blob: 1bd7dc3b34eb54a599e441566aef0ddb4fbd78e5 [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 'package:http/http.dart' as http;
import 'package:path/path.dart' as p;
import 'package:shelf/shelf.dart';
/// A handler that proxies requests to [url].
/// To generate the proxy request, this concatenates [url] and [Request.url].
/// This means that if the handler mounted under `/documentation` and [url] is
/// ``, a request to `/documentation/tutorials`
/// will be proxied to ``.
/// [url] must be a [String] or [Uri].
/// [client] is used internally to make HTTP requests. It defaults to a
/// `dart:io`-based client.
/// [proxyName] is used in headers to identify this proxy. It should be a valid
/// HTTP token or a hostname. It defaults to `shelf_proxy`.
Handler proxyHandler(url, {http.Client? client, String? proxyName}) {
Uri uri;
if (url is String) {
uri = Uri.parse(url);
} else if (url is Uri) {
uri = url;
} else {
throw ArgumentError.value(url, 'url', 'url must be a String or Uri.');
final nonNullClient = client ?? http.Client();
proxyName ??= 'shelf_proxy';
return (serverRequest) async {
// TODO(nweiz): Support WebSocket requests.
// TODO(nweiz): Handle TRACE requests correctly. See
final requestUrl = uri.resolve(serverRequest.url.toString());
final clientRequest = http.StreamedRequest(serverRequest.method, requestUrl)
..followRedirects = false
..headers['Host'] = uri.authority;
// Add a Via header. See
_addHeader(clientRequest.headers, 'via',
'${serverRequest.protocolVersion} $proxyName');
final clientResponse = await nonNullClient.send(clientRequest);
// Add a Via header. See
_addHeader(clientResponse.headers, 'via', '1.1 $proxyName');
// Remove the transfer-encoding since the body has already been decoded by
// [client].
// If the original response was gzipped, it will be decoded by [client]
// and we'll have no way of knowing its actual content-length.
if (clientResponse.headers['content-encoding'] == 'gzip') {
// Add a Warning header. See
clientResponse.headers, 'warning', '214 $proxyName "GZIP decoded"');
// Make sure the Location header is pointing to the proxy server rather
// than the destination server, if possible.
if (clientResponse.isRedirect &&
clientResponse.headers.containsKey('location')) {
final location =
if (p.url.isWithin(uri.toString(), location)) {
clientResponse.headers['location'] =
'/${p.url.relative(location, from: uri.toString())}';
} else {
clientResponse.headers['location'] = location;
return Response(clientResponse.statusCode,
body:, headers: clientResponse.headers);
// TODO(nweiz): use built-in methods for this when http and shelf support them.
/// Add a header with [name] and [value] to [headers], handling existing headers
/// gracefully.
void _addHeader(Map<String, String> headers, String name, String value) {
final existing = headers[name];
headers[name] = existing == null ? value : '$existing, $value';