Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ServiceModel/System/ServiceModel/Channels/DnsCache.cs

@@ -0,0 +1,147 @@
+//----------------------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//----------------------------------------------------------------------------
+namespace System.ServiceModel.Channels
+{
+    using System.Collections.Generic;
+    using System.Diagnostics;
+    using System.Net;
+    using System.Net.NetworkInformation;
+    using System.Net.Sockets;
+    using System.Runtime;
+    using System.Security.Permissions;
+    using System.ServiceModel;
+    using System.ServiceModel.Dispatcher;
+    using System.Text;
+
+    static class DnsCache
+    {
+        const int mruWatermark = 64;
+        static MruCache<string, DnsCacheEntry> resolveCache = new MruCache<string, DnsCacheEntry>(mruWatermark);
+        static readonly TimeSpan cacheTimeout = TimeSpan.FromSeconds(2);
+
+        // Double-checked locking pattern requires volatile for read/write synchronization
+        static volatile string machineName;
+
+        static object ThisLock
+        {
+            get
+            {
+                return resolveCache;
+            }
+        }
+
+        public static string MachineName
+        {
+            get
+            {
+                if (machineName == null)
+                {
+                    lock (ThisLock)
+                    {
+                        if (machineName == null)
+                        {
+                            try
+                            {
+                                machineName = Dns.GetHostEntry(String.Empty).HostName;
+                            }
+                            catch (SocketException exception)
+                            {
+                                DiagnosticUtility.TraceHandledException(exception,
+                                        TraceEventType.Information);                                
+                                // we fall back to the NetBios machine if Dns fails
+                                machineName = UnsafeNativeMethods.GetComputerName(ComputerNameFormat.PhysicalNetBIOS);
+                            }
+                        }
+                    }
+                }
+
+                return machineName;
+            }
+        }
+
+        public static IPHostEntry Resolve(Uri uri)
+        {
+            string hostName = uri.DnsSafeHost;
+            IPHostEntry hostEntry = null;
+            DateTime now = DateTime.UtcNow;
+
+            lock (ThisLock)
+            {
+                DnsCacheEntry cacheEntry;
+                if (resolveCache.TryGetValue(hostName, out cacheEntry))
+                {
+                    if (now.Subtract(cacheEntry.TimeStamp) > cacheTimeout)
+                    {
+                        resolveCache.Remove(hostName);
+                    }
+                    else
+                    {
+                        if (cacheEntry.HostEntry == null)
+                        {
+                            throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
+                                new EndpointNotFoundException(SR.GetString(SR.DnsResolveFailed, hostName)));
+                        }
+                        hostEntry = cacheEntry.HostEntry;
+                    }
+                }
+            }
+
+            if (hostEntry == null)
+            {
+                SocketException dnsException = null;
+                try
+                {
+                    hostEntry = Dns.GetHostEntry(hostName);
+                }
+                catch (SocketException e)
+                {
+                    dnsException = e;
+                }
+
+                lock (ThisLock)
+                {
+                    // MruCache doesn't have a this[] operator, so we first remove (just in case it exists already)
+                    resolveCache.Remove(hostName);
+                    resolveCache.Add(hostName, new DnsCacheEntry(hostEntry, now));
+                }
+
+                if (dnsException != null)
+                {
+                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
+                        new EndpointNotFoundException(SR.GetString(SR.DnsResolveFailed, hostName), dnsException));
+                }
+            }
+
+            return hostEntry;
+        }
+
+        class DnsCacheEntry
+        {
+            IPHostEntry hostEntry;
+            DateTime timeStamp;
+
+            public DnsCacheEntry(IPHostEntry hostEntry, DateTime timeStamp)
+            {
+                this.hostEntry = hostEntry;
+                this.timeStamp = timeStamp;
+            }
+
+            public IPHostEntry HostEntry
+            {
+                get
+                {
+                    return hostEntry;
+                }
+            }
+
+            public DateTime TimeStamp
+            {
+                get
+                {
+                    return timeStamp;
+                }
+            }
+        }
+    }
+}