halkyon/packages/halkyon_llm/test/support/fixture.dart

import 'dart:convert';
import 'dart:io';
import 'dart:typed_data';

import 'package:http/http.dart' as http;
import 'package:http/testing.dart';

/// A provider's reply as a fixture file keeps it (`.http`): `HTTP <status>`,
/// the headers that matter, one per line, an empty line, then the body as it
/// came, byte for byte. `tool/record_llm.dart` writes recorded replies so.
final class const Fixture({
  required final String name,
  required final int status,
  required final Map<String, String> headers,
  required final Uint8List body,
}) {
  /// The fixture in [file].
  factory read(File file) => Fixture.parse(
    file.uri.pathSegments.last.replaceAll('.http', ''),
    file.readAsBytesSync(),
  );

  /// The fixture [bytes] hold.
  factory parse(String name, Uint8List bytes) {
    final end = _headEnd(bytes);
    final head = utf8.decode(bytes.sublist(0, end)).split('\n');
    final status = RegExp(r'^HTTP (\d{3})$').firstMatch(head.first);
    if (status == null) {
      throw FormatException('No status in $name');
    }
    return Fixture(
      name: name,
      status: int.parse(status[1]!),
      headers: {
        for (final line in head.skip(1).where((line) => line.isNotEmpty))
          line.substring(0, line.indexOf(':')).toLowerCase(): line
              .substring(line.indexOf(':') + 1)
              .trim(),
      },
      body: bytes.sublist(end + 2),
    );
  }

  /// The bytes of a fixture of [status], [headers] and [body].
  static Uint8List write(
    int status,
    Map<String, String> headers,
    List<int> body,
  ) => Uint8List.fromList([
    ...utf8.encode('HTTP $status\n'),
    for (final MapEntry(:key, :value) in headers.entries)
      ...utf8.encode('$key: $value\n'),
    ...utf8.encode('\n'),
    ...body,
  ]);

  static int _headEnd(Uint8List bytes) {
    for (var i = 0; i + 1 < bytes.length; i++) {
      if (bytes[i] == 0x0A && bytes[i + 1] == 0x0A) {
        return i;
      }
    }
    throw const FormatException('No end of the head');
  }

  /// The body in pieces of [size] bytes, as a network may cut it (cutting
  /// characters and lines in two).
  Stream<List<int>> chunked(int size) => Stream.fromIterable([
    for (var at = 0; at < body.length; at += size)
      body.sublist(at, at + size > body.length ? body.length : at + size),
  ]);
}

/// The fixtures in `test/fixtures/<kind>/<protocol>/`, by name.
Map<String, Fixture> fixturesOf(String kind, String protocol) {
  final folder = Directory('test/fixtures/$kind/$protocol');
  if (!folder.existsSync()) {
    return const {};
  }
  final files =
      folder
          .listSync()
          .whereType<File>()
          .where(
            (file) => file.path.endsWith('.http'),
          )
          .toList()
        ..sort((a, b) => a.path.compareTo(b.path));
  return {
    for (final file in files) Fixture.read(file).name: Fixture.read(file),
  };
}

/// What a [MockClient] was sent.
final class Sent() {
  late http.BaseRequest request;
  late Map<String, Object?> body;
  bool aborted = false;
}

/// An HTTP client replying [fixture] in pieces of [chunk] bytes, keeping
/// what it was sent in [sent].
http.Client replying(Fixture fixture, {Sent? sent, int chunk = 7}) =>
    MockClient.streaming((request, bodyStream) async {
      sent?.request = request;
      sent?.body = jsonDecode(
        utf8.decode(await bodyStream.toBytes()),
      ) as Map<String, Object?>;
      if (request case http.Abortable(:final abortTrigger?)) {
        abortTrigger.whenComplete(() => sent?.aborted = true).ignore();
      }
      return http.StreamedResponse(
        fixture.chunked(chunk),
        fixture.status,
        headers: fixture.headers,
      );
    });