Allow additional headers for WebSocket connect

sdk/lib/io/websocket_impl.dart

Index: sdk/lib/io/websocket_impl.dart
diff --git a/sdk/lib/io/websocket_impl.dart b/sdk/lib/io/websocket_impl.dart
index 872cd321ad7b223deadefd840311925fe9f123b8..19ebfbf532e2843392053a16f0b33869a728446c 100644
--- a/sdk/lib/io/websocket_impl.dart
+++ b/sdk/lib/io/websocket_impl.dart
@@ -769,7 +769,8 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
 
   static final HttpClient _httpClient = new HttpClient();
 
-  static Future<WebSocket> connect(String url, List<String> protocols) {
+  static Future<WebSocket> connect(
+      String url, Iterable<String> protocols, Map<String, dynamic> headers) {
     Uri uri = Uri.parse(url);
     if (uri.scheme != "ws" && uri.scheme != "wss") {
       throw new WebSocketException("Unsupported URL scheme '${uri.scheme}'");
@@ -795,6 +796,9 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
                   fragment: uri.fragment);
     return _httpClient.openUrl("GET", uri)
       .then((request) {
+        if (headers != null) {
+          headers.forEach((field, value) => request.headers.add(field, value));
+        }
         // Setup the initial handshake.
         request.headers
             ..add(HttpHeaders.CONNECTION, "Upgrade")

[kustermann, 2015/01/14 11:42:17]

Why is this an .add() and not a .set(). 

If the user supplied a connection header as well, you have 2 of them, right?
That's not what we want if I see this right.

[Søren Gjesse, 2015/01/14 13:54:26]

Good catch.