+        }
+    }
+
+
+
+    public sealed class DecoderReplacementFallbackBuffer : DecoderFallbackBuffer
+    {
+        // Store our default string
+        private String strDefault;
+        int fallbackCount = -1;
+        int fallbackIndex = -1;
+
+        // Construction
+        public DecoderReplacementFallbackBuffer(DecoderReplacementFallback fallback)
+        {
+            this.strDefault = fallback.DefaultString;
+        }
+
+        // Fallback Methods
+        public override bool Fallback(byte[] bytesUnknown, int index)
+        {
+            // We expect no previous fallback in our buffer
+            // We can't call recursively but others might (note, we don't test on last char!!!)
+            if (fallbackCount >= 1)
+            {
+                ThrowLastBytesRecursive(bytesUnknown);
+            }
+
+            // Go ahead and get our fallback
+            if (strDefault.Length == 0)
+                return false;
+
+            fallbackCount = strDefault.Length;
+            fallbackIndex = -1;
+
+            return true;
+        }
+
+        public override char GetNextChar()
+        {
+            // We want it to get < 0 because == 0 means that the current/last character is a fallback
+            // and we need to detect recursion.  We could have a flag but we already have this counter.
+            fallbackCount--;
+            fallbackIndex++;
+
+            // Do we have anything left? 0 is now last fallback char, negative is nothing left
+            if (fallbackCount < 0)
+                return '\0';
+
+            // Need to get it out of the buffer.
+            // Make sure it didn't wrap from the fast count-- path
+            if (fallbackCount == int.MaxValue)
+            {
+                fallbackCount = -1;
+                return '\0';
+            }
+
+            // Now make sure its in the expected range
+            Contract.Assert(fallbackIndex < strDefault.Length && fallbackIndex >= 0,
+                            "Index exceeds buffer range");
+
+            return strDefault[fallbackIndex];            
+        }
+
+        public override bool MovePrevious()
+        {
+            // Back up one, only if we just processed the last character (or earlier)
+            if (fallbackCount >= -1 && fallbackIndex >= 0)
+            {
+                fallbackIndex--;
+                fallbackCount++;
+                return true;
+            }
+
+            // Return false 'cause we couldn't do it.
+            return false;
+        }
+
+        // How many characters left to output?
+        public override int Remaining
+        {
+            get
+            {
+                // Our count is 0 for 1 character left.
+                return (fallbackCount < 0) ? 0 : fallbackCount;
+            }
+        }
+
+        // Clear the buffer
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe void Reset()
+        {
+            fallbackCount = -1;
+            fallbackIndex = -1;
+            byteStart = null;
+        }
+
+        // This version just counts the fallback and doesn't actually copy anything.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe override int InternalFallback(byte[] bytes, byte* pBytes)
+        // Right now this has both bytes and bytes[], since we might have extra bytes, hence the
+        // array, and we might need the index, hence the byte*
+        {
+            // return our replacement string Length
+            return strDefault.Length;
+        }
+    }
+}
+

