SocketsHttpHandler, support for custom endpoint address resolving

src/System.Net.Http/ref/System.Net.Http.cs

@@ -176,6 +176,8 @@ public partial class HttpRequestMessage : System.IDisposable
         public HttpRequestMessage() { }
         public HttpRequestMessage(System.Net.Http.HttpMethod method, string requestUri) { }
         public HttpRequestMessage(System.Net.Http.HttpMethod method, System.Uri requestUri) { }
+        public HttpRequestMessage(HttpMethod method, Uri requestUri, System.Net.Sockets.AddressFamily resolveAddressFamily) { }
+        public HttpRequestMessage(HttpMethod method, string requestUri, System.Net.Sockets.AddressFamily resolveAddressFamily) { }
         public System.Net.Http.HttpContent Content { get { throw null; } set { } }
         public System.Net.Http.Headers.HttpRequestHeaders Headers { get { throw null; } }
         public System.Net.Http.HttpMethod Method { get { throw null; } set { } }
@@ -185,6 +187,7 @@ public HttpRequestMessage(System.Net.Http.HttpMethod method, System.Uri requestU
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
         public override string ToString() { throw null; }
+        public System.Net.Sockets.AddressFamily ResolveAddressFamily { get { throw null; } set { } }
     }
     public partial class HttpResponseMessage : System.IDisposable
     {

src/System.Net.Http/src/System/Net/Http/HttpRequestMessage.cs

@@ -7,6 +7,7 @@
 using System.Text;
 using System.Threading;
 using System.Collections.Generic;
+using System.Net.Sockets;
 
 namespace System.Net.Http
 {
@@ -26,6 +27,7 @@ public class HttpRequestMessage : IDisposable
         private HttpContent _content;
         private bool _disposed;
         private IDictionary<String, Object> _properties;
+        private AddressFamily _resolveAddressFamily;
 
         public Version Version
         {
@@ -98,6 +100,16 @@ public Uri RequestUri
             }
         }
 
+        public AddressFamily ResolveAddressFamily
+        {
+            get { return _resolveAddressFamily; }
+            set
+            {
+                CheckDisposed();
+                _resolveAddressFamily = value;
+            }
+        }
+
         public HttpRequestHeaders Headers
         {
             get
@@ -129,16 +141,26 @@ public HttpRequestMessage()
         {
         }
 
-        public HttpRequestMessage(HttpMethod method, Uri requestUri)
+        private const AddressFamily DefaultAddressFamily = AddressFamily.Unspecified;
+
+        public HttpRequestMessage(HttpMethod method, Uri requestUri) : this(method, requestUri, DefaultAddressFamily)
+        {
+        }
+
+        public HttpRequestMessage(HttpMethod method, Uri requestUri, AddressFamily resolveAddressFamily)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this, method, requestUri);
-            InitializeValues(method, requestUri);
+            InitializeValues(method, requestUri, resolveAddressFamily);
             if (NetEventSource.IsEnabled) NetEventSource.Exit(this);
         }
 
+        public HttpRequestMessage(HttpMethod method, string requestUri) : this(method, requestUri, DefaultAddressFamily)
+        {
+        }
+
         [SuppressMessage("Microsoft.Design", "CA1057:StringUriOverloadsCallSystemUriOverloads",
             Justification = "It is OK to provide 'null' values. A Uri instance is created from 'requestUri' if it is != null.")]
-        public HttpRequestMessage(HttpMethod method, string requestUri)
+        public HttpRequestMessage(HttpMethod method, string requestUri, AddressFamily resolveAddressFamily)
         {
             if (NetEventSource.IsEnabled) NetEventSource.Enter(this, method, requestUri);
 
@@ -147,11 +169,11 @@ public HttpRequestMessage(HttpMethod method, string requestUri)
             // Note that we also allow the string to be empty: null and empty are considered equivalent.
             if (string.IsNullOrEmpty(requestUri))
             {
-                InitializeValues(method, null);
+                InitializeValues(method, null, resolveAddressFamily);
             }
             else
             {
-                InitializeValues(method, new Uri(requestUri, UriKind.RelativeOrAbsolute));
+                InitializeValues(method, new Uri(requestUri, UriKind.RelativeOrAbsolute), resolveAddressFamily);
             }
 
             if (NetEventSource.IsEnabled) NetEventSource.Exit(this);
@@ -179,7 +201,7 @@ public override string ToString()
             return sb.ToString();
         }
 
