Add mDNS discovery to the Fletch compiler

pkg/fletchc/lib/src/driver/developer.dart

 // Copyright (c) 2015, the Fletch 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.md file.
 
 library fletchc.driver.developer;
 
 import 'dart:async' show
     Future,
     Timer;
 
@@ skipping 14 matching lines @@
 
 import 'package:fletch_agent/agent_connection.dart' show
     AgentConnection,
     AgentException,
     VmData;
 
 import 'package:fletch_agent/messages.dart' show
     AGENT_DEFAULT_PORT,
     MessageDecodeException;
 
+import 'package:mdns/mdns.dart' show
+    MDnsClient,
+    ResourceRecord,
+    RRType;
+
 import '../../commands.dart' show
     CommandCode,
     HandShakeResult,
     ProcessBacktrace,
     ProcessBacktraceRequest,
     ProcessRun,
     ProcessSpawnForMain,
     SessionEnd,
     WriteSnapshotResult;
 
@@ skipping 282 matching lines @@
   settings = settings.copyWith(packages: packagesUri, deviceAddress: address);
   print("Created settings file '$uri'");
   await new File.fromUri(uri).writeAsString(
       "${const JsonEncoder.withIndent('  ').convert(settings)}\n");
   return settings;
 }
 
 Future<Address> readAddressFromUser(
     CommandSender commandSender,
     StreamIterator<Command> commandIterator) async {
+  String message =
+      "Please enter IP address of remote device (press enter for discovery): ";
   commandSender.sendEventLoopStarted();
-  commandSender.sendStdout("Please enter IP address of remote device: ");
+  commandSender.sendStdout(message);
   while (await commandIterator.moveNext()) {
     Command command = commandIterator.current;
     switch (command.code) {
       case DriverCommand.Stdin:
         if (command.data.length == 0) {
           // TODO(ahe): It may be safe to return null here, but we need to
           // check how this interacts with the debugger's InputHandler.
           throwInternalError("Unexpected end of input");
         }
         // TODO(ahe): This assumes that the user's input arrives as one
         // message. It is relatively safe to assume this for a normal terminal
         // session because we use canonical input processing (Unix line
         // buffering), but it doesn't work in general. So we should fix that.
         String line = UTF8.decode(command.data).trim();
-        return parseAddress(line, defaultPort: AGENT_DEFAULT_PORT);
+        if (line.isEmpty) {
+          await discoverDevices();
+          commandSender.sendStdout(message);
+        } else {
+          return parseAddress(line, defaultPort: AGENT_DEFAULT_PORT);
+        }
+        break;
 
       case DriverCommand.Signal:
         // Send an empty line as the user didn't hit enter.
         commandSender.sendStdout("\n");
         // Assume user aborted data entry.
         return null;
 
       default:
         throwInternalError("Unexpected ${command.code}");
         return null;
@@ skipping 379 matching lines @@
 
 Future<int> invokeCombinedTasks(
     CommandSender commandSender,
     StreamIterator<Command> commandIterator,
     SharedTask task1,
     SharedTask task2) async {
   await task1(commandSender, commandIterator);
   return task2(commandSender, commandIterator);
 }
 
+Future discoverDevices() async {
+  print('Looking for Fletch capable devices...');
+  MDnsClient client = new MDnsClient();
+  await client.start();
+  String name = '_fletch_agent._tcp.local';
+  await for (ResourceRecord ptr in client.lookup(RRType.PTR, name)) {
+    String domain = ptr.domainName;
+    await for (ResourceRecord srv in client.lookup(RRType.SRV, domain)) {
+      String target = srv.target;
+      await for (ResourceRecord a in client.lookup(RRType.A, target)) {
+        InternetAddress address = a.address;
+        if (!address.isLinkLocal) {
+          print('Found device $target on address ${address.address}.');
+        }
+      }
+    }
+  }
+  client.stop();
+}
+
 Address parseAddress(String address, {int defaultPort: 0}) {
   String host;
   int port;
   List<String> parts = address.split(":");
   if (parts.length == 1) {
     host = InternetAddress.LOOPBACK_IP_V4.address;
     port = int.parse(
         parts[0],
         onError: (String source) {
           host = source;
@@ skipping 204 matching lines @@
       "packages": packages == null ? null : "$packages",
       "options": options,
       "constants": constants,
       "device_address": deviceAddress,
       "device_type": (deviceType == null)
           ? null
           : unParseDeviceType(deviceType),
     };
   }
 }