Add a shelf_web_socket package.

pkg/shelf_web_socket/lib/src/web_socket_handler.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library shelf_web_socket.web_socket_handler;
+
+import 'dart:convert';
+
+import 'package:http_parser/http_parser.dart';
+import 'package:shelf/shelf.dart';
+
+/// A class that exposes a handler for upgrading WebSocket requests.
+class WebSocketHandler {
+  /// The function to call when a request is upgraded.
+  final Function _onConnection;
+
+  /// The set of protocols the user supports, or `null`.
+  final Set<String> _protocols;
+
+  /// The set of allowed browser origin connections, or `null`..
+  final Set<String> _allowedOrigins;
+
+  WebSocketHandler(this._onConnection, this._protocols, this._allowedOrigins);
+
+  /// The [Handler].
+  Response handle(Request request) {
+    if (request.method != 'GET') return _notFound();
+
+    var connection = request.headers['Connection'];
+    if (connection == null) return _notFound();
+    if (connection.toLowerCase() != 'upgrade') return _notFound();
+
+    var upgrade = request.headers['Upgrade'];
+    if (upgrade == null) return _notFound();
+    if (upgrade.toLowerCase() != 'websocket') return _notFound();
+
+    var version = request.headers['Sec-WebSocket-Version'];
+    if (version == null) {
+      return _badRequest('missing Sec-WebSocket-Version header.');
+    } else if (version != '13') {
+      return _notFound();
+    }
+
+    if (request.protocolVersion != '1.1') {
+      return _badRequest('unexpected HTTP version '
+          '"${request.protocolVersion}".');
+    }
+
+    var key = request.headers['Sec-WebSocket-Key'];
+    if (key == null) return _badRequest('missing Sec-WebSocket-Key header.');
+
+    if (!request.canHijack) {
+      throw new ArgumentError("webSocketHandler may only be used with a server "
+          "that supports request hijacking.");
+    }
+
+    // The Origin header is always set by browser connections. By filtering out
+    // unexpected origins, we ensure that malicious JavaScript is unable to fake
+    // a WebSocket handshake.
+    var origin = request.headers['Origin'];
+    if (origin != null && _allowedOrigins != null &&
+        !_allowedOrigins.contains(origin.toLowerCase())) {
+      return _forbidden('invalid origin "$origin".');
+    }
+
+    var protocol = _chooseProtocol(request);
+    request.hijack((stream, byteSink) {
+      var sink = UTF8.encoder.startChunkedConversion(byteSink);
+      sink.add(
+          "HTTP/1.1 101 Switching Protocols\r\n"
+          "Upgrade: websocket\r\n"
+          "Connection: Upgrade\r\n"
+          "Sec-WebSocket-Accept: ${CompatibleWebSocket.signKey(key)}\r\n");
+      if (protocol != null) sink.add("Sec-WebSocket-Protocol: $protocol\r\n");
+      sink.add("\r\n");
+
+      _onConnection(new CompatibleWebSocket(stream, sink: byteSink), protocol);
+    });
+
+    // [request.hijack] is guaranteed to throw a [HijackException], so we'll
+    // never get here.
+    assert(false);
+    return null;
+  }
+
+  /// Selects a subprotocol to use for the given connection.
+  ///
+  /// If no matching protocol can be found, returns `null`.
+  String _chooseProtocol(Request request) {
+    var protocols = request.headers['Sec-WebSocket-Protocol'];
+    if (protocols == null) return null;
+    for (var protocol in protocols.split(',')) {
+      protocol = protocol.trim();
+      if (_protocols.contains(protocol)) return protocol;
+    }
+    return null;
+  }
+
+  /// Returns a 404 Not Found response.
+  Response _notFound() => _htmlResponse(404, "404 Not Found",
+      "Only WebSocket connections are supported.");
+
+  /// Returns a 400 Bad Request response.
+  ///
+  /// [message] will be HTML-escaped before being included in the response body.
+  Response _badRequest(String message) => _htmlResponse(400, "400 Bad Request",
+      "Invalid WebSocket upgrade request: $message");
+
+  /// Returns a 403 Forbidden response.
+  ///
+  /// [message] will be HTML-escaped before being included in the response body.
+  Response _forbidden(String message) => _htmlResponse(403, "403 Forbidden",
+      "WebSocket upgrade refused: $message");
+
+  /// Creates an HTTP response with the given [statusCode] and an HTML body with
+  /// [title] and [message].
+  ///
+  /// [title] and [message] will be automatically HTML-escaped.
+  Response _htmlResponse(int statusCode, String title, String message) {
+    title = HTML_ESCAPE.convert(title);
+    message = HTML_ESCAPE.convert(message);
+    return new Response(statusCode, body: """
+      <!doctype html>
+      <html>
+        <head><title>$title</title></head>
+        <body>
+          <h1>$title</h1>
+          <p>$message</p>
+        </body>
+      </html>
+    """, headers: {'content-type': 'text/html'});
+  }
+}