Raise connection error when server endpoint not reachable (#768)

StackExchange.Redis/StackExchange/Redis/ResultProcessor.cs

@@ -152,6 +152,7 @@ public virtual bool SetResult(PhysicalConnection connection, Message message, Ra
                 bool log = !message.IsInternalCall;
                 bool isMoved = result.AssertStarts(MOVED);
                 string err = string.Empty;
+                bool unableToConnectError = false;
                 if (isMoved || result.AssertStarts(ASK))
                 {
                     message.SetResponseReceived();
@@ -178,6 +179,7 @@ public virtual bool SetResult(PhysicalConnection connection, Message message, Ra
                                 }
                                 else
                                 {
+                                    unableToConnectError = true;
                                     err = $"Endpoint {endpoint} serving hashslot {hashSlot} is not reachable at this point of time. Please check connectTimeout value. If it is low, try increasing it to give the ConnectionMultiplexer a chance to recover from the network disconnect.  ";
                                 }
 #if FEATURE_PERFCOUNTER
@@ -198,8 +200,15 @@ public virtual bool SetResult(PhysicalConnection connection, Message message, Ra
                     bridge.Multiplexer.OnErrorMessage(server.EndPoint, err);
                 }
                 connection.Multiplexer.Trace("Completed with error: " + err + " (" + GetType().Name + ")", ToString());
+                if (unableToConnectError)
+                {
+                    ConnectionFail(message, ConnectionFailureType.UnableToConnect, err);
+                }
+                else
+                {
                     ServerFail(message, err);
                 }
+            }
             else
             {
                 bool coreResult = SetResultCore(connection, message, result);