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Add a mDNS package
Implementation of mDNS one-shot query. This package uses dart:io and runs only on the Dart VM. R=karlklose@google.com BUG= Review URL: https://codereview.chromium.org/1426863003 .
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‎.packages‎

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@@ -20,6 +20,7 @@ isolate:pkg/isolate/lib
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js_ast:third_party/dart/pkg/js_ast/lib
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js_runtime:third_party/dart/sdk/lib/_internal/js_runtime/lib/
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lk:pkg/lk/lib
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mdns:pkg/mdns/lib
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os:pkg/os/lib
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package_config:third_party/package_config/lib
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path:third_party/path/lib

‎pkg/mdns/lib/mdns.dart‎

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// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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import 'dart:async';
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import 'dart:collection';
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import 'dart:io';
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import 'dart:typed_data';
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import 'package:mdns/src/constants.dart';
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import 'package:mdns/src/lookup_resolver.dart';
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import 'package:mdns/src/packet.dart';
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/// Client for DNS lookup using the mDNS protocol.
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///
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/// This client only support "One-Shot Multicast DNS Queries" as described in
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/// section 5.1 of https://tools.ietf.org/html/rfc6762
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class MDnsClient {
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bool _starting = false;
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bool _started = false;
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RawDatagramSocket _incoming;
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final List<RawDatagramSocket> _sockets = <RawDatagramSocket>[];
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final LookupResolver _resolver = new LookupResolver();
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/// Start the mDNS client.
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Future start() async {
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if (_started && _starting) {
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throw new StateError('mDNS client already started');
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}
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_starting = true;
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// Listen on all addresses.
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_incoming = await RawDatagramSocket.bind(
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InternetAddress.ANY_IP_V4, mDnsPort, reuseAddress: true);
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// Find all network interfaces with an IPv4 address.
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var interfaces =
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await NetworkInterface.list(type: InternetAddressType.IP_V4);
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for (NetworkInterface interface in interfaces) {
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// Create a socket for sending on each adapter.
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var socket = await RawDatagramSocket.bind(
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interface.addresses[0], mDnsPort, reuseAddress: true);
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_sockets.add(socket);
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// Join multicast on this interface.
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_incoming.joinMulticast(mDnsAddress, interface);
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}
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_incoming.listen(_handleIncoming);
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_starting = false;
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_started = true;
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}
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/// Stop the mDNS client.
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void stop() {
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if (!_started) return;
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if (_starting) {
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throw new StateError('Cannot stop mDNS client wile it is starting');
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}
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_sockets.forEach((socket) => socket.close());
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_incoming.close();
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_started = false;
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}
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/// Lookup [hostname] using mDNS.
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///
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/// The `hostname` must have the form `single-dns-label.local`,
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/// e.g. `printer.local`.
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///
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/// If no answer has been received within the specified [timeout]
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/// this method will complete with the value `null`.
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Future<InternetAddress> lookup(
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String hostname, {Duration timeout: const Duration(seconds: 5)}) {
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if (!_started) {
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throw new StateError('mDNS client is not started');
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}
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// Add the pending request before sending the query.
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var future = _resolver.addPendingRequest(hostname, timeout);
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// Send the request on all interfaces.
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List<int> packet = encodeMDnsQuery(hostname);
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for (int i = 0; i < _sockets.length; i++) {
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_sockets[i].send(packet, mDnsAddress, mDnsPort);
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}
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return future;
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}
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// Process incoming datagrams.
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_handleIncoming(event) {
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if (event == RawSocketEvent.READ) {
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var data = _incoming.receive();
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var response = decodeMDnsResponse(data.data);
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if (response != null) {
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_resolver.handleResponse(response);
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}
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}
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}
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}
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// Simple standalone test.
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main() async {
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var client = new MDnsClient();
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await client.start();
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var address = await client.lookup('raspberrypi.local');
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client.stop();
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print(address);
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}

