buzz/mobile/lib/shared/relay/relay_http_query_client.dart

import 'dart:async';
import 'dart:io';

import 'package:http/http.dart' as http;
import 'package:http/io_client.dart';
import 'package:buzz/shared/http/app_http_client.dart';

/// The default transport. On iOS, the app-wide `NSURLSession` inflates gzip
/// natively, off the Dart isolate. `dart:io` would inflate on the calling
/// isolate, so leave its responses compressed for the response decoder.
///
/// A non-`dart:io` client supplied through `http.runWithClient`, such as a
/// `MockClient`, is used as is. An `IOClient` is replaced, not closed, since
/// it may be shared.
http.Client _defaultTransport() {
  if (Platform.isIOS) return newAppHttpClient();
  final client = http.Client();
  if (client is! IOClient) return client;
  return IOClient(HttpClient()..autoUncompress = false);
}

/// Owns the reusable HTTP transport used for relay `/query` requests.
///
/// Requests advertise gzip. A response body may therefore come back
/// compressed; decode it with `relayResponseText` or `decodeRelayQueryResponse`.
class RelayHttpQueryClient {
  RelayHttpQueryClient({
    http.Client? client,
    http.Client Function()? clientFactory,
  }) : _injectedClient = client,
       _clientFactory = clientFactory ?? _defaultTransport;

  final http.Client? _injectedClient;
  final http.Client Function() _clientFactory;
  _ClientGeneration? _currentGeneration;
  final Set<_ClientGeneration> _generations = {};

  Future<http.Response> post(
    Uri url, {
    required Map<String, String> headers,
    required List<int> body,
    required Duration timeout,
    http.Client Function(http.Client, bool Function())? decorate,
  }) async {
    final generation = _injectedClient == null
        ? (_currentGeneration ??= _createGeneration())
        : null;
    generation?.acquire();
    var active = true;
    // Retiring a generation cannot stop a request on a shared session, so a
    // timed-out request is aborted rather than left holding bandwidth.
    final abort = Completer<void>();
    try {
      final request =
          http.AbortableRequest('POST', url, abortTrigger: abort.future)
            ..followRedirects = false
            ..headers['Accept-Encoding'] = 'gzip'
            ..headers.addAll(headers)
            ..bodyBytes = body;
      final transport = _injectedClient ?? generation!.client;
      final client = decorate?.call(transport, () => active) ?? transport;
      return await client
          .send(request)
          .then(http.Response.fromStream)
          .timeout(timeout);
    } on TimeoutException {
      if (!abort.isCompleted) abort.complete();
      if (identical(_currentGeneration, generation)) {
        _currentGeneration = null;
      }
      generation?.retire();
      rethrow;
    } finally {
      active = false;
      generation?.release();
    }
  }

  /// Sends a non-redirecting request, bounding bytes before buffering or parsing.
  /// The deadline includes headers and the entire response body.
  Future<http.Response> sendBounded(
    http.Request request, {
    required int maxBytes,
    required Duration timeout,
    http.Client Function(http.Client, bool Function())? decorate,
  }) async {
    // As in [post], a timed-out request on a shared session is aborted.
    final abort = Completer<void>();
    final sent =
        http.AbortableRequest(
            request.method,
            request.url,
            abortTrigger: abort.future,
          )
          ..followRedirects = false
          ..headers.addAll(request.headers)
          ..bodyBytes = request.bodyBytes;
    final generation = _injectedClient == null
        ? (_currentGeneration ??= _createGeneration())
        : null;
    generation?.acquire();
    StreamIterator<List<int>>? iterator;
    var finished = false;
    Future<http.Response> receive() async {
      final transport = _injectedClient ?? generation!.client;
      final client = decorate?.call(transport, () => !finished) ?? transport;
      final response = await client.send(sent);
      if (finished) {
        await response.stream.listen(null).cancel();
        throw StateError('Relay request already timed out');
      }
      iterator = StreamIterator(response.stream);
      if ((response.contentLength ?? 0) > maxBytes) {
        throw const FormatException('Relay response exceeds byte limit');
      }
      final bytes = <int>[];
      while (await iterator!.moveNext()) {
        final chunk = iterator!.current;
        if (bytes.length + chunk.length > maxBytes) {
          throw const FormatException('Relay response exceeds byte limit');
        }
        bytes.addAll(chunk);
      }
      iterator = null; // An exhausted stream needs no cancellation.
      return http.Response.bytes(
        bytes,
        response.statusCode,
        headers: response.headers,
        request: request,
      );
    }

    try {
      return await receive().timeout(timeout);
    } on TimeoutException {
      if (!abort.isCompleted) abort.complete();
      if (identical(_currentGeneration, generation)) {
        _currentGeneration = null;
      }
      generation?.retire();
      rethrow;
    } finally {
      finished = true;
      // Cancelling an iterator that never listened leaves the body
      // downloading on a shared session, so abort on every exit.
      if (!abort.isCompleted) abort.complete();
      if (iterator != null) await iterator!.cancel();
      generation?.release();
    }
  }

  void close() {
    for (final generation in _generations.toList()) {
      generation.close();
    }
    _currentGeneration = null;
    _injectedClient?.close();
  }

  _ClientGeneration _createGeneration() {
    late final _ClientGeneration generation;
    generation = _ClientGeneration(
      _clientFactory(),
      onClosed: () => _generations.remove(generation),
    );
    _generations.add(generation);
    return generation;
  }
}

class _ClientGeneration {
  _ClientGeneration(this.client, {required this.onClosed});

  final http.Client client;
  final void Function() onClosed;
  int _activeRequests = 0;
  bool _retired = false;
  bool _closed = false;

  void acquire() {
    assert(!_closed);
    _activeRequests++;
  }

  void release() {
    assert(_activeRequests > 0);
    _activeRequests--;
    _closeIfIdle();
  }

  void retire() {
    _retired = true;
    _closeIfIdle();
  }

  void close() {
    if (_closed) return;
    _closed = true;
    client.close();
    onClosed();
  }

  void _closeIfIdle() {
    if (_retired && _activeRequests == 0) close();
  }
}