mcs/class/referencesource/mscorlib/system/text/encoder.cs

@@ -0,0 +1,344 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System.Runtime.Serialization;
+    using System.Text;
+    using System;
+    using System.Diagnostics.Contracts;
+    // An Encoder is used to encode a sequence of blocks of characters into
+    // a sequence of blocks of bytes. Following instantiation of an encoder,
+    // sequential blocks of characters are converted into blocks of bytes through
+    // calls to the GetBytes method. The encoder maintains state between the
+    // conversions, allowing it to correctly encode character sequences that span
+    // adjacent blocks.
+    //
+    // Instances of specific implementations of the Encoder abstract base
+    // class are typically obtained through calls to the GetEncoder method
+    // of Encoding objects.
+    //
+    [System.Runtime.InteropServices.ComVisible(true)]
+    [Serializable]
+    public abstract class Encoder
+    {
+        internal EncoderFallback         m_fallback = null;
+
+        [NonSerialized]
+        internal EncoderFallbackBuffer   m_fallbackBuffer = null;
+
+        internal void SerializeEncoder(SerializationInfo info)
+        {
+            info.AddValue("m_fallback", this.m_fallback);
+        }
+
+        protected Encoder()
+        {
+            // We don't call default reset because default reset probably isn't good if we aren't initialized.
+        }
+
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public EncoderFallback Fallback
+        {
+            get
+            {
+                return m_fallback;
+            }
+
+            set
+            {
+                if (value == null)
+                    throw new ArgumentNullException("value");
+                Contract.EndContractBlock();
+
+                // Can't change fallback if buffer is wrong
+                if (m_fallbackBuffer != null && m_fallbackBuffer.Remaining > 0)
+                    throw new ArgumentException(
+                      Environment.GetResourceString("Argument_FallbackBufferNotEmpty"), "value");
+
+                m_fallback = value;
+                m_fallbackBuffer = null;
+            }
+        }
+
+        // Note: we don't test for threading here because async access to Encoders and Decoders
+        // doesn't work anyway.
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public EncoderFallbackBuffer FallbackBuffer
+        {
+            get
+            {
+                if (m_fallbackBuffer == null)
+                {
+                    if (m_fallback != null)
+                        m_fallbackBuffer = m_fallback.CreateFallbackBuffer();
+                    else
+                        m_fallbackBuffer = EncoderFallback.ReplacementFallback.CreateFallbackBuffer();
+                }
+
+                return m_fallbackBuffer;
+            }
+        }
+
+        internal bool InternalHasFallbackBuffer
+        {
+            get
+            {
+                return m_fallbackBuffer != null;
+            }
+        }
+
+        // Reset the Encoder
+        //
+        // Normally if we call GetBytes() and an error is thrown we don't change the state of the encoder.  This
+        // would allow the caller to correct the error condition and try again (such as if they need a bigger buffer.)
+        //
+        // If the caller doesn't want to try again after GetBytes() throws an error, then they need to call Reset().
+        //
+        // Virtual implimentation has to call GetBytes with flush and a big enough buffer to clear a 0 char string
+        // We avoid GetMaxByteCount() because a) we can't call the base encoder and b) it might be really big.
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual void Reset()
+        {
+            char[] charTemp = {};
+            byte[] byteTemp = new byte[GetByteCount(charTemp, 0, 0, true)];
+            GetBytes(charTemp, 0, 0, byteTemp, 0, true);
+            if (m_fallbackBuffer != null)
+                m_fallbackBuffer.Reset();
+        }
+
+        // Returns the number of bytes the next call to GetBytes will
+        // produce if presented with the given range of characters and the given
+        // value of the flush parameter. The returned value takes into
+        // account the state in which the encoder was left following the last call
+        // to GetBytes. The state of the encoder is not affected by a call
+        // to this method.
+        //
+        public abstract int GetByteCount(char[] chars, int index, int count, bool flush);
+
+        // We expect this to be the workhorse for NLS encodings
+        // unfortunately for existing overrides, it has to call the [] version,
+        // which is really slow, so avoid this method if you might be calling external encodings.
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe int GetByteCount(char* chars, int count, bool flush)
+        {
+            // Validate input parameters
+            if (chars == null)
+                throw new ArgumentNullException("chars",
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count",
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            char[] arrChar = new char[count];
+            int index;
+
+            for (index = 0; index < count; index++)
+                arrChar[index] = chars[index];
+
+            return GetByteCount(arrChar, 0, count, flush);
+        }
+
+        // Encodes a range of characters in a character array into a range of bytes
+        // in a byte array. The method encodes charCount characters from
+        // chars starting at index charIndex, storing the resulting
+        // bytes in bytes starting at index byteIndex. The encoding
+        // takes into account the state in which the encoder was left following the
+        // last call to this method. The flush parameter indicates whether
+        // the encoder should flush any shift-states and partial characters at the
+        // end of the conversion. To ensure correct termination of a sequence of
+        // blocks of encoded bytes, the last call to GetBytes should specify
+        // a value of true for the flush parameter.
+        //
+        // An exception occurs if the byte array is not large enough to hold the
+        // complete encoding of the characters. The GetByteCount method can
+        // be used to determine the exact number of bytes that will be produced for
+        // a given range of characters. Alternatively, the GetMaxByteCount
+        // method of the Encoding that produced this encoder can be used to
+        // determine the maximum number of bytes that will be produced for a given
+        // number of characters, regardless of the actual character values.
+        //
+        public abstract int GetBytes(char[] chars, int charIndex, int charCount,
+                                        byte[] bytes, int byteIndex, bool flush);
+
+        // We expect this to be the workhorse for NLS Encodings, but for existing
+        // ones we need a working (if slow) default implimentation)
+        //
+        // WARNING WARNING WARNING
+        //
+        // WARNING: If this breaks it could be a security threat.  Obviously we
+        // call this internally, so you need to make sure that your pointers, counts
+        // and indexes are correct when you call this method.
+        //
+        // In addition, we have internal code, which will be marked as "safe" calling
+        // this code.  However this code is dependent upon the implimentation of an
+        // external GetBytes() method, which could be overridden by a third party and
+        // the results of which cannot be guaranteed.  We use that result to copy
+        // the byte[] to our byte* output buffer.  If the result count was wrong, we
+        // could easily overflow our output buffer.  Therefore we do an extra test
+        // when we copy the buffer so that we don't overflow byteCount either.
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe int GetBytes(char* chars, int charCount,
+                                              byte* bytes, int byteCount, bool flush)
+        {
+            // Validate input parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charCount < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // Get the char array to convert
+            char[] arrChar = new char[charCount];
+
+            int index;
+            for (index = 0; index < charCount; index++)
+                arrChar[index] = chars[index];
+
+            // Get the byte array to fill
+            byte[] arrByte = new byte[byteCount];
+
+            // Do the work
+            int result = GetBytes(arrChar, 0, charCount, arrByte, 0, flush);
+
+            // The only way this could fail is a bug in GetBytes
+            Contract.Assert(result <= byteCount, "Returned more bytes than we have space for");
+
+            // Copy the byte array
+            // WARNING: We MUST make sure that we don't copy too many bytes.  We can't
+            // rely on result because it could be a 3rd party implimentation.  We need
+            // to make sure we never copy more than byteCount bytes no matter the value
+            // of result
+            if (result < byteCount)
+                byteCount = result;
+
+            // Don't copy too many bytes!
+            for (index = 0; index < byteCount; index++)
+                bytes[index] = arrByte[index];
+
+            return byteCount;
+        }
+
+        // This method is used to avoid running out of output buffer space.
+        // It will encode until it runs out of chars, and then it will return
+        // true if it the entire input was converted.  In either case it
+        // will also return the number of converted chars and output bytes used.
+        // It will only throw a buffer overflow exception if the entire lenght of bytes[] is
+        // too small to store the next byte. (like 0 or maybe 1 or 4 for some encodings)
+        // We're done processing this buffer only if completed returns true.
+        //
+        // Might consider checking Max...Count to avoid the extra counting step.
+        //
+        // Note that if all of the input chars are not consumed, then we'll do a /2, which means
+        // that its likely that we didn't consume as many chars as we could have.  For some
+        // applications this could be slow.  (Like trying to exactly fill an output buffer from a bigger stream)
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual void Convert(char[] chars, int charIndex, int charCount,
+                                      byte[] bytes, int byteIndex, int byteCount, bool flush,
+                                      out int charsUsed, out int bytesUsed, out bool completed)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            charsUsed = charCount;
+
+            // Its easy to do if it won't overrun our buffer.
+            // Note: We don't want to call unsafe version because that might be an untrusted version
+            // which could be really unsafe and we don't want to mix it up.
+            while (charsUsed > 0)
+            {
+                if (GetByteCount(chars, charIndex, charsUsed, flush) <= byteCount)
+                {
+                    bytesUsed = GetBytes(chars, charIndex, charsUsed, bytes, byteIndex, flush);
+                    completed = (charsUsed == charCount &&
+                        (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0));
+                    return;
+                }
+
+                // Try again with 1/2 the count, won't flush then 'cause won't read it all
+                flush = false;
+                charsUsed /= 2;
+            }
+
+            // Oops, we didn't have anything, we'll have to throw an overflow
+            throw new ArgumentException(Environment.GetResourceString("Argument_ConversionOverflow"));
+        }
+
+        // Same thing, but using pointers
+        //
+        // Might consider checking Max...Count to avoid the extra counting step.
+        //
+        // Note that if all of the input chars are not consumed, then we'll do a /2, which means
+        // that its likely that we didn't consume as many chars as we could have.  For some
+        // applications this could be slow.  (Like trying to exactly fill an output buffer from a bigger stream)
+        [System.Security.SecurityCritical]  // auto-generated
+        [CLSCompliant(false)]
+        [System.Runtime.InteropServices.ComVisible(false)]
+        public virtual unsafe void Convert(char* chars, int charCount,
+                                             byte* bytes, int byteCount, bool flush,
+                                             out int charsUsed, out int bytesUsed, out bool completed)
+        {
+            // Validate input parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+                if (charCount < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"),
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+                Contract.EndContractBlock();
+
+            // Get ready to do it
+            charsUsed = charCount;
+
+            // Its easy to do if it won't overrun our buffer.
+            while (charsUsed > 0)
+            {
+                if (GetByteCount(chars, charsUsed, flush) <= byteCount)
+                {
+                    bytesUsed = GetBytes(chars, charsUsed, bytes, byteCount, flush);
+                    completed = (charsUsed == charCount &&
+                        (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0));
+                    return;
+                }
+
+                // Try again with 1/2 the count, won't flush then 'cause won't read it all
+                flush = false;
+                charsUsed /= 2;
+            }
+
+            // Oops, we didn't have anything, we'll have to throw an overflow
+            throw new ArgumentException(Environment.GetResourceString("Argument_ConversionOverflow"));
+        }
+    }
+}
+

