A Dart implementation use "JSON-RPC 2.0" to connect Aria2.
final _aria2 = await DartAria2().open('ws://127.0.0.1:6800/jsonrpc', 'passu');
// aria2.tellActive
final resp = await _aria2.invokeRpc('aria2.tellActive');
// aria2.addUri
final gid = await _aria2.invokeRpc('aria2.addUri', params: [['https://cdimage.debian.org/debian-cd/current/amd64/bt-dvd/debian-9.9.0-amd64-DVD-1.iso.torrent']]);