Idiomatic default CompressionMode

[tayadelmar]

It would be idiomatic to have CompressionDisabled as a default CompressionMode.

Now it's a bit confusing, because the default mode is CompressionNoContextTakeover and the lib encourages to use context.Context, which is actually very cool, But using the default compression mode with the context leads to a reading error:

failed to read JSON message: failed to read: flate: corrupt input before offset 11

So user needs to investigate the error and research about compression modes if he wants just to connect with default DialOptions.

[nhooyr]

Hmm that's an unexpected error. What client are you getting that from? Indicates a bug somewhere.

But either way, compression is going to be changed to be disabled by default. See #220

[tayadelmar]

The client is:

type Ws struct {
	conn *websocket.Conn
}

func Connect(ctx context.Context) (*Ws, error) {
	c, _, err := websocket.Dial(ctx, "wss://testnet.bitmex.com/realtime", nil)
	if err != nil {
		return nil, fmt.Errorf("dial failed: %w", err)
	}

	ws:=&Ws{c}

	go ws.readLoop()

	return ws, nil
}

func (ws *Ws) readLoop() {
	for {
		var msg interface{}

		ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
		defer cancel()

		if err := wsjson.Read(ctx, ws.conn, &msg); err != nil {
			log.Println(err)
			break
		}

		log.Println("message: ", msg)
	}
}

func (ws *Ws) WriteJSON(ctx context.Context, v interface{}) {
	ctx, cancel := context.WithTimeout(ctx, 15*time.Second)
	defer cancel()
	return wsjson.Write(ctx, ws.conn, v)
}

func (ws *Ws) Disconnect() {
	ws.conn.Close(websocket.StatusNormalClosure, "")
}

I try to subscribe to a trade feed, for example:

func TestSubscription(t *testing.T) {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	ws, _ := Connect(ctx)
	defer ws.Disconnect()

	msg := map[string]interface{}{
		"op":   "subscribe",
		"args": []string{"trade:XRPM20"},
	}

	ctx, cancel = context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	_ = ws.WriteJSON(ctx, msg)

	// wait till message received
}

After connect I get an info message:

{"docs":"https://testnet.bitmex.com/app/wsAPI","info":"Welcome to the BitMEX Realtime API.","limit":{"remaining":39},"timestamp":"2020-04-26T19:17:24.517Z","version":"2020-04-20T21:56:03.000Z"}

Then I write message to subscribe and get the reading error:

failed to read JSON message: failed to read: flate: corrupt input before offset 11

The message, which failed to read, is:

{"request":{"args":["trade:XRPM20"],"op":"subscribe"},"subscribe":"trade:XRPM20","success":true}

Changing CompressMode to CompressionContextTakeover or CompressionDisabled solves the issue.

[nhooyr]

Will debug soon, thanks for reporting!

[nhooyr]

@tayadelmar What happens if you use CompressionContextTakeover?

[tayadelmar]

CompressionContextTakeover doesn't cause the error, which I mentioned above.

[nhooyr]

Awesome, likely looks like it's a bug in their service then that doesn't negotiate context takeover correctly as we test against autobahn but I'll double check the code.