mcs/class/referencesource/mscorlib/system/text/encoderbestfitfallback.cs

@@ -0,0 +1,249 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// EncoderBestFitFallback.cs
+//
+// This is used internally to create best fit behavior as per the original windows best fit behavior.
+//
+namespace System.Text
+{
+    using System;
+    using System.Globalization;
+    using System.Text;
+    using System.Threading;
+    using System.Diagnostics.Contracts;
+
+    [Serializable]
+    internal class InternalEncoderBestFitFallback : EncoderFallback
+    {
+        // Our variables
+        internal Encoding encoding = null;
+        internal char[]   arrayBestFit = null;
+
+        internal InternalEncoderBestFitFallback(Encoding encoding)
+        {
+            // Need to load our replacement characters table.
+            this.encoding = encoding;
+            this.bIsMicrosoftBestFitFallback = true;
+        }
+
+        public override EncoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new InternalEncoderBestFitFallbackBuffer(this);
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return 1;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            InternalEncoderBestFitFallback that = value as InternalEncoderBestFitFallback;
+            if (that != null)
+            {
+                return (this.encoding.CodePage == that.encoding.CodePage);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return this.encoding.CodePage;
+        }
+    }
+
+    internal sealed class InternalEncoderBestFitFallbackBuffer : EncoderFallbackBuffer
+    {
+        // Our variables
+        private char                    cBestFit = '\0';
+        private InternalEncoderBestFitFallback  oFallback;
+        private int                     iCount = -1;
+        private int                     iSize;
+
+        // Private object for locking instead of locking on a public type for SQL reliability work.
+        private static Object s_InternalSyncObject;
+        private static Object InternalSyncObject
+        {
+            get
+            {
+                if (s_InternalSyncObject == null)
+                {
+                    Object o = new Object();
+                    Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
+                }
+                return s_InternalSyncObject;
+            }
+        }
+
+        // Constructor
+        public InternalEncoderBestFitFallbackBuffer(InternalEncoderBestFitFallback fallback)
+        {
+            this.oFallback = fallback;
+
+            if (oFallback.arrayBestFit == null)
+            {
+                // Lock so we don't confuse ourselves.
+                lock(InternalSyncObject)
+                {
+                    // Double check before we do it again.
+                    if (oFallback.arrayBestFit == null)
+                        oFallback.arrayBestFit = fallback.encoding.GetBestFitUnicodeToBytesData();
+                }
+            }
+        }
+
+        // Fallback methods
+        public override bool Fallback(char charUnknown, int index)
+        {
+            // If we had a buffer already we're being recursive, throw, it's probably at the suspect
+            // character in our array.
+            // Shouldn't be able to get here for all of our code pages, table would have to be messed up.
+            Contract.Assert(iCount < 1, "[InternalEncoderBestFitFallbackBuffer.Fallback(non surrogate)] Fallback char " + ((int)cBestFit).ToString("X4", CultureInfo.InvariantCulture) + " caused recursive fallback");
+
+            iCount = iSize = 1;
+            cBestFit = TryBestFit(charUnknown);
+            if (cBestFit == '\0')
+                cBestFit = '?';
+
+            return true;
+        }
+
+        public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
+        {
+            // Double check input surrogate pair
+            if (!Char.IsHighSurrogate(charUnknownHigh))
+                throw new ArgumentOutOfRangeException("charUnknownHigh",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xD800, 0xDBFF));
+
+            if (!Char.IsLowSurrogate(charUnknownLow))
+                throw new ArgumentOutOfRangeException("CharUnknownLow",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xDC00, 0xDFFF));
+            Contract.EndContractBlock();
+
+            // If we had a buffer already we're being recursive, throw, it's probably at the suspect
+            // character in our array.  0 is processing last character, < 0 is not falling back
+            // Shouldn't be able to get here, table would have to be messed up.
+            Contract.Assert(iCount < 1, "[InternalEncoderBestFitFallbackBuffer.Fallback(surrogate)] Fallback char " + ((int)cBestFit).ToString("X4", CultureInfo.InvariantCulture) + " caused recursive fallback");
+
+            // Go ahead and get our fallback, surrogates don't have best fit
+            cBestFit = '?';
+            iCount = iSize = 2;
+
+            return true;
+        }
+
+        // Default version is overridden in EncoderReplacementFallback.cs
+        public override char GetNextChar()
+        {
+            // We want it to get < 0 because == 0 means that the current/last character is a fallback
+            // and we need to detect recursion.  We could have a flag but we already have this counter.
+            iCount--;
+            
+            // Do we have anything left? 0 is now last fallback char, negative is nothing left
+            if (iCount < 0)
+                return '\0';
+
+            // Need to get it out of the buffer.
+            // Make sure it didn't wrap from the fast count-- path
+            if (iCount == int.MaxValue)
+            {
+                iCount = -1;
+                return '\0';
+            }
+
+            // Return the best fit character
+            return cBestFit;
+        }
+
+        public override bool MovePrevious()
+        {
+            // Exception fallback doesn't have anywhere to back up to.
+            if (iCount >= 0)
+                iCount++;
+
+            // Return true if we could do it.
+            return (iCount >= 0 && iCount <= iSize);
+        }
+
+
+        // How many characters left to output?
+        public override int Remaining
+        {
+            get
+            {
+                return (iCount > 0) ? iCount : 0;
+            }
+        }
+
+        // Clear the buffer
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe void Reset()
+        {
+            iCount = -1;
+            charStart = null;
+            bFallingBack = false;
+        }
+
+        // private helper methods
+        private char TryBestFit(char cUnknown)
+        {
+            // Need to figure out our best fit character, low is beginning of array, high is 1 AFTER end of array
+            int lowBound = 0;
+            int highBound = oFallback.arrayBestFit.Length;
+            int index;
+
+            // Binary search the array
+            int iDiff;
+            while ((iDiff = (highBound - lowBound)) > 6)
+            {
+                // Look in the middle, which is complicated by the fact that we have 2 #s for each pair,
+                // so we don't want index to be odd because we want to be on word boundaries.
+                // Also note that index can never == highBound (because diff is rounded down)
+                index = ((iDiff / 2) + lowBound) & 0xFFFE;
+
+                char cTest = oFallback.arrayBestFit[index];
+                if (cTest == cUnknown)
+                {
+                    // We found it
+                    Contract.Assert(index + 1 < oFallback.arrayBestFit.Length,
+                        "[InternalEncoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array");
+                    return oFallback.arrayBestFit[index + 1];
+                }
+                else if (cTest < cUnknown)
+                {
+                    // We weren't high enough
+                    lowBound = index;
+                }
+                else
+                {
+                    // We weren't low enough
+                    highBound = index;
+                }
+            }
+
+            for (index = lowBound; index < highBound; index += 2)
+            {
+                if (oFallback.arrayBestFit[index] == cUnknown)
+                {
+                    // We found it
+                    Contract.Assert(index + 1 < oFallback.arrayBestFit.Length,
+                        "[InternalEncoderBestFitFallbackBuffer.TryBestFit]Expected replacement character at end of array");
+                    return oFallback.arrayBestFit[index + 1];
+                }
+            }
+
+            // Char wasn't in our table
+            return '\0';
+        }
+    }
+}
+

