blob: 3eac69f04d6be3fb07a2bba7de91c9b40d127a5f [file] [log] [blame]
// 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 'request.dart';
import 'response.dart';
import 'handler.dart';
import 'hijack_exception.dart';
/// A function which creates a new [Handler] by wrapping a [Handler].
/// You can extend the functions of a [Handler] by wrapping it in
/// [Middleware] that can intercept and process a request before it it sent
/// to a handler, a response after it is sent by a handler, or both.
/// Because [Middleware] consumes a [Handler] and returns a new
/// [Handler], multiple [Middleware] instances can be composed
/// together to offer rich functionality.
/// Common uses for middleware include caching, logging, and authentication.
/// Middleware that captures exceptions should be sure to pass
/// [HijackException]s on without modification.
/// A simple [Middleware] can be created using [createMiddleware].
typedef Handler Middleware(Handler innerHandler);
/// Creates a [Middleware] using the provided functions.
/// If provided, [requestHandler] receives a [Request]. It can respond to
/// the request by returning a [Response] or [Future<Response>].
/// [requestHandler] can also return `null` for some or all requests in which
/// case the request is sent to the inner [Handler].
/// If provided, [responseHandler] is called with the [Response] generated
/// by the inner [Handler]. Responses generated by [requestHandler] are not
/// sent to [responseHandler].
/// [responseHandler] should return either a [Response] or
/// [Future<Response>]. It may return the response parameter it receives or
/// create a new response object.
/// If provided, [errorHandler] receives errors thrown by the inner handler. It
/// does not receive errors thrown by [requestHandler] or [responseHandler], nor
/// does it receive [HijackException]s. It can either return a new response or
/// throw an error.
Middleware createMiddleware({requestHandler(Request request),
responseHandler(Response response),
errorHandler(error, StackTrace stackTrace)}) {
if (requestHandler == null) requestHandler = (request) => null;
if (responseHandler == null) responseHandler = (response) => response;
var onError = null;
if (errorHandler != null) {
onError = (error, stackTrace) {
if (error is HijackException) throw error;
return errorHandler(error, stackTrace);
return (Handler innerHandler) {
return (request) {
return new Future.sync(() => requestHandler(request)).then((response) {
if (response != null) return response;
return new Future.sync(() => innerHandler(request)).then(
(response) => responseHandler(response), onError: onError);