Flutter

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import 'package:permission_handler/permission_handler.dart';
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Future<bool> ensureMicPermission() async {
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  final status = await Permission.microphone.request();
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  return status.isGranted;
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}

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import 'dart:async';
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import 'dart:convert';
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import 'dart:typed_data';
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import 'package:flutter/material.dart';
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import 'package:flutter_pcm_sound/flutter_pcm_sound.dart';
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import 'package:mic_stream/mic_stream.dart';
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import 'package:web_socket_channel/web_socket_channel.dart';
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class VoiceAgentScreen extends StatefulWidget {
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  const VoiceAgentScreen({super.key});
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  @override
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  State<VoiceAgentScreen> createState() => _VoiceAgentScreenState();
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}
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class _VoiceAgentScreenState extends State<VoiceAgentScreen> {
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  static const apiKey     = 'sk_...';
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  static const agentId    = '...';
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  static const sampleRate = 24000;
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  WebSocketChannel? _channel;
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  StreamSubscription<Uint8List>? _micSub;
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  bool _connected = false;
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  Future<void> _start() async {
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    if (!await ensureMicPermission()) return;
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    final uri = Uri.parse(
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      'wss://api.smallest.ai/atoms/v1/agent/connect'
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      '?token=${Uri.encodeComponent(apiKey)}'
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      '&agent_id=${Uri.encodeComponent(agentId)}'
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      '&mode=webcall'
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      '&sample_rate=$sampleRate',
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    );
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    _channel = WebSocketChannel.connect(uri);
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    _channel!.stream.listen(
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      _handleServerEvent,
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      onDone: _stop,
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      onError: (_) => _stop(),
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    );
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    await FlutterPcmSound.setup(sampleRate: sampleRate, channelCount: 1);
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    FlutterPcmSound.start();
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    await _startMicStream();
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    setState(() => _connected = true);
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  }
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  Future<void> _stop() async {
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    await _micSub?.cancel();
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    await FlutterPcmSound.release();
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    await _channel?.sink.close();
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    _channel = null;
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    if (mounted) setState(() => _connected = false);
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  }
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  @override
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  void dispose() {
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    _stop();
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    super.dispose();
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  }
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  @override
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  Widget build(BuildContext context) {
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    return Scaffold(
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      body: Center(
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        child: _connected
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            ? ElevatedButton(onPressed: _stop, child: const Text('End call'))
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            : ElevatedButton(onPressed: _start, child: const Text('Start call')),
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      ),
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    );
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  }
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}

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Future<void> _startMicStream() async {
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  final isIOS = Theme.of(context).platform == TargetPlatform.iOS;
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  final micStream = MicStream.microphone(
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    // mic_stream's iOS plugin only supports AudioSource.DEFAULT. Passing
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    // VOICE_COMMUNICATION on iOS crashes with a nil force-unwrap.
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    audioSource:   isIOS ? AudioSource.DEFAULT : AudioSource.VOICE_COMMUNICATION,
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    sampleRate:    sampleRate,
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    channelConfig: ChannelConfig.CHANNEL_IN_MONO,
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    audioFormat:   AudioFormat.ENCODING_PCM_16BIT,
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  );
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  _micSub = micStream.listen((Uint8List bytes) {
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    if (_channel == null) return;
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    _channel!.sink.add(jsonEncode({
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      'type':  'input_audio_buffer.append',
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      'audio': base64Encode(bytes),
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    }));
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  });
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}

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void _handleServerEvent(dynamic raw) {
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  final ev = jsonDecode(raw as String) as Map<String, dynamic>;
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  switch (ev['type']) {
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    case 'session.created':
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      // update UI
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      break;
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    case 'output_audio.delta':
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      final bytes = base64Decode(ev['audio'] as String);
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      final byteData = bytes.buffer.asByteData(bytes.offsetInBytes, bytes.lengthInBytes);
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      FlutterPcmSound.feed(PcmArrayInt16(bytes: byteData));
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      break;
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    case 'agent_start_talking':
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      // UI: show "speaking" indicator
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      break;
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    case 'agent_stop_talking':
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      // UI: hide "speaking" indicator
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      break;
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    case 'interruption':
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      // No public flush API in flutter_pcm_sound. The residual buffer
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      // (~100 ms at 24 kHz) will play out. Stop feeding and wait for
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      // the next agent_start_talking.
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      break;
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    case 'session.closed':
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      _stop();
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      break;
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    case 'error':
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      debugPrint('agent error [${ev['code']}]: ${ev['message']}');
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      break;
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  }
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}

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import 'package:audio_session/audio_session.dart';
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final session = await AudioSession.instance;
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await session.configure(const AudioSessionConfiguration(
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  avAudioSessionCategory:     AVAudioSessionCategory.playAndRecord,
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  avAudioSessionMode:         AVAudioSessionMode.voiceChat,
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  avAudioSessionCategoryOptions:
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      AVAudioSessionCategoryOptions.defaultToSpeaker |
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      AVAudioSessionCategoryOptions.allowBluetooth,
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));
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await session.setActive(true);

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import 'package:audio_session/audio_session.dart';
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Future<void> _installInterruptionHandler() async {
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  final session = await AudioSession.instance;
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  await session.configure(const AudioSessionConfiguration.speech());
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  session.interruptionEventStream.listen((event) {
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    if (event.begin) {
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      _stop();
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    }
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  });
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}

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int _retryMs = 500;
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void _onWebSocketClosed(int? code) {
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  if (code == 1000 || code == 4401 || code == 4403) return;
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  Future.delayed(Duration(milliseconds: _retryMs), _start);
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  _retryMs = (_retryMs * 2).clamp(500, 30000);
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}

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class _VoiceAgentScreenState extends State<VoiceAgentScreen> with WidgetsBindingObserver {
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  @override
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  void initState() {
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    super.initState();
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    WidgetsBinding.instance.addObserver(this);
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  }
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  @override
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  void didChangeAppLifecycleState(AppLifecycleState state) {
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    if (state == AppLifecycleState.paused) _stop();
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  }
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  @override
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  void dispose() {
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    WidgetsBinding.instance.removeObserver(this);
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    super.dispose();
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  }
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}