mcs/class/referencesource/mscorlib/system/text/encoderexceptionfallback.cs

@@ -0,0 +1,205 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// EncoderExceptionFallback.cs
+namespace System.Text
+{
+    using System;
+    using System.Runtime.Serialization;
+    using System.Diagnostics.Contracts;
+
+    [Serializable]
+    public sealed class EncoderExceptionFallback : EncoderFallback
+    {
+        // Construction
+        public EncoderExceptionFallback()
+        {
+        }
+
+        public override EncoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new EncoderExceptionFallbackBuffer();
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return 0;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            EncoderExceptionFallback that = value as EncoderExceptionFallback;
+            if (that != null)
+            {
+                return (true);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return 654;
+        }
+    }
+
+
+    public sealed class EncoderExceptionFallbackBuffer : EncoderFallbackBuffer
+    {
+        public EncoderExceptionFallbackBuffer(){}
+        public override bool Fallback(char charUnknown, int index)
+        {
+            // Fall back our char
+            throw new EncoderFallbackException(
+                Environment.GetResourceString("Argument_InvalidCodePageConversionIndex",
+                    (int)charUnknown, index), charUnknown, index);
+        }
+
+        public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
+        {
+            if (!Char.IsHighSurrogate(charUnknownHigh))
+            {
+                throw new ArgumentOutOfRangeException("charUnknownHigh",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xD800, 0xDBFF));
+            }
+            if (!Char.IsLowSurrogate(charUnknownLow))
+            {
+                throw new ArgumentOutOfRangeException("CharUnknownLow",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xDC00, 0xDFFF));
+            }
+            Contract.EndContractBlock();
+
+            int iTemp = Char.ConvertToUtf32(charUnknownHigh, charUnknownLow);
+
+            // Fall back our char
+            throw new EncoderFallbackException(
+                Environment.GetResourceString("Argument_InvalidCodePageConversionIndex",
+                    iTemp, index), charUnknownHigh, charUnknownLow, index);
+        }
+
+        public override char GetNextChar()
+        {
+            return (char)0;
+        }
+
+        public override bool MovePrevious()
+        {
+            // Exception fallback doesn't have anywhere to back up to.
+            return false;
+        }
+
+        // Exceptions are always empty
+        public override int Remaining
+        {
+            get
+            {
+                return 0;
+            }
+        }
+    }
+
+    [Serializable]
+    public sealed class EncoderFallbackException : ArgumentException
+    {
+        char    charUnknown;
+        char    charUnknownHigh;
+        char    charUnknownLow;
+        int     index;
+
+        public EncoderFallbackException()
+            : base(Environment.GetResourceString("Arg_ArgumentException"))
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        public EncoderFallbackException(String message)
+            : base(message)
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        public EncoderFallbackException(String message, Exception innerException)
+            : base(message, innerException)
+        {
+            SetErrorCode(__HResults.COR_E_ARGUMENT);
+        }
+
+        internal EncoderFallbackException(SerializationInfo info, StreamingContext context) : base(info, context)
+        {
+        }
+
+        internal EncoderFallbackException(
+            String message, char charUnknown, int index) : base(message)
+        {
+            this.charUnknown = charUnknown;
+            this.index = index;
+        }
+
+        internal EncoderFallbackException(
+            String message, char charUnknownHigh, char charUnknownLow, int index) : base(message)
+        {
+            if (!Char.IsHighSurrogate(charUnknownHigh))
+            {
+                throw new ArgumentOutOfRangeException("charUnknownHigh",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xD800, 0xDBFF));
+            }
+            if (!Char.IsLowSurrogate(charUnknownLow))
+            {
+                throw new ArgumentOutOfRangeException("CharUnknownLow",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xDC00, 0xDFFF));
+            }
+            Contract.EndContractBlock();
+
+            this.charUnknownHigh = charUnknownHigh;
+            this.charUnknownLow = charUnknownLow;
+            this.index = index;
+        }
+
+        public char CharUnknown
+        {
+            get
+            {
+                return (charUnknown);
+            }
+        }
+
+        public char CharUnknownHigh
+        {
+            get
+            {
+                return (charUnknownHigh);
+            }
+        }
+
+        public char CharUnknownLow
+        {
+            get
+            {
+                return (charUnknownLow);
+            }
+        }
+
+        public int Index
+        {
+            get
+            {
+                return index;
+            }
+        }
+
+        // Return true if the unknown character is a surrogate pair.
+        public bool IsUnknownSurrogate()
+        {
+            return (this.charUnknownHigh != '\0');
+        }
+    }
+}

mcs/class/referencesource/mscorlib/system/text/encoderfallback.cs

@@ -0,0 +1,237 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+using System;
+using System.Security;
+using System.Threading;
+using System.Diagnostics.Contracts;
+
+namespace System.Text
+{
+    [Serializable]
+    public abstract class EncoderFallback
+    {
+// disable csharp compiler warning #0414: field assigned unused value
+#pragma warning disable 0414
+        internal bool                 bIsMicrosoftBestFitFallback = false;
+#pragma warning restore 0414
+
+        private static volatile EncoderFallback replacementFallback; // Default fallback, uses no best fit & "?"
+        private static volatile EncoderFallback exceptionFallback;
+
+        // Private object for locking instead of locking on a public type for SQL reliability work.
+        private static Object s_InternalSyncObject;
+        private static Object InternalSyncObject
+        {
+            get
+            {
+                if (s_InternalSyncObject == null)
+                {
+                    Object o = new Object();
+                    Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
+                }
+                return s_InternalSyncObject;
+            }
+        }
+
+        // Get each of our generic fallbacks.
+
+        public static EncoderFallback ReplacementFallback
+        {
+            get
+            {
+                if (replacementFallback == null)
+                    lock(InternalSyncObject)
+                        if (replacementFallback == null)
+                            replacementFallback = new EncoderReplacementFallback();
+
+                return replacementFallback;
+            }
+        }
+
+
+        public static EncoderFallback ExceptionFallback
+        {
+            get
+            {
+                if (exceptionFallback == null)
+                    lock(InternalSyncObject)
+                        if (exceptionFallback == null)
+                            exceptionFallback = new EncoderExceptionFallback();
+
+                return exceptionFallback;
+            }
+        }
+
+        // Fallback
+        //
+        // Return the appropriate unicode string alternative to the character that need to fall back.
+        // Most implimentations will be:
+        //      return new MyCustomEncoderFallbackBuffer(this);
+
+        public abstract EncoderFallbackBuffer CreateFallbackBuffer();
+
+        // Maximum number of characters that this instance of this fallback could return
+
+        public abstract int MaxCharCount { get; }
+    }
+
+
+    public abstract class EncoderFallbackBuffer
+    {
+        // Most implementations will probably need an implemenation-specific constructor
+
+        // Public methods that cannot be overriden that let us do our fallback thing
+        // These wrap the internal methods so that we can check for people doing stuff that is incorrect
+
+        public abstract bool Fallback(char charUnknown, int index);
+
+        public abstract bool Fallback(char charUnknownHigh, char charUnknownLow, int index);
+
+        // Get next character
+
+        public abstract char GetNextChar();
+
+        // Back up a character
+
+        public abstract bool MovePrevious();
+
+        // How many chars left in this fallback?
+
+        public abstract int Remaining { get; }
+
+        // Not sure if this should be public or not.
+        // Clear the buffer
+
+        public virtual void Reset()
+        {
+            while (GetNextChar() != (char)0);
+        }
+
+        // Internal items to help us figure out what we're doing as far as error messages, etc.
+        // These help us with our performance and messages internally
+        [SecurityCritical]
+        internal    unsafe char*   charStart;
+        [SecurityCritical]
+        internal    unsafe char*   charEnd;
+        internal    EncoderNLS     encoder;
+        internal    bool           setEncoder;
+        internal    bool           bUsedEncoder;
+        internal    bool           bFallingBack = false;
+        internal    int            iRecursionCount = 0;
+        private const int          iMaxRecursion = 250;
+
+        // Internal Reset
+        // For example, what if someone fails a conversion and wants to reset one of our fallback buffers?
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe void InternalReset()
+        {
+            charStart = null;
+            bFallingBack = false;
+            iRecursionCount = 0;
+            Reset();
+        }
+
+        // Set the above values
+        // This can't be part of the constructor because EncoderFallbacks would have to know how to impliment these.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe void InternalInitialize(char* charStart, char* charEnd, EncoderNLS encoder, bool setEncoder)
+        {
+            this.charStart = charStart;
+            this.charEnd = charEnd;
+            this.encoder = encoder;
+            this.setEncoder = setEncoder;
+            this.bUsedEncoder = false;
+            this.bFallingBack = false;
+            this.iRecursionCount = 0;
+        }
+
+        internal char InternalGetNextChar()
+        {
+            char ch = GetNextChar();
+            bFallingBack = (ch != 0);
+            if (ch == 0) iRecursionCount = 0;
+            return ch;
+        }
+
+        // Fallback the current character using the remaining buffer and encoder if necessary
+        // This can only be called by our encodings (other have to use the public fallback methods), so
+        // we can use our EncoderNLS here too.
+        // setEncoder is true if we're calling from a GetBytes method, false if we're calling from a GetByteCount
+        //
+        // Note that this could also change the contents of this.encoder, which is the same
+        // object that the caller is using, so the caller could mess up the encoder for us
+        // if they aren't careful.
+        [System.Security.SecurityCritical]  // auto-generated
+        internal unsafe virtual bool InternalFallback(char ch, ref char* chars)
+        {
+            // Shouldn't have null charStart
+            Contract.Assert(charStart != null,
+                "[EncoderFallback.InternalFallbackBuffer]Fallback buffer is not initialized");
+
+            // Get our index, remember chars was preincremented to point at next char, so have to -1
+            int index = (int)(chars - charStart) - 1;
+
+            // See if it was a high surrogate
+            if (Char.IsHighSurrogate(ch))
+            {
+                // See if there's a low surrogate to go with it
+                if (chars >= this.charEnd)
+                {
+                    // Nothing left in input buffer
+                    // No input, return 0 if mustflush is false
+                    if (this.encoder != null && !this.encoder.MustFlush)
+                    {
+                        // Done, nothing to fallback
+                        if (this.setEncoder)
+                        {
+                            bUsedEncoder = true;
+                            this.encoder.charLeftOver = ch;
+                        }
+                        bFallingBack = false;
+                        return false;
+                    }
+                }
+                else
+                {
+                    // Might have a low surrogate
+                    char cNext = *chars;
+                    if (Char.IsLowSurrogate(cNext))
+                    {
+                        // If already falling back then fail
+                        if (bFallingBack && iRecursionCount++ > iMaxRecursion)
+                            ThrowLastCharRecursive(Char.ConvertToUtf32(ch, cNext));
+
+                        // Next is a surrogate, add it as surrogate pair, and increment chars
+                        chars++;
+                        bFallingBack = Fallback(ch, cNext, index);
+                        return bFallingBack;
+                    }
+
+                    // Next isn't a low surrogate, just fallback the high surrogate
+                }
+            }
+
+            // If already falling back then fail
+            if (bFallingBack && iRecursionCount++ > iMaxRecursion)
+                ThrowLastCharRecursive((int)ch);
+
+            // Fall back our char
+            bFallingBack = Fallback(ch, index);
+
+            return bFallingBack;
+        }
+
+        // private helper methods
+        internal void ThrowLastCharRecursive(int charRecursive)
+        {
+            // Throw it, using our complete character
+            throw new ArgumentException(
+                Environment.GetResourceString("Argument_RecursiveFallback",
+                    charRecursive), "chars");
+        }
+
+    }
+}

