pkg/frontend_server/lib/src/resident_frontend_server.dart

// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// ignore_for_file: implementation_imports

// front_end/src imports below that require lint `ignore_for_file` are a
// temporary state of things until frontend team builds better api that would
// replace api used below. This api was made private in an effort to discourage
// further use.

import 'dart:async';
import 'dart:convert';
import 'dart:io'
    show exit, File, InternetAddress, ProcessSignal, ServerSocket, Socket;
import 'dart:typed_data' show Uint8List;

import 'package:args/args.dart';
import 'package:front_end/src/api_unstable/vm.dart';
import 'package:kernel/binary/tag.dart' show expectedSdkHash;
import 'package:kernel/kernel.dart' show Component, loadComponentFromBytes;
import 'package:path/path.dart' as path;

import '../frontend_server.dart';
import '../resident_frontend_server_utils.dart' show computeCachedDillPath;

/// Floor the system time by this amount in order to correctly detect modified
/// source files on all platforms. This has no effect on correctness,
/// but may result in more files being marked as modified than strictly
/// required.
const Duration _stateGranularity = const Duration(seconds: 1);

/// Ensures the info file is removed if Ctrl-C is sent to the server.
/// Mostly used when debugging.
StreamSubscription<ProcessSignal>? _cleanupHandler;

extension on DateTime {
  /// Truncates by [amount].
  ///
  /// This is needed because the 1 second granularity on DateTime objects
  /// returned by file stat on Windows is different than the system-times
  /// granularity. We must floor the system time
  /// by 1 second so that if a file is modified within the same second of
  /// the last compile time, it will be correctly detected as being modified.
  DateTime floorTime({Duration amount = _stateGranularity}) {
    return new DateTime.fromMillisecondsSinceEpoch(millisecondsSinceEpoch -
        millisecondsSinceEpoch % amount.inMilliseconds);
  }
}

enum _ResidentState {
  waitingForFirstCompile,
  compiling,
  waitingForRecompile,
}

/// A wrapper around the FrontendCompiler, along with all the state needed
/// to perform incremental compilations
///
/// TODO: Fix the race condition that occurs when the ResidentCompiler returns
///   a kernel file to the CLI and another compilation request is given before
///   the VM is able to launch from the kernel that was returned in the first
///   compile request. The ResidentCompiler will be in the state of waiting for
///   a recompile request and will subsequently process the request and modify
///   the kernel file. However, it should be waiting for the VM to finish
///   launching itself from this kernel until it modifies the kernel.
///   As far as I can tell this race also exists in the current CLI run
///   command when using pub's precompile pipeline.
///
/// TODO Fix the race condition that occurs when the same entry point is
///   compiled concurrently.
class ResidentCompiler {
  final File _entryPoint;
  File? _currentPackage;
  ArgResults _compileOptions;
  late FrontendCompiler _compiler;
  DateTime _lastCompileStartTime = new DateTime.now().floorTime();
  _ResidentState _state = _ResidentState.waitingForFirstCompile;
  final StringBuffer _compilerOutput = new StringBuffer();
  final Set<Uri> trackedSources = <Uri>{};
  final List<String> _formattedOutput = <String>[];
  bool incrementalMode = false;

  /// The file where kernel data will be output by this [ResidentCompiler].
  File get _outputDill =>
      new File(_compileOptions.option(ResidentFrontendServer._outputString)!);

  ResidentCompiler(this._entryPoint, this._compileOptions) {
    _compiler = new FrontendCompiler(_compilerOutput);
    updateState(_compileOptions);
  }

  void resetStateToWaitingForFirstCompile() {
    _state = _ResidentState.waitingForFirstCompile;
  }

  /// The [ResidentCompiler] will use the [newOptions] for future compilation
  /// requests.
  void updateState(ArgResults newOptions) {
    final String? packages = newOptions['packages'];
    incrementalMode = newOptions['incremental'] == true;
    _compileOptions = newOptions;
    _currentPackage = packages == null ? null : new File(packages);
    // Refresh the compiler's output for the next compile
    _compilerOutput.clear();
    _formattedOutput.clear();
    resetStateToWaitingForFirstCompile();
  }

  /// The current compiler options are outdated when any option has changed
  /// since the last compile, or when the packages file has been modified
  bool areOptionsOutdated(ArgResults newOptions) {
    if (newOptions.arguments.length != _compileOptions.arguments.length) {
      return true;
    }
    if (!newOptions.arguments
        .toSet()
        .containsAll(_compileOptions.arguments.toSet())) {
      return true;
    }
    return _currentPackage != null &&
        !_lastCompileStartTime
            .isAfter(_currentPackage!.statSync().modified.floorTime());
  }