‎pkg/mdns/lib/src/constants.dart‎

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// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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library mdns.src.constants;
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import 'dart:io';
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InternetAddress mDnsAddress = new InternetAddress('224.0.0.251');
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const int mDnsPort = 5353;
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// Offsets into the header. See https://tools.ietf.org/html/rfc1035.
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const int idOffset = 0;
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const int flagsOffset = 2;
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const int qdcountOffset = 4;
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const int ancountOffset = 6;
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const int nscountOffset = 8;
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const int arcountOffset = 10;
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const int headerSize = 12;
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const int responseFlags = 0x8400;
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const int ipV4AddressType = 0x0001;
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const int ipV4Class = 0x8001;
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const int ipV6AddressType = 0x001c;
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const int ipV6Class = 0x8001;

‎pkg/mdns/lib/src/lookup_resolver.dart‎

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// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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library mdns.src.lookup_resolver;
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import 'dart:async';
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import 'dart:collection';
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import 'package:mdns/src/packet.dart';
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class PendingRequest extends LinkedListEntry {
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final String hostname;
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final Completer completer;
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PendingRequest(this.hostname, this.completer);
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}
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/// Class for keeping track of pending lookups and process incoming
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/// query responses.
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///
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/// Currently the responses are no cached.
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class LookupResolver {
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LinkedList pendingRequests = new LinkedList();
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Future addPendingRequest(String hostname, Duration timeout) {
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var completer = new Completer();
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var request = new PendingRequest(hostname, completer);
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pendingRequests.add(request);
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return completer.future.timeout(timeout, onTimeout: () {
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request.unlink();
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return null;
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});
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}
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void handleResponse(List<DecodeResult> response) {
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for (var r in response) {
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pendingRequests
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.where((pendingRequest) => pendingRequest.hostname == r.name)
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.forEach((pendingRequest) {
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pendingRequest.completer.complete(r.address);
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pendingRequest.unlink();
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});
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}
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}
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}
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‎pkg/mdns/lib/src/packet.dart‎