mcs/class/referencesource/mscorlib/system/text/encodernls.cs

@@ -0,0 +1,299 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System.Runtime.Serialization;
+    using System.Security.Permissions;
+    using System.Text;
+    using System;
+    using System.Diagnostics.Contracts;
+    // An Encoder is used to encode a sequence of blocks of characters into
+    // a sequence of blocks of bytes. Following instantiation of an encoder,
+    // sequential blocks of characters are converted into blocks of bytes through
+    // calls to the GetBytes method. The encoder maintains state between the
+    // conversions, allowing it to correctly encode character sequences that span
+    // adjacent blocks.
+    //
+    // Instances of specific implementations of the Encoder abstract base
+    // class are typically obtained through calls to the GetEncoder method
+    // of Encoding objects.
+    //
+
+    [Serializable]
+    internal class EncoderNLS : Encoder, ISerializable
+    {
+        // Need a place for the last left over character, most of our encodings use this
+        internal char   charLeftOver;
+        
+        protected Encoding m_encoding;
+        
+        [NonSerialized] protected   bool     m_mustFlush;
+        [NonSerialized] internal    bool     m_throwOnOverflow;
+        [NonSerialized] internal    int      m_charsUsed;
+
+#region Serialization
+
+        // Constructor called by serialization. called during deserialization.
+        internal EncoderNLS(SerializationInfo info, StreamingContext context)
+        {
+            throw new NotSupportedException(
+                        String.Format(
+                            System.Globalization.CultureInfo.CurrentCulture, 
+                            Environment.GetResourceString("NotSupported_TypeCannotDeserialized"), this.GetType()));
+        }
+
+#if FEATURE_SERIALIZATION
+        // ISerializable implementation. called during serialization.
+        [System.Security.SecurityCritical]  // auto-generated_required
+        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            SerializeEncoder(info);
+            info.AddValue("encoding", this.m_encoding);
+            info.AddValue("charLeftOver", this.charLeftOver);
+            info.SetType(typeof(Encoding.DefaultEncoder));
+        }
+#endif
+
+#endregion Serialization 
+
+        internal EncoderNLS(Encoding encoding)
+        {
+            this.m_encoding = encoding;
+            this.m_fallback = this.m_encoding.EncoderFallback;
+            this.Reset();
+        }
+
+        // This one is used when deserializing (like UTF7Encoding.Encoder)
+        internal EncoderNLS()
+        {
+            this.m_encoding = null;
+            this.Reset();
+        }
+
+        public override void Reset()
+        {
+            this.charLeftOver = (char)0;
+            if (m_fallbackBuffer != null)
+                m_fallbackBuffer.Reset();
+        }
+
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe int GetByteCount(char[] chars, int index, int count, bool flush)
+        {
+            // Validate input parameters
+            if (chars == null)
+                throw new ArgumentNullException( "chars",
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (index < 0 || count < 0)
+                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - index < count)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            // Avoid empty input problem
+            if (chars.Length == 0)
+                chars = new char[1];
+
+            // Just call the pointer version
+            int result = -1;
+            fixed (char* pChars = chars)
+            {
+                result = GetByteCount(pChars + index, count, flush);
+            }
+            return result;
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override int GetByteCount(char* chars, int count, bool flush)
+        {
+            // Validate input parameters
+            if (chars == null)
+                throw new ArgumentNullException( "chars",
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count",
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            this.m_mustFlush = flush;
+            this.m_throwOnOverflow = true;
+            return m_encoding.GetByteCount(chars, count, this);
+        }
+
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe int GetBytes(char[] chars, int charIndex, int charCount,
+                                              byte[] bytes, int byteIndex, bool flush)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (byteIndex < 0 || byteIndex > bytes.Length)
+                throw new ArgumentOutOfRangeException("byteIndex",
+                     Environment.GetResourceString("ArgumentOutOfRange_Index"));
+            Contract.EndContractBlock();
+
+            if (chars.Length == 0)
+                chars = new char[1];
+
+            int byteCount = bytes.Length - byteIndex;
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            // Just call pointer version
+            fixed (char* pChars = chars)
+                fixed (byte* pBytes = bytes)
+
+                    // Remember that charCount is # to decode, not size of array.
+                    return GetBytes(pChars + charIndex, charCount,
+                                    pBytes + byteIndex, byteCount, flush);
+        }
+
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override int GetBytes(char* chars, int charCount, byte* bytes, int byteCount, bool flush)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteCount < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((byteCount<0 ? "byteCount" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            this.m_mustFlush = flush;
+            this.m_throwOnOverflow = true;
+            return m_encoding.GetBytes(chars, charCount, bytes, byteCount, this);
+        }
+
+        // This method is used when your output buffer might not be large enough for the entire result.
+        // Just call the pointer version.  (This gets bytes)
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe void Convert(char[] chars, int charIndex, int charCount,
+                                              byte[] bytes, int byteIndex, int byteCount, bool flush,
+                                              out int charsUsed, out int bytesUsed, out bool completed)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"),
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"),
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            Contract.EndContractBlock();
+
+            // Avoid empty input problem
+            if (chars.Length == 0)
+                chars = new char[1];
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            // Just call the pointer version (can't do this for non-msft encoders)
+            fixed (char* pChars = chars)
+            {
+                fixed (byte* pBytes = bytes)
+                {
+                    Convert(pChars + charIndex, charCount, pBytes + byteIndex, byteCount, flush,
+                        out charsUsed, out bytesUsed, out completed);
+                }
+            }
+        }
+
+        // This is the version that uses pointers.  We call the base encoding worker function
+        // after setting our appropriate internal variables.  This is getting bytes
+        [System.Security.SecurityCritical]  // auto-generated
+        public override unsafe void Convert(char* chars, int charCount,
+                                              byte* bytes, int byteCount, bool flush,
+                                              out int charsUsed, out int bytesUsed, out bool completed)
+        {
+            // Validate input parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+            if (charCount < 0 || byteCount < 0)
+            throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"),
+                Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            // We don't want to throw
+            this.m_mustFlush = flush;
+            this.m_throwOnOverflow = false;
+            this.m_charsUsed = 0;
+
+            // Do conversion
+            bytesUsed = this.m_encoding.GetBytes(chars, charCount, bytes, byteCount, this);
+            charsUsed = this.m_charsUsed;
+
+            // Its completed if they've used what they wanted AND if they didn't want flush or if we are flushed
+            completed = (charsUsed == charCount) && (!flush || !this.HasState) &&
+                (m_fallbackBuffer == null || m_fallbackBuffer.Remaining == 0);
+
+            // Our data thingys are now full, we can return
+        }
+
+        public Encoding Encoding
+        {
+            get
+            {
+                return m_encoding;
+            }
+        }
+
+        public bool MustFlush
+        {
+            get
+            {
+                return m_mustFlush;
+            }
+        }
+
+
+        // Anything left in our encoder?
+        internal virtual bool HasState
+        {
+            get
+            {
+                return (this.charLeftOver != (char)0);
+            }
+        }
+
+        // Allow encoding to clear our must flush instead of throwing (in ThrowBytesOverflow)
+        internal void ClearMustFlush()
+        {
+            m_mustFlush = false;
+        }
+
+    }
+}

