dart-sdk/pkg/dds

A package used to spawn the Dart Developer Service (DDS), which is used to communicate with a Dart VM Service instance and provide extended functionality to the core VM Service Protocol.

Functionality

Existing VM Service clients can issue both HTTP, websocket, and SSE requests to a running DDS instance as if it were an instance of the VM Service itself. If a request corresponds to an RPC defined in the VM Service Protocol, DDS will forward the request and return the response from the VM Service. Requests corresponding to an RPC defined in the DDS Protocol will be handled directly by the DDS instance.

SSE Support

For certain web clients it may be preferable or required to communicate with DDS using server-sent events (SSE). DDS has an SSE handler listening for requests on /$debugHandler.

SSE and package:vm_service example

import 'package:sse/sse.dart';
import 'package:vm_service/vm_service.dart';

void main() {
  // Establish connection with DDS using SSE.
  final ddsChannel = SseClient('${ddsUri}\$debugHandler');

  // Wait for ddsChannel to be established
  await ddsChannel.onOpen.first;

  // Initialize VmService using the sink and stream from ddsChannel.
  final vmService = VmService(
    ddsChannel.stream,
    (e) => ddsChannel.sink.add(e),
  );

  // You're ready to query DDS and the VM service!
  print(await vmService.getVersion());
}

Debugging DDS

One way to get stdout from files in DDS while debugging is to log messages to a file. You can add a method such as:

void _fileLog(String message) {
  final file = File('/tmp/dds.log');
  if (!file.existsSync()) {
    file.createSync();
  }
  file.writeAsStringSync(
'''
$message
''',
    mode: FileMode.append,
  );
}

Then you can call _fileLog('some print debugging message'), and the log message will be written to a temp file.

To get logging output in real time, run tail -f /tmp/dds.log.