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// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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library mdns.src.packet;
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import 'dart:convert';
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import 'dart:io';
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import 'dart:typed_data';
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import 'package:mdns/src/constants.dart';
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// Encode a mDNS query packet.
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List<int> encodeMDnsQuery(String hostname) {
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List parts = hostname.split('.');
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// Calculate the size of the packet.
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int size = headerSize;
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for (int i = 0; i < parts.length; i++) {
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parts[i] = UTF8.encode(parts[i]);
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size += 1 + parts[i].length;
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}
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size += 1; // End with empty part
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size += 4; // Trailer (QTYPE and QCLASS).
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Uint8List data = new Uint8List(size);
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ByteData bd = new ByteData.view(data.buffer);
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// Query identifier - just use 0.
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bd.setUint16(idOffset, 0);
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// Flags - 0 for query.
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bd.setUint16(flagsOffset, 0);
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// Query count.
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bd.setUint16(qdcountOffset, 1);
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// Number of answers - 0 for query.
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bd.setUint16(ancountOffset, 0);
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// Number of name server records - 0 for query.
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bd.setUint16(nscountOffset, 0);
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// Number of resource records - 0 for query.
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bd.setUint16(arcountOffset, 0);
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int offset = headerSize;
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for (int i = 0; i < parts.length; i++) {
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data[offset++] = parts[i].length;
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data.setRange(offset, offset + parts[i].length, parts[i]);
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offset += parts[i].length;
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}
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data[offset] = 0; // Empty part.
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offset++;
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bd.setUint16(offset, 1); // QTYPE.
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offset += 2;
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bd.setUint16(offset, 1); // QCLASS.
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return data;
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}
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/// FQDN and address decoded from response.
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class DecodeResult {
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final String name;
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final InternetAddress address;
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DecodeResult(this.name, this.address);
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}
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/// Result of reading a FQDN. The FQDN parts and the bytes consumed.
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class FQDNReadResult {
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final List<String> fqdn;
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final int bytesRead;
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FQDNReadResult(this.fqdn, this.bytesRead);
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}
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/// Decode a mDNS package.
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///
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/// If decoding fails (e.g. due to an invalid packet) `null` is returned.
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///
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/// See See https://tools.ietf.org/html/rfc1035 for the format.
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List<DecodeResult> decodeMDnsResponse(List<int> packet) {
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int length = packet.length;
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if (length < headerSize) return null;
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Uint8List data =
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packet is Uint8List ? packet : new Uint8List.fromList(packet);
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ByteData bd = new ByteData.view(data.buffer);
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// Query identifier.
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int id = bd.getUint16(idOffset);
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// Flags.
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int flags = bd.getUint16(flagsOffset);
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if (flags != responseFlags) return;
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// Query count.
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int qdcount = bd.getUint16(qdcountOffset);
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// Number of answers.
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int ancount = bd.getUint16(ancountOffset);
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// Number of name server records.
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int nscount = bd.getUint16(nscountOffset);
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// Number of resource records.
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int arcount = bd.getUint16(arcountOffset);
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int offset = headerSize;
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void checkLength(int required) {
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if (length < required) throw new MDnsDecodeException(required);
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}
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// Read a FQDN at the given offset. Returns a pair with the FQDN
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// parts and the number of bytes consumed.
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//
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// If decoding fails (e.g. die to an invalid packet) `null` is returned.
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FQDNReadResult readFQDN(int offset) {
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List<String> parts = [];
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int prevOffset = offset;
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while (true) {
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// At least two bytes required.
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checkLength(offset + 2);
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// Check for compressed.
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if (data[offset] & 0xc0 == 0xc0) {
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// A compressed FQDN has a new offset in the lower 14 bits.
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FQDNReadResult result = readFQDN(bd.getUint16(offset) & ~0xc000);
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parts.addAll(result.fqdn);
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offset += 2;
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break;
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} else {
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// A normal FQDN part has a length and a UTF-8 encoded name
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// part. If the length is 0 this is the end of the FQDN.
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var partLength = data[offset];
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offset++;
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if (partLength != 0) {
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checkLength(offset + partLength);
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var partBytes = new Uint8List.view(data.buffer, offset, partLength);
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offset += partLength;
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parts.add(UTF8.decode(partBytes));
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} else {
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break;
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}
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}
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}
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return new FQDNReadResult(parts, offset - prevOffset);
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}
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DecodeResult readAddress() {
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// First read the FQDN.
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FQDNReadResult result = readFQDN(offset);
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var fqdn = result.fqdn.join('.');
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offset += result.bytesRead;
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checkLength(offset + 2);
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int type = bd.getUint16(offset);
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offset += 2;
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checkLength(offset + 2);
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int cls = bd.getUint16(offset);
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offset += 2;
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checkLength(offset + 4);
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int ttl = bd.getInt32(offset);
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offset += 4;
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checkLength(offset + 2);
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int addressLength = bd.getUint16(offset);
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offset += 2;
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checkLength(offset + addressLength);
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var addressBytes = new Uint8List.view(data.buffer, offset, addressLength);
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offset += addressLength;
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if (type == ipV4AddressType && cls == ipV4Class && addressLength == 4) {
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String addr = addressBytes.map((n) => n.toString()).join('.');
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return new DecodeResult(fqdn, new InternetAddress(addr));
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} else {
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return null;
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}
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}
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// We don't use the number of records - just read through all
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// resource records and filter.
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var result = [];
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try {
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while (data.length - offset >= 16) {
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var address = readAddress();
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if (address != null) result.add(address);
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}
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} on MDnsDecodeException catch (e, s) {
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// If decoding fails return null.
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return null;
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}
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return result;
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}
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/// Exceptions thrown by decoder when the packet is invalid.
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class MDnsDecodeException implements Exception {
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/// Exception message.
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final int offset;
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const MDnsDecodeException(this.offset);
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String toString() => 'Decoding error at $offset';
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}

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