Close a connection is sending fails.

protocol/connections/peerapp.go

@@ -153,7 +153,21 @@ func (pa *PeerApp) SendMessage(message model2.PeerMessage) error {
 	}
 
 	if err == nil {
-		return pa.connection.Send(serialized)
+		err = pa.connection.Send(serialized)
+
+		// at this point we have tried to send a connection to a peer only to find that something went wrong.
+		// we don't know *what* went wrong - the most likely explanation is the peer went offline in the time between
+		// sending the message and it arriving in the engine to be sent. Other explanations include problems with Tor,
+		// a dropped wifi connection.
+		// Regardless, we error out this message and close this peer app assuming it cannot be used again.
+		// We expect that cwtch will eventually recreate this connection and the app.
+		if err != nil {
+			// close any associated sockets
+			pa.connection.Close()
+			// tell cwtch this connection is no longer valid
+			pa.OnClose(err.Error())
+		}
+		return err
 	}
 	return err
 }