From 25fd476328ca51252430eedf90e60c7b814f40d4 Mon Sep 17 00:00:00 2001
From: Wichert Akkerman <wichert@wiggy.net>
Date: Wed, 16 Oct 2019 14:44:22 +0200
Subject: [PATCH] Negotiate xmpp websocket subprotocol

---
 websocket_transport.go | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/websocket_transport.go b/websocket_transport.go
index 26ab511..690bc1d 100644
--- a/websocket_transport.go
+++ b/websocket_transport.go
@@ -2,6 +2,7 @@ package xmpp
 
 import (
 	"context"
+	"errors"
 	"net"
 	"strings"
 	"time"
@@ -11,6 +12,8 @@ import (
 
 const pingTimeout = time.Duration(5) * time.Second
 
+var ServerDoesNotSupportXmppOverWebsocket = errors.New("The websocket server does not support the xmpp subprotocol")
+
 type WebsocketTransport struct {
 	Config  TransportConfiguration
 	wsConn  *websocket.Conn
@@ -27,10 +30,15 @@ func (t *WebsocketTransport) Connect() error {
 		defer cancel()
 	}
 
-	wsConn, _, err := websocket.Dial(t.ctx, t.Config.Address, nil)
+	wsConn, response, err := websocket.Dial(t.ctx, t.Config.Address, &websocket.DialOptions{
+		Subprotocols: []string{"xmpp"},
+	})
 	if err != nil {
 		return NewConnError(err, true)
 	}
+	if response.Header.Get("Sec-WebSocket-Protocol") != "xmpp" {
+		return ServerDoesNotSupportXmppOverWebsocket
+	}
 	t.wsConn = wsConn
 	t.netConn = websocket.NetConn(t.ctx, t.wsConn, websocket.MessageText)
 	return nil