| // 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. |
| |
| import 'dart:async'; |
| |
| import 'handler.dart'; |
| import 'response.dart'; |
| |
| /// A typedef for [Cascade._shouldCascade]. |
| typedef _ShouldCascade = bool Function(Response response); |
| |
| /// A helper that calls several handlers in sequence and returns the first |
| /// acceptable response. |
| /// |
| /// By default, a response is considered acceptable if it has a status other |
| /// than 404 or 405; other statuses indicate that the handler understood the |
| /// request. |
| /// |
| /// If all handlers return unacceptable responses, the final response will be |
| /// returned. |
| /// |
| /// var handler = new Cascade() |
| /// .add(webSocketHandler) |
| /// .add(staticFileHandler) |
| /// .add(application) |
| /// .handler; |
| class Cascade { |
| /// The function used to determine whether the cascade should continue on to |
| /// the next handler. |
| final _ShouldCascade _shouldCascade; |
| |
| final Cascade _parent; |
| final Handler _handler; |
| |
| /// Creates a new, empty cascade. |
| /// |
| /// If [statusCodes] is passed, responses with those status codes are |
| /// considered unacceptable. If [shouldCascade] is passed, responses for which |
| /// it returns `true` are considered unacceptable. [statusCodes] and |
| /// [shouldCascade] may not both be passed. |
| Cascade({Iterable<int> statusCodes, bool Function(Response) shouldCascade}) |
| : _shouldCascade = _computeShouldCascade(statusCodes, shouldCascade), |
| _parent = null, |
| _handler = null { |
| if (statusCodes != null && shouldCascade != null) { |
| throw ArgumentError('statusCodes and shouldCascade may not both be ' |
| 'passed.'); |
| } |
| } |
| |
| Cascade._(this._parent, this._handler, this._shouldCascade); |
| |
| /// Returns a new cascade with [handler] added to the end. |
| /// |
| /// [handler] will only be called if all previous handlers in the cascade |
| /// return unacceptable responses. |
| Cascade add(Handler handler) => Cascade._(this, handler, _shouldCascade); |
| |
| /// Exposes this cascade as a single handler. |
| /// |
| /// This handler will call each inner handler in the cascade until one returns |
| /// an acceptable response, and return that. If no inner handlers return an |
| /// acceptable response, this will return the final response. |
| Handler get handler { |
| if (_handler == null) { |
| throw StateError("Can't get a handler for a cascade with no inner " |
| 'handlers.'); |
| } |
| |
| return (request) { |
| if (_parent._handler == null) return _handler(request); |
| return Future.sync(() => _parent.handler(request)).then((response) { |
| if (_shouldCascade(response)) return _handler(request); |
| return response; |
| }); |
| }; |
| } |
| } |
| |
| /// Computes the [Cascade._shouldCascade] function based on the user's |
| /// parameters. |
| _ShouldCascade _computeShouldCascade( |
| Iterable<int> statusCodes, bool Function(Response) shouldCascade) { |
| if (shouldCascade != null) return shouldCascade; |
| statusCodes ??= [404, 405]; |
| statusCodes = statusCodes.toSet(); |
| return (response) => statusCodes.contains(response.statusCode); |
| } |