Add workaround for mono/mono#17710. (#387)

Mono-specific workaround of https://github.com/mono/mono/issues/17710.

2 files changed, 78 insertions, 0 deletions

diff --git a/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs b/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
index 9701716f1a..e7ffaef7bc 100644
--- a/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
+++ b/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnection.cs
@@ -193,6 +193,19 @@ namespace System.Net.Http
                 _readAheadTask = new ValueTask<int>(0);
             }
 
+#if MONO
+            if (!_readAheadTask.Value.IsCompleted && _socket != null)
+            {
+                try
+                {
+                    return _socket.Poll(0, SelectMode.SelectRead);
+                }
+                catch
+                {
+                    return false;
+                }
+            }
+#endif
             return _readAheadTask.Value.IsCompleted; // equivalent to polling
         }
 
diff --git a/src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.ConnectionReuse.cs b/src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.ConnectionReuse.cs
new file mode 100644
index 0000000000..b17839048b
--- /dev/null
+++ b/src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.ConnectionReuse.cs
@@ -0,0 +1,65 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Net.Sockets;
+using System.Net.Test.Common;
+using System.Text;
+using System.Threading.Tasks;
+
+#if !MONO
+using Microsoft.DotNet.XUnitExtensions;
+using Microsoft.DotNet.RemoteExecutor;
+#endif
+
+using Xunit;
+using Xunit.Abstractions;
+
+namespace System.Net.Http.Functional.Tests
+{
+    using Configuration = System.Net.Test.Common.Configuration;
+
+    public class HttpClientHandler_ConnectionReuse_Test : HttpClientTestBase
+    {
+        [Fact]
+        public async Task Test17710()
+        {
+            using (HttpClient client = CreateHttpClient())
+            {
+                const string text = "THE POST CONTENT";
+                var data = new StringContent(text);
+                await LoopbackServer.CreateServerAsync(async (server, url) =>
+                {
+                    Task serverTask1 = server.AcceptConnectionAsync(async connection1 =>
+                    {
+                        await connection1.ReadRequestHeaderAsync();
+                        var buffer = new char[text.Length];
+                        var ret = await connection1.Reader.ReadBlockAsync(buffer, 0, buffer.Length);
+                        Assert.Equal(text.Length, ret);
+                        await connection1.SendResponseAsync(HttpStatusCode.OK, null, "hello");
+                        await Task.Delay(500);
+                        connection1.Dispose();
+                    });
+
+                    await client.PostAsync(url, data);
+
+                    await serverTask1;
+
+                    Task serverTask2 = server.AcceptConnectionAsync(async connection2 =>
+                    {
+                        await connection2.ReadRequestHeaderAsync();
+                        var buffer = new char[text.Length];
+                        var ret = await connection2.Reader.ReadBlockAsync(buffer, 0, buffer.Length);
+                        Assert.Equal(text.Length, ret);
+                        await connection2.SendResponseAsync(HttpStatusCode.OK, null, "hello");
+                        await Task.Delay(500);
+                        connection2.Dispose();
+                    });
+
+                    await client.PostAsync(url, data);
+                });
+            }
+        }
+    }
+}