Expose the Observatory URL when debugging.

lib/src/runner/browser/dartium.dart

Index: lib/src/runner/browser/dartium.dart
diff --git a/lib/src/runner/browser/dartium.dart b/lib/src/runner/browser/dartium.dart
index 0783f1005e43bebcff04656b0eb3a03752959e6f..8e6a8a30c6431d2b6f10ed80ca7e98a4332a8a72 100644
--- a/lib/src/runner/browser/dartium.dart
+++ b/lib/src/runner/browser/dartium.dart
@@ -5,13 +5,19 @@
 library test.runner.browser.dartium;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 
+import 'package:async/async.dart';
 import 'package:path/path.dart' as p;
 
+import '../../util/cancelable_future.dart';
 import '../../util/io.dart';
+import '../../utils.dart';
 import 'browser.dart';
 
+final _observatoryRegExp = new RegExp(r"^Observatory listening on ([^ ]+)");
+
 /// A class for running an instance of Dartium.
 ///
 /// Most of the communication with the browser is expected to happen via HTTP,
@@ -22,35 +28,45 @@ import 'browser.dart';
 class Dartium extends Browser {
   final name = "Dartium";
 
-  Dartium(url, {String executable})
-      : super(() => _startBrowser(url, executable));
+  final Future<Uri> observatoryUrl;
+
+  factory Dartium(url, {String executable}) {
+    var completer = new Completer.sync();
+    return new Dartium._(() async {
+      if (executable == null) executable = _defaultExecutable();
+
+      var dir = createTempDir();
+      var process = await Process.start(executable, [
+        "--user-data-dir=$dir",
+        url.toString(),
+        "--disable-extensions",
+        "--disable-popup-blocking",
+        "--bwsi",
+        "--no-first-run",
+        "--no-default-browser-check",
+        "--disable-default-apps",
+        "--disable-translate"
+      ], environment: {"DART_FLAGS": "--checked"});
+
+      // The first observatory URL emitted is for the empty start page; the
+      // second is actually for the host page.
+      completer.complete(_getObservatoryUrl(process.stdout));
+
+      process.exitCode
+          .then((_) => new Directory(dir).deleteSync(recursive: true));
+
+      return process;
+    }, completer.future);
+  }
+
+  Dartium._(Future<Process> startBrowser(), this.observatoryUrl)
+      : super(startBrowser);
 
   /// Starts a new instance of Dartium open to the given [url], which may be a
   /// [Uri] or a [String].
   ///
   /// If [executable] is passed, it's used as the Dartium executable. Otherwise
   /// the default executable name for the current OS will be used.
-  static Future<Process> _startBrowser(url, [String executable]) async {
-    if (executable == null) executable = _defaultExecutable();
-
-    var dir = createTempDir();
-    var process = await Process.start(executable, [
-      "--user-data-dir=$dir",
-      url.toString(),
-      "--disable-extensions",
-      "--disable-popup-blocking",
-      "--bwsi",
-      "--no-first-run",
-      "--no-default-browser-check",
-      "--disable-default-apps",
-      "--disable-translate"
-    ], environment: {"DART_FLAGS": "--checked"});
-
-    process.exitCode
-        .then((_) => new Directory(dir).deleteSync(recursive: true));
-
-    return process;
-  }
 
