Handle tcp self connection issues (#4599)

src/endpoint.hpp

@@ -29,6 +29,8 @@ struct endpoint_uri_pair_t
         return local_type == endpoint_type_bind ? local : remote;
     }
 
+    const bool clash () const { return local == remote; }
+
     std::string local, remote;
     endpoint_type_t local_type;
 };

src/stream_engine_base.cpp

@@ -294,8 +294,14 @@ bool zmq::stream_engine_base_t::in_event_internal ()
     //  or the session has rejected the message.
     if (rc == -1) {
         if (errno != EAGAIN) {
-            error (protocol_error);
-            return false;
+            // In cases where the src/dst have the same IP and the dst uses an ephemeral port, reconnection
+            // eventually results in the src and dest IP and port clashing (google tcp self connection)
+            // While this is a protocol_error (you have the single zmq socket handshaking with itself)
+            // we do not want to to stop reconnection from happening
+            if (!_endpoint_uri_pair.clash ()) {
+                error (protocol_error);
+                return false;
+            }
         }
         _input_stopped = true;
         reset_pollin (_handle);