mcs/class/referencesource/mscorlib/system/text/encoderreplacementfallback.cs

@@ -0,0 +1,236 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+// EncoderReplacementFallback.cs
+//
+namespace System.Text
+{
+    using System;
+    using System.Runtime;
+    using System.Diagnostics.Contracts;
+
+    [Serializable]
+    public sealed class EncoderReplacementFallback : EncoderFallback
+    {
+        // Our variables
+        private String strDefault;
+
+        // Construction.  Default replacement fallback uses no best fit and ? replacement string
+        public EncoderReplacementFallback() : this("?")
+        {
+        }
+
+        public EncoderReplacementFallback(String replacement)
+        {
+            // Must not be null
+            if (replacement == null)
+                throw new ArgumentNullException("replacement");
+            Contract.EndContractBlock();
+
+            // Make sure it doesn't have bad surrogate pairs
+            bool bFoundHigh=false;
+            for (int i = 0; i < replacement.Length; i++)
+            {
+                // Found a surrogate?
+                if (Char.IsSurrogate(replacement,i))
+                {
+                    // High or Low?
+                    if (Char.IsHighSurrogate(replacement, i))
+                    {
+                        // if already had a high one, stop
+                        if (bFoundHigh)
+                            break;  // break & throw at the bFoundHIgh below
+                        bFoundHigh = true;
+                    }
+                    else
+                    {
+                        // Low, did we have a high?
+                        if (!bFoundHigh)
+                        {
+                            // Didn't have one, make if fail when we stop
+                            bFoundHigh = true;
+                            break;
+                        }
+
+                        // Clear flag
+                        bFoundHigh = false;
+                    }
+                }
+                // If last was high we're in trouble (not surrogate so not low surrogate, so break)
+                else if (bFoundHigh)
+                    break;
+            }
+            if (bFoundHigh)
+                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidCharSequenceNoIndex", "replacement"));
+
+            strDefault = replacement;
+        }
+
+        public String DefaultString
+        {
+             get
+             {
+                return strDefault;
+             }
+        }
+
+        public override EncoderFallbackBuffer CreateFallbackBuffer()
+        {
+            return new EncoderReplacementFallbackBuffer(this);
+        }
+
+        // Maximum number of characters that this instance of this fallback could return
+        public override int MaxCharCount
+        {
+            get
+            {
+                return strDefault.Length;
+            }
+        }
+
+        public override bool Equals(Object value)
+        {
+            EncoderReplacementFallback that = value as EncoderReplacementFallback;
+            if (that != null)
+            {
+                return (this.strDefault == that.strDefault);
+            }
+            return (false);
+        }
+
+        public override int GetHashCode()
+        {
+            return strDefault.GetHashCode();
+        }
+    }
+
+
+
+    public sealed class EncoderReplacementFallbackBuffer : EncoderFallbackBuffer
+    {
+        // Store our default string
+        private String strDefault;
+        int fallbackCount = -1;
+        int fallbackIndex = -1;
+
+        // Construction
+        public EncoderReplacementFallbackBuffer(EncoderReplacementFallback fallback)
+        {
+            // 2X in case we're a surrogate pair
+            this.strDefault = fallback.DefaultString + fallback.DefaultString;
+        }
+
+        // Fallback Methods
+        public override bool Fallback(char charUnknown, int index)
+        {
+            // If we had a buffer already we're being recursive, throw, it's probably at the suspect
+            // character in our array.
+            if (fallbackCount >= 1)
+            {
+                // If we're recursive we may still have something in our buffer that makes this a surrogate
+                if (char.IsHighSurrogate(charUnknown) && fallbackCount >= 0 &&
+                    char.IsLowSurrogate(strDefault[fallbackIndex+1]))
+                    ThrowLastCharRecursive(Char.ConvertToUtf32(charUnknown, strDefault[fallbackIndex+1]));
+
+                // Nope, just one character
+                ThrowLastCharRecursive(unchecked((int)charUnknown));
+            }
+
+            // Go ahead and get our fallback
+            // Divide by 2 because we aren't a surrogate pair
+            fallbackCount = strDefault.Length/2;
+            fallbackIndex = -1;
+
+            return fallbackCount != 0;
+        }
+
+        public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
+        {
+            // Double check input surrogate pair
+            if (!Char.IsHighSurrogate(charUnknownHigh))
+                throw new ArgumentOutOfRangeException("charUnknownHigh",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xD800, 0xDBFF));
+
+            if (!Char.IsLowSurrogate(charUnknownLow))
+                throw new ArgumentOutOfRangeException("CharUnknownLow",
+                    Environment.GetResourceString("ArgumentOutOfRange_Range",
+                    0xDC00, 0xDFFF));
+            Contract.EndContractBlock();
+
+            // If we had a buffer already we're being recursive, throw, it's probably at the suspect
+            // character in our array.
+            if (fallbackCount >= 1)
+                ThrowLastCharRecursive(Char.ConvertToUtf32(charUnknownHigh, charUnknownLow));
+
+            // Go ahead and get our fallback
+            fallbackCount = strDefault.Length;
+            fallbackIndex = -1;
+
+            return fallbackCount != 0;
+        }
+
+        public override char GetNextChar()
+        {
+            // We want it to get < 0 because == 0 means that the current/last character is a fallback
+            // and we need to detect recursion.  We could have a flag but we already have this counter.
+            fallbackCount--;
+            fallbackIndex++;
+            
+            // Do we have anything left? 0 is now last fallback char, negative is nothing left
+            if (fallbackCount < 0)
+                return '\0';
+
+            // Need to get it out of the buffer.
+            // Make sure it didn't wrap from the fast count-- path
+            if (fallbackCount == int.MaxValue)
+            {
+                fallbackCount = -1;
+                return '\0';
+            }
+
+            // Now make sure its in the expected range
+            Contract.Assert(fallbackIndex < strDefault.Length && fallbackIndex >= 0,
+                            "Index exceeds buffer range");
+
+            return strDefault[fallbackIndex];
+        }
+
+        public override bool MovePrevious()
+        {
+            // Back up one, only if we just processed the last character (or earlier)
+            if (fallbackCount >= -1 && fallbackIndex >= 0)
+            {
+                fallbackIndex--;
+                fallbackCount++;
+                return true;
+            }
+
+            // Return false 'cause we couldn't do it.
+            return false;
+        }
+
+        // How many characters left to output?
+        public override int Remaining
+        {
+            get
+            {
+                // Our count is 0 for 1 character left.
+                return (fallbackCount < 0) ? 0 : fallbackCount;
+            }
+        }
+
+        // Clear the buffer
+        [System.Security.SecuritySafeCritical]  // auto-generated
+        public override unsafe void Reset()
+        {
+            fallbackCount = -1;
+            fallbackIndex = 0;
+            charStart = null;
+            bFallingBack = false;
+        }
+    }
+}
+

