Implemented Fraser's suggestion

Typically client offers supported encodings, then the server chooses the
optimal one.

protocol.go

@@ -200,23 +200,37 @@ func addPlayer(ws *websocket.Conn) {
 		return
 	}
 
-	err = websocket.JSON.Send(ws,
-		[]string{"json", "jsonz", "gob"},
-	)
+	reqEncs := []string{}
+	err = websocket.JSON.Receive(ws, &reqEncs)
 	if err != nil {
-		log.Printf("%s %s unable to send supported encodings msg", gid.Id, player_id)
-		websocket.JSON.Send(ws, NewFailure("encoding send error"))
-		return
-	}
-	var encoding string
-	err = websocket.JSON.Receive(ws, &encoding)
-	if err != nil {
-		log.Printf("%s %s unable to parse encoding", gid.Id, player_id)
+		log.Printf("%s %s unable to parse requested encodings", gid.Id, player_id)
 		websocket.JSON.Send(ws, NewFailure("encoding recieve error"))
 		return
 	}
-	log.Printf("negociated encoding: %s", encoding)
-	// TODO: use this negociated encoding
+	prefEncs := []string{
+		"gob",
+		"json",
+	}
+
+	var encoding string
+encodingLoops:
+	for _, prefEnc := range prefEncs {
+		for _, reqEnc := range reqEncs {
+			if reqEnc == prefEnc {
+				encoding = prefEnc
+				log.Println("selected following encoding:", encoding)
+				break encodingLoops
+			}
+		}
+	}
+	if encoding == "" {
+		log.Printf("%s %s unable to negociate encoding", gid.Id, player_id)
+		websocket.JSON.Send(
+			ws,
+			NewFailure("no overlap on supported encodings; I suggest using json"),
+		)
+		return
+	}
 
 	gameParam := game.gameParam()
 	gp := struct {