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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][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][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

```dart
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());
}
```

[dds-protocol]: dds_protocol.md
[service-protocol]: https://github.com/dart-lang/sdk/blob/main/runtime/vm/service/service.md

# 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:

```dart
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`.