mcs/class/referencesource/mscorlib/system/text/encodinginfo.cs

@@ -0,0 +1,75 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System;
+    using System.Text;
+
+
+    [Serializable]
+    public sealed class EncodingInfo
+    {
+        int     iCodePage;          // Code Page #
+        String  strEncodingName;    // Short name (web name)
+        String  strDisplayName;     // Full localized name
+
+        internal EncodingInfo(int codePage, string name, string displayName)
+        {
+            this.iCodePage = codePage;
+            this.strEncodingName = name;
+            this.strDisplayName = displayName;
+        }
+
+
+        public int CodePage
+        {
+            get
+            {
+                return iCodePage;
+            }
+        }
+
+
+        public String Name
+        {
+            get
+            {
+                return strEncodingName;
+            }
+        }
+
+
+        public String DisplayName
+        {
+            get
+            {
+                return strDisplayName;
+            }
+        }
+
+
+        public Encoding GetEncoding()
+        {
+            return Encoding.GetEncoding(this.iCodePage);
+        }
+
+        public override bool Equals(Object value)
+        {
+            EncodingInfo that = value as EncodingInfo;
+            if (that != null)
+            {
+                return (this.CodePage == that.CodePage);
+            }
+            return (false);
+        }
+        
+        public override int GetHashCode()
+        {
+            return this.CodePage;
+        }
+        
+    }
+}

mcs/class/referencesource/mscorlib/system/text/encodingnls.cs

@@ -0,0 +1,375 @@
+// ==++==
+// 
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+// 
+// ==--==
+#if FEATURE_ENCODINGNLS
+namespace System.Text
+{
+    
+    using System;
+    using System.Diagnostics.Contracts;
+    using System.Collections;
+    using System.Runtime.Remoting;
+    using System.Globalization;
+    using System.Threading;
+    using Win32Native = Microsoft.Win32.Win32Native;
+    
+    // This class overrides Encoding with the things we need for our NLS Encodings
+    //
+    // All of the GetBytes/Chars GetByte/CharCount methods are just wrappers for the pointer
+    // plus decoder/encoder method that is our real workhorse.  Note that this is an internal
+    // class, so our public classes cannot derive from this class.  Because of this, all of the
+    // GetBytes/Chars GetByte/CharCount wrapper methods are duplicated in all of our public
+    // encodings, which currently include:
+    //
+    //      EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, & UnicodeEncoding
+    //
+    // So if you change the wrappers in this class, you must change the wrappers in the other classes
+    // as well because they should have the same behavior.
+    //
+    [System.Runtime.InteropServices.ComVisible(true)]
+    [Serializable]
+    internal abstract class EncodingNLS : Encoding
+    {    
+        protected EncodingNLS(int codePage) : base(codePage)
+        {
+        }
+
+        // Returns the number of bytes required to encode a range of characters in
+        // a character array.
+        // 
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetByteCount(char[] chars, int index, int count)
+        {
+            // Validate input parameters
+            if (chars == null)
+                throw new ArgumentNullException("chars", 
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (index < 0 || count < 0)
+                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"), 
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - index < count)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            // If no input, return 0, avoid fixed empty array problem
+            if (chars.Length == 0)
+                return 0;
+
+            // Just call the pointer version
+            fixed (char* pChars = chars)
+                return GetByteCount(pChars + index, count, null);
+        }
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetByteCount(String s)
+        {
+            // Validate input
+            if (s==null)
+                throw new ArgumentNullException("s");
+            Contract.EndContractBlock();
+
+            fixed (char* pChars = s)
+                return GetByteCount(pChars, s.Length, null);
+        }       
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        [System.Security.SecurityCritical]  // auto-generated
+        public override unsafe int GetByteCount(char* chars, int count)
+        {
+            // Validate Parameters
+            if (chars == null)
+                throw new ArgumentNullException("chars", 
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count", 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+            
+            // Call it with empty encoder
+            return GetByteCount(chars, count, null);
+        }
+
+        // Parent method is safe.
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetBytes(String s, int charIndex, int charCount,
+                                              byte[] bytes, int byteIndex)
+        {
+            if (s == null || bytes == null)
+                throw new ArgumentNullException((s == null ? "s" : "bytes"), 
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"), 
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (s.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("s",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCount"));
+
+            if (byteIndex < 0 || byteIndex > bytes.Length)
+                throw new ArgumentOutOfRangeException("byteIndex", 
+                    Environment.GetResourceString("ArgumentOutOfRange_Index"));
+            Contract.EndContractBlock();
+
+            int byteCount = bytes.Length - byteIndex;
+
+            // Fixed doesn't like empty arrays
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            fixed (char* pChars = s)
+                fixed ( byte* pBytes = bytes)
+                    return GetBytes(pChars + charIndex, charCount,
+                                    pBytes + byteIndex, byteCount, null);
+        }
+    
+        // Encodes a range of characters in a character array into a range of bytes
+        // in a byte array. An exception occurs if the byte array is not large
+        // enough to hold the complete encoding of the characters. The
+        // GetByteCount method can be used to determine the exact number of
+        // bytes that will be produced for a given range of characters.
+        // Alternatively, the GetMaxByteCount method can be used to
+        // determine the maximum number of bytes that will be produced for a given
+        // number of characters, regardless of the actual character values.
+        // 
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetBytes(char[] chars, int charIndex, int charCount,
+                                               byte[] bytes, int byteIndex)
+        {
+            // Validate parameters
+            if (chars == null || bytes == null)
+                throw new ArgumentNullException((chars == null ? "chars" : "bytes"), 
+                      Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charIndex < 0 || charCount < 0)
+                throw new ArgumentOutOfRangeException((charIndex<0 ? "charIndex" : "charCount"), 
+                      Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (chars.Length - charIndex < charCount)
+                throw new ArgumentOutOfRangeException("chars",
+                      Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (byteIndex < 0 || byteIndex > bytes.Length)
+                throw new ArgumentOutOfRangeException("byteIndex",
+                     Environment.GetResourceString("ArgumentOutOfRange_Index"));
+            Contract.EndContractBlock();
+
+            // If nothing to encode return 0, avoid fixed problem
+            if (chars.Length == 0)
+                return 0;
+
+            // Just call pointer version
+            int byteCount = bytes.Length - byteIndex;
+
+            // Fixed doesn't like empty arrays
+            if (bytes.Length == 0)
+                bytes = new byte[1];
+
+            fixed (char* pChars = chars)
+                fixed (byte* pBytes = bytes)
+                    // Remember that byteCount is # to decode, not size of array.
+                    return GetBytes(pChars + charIndex, charCount,
+                                    pBytes + byteIndex, byteCount, null);            
+        }
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        [System.Security.SecurityCritical]  // auto-generated
+        public override unsafe int GetBytes(char* chars, int charCount, byte* bytes, int byteCount)
+        {
+            // Validate Parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charCount < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"), 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+
+            return GetBytes(chars, charCount, bytes, byteCount, null);
+        }                                              
+
+        // Returns the number of characters produced by decoding a range of bytes
+        // in a byte array.
+        // 
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetCharCount(byte[] bytes, int index, int count)
+        {
+            // Validate Parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes", 
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (index < 0 || count < 0)
+                throw new ArgumentOutOfRangeException((index<0 ? "index" : "count"), 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+                                   
+            if (bytes.Length - index < count)
+                throw new ArgumentOutOfRangeException("bytes",
+                    Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            // If no input just return 0, fixed doesn't like 0 length arrays
+            if (bytes.Length == 0)
+                return 0;
+
+            // Just call pointer version
+            fixed (byte* pBytes = bytes)
+                return GetCharCount(pBytes + index, count, null);
+        }
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        [System.Security.SecurityCritical]  // auto-generated
+        public override unsafe int GetCharCount(byte* bytes, int count)
+        {
+            // Validate Parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes", 
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (count < 0)
+                throw new ArgumentOutOfRangeException("count", 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+            
+            return GetCharCount(bytes, count, null);
+        }        
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe int GetChars(byte[] bytes, int byteIndex, int byteCount,
+                                              char[] chars, int charIndex)
+        {
+            // Validate Parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (byteIndex < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((byteIndex<0 ? "byteIndex" : "byteCount"), 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if ( bytes.Length - byteIndex < byteCount)
+                throw new ArgumentOutOfRangeException("bytes",
+                    Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+
+            if (charIndex < 0 || charIndex > chars.Length)
+                throw new ArgumentOutOfRangeException("charIndex", 
+                    Environment.GetResourceString("ArgumentOutOfRange_Index"));
+            Contract.EndContractBlock();
+
+            // If no input, return 0 & avoid fixed problem
+            if (bytes.Length == 0)
+                return 0;
+
+            // Just call pointer version
+            int charCount = chars.Length - charIndex;
+
+            // Fixed doesn't like empty arrays
+            if (chars.Length == 0)
+                chars = new char[1];
+
+            fixed (byte* pBytes = bytes)
+                fixed (char* pChars = chars)
+                    // Remember that charCount is # to decode, not size of array
+                    return GetChars(pBytes + byteIndex, byteCount,
+                                    pChars + charIndex, charCount, null);
+        }
+
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        [System.Security.SecurityCritical]  // auto-generated
+        public unsafe override int GetChars(byte* bytes, int byteCount, char* chars, int charCount)
+        {
+            // Validate Parameters
+            if (bytes == null || chars == null)
+                throw new ArgumentNullException(bytes == null ? "bytes" : "chars",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (charCount < 0 || byteCount < 0)
+                throw new ArgumentOutOfRangeException((charCount<0 ? "charCount" : "byteCount"), 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+            Contract.EndContractBlock();
+            
+            return GetChars(bytes, byteCount, chars, charCount, null);
+        }
+    
+        // Returns a string containing the decoded representation of a range of
+        // bytes in a byte array.
+        // 
+        // All of our public Encodings that don't use EncodingNLS must have this (including EncodingNLS)
+        // So if you fix this, fix the others.  Currently those include:
+        // EncodingNLS, UTF7Encoding, UTF8Encoding, UTF32Encoding, ASCIIEncoding, UnicodeEncoding
+        // parent method is safe
+        [System.Security.SecuritySafeCritical] // overrides public transparent member
+        public override unsafe String GetString(byte[] bytes, int index, int count)
+        {
+            // Validate Parameters
+            if (bytes == null)
+                throw new ArgumentNullException("bytes",
+                    Environment.GetResourceString("ArgumentNull_Array"));
+
+            if (index < 0 || count < 0)
+                throw new ArgumentOutOfRangeException((index < 0 ? "index" : "count"), 
+                    Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
+
+            if (bytes.Length - index < count)
+                throw new ArgumentOutOfRangeException("bytes",
+                    Environment.GetResourceString("ArgumentOutOfRange_IndexCountBuffer"));
+            Contract.EndContractBlock();
+
+            // Avoid problems with empty input buffer
+            if (bytes.Length == 0) return String.Empty;
+            
+            fixed (byte* pBytes = bytes)
+                return String.CreateStringFromEncoding(
+                    pBytes + index, count, this);
+        }
+
+        public override Decoder GetDecoder()
+        {
+            return new DecoderNLS(this);
+        }
+
+        public override Encoder GetEncoder()
+        {
+            return new EncoderNLS(this);
+        }
+    }
+}
+#endif // FEATURE_ENCODINGNLS