-        private void InitializeValues(HttpMethod method, Uri requestUri)
+        private void InitializeValues(HttpMethod method, Uri requestUri, AddressFamily resolveAddressFamily)
         {
             if (method == null)
             {
@@ -192,6 +214,7 @@ private void InitializeValues(HttpMethod method, Uri requestUri)
 
             _method = method;
             _requestUri = requestUri;
+            _resolveAddressFamily = resolveAddressFamily;
             _version = HttpUtilities.DefaultRequestVersion;
         }
 

src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs

@@ -32,7 +32,7 @@ public CertificateCallbackMapper(Func<HttpRequestMessage, X509Certificate2, X509
             }
         }
 
-        public static async ValueTask<Stream> ConnectAsync(string host, int port, CancellationToken cancellationToken)
+        public static async ValueTask<Stream> ConnectAsync(string host, int port, AddressFamily addressFamily, CancellationToken cancellationToken)
         {
             try
             {
@@ -42,9 +42,18 @@ public static async ValueTask<Stream> ConnectAsync(string host, int port, Cancel
                 using (var saea = new BuilderAndCancellationTokenSocketAsyncEventArgs(cancellationToken))
                 {
                     // Configure which server to which to connect.
-                    saea.RemoteEndPoint = IPAddress.TryParse(host, out IPAddress address) ?
+                    if (SocketsHttpHandler.ResolveEndpointAsync == null)
+                    {
+                        saea.RemoteEndPoint = IPAddress.TryParse(host, out IPAddress address) ?
                         (EndPoint)new IPEndPoint(address, port) :
                         new DnsEndPoint(host, port);
+                    }
+                    else
+                    {
+                        //give user control how to resolve endpoint address
+                        var resolveEndpointTask = SocketsHttpHandler.ResolveEndpointAsync(host, port, addressFamily, cancellationToken);
+                        saea.RemoteEndPoint = resolveEndpointTask.IsCompleted ? resolveEndpointTask.Result : await resolveEndpointTask.ConfigureAwait(false);
+                    }
 
                     // Hook up a callback that'll complete the Task when the operation completes.
                     saea.Completed += (s, e) =>

src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

@@ -306,11 +306,11 @@ public Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, bool doRe
                     case HttpConnectionKind.Http:
                     case HttpConnectionKind.Https:
                     case HttpConnectionKind.ProxyConnect:
-                        stream = await ConnectHelper.ConnectAsync(_host, _port, cancellationToken).ConfigureAwait(false);
+                        stream = await ConnectHelper.ConnectAsync(_host, _port, request.ResolveAddressFamily, cancellationToken).ConfigureAwait(false);
                         break;
 
                     case HttpConnectionKind.Proxy:
-                        stream = await ConnectHelper.ConnectAsync(_proxyUri.IdnHost, _proxyUri.Port, cancellationToken).ConfigureAwait(false);
+                        stream = await ConnectHelper.ConnectAsync(_proxyUri.IdnHost, _proxyUri.Port, request.ResolveAddressFamily, cancellationToken).ConfigureAwait(false);
                         break;
 
                     case HttpConnectionKind.SslProxyTunnel:

src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocketsHttpHandler.cs

@@ -4,6 +4,7 @@
 
 using System.Collections.Generic;
 using System.Net.Security;
+using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -388,5 +389,14 @@ private Exception ValidateAndNormalizeRequest(HttpRequestMessage request)
 
             return null;
         }
+
+        public delegate Task<EndPoint> ResolveEndpointAsyncDelegate(string host, int port, AddressFamily addressFamily, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// With this property user can have more control when resolving IP address. For example one could prefer to resolve IPv6 addresses over IPv4
+        /// or completely override system default DNS resolving logic.
+        /// If set to null (default) client behaves same as before (backward compatible).
+        /// </summary>
+        public static ResolveEndpointAsyncDelegate ResolveEndpointAsync { get; set; } = null;
     }
 }