Add a ScheduledServer class.

pkg/scheduled_test/lib/src/scheduled_server/handler.dart

+// Copyright (c) 2013, 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 scheduled_server.handler;
+
+import 'dart:async';
+import 'dart:io';
+
+import '../../scheduled_server.dart';
+import '../../scheduled_test.dart';
+import '../utils.dart';
+
+/// A handler for a single request to a [ScheduledServer].
+class Handler {
+  /// The server for which this handler will handle a request.
+  final ScheduledServer server;
+
+  /// The expected method of the request to be handled.
+  final String method;
+
+  /// The expected path of the request to be handled.
+  final String path;
+
+  /// The function to run to handle the request.
+  ScheduledHandler get fn => _fn;
+  ScheduledHandler _fn;
+
+  /// The scheduled task immediately prior to this handler. If this task is
+  /// running when this handler receives a request, it should wait until the
+  /// task has completed.
+  ///
+  /// The last task in the queue will be the prior task because a Handler is
+  /// created before its associated [schedule] call.
+  final Task _taskBefore = currentSchedule.tasks.contents.last;
+
+  /// The result of running this handler. If an error occurs while running the
+  /// handler, that will be piped through this [Future].
+  Future get result => _resultCompleter.future;
+  final _resultCompleter = new Completer();
+
+  /// Whether it's time for the handler to receive its request.
+  var ready = false;
+
+  Handler(this.server, this.method, this.path, ScheduledHandler fn) {
+    _fn = (request) {
+      return _waitForTask().then((_) {
+        if (!ready) {
+          throw "'${server.description}' received $method $path earlier than "
+              "expected.";
+        }
+
+        // Use a nested call to [schedule] to help the user tell the difference
+        // between a test failing while waiting for a handler and a test failing
+        // while executing a handler.
+        chainToCompleter(schedule(() {
+          return new Future.of(() {
+            if (request.method != method || request.uri.path != path) {
+              throw "'${server.description}' expected $method $path, "
+                  "but got ${request.method} ${request.uri.path}.";
+            }
+
+            return fn(request);
+          });
+        }, "'${server.description}' handling ${request.method} ${request.uri}"),
+            _resultCompleter);
+      });
+    };
+  }
+
+  /// If the current task is [_taskBefore], waits for it to finish before
+  /// completing. Otherwise, completes immediately.
+  Future _waitForTask() {
+    return pumpEventQueue().then((_) {
+      if (currentSchedule.currentTask != _taskBefore) return;
+      // If we're one task before the handler was scheduled, wait for that
+      // task to complete and pump the event queue so that [ready] will be
+      // set.
+      return _taskBefore.result.then((_) => pumpEventQueue());
+    });
+  }
+}