mcs/class/referencesource/mscorlib/system/text/encodingprovider.cs

@@ -0,0 +1,138 @@
+// ==++==
+//
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+//
+// ==--==
+namespace System.Text
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+
+    [System.Runtime.InteropServices.ComVisible(true)]
+    public abstract class EncodingProvider
+    {
+        public EncodingProvider() { }
+        public abstract Encoding GetEncoding(string name);
+        public abstract Encoding GetEncoding(int codepage);
+
+        // GetEncoding should return either valid encoding or null. shouldn't throw any exception except on null name
+        public virtual Encoding GetEncoding(string name, EncoderFallback encoderFallback, DecoderFallback decoderFallback)
+        {
+            Encoding enc = GetEncoding(name);
+            if (enc != null)
+            {
+                enc = (Encoding)GetEncoding(name).Clone();
+                enc.EncoderFallback = encoderFallback;
+                enc.DecoderFallback = decoderFallback;
+            }
+
+            return enc;
+        }
+
+        public virtual Encoding GetEncoding(int codepage, EncoderFallback encoderFallback, DecoderFallback decoderFallback)
+        {
+            Encoding enc = GetEncoding(codepage);
+            if (enc != null)
+            {
+                enc = (Encoding)GetEncoding(codepage).Clone();
+                enc.EncoderFallback = encoderFallback;
+                enc.DecoderFallback = decoderFallback;
+            }
+
+            return enc;
+        }
+
+        internal static void AddProvider(EncodingProvider provider)
+        {
+            if (provider == null)
+                throw new ArgumentNullException("provider");
+
+            lock (s_InternalSyncObject)
+            {
+                if (s_providers == null)
+                {
+                    s_providers = new EncodingProvider[1] { provider };
+                    return;
+                }
+
+                if (Array.IndexOf(s_providers, provider) >= 0)
+                {
+                    return;
+                }
+
+                var providers = new EncodingProvider[s_providers.Length + 1];
+                Array.Copy(s_providers, providers, s_providers.Length);
+                providers[providers.Length - 1] = provider;
+                s_providers = providers;
+            }
+        }
+
+        internal static Encoding GetEncodingFromProvider(int codepage)
+        {
+            if (s_providers == null)
+                return null;
+
+            var providers = s_providers;
+            foreach (EncodingProvider provider in providers)
+            {
+                Encoding enc = provider.GetEncoding(codepage);
+                if (enc != null)
+                    return enc;
+            }
+
+            return null;
+        }
+
+        internal static Encoding GetEncodingFromProvider(string encodingName)
+        {
+            if (s_providers == null)
+                return null;
+
+            var providers = s_providers;
+            foreach (EncodingProvider provider in providers)
+            {
+                Encoding enc = provider.GetEncoding(encodingName);
+                if (enc != null)
+                    return enc;
+            }
+
+            return null;
+        }
+
+        internal static Encoding GetEncodingFromProvider(int codepage, EncoderFallback enc, DecoderFallback dec)
+        {
+            if (s_providers == null)
+                return null;
+
+            var providers = s_providers;
+            foreach (EncodingProvider provider in providers)
+            {
+                Encoding encing = provider.GetEncoding(codepage, enc, dec);
+                if (encing != null)
+                    return encing;
+            }
+
+            return null;
+        }
+
+        internal static Encoding GetEncodingFromProvider(string encodingName, EncoderFallback enc, DecoderFallback dec)
+        {
+            if (s_providers == null)
+                return null;
+
+            var providers = s_providers;
+            foreach (EncodingProvider provider in providers)
+            {
+                Encoding encoding = provider.GetEncoding(encodingName, enc, dec);
+                if (encoding != null)
+                    return encoding;
+            }
+
+            return null;
+        }
+
+        private static Object s_InternalSyncObject = new Object();
+        private static volatile EncodingProvider[] s_providers;
+    }
+}