Add a diagnostic.getServerPort analysis server request.

pkg/analysis_server/lib/src/server/http_server.dart

Index: pkg/analysis_server/lib/src/server/http_server.dart
diff --git a/pkg/analysis_server/lib/src/server/http_server.dart b/pkg/analysis_server/lib/src/server/http_server.dart
index 85c355700c0aa4c5438f25b221e0564db3c07eb9..4d88eb4d01214847e26cc4d655a8560addd30c06 100644
--- a/pkg/analysis_server/lib/src/server/http_server.dart
+++ b/pkg/analysis_server/lib/src/server/http_server.dart
@@ -14,8 +14,10 @@ import 'package:analysis_server/src/status/get_handler2.dart';
 
 /**
  * Instances of the class [HttpServer] implement a simple HTTP server. The
- * primary responsibility of this server is to listen for an UPGRADE request and
- * to start an analysis server.
+ * server:
+ *
+ * - listens for an UPGRADE request in order to start an analysis server
+ * - serves diagnostic information as html pages
  */
 class HttpAnalysisServer {
   /**
@@ -49,6 +51,11 @@ class HttpAnalysisServer {
    */
   HttpAnalysisServer(this.socketServer);
 
+  /**
+   * Return the port this server is bound to.
+   */
+  Future<int> get boundPort async => (await _server)?.port;
+
   void close() {
     _server.then((HttpServer server) {
       server.close();
@@ -69,9 +76,20 @@ class HttpAnalysisServer {
   /**
    * Begin serving HTTP requests over the given port.
    */
-  void serveHttp(int port) {
-    _server = HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, port);
-    _server.then(_handleServer).catchError((_) {/* Ignore errors. */});
+  Future<int> serveHttp([int initialPort]) async {
+    if (_server != null) {
+      return boundPort;
+    }
+
+    try {
+      _server =
+          HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, initialPort ?? 0);
+      HttpServer server = await _server;
+      _handleServer(server);
+      return server.port;
+    } catch (ignore) {
+      return null;
+    }
   }
 
   /**
@@ -111,6 +129,8 @@ class HttpAnalysisServer {
    * running an analysis server on a [WebSocket]-based communication channel.
    */
   void _handleWebSocket(WebSocket socket) {
+    // TODO(devoncarew): This is serving the analysis server over a websocket
+    // connection (as well as the diagnostics page over http); is this intended?

[Brian Wilkerson, 2017/02/18 21:41:03]

It's there for historic reasons. The original plan was for analysis server to
connect over http, but then we decided that stdio would be more secure and
faster. The old code has never been cleaned up.

[devoncarew, 2017/02/19 02:43:05]

Makes sense. I updated the comment a bit to mention this.

     socketServer.createAnalysisServer(new WebSocketServerChannel(
         socket, socketServer.instrumentationService));
   }