  /// Compiles the entry point that this ResidentCompiler is hooked to, abiding
  /// by [_compileOptions], and returns a response map detailing compilation
  /// results. See [_createResponseMap] for more information about that map.
  ///
  /// Incremental compilations will be performed when possible.
  Future<Map<String, dynamic>> compile() async {
    bool incremental = false;

    // If this entrypoint was previously compiled on this compiler instance,
    // check which source files need to be recompiled in the incremental
    // compilation request. If no files have been modified, we can return
    // the cached kernel. Otherwise, perform an incremental compilation.
    if (_state == _ResidentState.waitingForRecompile) {
      List<Uri> invalidatedUris =
          await _getSourceFilesToRecompile(_lastCompileStartTime);
      // No changes to source files detected and cached kernel file exists
      // If a kernel file is removed in between compilation requests,
      // fall through to produce the kernel in recompileDelta.
      if (invalidatedUris.isEmpty && _outputDill.existsSync()) {
        return _createResponseMap(
            _outputDill.path, _formattedOutput, _compiler.errors.length,
            usingCachedKernel: true);
      }
      _state = _ResidentState.compiling;
      incremental = true;
      for (Uri invalidatedUri in invalidatedUris) {
        _compiler.invalidate(invalidatedUri);
      }
      _compiler.errors.clear();
      _lastCompileStartTime = new DateTime.now().floorTime();
      await _compiler.recompileDelta(entryPoint: _entryPoint.path);
    } else {
      _state = _ResidentState.compiling;
      _lastCompileStartTime = new DateTime.now().floorTime();
      _compiler.errors.clear();
      await _compiler.compile(_entryPoint.path, _compileOptions);
    }

    _interpretCompilerOutput(new LineSplitter()
        .convert(_compilerOutput.toString())
        .where((line) => line.isNotEmpty)
        .toList());
    _compilerOutput.clear();

    if (incrementalMode) {
      // forces the compiler to produce complete kernel files on each
      // request, even when incrementally compiled.
      _compiler
        ..acceptLastDelta()
        ..resetIncrementalCompiler();
      _state = _ResidentState.waitingForRecompile;
    } else {
      resetStateToWaitingForFirstCompile();
    }

    return _createResponseMap(
        _outputDill.path, _formattedOutput, _compiler.errors.length,
        incrementalCompile: incremental);
  }

  /// WARNING: [compile] must be called on this compiler to populate the
  /// required context in it before [compileExpression] can be called on it.
  Future<String> compileExpression(
    String expression,
    List<String> definitions,
    List<String> definitionTypes,
    List<String> typeDefinitions,
    List<String> typeBounds,
    List<String> typeDefaults,
    String libraryUri,
    String? klass,
    String? method,
    int offset,
    String? scriptUri,
    bool isStatic,
  ) async {
    await _compiler.compileExpression(
      expression,
      definitions,
      definitionTypes,
      typeDefinitions,
      typeBounds,
      typeDefaults,
      libraryUri,
      klass,
      method,
      offset,
      scriptUri,
      isStatic,
    );

    _compilerOutput.clear();
    // [incrementalMode] can only ever be [false] if `--aot` was passed in the
    // 'compileExpression' request received by the [ResidentFrontendServer],
    //  which should be impossible.
    assert(incrementalMode);
    // Force the compiler to produce complete kernel files on each request, even
    // when incrementally compiled.
    _compiler
      ..acceptLastDelta()
      ..resetIncrementalCompiler();
    resetStateToWaitingForFirstCompile();

    final List<String> errors = _compiler.errors;
    final int errorCount = errors.length;
    return jsonEncode({
      'success': errorCount == 0,
      'errorCount': errorCount,
      if (errorCount > 0) 'compilerOutputLines': errors,
      'kernelBytes': base64Encode(_outputDill.readAsBytesSync()),
    });
  }

  /// Reads the compiler's [outputLines] to keep track of which files
  /// need to be tracked. Adds correctly ANSI formatted output to
  /// the [_formattedOutput] list.
  void _interpretCompilerOutput(List<String> outputLines) {
    _formattedOutput.clear();
    int outputLineIndex = 0;
    bool acceptingErrorsOrVerboseOutput = true;
    final String boundaryKey = outputLines[outputLineIndex]
        .substring(outputLines[outputLineIndex++].indexOf(' ') + 1);
    String line = outputLines[outputLineIndex++];

    while (acceptingErrorsOrVerboseOutput || !line.startsWith(boundaryKey)) {
      if (acceptingErrorsOrVerboseOutput) {
        if (line == boundaryKey) {
          acceptingErrorsOrVerboseOutput = false;
        } else {
          _formattedOutput.add(line);
        }
      } else {
        final String diffUri = line.substring(1);
        if (line.startsWith('+')) {
          trackedSources.add(Uri.parse(diffUri));
        } else if (line.startsWith('-')) {
          trackedSources.remove(Uri.parse(diffUri));
        }
      }
      line = outputLines[outputLineIndex++];
    }
  }

