Imported Upstream version 4.4.2.4

Former-commit-id: 92904c9c5915c37244316e42ba99e7b934ed7ee2

mcs/class/System.IO.Compression/SharpCompress/IO/ReadOnlySubStream.cs

@@ -16,6 +16,7 @@ namespace SharpCompress.IO
             {
                 stream.Position = origin.Value;
             }
+            length = bytesToRead;
             BytesLeftToRead = bytesToRead;
         }
 
@@ -27,6 +28,8 @@ namespace SharpCompress.IO
             }
         }
 
+        private long length;
+
         private long BytesLeftToRead { get; set; }
 
         public Stream Stream { get; private set; }
@@ -53,12 +56,12 @@ namespace SharpCompress.IO
 
         public override long Length
         {
-            get { throw new System.NotImplementedException(); }
+            get { return length; }
         }
 
         public override long Position
         {
-            get { throw new System.NotImplementedException(); }
+            get { return Length - BytesLeftToRead; }
             set { throw new System.NotImplementedException(); }
         }