   /// Return the default executable for the current operating system.
   static String _defaultExecutable() {
@@ -86,4 +102,150 @@ class Dartium extends Browser {
     var dartium = p.join(dir, "chromium", "chrome");
     return new File(dartium).existsSync() ? dartium : null;
   }
+
+  // TODO(nweiz): simplify this when sdk#23923 is fixed.
+  /// Returns the Observatory URL for the Dartium executable with the given
+  /// [stdout] stream, or `null` if the correct one couldn't be found.
+  ///
+  /// Dartium prints out three different Observatory URLs when it starts. Only
+  /// one of them is connected to the VM instance running the host page, and the
+  /// ordering isn't guaranteed, so we need to figure out which one is correct.
+  /// We do so by connecting to the VM service via WebSockets and looking for
+  /// the Observatory instance that actually contains an isolate, and returning
+  /// the corresponding URI.
+  static Future<Uri> _getObservatoryUrl(Stream<List<int>> stdout) async {
+    var urlQueue = new StreamQueue(lineSplitter.bind(stdout).map((line) {
+      var match = _observatoryRegExp.firstMatch(line);
+      return match == null ? null : Uri.parse(match[1]);
+    }).where((line) => line != null));
+
+    var futures = [
+      urlQueue.next,
+      urlQueue.next,
+      urlQueue.next
+    ].map(_checkObservatoryUrl);
+
+    urlQueue.cancel();
+
+    /// Dartium will print three possible observatory URLs. For each one, we
+    /// check whether it's actually connected to an isolate, indicating that
+    /// it's the observatory for the main page. Once we find the one that is, we
+    /// cancel the other requests and return it.
+    return inCompletionOrder(futures)
+        .firstWhere((url) => url != null, defaultValue: () => null);
+  }
+
+  /// If the URL returned by [future] corresponds to the correct Observatory
+  /// instance, returns it. Otherwise, returns `null`.
+  ///
+  /// If the returned future is canceled before it fires, the WebSocket
+  /// connection with the given Observatory will be closed immediately.
+  static CancelableFuture<Uri> _checkObservatoryUrl(Future<Uri> future) {
+    var webSocket;
+    var canceled = false;
+    var completer = new CancelableCompleter(() {
+      canceled = true;
+      if (webSocket != null) webSocket.close();
+    });
+
+    // We've encountered a format we don't understand. Close the web socket and
+    // complete to null.
+    giveUp() {
+      webSocket.close();
+      if (!completer.isCompleted) completer.complete();
+    }
+
+    future.then((url) async {
+      try {
+        webSocket = await WebSocket.connect(
+            url.replace(scheme: 'ws', path: '/ws').toString());
+        if (canceled) {
+          webSocket.close();
+          return null;
+        }
+
+        webSocket.add(JSON.encode({
+          "jsonrpc": "2.0",
+          "method": "streamListen",
+          "params": {"streamId": "Isolate"},
+          "id": "0"
+        }));
+
+        webSocket.add(JSON.encode({
+          "jsonrpc": "2.0",
+          "method": "getVM",
+          "params": {},
+          "id": "1"
+        }));
+
+        webSocket.listen((response) {
+          try {
+            response = JSON.decode(response);
+          } on FormatException catch (_) {
+            giveUp();
+            return;
+          }
+
+          // If there's a "response" key, we're probably talking to the pre-1.0
+          // VM service protocol, in which case we should just give up.
+          if (response is! Map || response.containsKey("response")) {
+            giveUp();
+            return;
+          }
+
+          if (response["id"] == "0") return;
+
+          if (response["id"] == "1") {
+            var result = response["result"];
+            if (result is! Map) {
+              giveUp();
+              return;
+            }
+
+            var isolates = result["isolates"];
+            if (isolates is! List) {
+              giveUp();
+              return;
+            }
+
+            if (isolates.isNotEmpty) {
+              webSocket.close();
+              if (!completer.isCompleted) completer.complete(url);
+            }
+            return;
+          }
+
+          // The 1.0 protocol used a raw "event" key, while the 2.0 protocol
+          // wraps it in JSON-RPC method params.
+          var event;
+          if (response.containsKey("event")) {
+            event = response["event"];
+          } else {
+            var params = response["params"];
+            if (params is Map) event = params["event"];
+          }
+
+          if (event is! Map) {
+            giveUp();
+            return;
+          }
+
+          if (event["kind"] != "IsolateStart") return;
+          webSocket.close();
+          if (completer.isCompleted) return;
+
+          // TODO(nweiz): include the isolate ID in the URL?
+          completer.complete(url);
+        });
+      } on IOException catch (_) {
+        // IO exceptions are probably caused by connecting to an
+        // incorrect WebSocket that already closed.
+        return null;
+      }
+    }).catchError((error, stackTrace) {
+      if (!completer.isCompleted) completer.completeError(error, stackTrace);
+    });
+
+    return completer.future;
+  }
 }