Fix fake tunnel failure

Author: justcoding121

src/Titanium.Web.Proxy/RequestHandler.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
+using System.Net.Sockets;
 #if NETCOREAPP2_1
 using System.Net.Security;
 #endif
@@ -188,8 +189,20 @@ await clientStreamWriter.WriteResponseAsync(args.HttpClient.Response,
                             //If prefetch task is available.
                             if (connection == null && prefetchTask != null)
                             {
-                                connection = await prefetchTask;
+                                try
+                                {
+                                    connection = await prefetchTask;
+                                }
+                                catch (SocketException e)
+                                {
+                                    if(e.SocketErrorCode != SocketError.HostNotFound)
+                                    {
+                                        throw;
+                                    }
+                                }
+
                                 prefetchTask = null;
+
                             }
 
                             // create a new connection if cache key changes.

tests/Titanium.Web.Proxy.IntegrationTests/HttpsTests.cs

@@ -33,5 +33,34 @@ public async Task Can_Handle_Https_Request()
             Assert.AreEqual("I am server. I received your greetings.", body);
         }
 
+        [TestMethod]
+        public async Task Can_Handle_Https_Fake_Tunnel_Request()
+        {
+            var testSuite = new TestSuite();
+
+            var server = testSuite.GetServer();
+            server.HandleRequest((context) =>
+            {
+                return context.Response.WriteAsync("I am server. I received your greetings.");
+            });
+
+            var proxy = testSuite.GetProxy();
+            proxy.BeforeRequest += async (sender, e) =>
+            {
+                e.HttpClient.Request.RequestUri = new Uri(server.ListeningHttpUrl);
+                await Task.FromResult(0);
+            };
+
+            var client = testSuite.GetClient(proxy);
+
+            var response = await client.PostAsync(new Uri($"https://{Guid.NewGuid().ToString()}.com"),
+                                        new StringContent("hello server. I am a client."));
+
+            Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
+            var body = await response.Content.ReadAsStringAsync();
+
+            Assert.AreEqual("I am server. I received your greetings.", body);
+        }
+
     }
 }