  /// Returns a list of uris that need to be recompiled, based on the
  /// [lastKernelCompileTime] timestamp.
  /// Due to Windows timestamp granularity, all timestamps are truncated by
  /// the second. This has no effect on correctness but may result in more
  /// files being marked as invalid than are strictly required.
  Future<List<Uri>> _getSourceFilesToRecompile(
      DateTime lastKernelCompileTime) async {
    final List<Uri> sourcesToRecompile = <Uri>[];
    for (Uri uri in trackedSources) {
      final DateTime sourceModifiedTime =
          new File(uri.toFilePath()).statSync().modified.floorTime();
      if (!lastKernelCompileTime.isAfter(sourceModifiedTime)) {
        sourcesToRecompile.add(uri);
      }
    }
    return sourcesToRecompile;
  }

  /// Returns a [Map] that can be serialized to JSON containing [outputDillPath]
  /// and any [formattedErrors].
  static Map<String, dynamic> _createResponseMap(
    String outputDillPath,
    List<String> formattedErrors,
    int errorCount, {
    bool usingCachedKernel = false,
    bool incrementalCompile = false,
  }) =>
      <String, Object>{
        "success": errorCount == 0,
        "errorCount": errorCount,
        "compilerOutputLines": formattedErrors,
        "output-dill": outputDillPath,
        if (usingCachedKernel) "returnedStoredKernel": true, // used for testing
        if (incrementalCompile) "incremental": true, // used for testing
      };
}

/// Maintains [FrontendCompiler] instances for kernel compilations, meant to be
/// used by the Dart CLI via sockets.
///
/// The [ResidentFrontendServer] manages compilation requests for VM targets
/// between any number of dart entry points, and utilizes incremental
/// compilation and existing kernel files for faster compile times.
///
/// Communication is handled on the socket set up by the
/// residentListenAndCompile method.
class ResidentFrontendServer {
  static const String _commandString = 'command';
  static const String _replaceCachedDillString = 'replaceCachedDill';
  static const String _replacementDillPathString = 'replacementDillPath';
  static const String _compileString = 'compile';
  static const String _executableString = 'executable';
  static const String _packageString = 'packages';
  static const String _successString = 'success';
  static const String _outputString = 'output-dill';
  static const String _compileExpressionString = 'compileExpression';
  static const String _libraryUriString = 'libraryUri';
  static const String _rootLibraryUriString = 'rootLibraryUri';
  static const String _dillExtensionString = '.dill';
  static const String _expressionString = 'expression';
  static const String _definitionsString = 'definitions';
  static const String _definitionTypesString = 'definitionTypes';
  static const String _typeDefinitionsString = 'typeDefinitions';
  static const String _typeBoundsString = 'typeBounds';
  static const String _typeDefaultsString = 'typeDefaults';
  static const String _classString = 'class';
  static const String _methodString = 'method';
  static const String _offsetString = 'offset';
  static const String _scriptUriString = 'scriptUri';
  static const String _isStaticString = 'isStatic';
  static const String _shutdownString = 'shutdown';
  static const int _compilerLimit = 3;

  static final String shutdownCommand =
      jsonEncode(<String, Object>{_commandString: _shutdownString});
  static final String _shutdownJsonResponse =
      jsonEncode(<String, Object>{_shutdownString: true});
  static final Uri _sdkBinariesUri = computePlatformBinariesLocation();
  static final Uri _sdkUri = _sdkBinariesUri.resolve('../../');
  static final Uri _platformKernelUri =
      _sdkBinariesUri.resolve('vm_platform_strong.dill');
  static final Map<String, ResidentCompiler> compilers = {};

  /// Returns a [ResidentCompiler] that has been configured with
  /// [compileOptions] and prepared to compile the [canonicalizedLibraryPath]
  /// entrypoint.
  static ResidentCompiler _getResidentCompilerForEntrypoint(
    String canonicalizedLibraryPath,
    ArgResults compileOptions,
  ) {
    late final ResidentCompiler residentCompiler;
    if (compilers[canonicalizedLibraryPath] == null) {
      // Avoids using too much memory.
      if (compilers.length >= ResidentFrontendServer._compilerLimit) {
        compilers.remove(compilers.keys.first);
      }
      residentCompiler = new ResidentCompiler(
        new File(canonicalizedLibraryPath),
        compileOptions,
      );
      compilers[canonicalizedLibraryPath] = residentCompiler;
    } else {
      residentCompiler = compilers[canonicalizedLibraryPath]!;
      if (residentCompiler.areOptionsOutdated(compileOptions)) {
        residentCompiler.updateState(compileOptions);
      }
    }

    return residentCompiler;
  }

  static Future<String> _handleReplaceCachedDillRequest(
    Map<String, dynamic> request,
  ) async {
    if (request[_replacementDillPathString] == null) {
      return _encodeErrorMessage(
        "'$_replaceCachedDillString' requests must include a "
        "'$_replacementDillPathString' property.",
      );
    }

    final File replacementDillFile =
        new File(request[_replacementDillPathString]);

    final String canonicalizedLibraryPath;
    try {
      final Component component =
          loadComponentFromBytes(replacementDillFile.readAsBytesSync());
      canonicalizedLibraryPath = path.canonicalize(
        component.mainMethod!.enclosingLibrary.fileUri.toFilePath(),
      );

      final String cachedDillPath =
          computeCachedDillPath(canonicalizedLibraryPath);
      replacementDillFile.copySync(cachedDillPath);
    } catch (e) {
      return _encodeErrorMessage('Failed to replace cached dill');
    }

    if (compilers[canonicalizedLibraryPath] != null) {
      compilers[canonicalizedLibraryPath]!.resetStateToWaitingForFirstCompile();
    }

    return jsonEncode({
      _successString: true,
    });
  }

  static Future<String> _handleCompileRequest(
    Map<String, dynamic> request,
  ) async {
    if (request[_executableString] == null || request[_outputString] == null) {
      return _encodeErrorMessage(
        "'$_compileString' requests must include an '$_executableString' "
        "property and an '$_outputString' property.",
      );
    }

    final String canonicalizedExecutablePath =
        path.canonicalize(request[_executableString]);

    late final String cachedDillPath;
    try {
      cachedDillPath = computeCachedDillPath(canonicalizedExecutablePath);
    } on Exception catch (e) {
      return _encodeErrorMessage(e.toString());
    }

    final ArgResults options = _generateCompilerOptions(
      request: request,
      outputDillOverride: cachedDillPath,
      initializeFromDillPath: cachedDillPath,
    );
    final ResidentCompiler residentCompiler = _getResidentCompilerForEntrypoint(
      canonicalizedExecutablePath,
      options,
    );
    final Map<String, dynamic> response = await residentCompiler.compile();

    if (response[_successString] != true) {
      return jsonEncode(response);
    }

    final String outputDillPath = request[_outputString];
    if (cachedDillPath != outputDillPath) {
      try {
        new File(cachedDillPath).copySync(outputDillPath);
      } catch (e) {
        return _encodeErrorMessage(
          'Could not write output dill to ${request[_outputString]}.',
        );
      }
    }
    return jsonEncode({...response, _outputString: outputDillPath});
  }

  static Future<String> _handleCompileExpressionRequest(
    Map<String, dynamic> request,
  ) async {
    final String canonicalizedLibraryPath;
    try {
      if ((request[_libraryUriString] as String).startsWith('dart:')) {
        // An argument to the [entrypoint] parameter of
        // [FrontendCompiler.compile] is mandatory, and
        // [canonicalizedLibraryPath] is what we will use as that argument, so
        // if the library URI provided in the request begins with 'dart:', then
        // we use the URI of the root library of the isolate group in which the
        // evaluation is taking place to compute [canonicalizedLibraryPath]
        // instead.
        canonicalizedLibraryPath = path.canonicalize(
          Uri.parse(request[_rootLibraryUriString]).toFilePath(),
        );
      } else {
        canonicalizedLibraryPath = path
            .canonicalize(Uri.parse(request[_libraryUriString]).toFilePath());
      }
    } catch (e) {
      return _encodeErrorMessage(
        "Request contains invalid '$_libraryUriString' property",
      );
    }

    final String cachedDillPath =
        computeCachedDillPath(canonicalizedLibraryPath);
    // Make the [ResidentCompiler] output the compiled expression to
    // [compiledExpressionDillPath] to prevent it from overwriting the
    // cached program dill.
    assert(cachedDillPath.endsWith(_dillExtensionString));
    final String compiledExpressionDillPath = cachedDillPath.replaceRange(
      cachedDillPath.length - _dillExtensionString.length,
      null,
      '.expr.dill',
    );
    final ArgResults options = _generateCompilerOptions(
      request: request,
      outputDillOverride: compiledExpressionDillPath,
      initializeFromDillPath: cachedDillPath,
    );

    final ResidentCompiler residentCompiler =
        _getResidentCompilerForEntrypoint(canonicalizedLibraryPath, options);

    final String expression = request[_expressionString];
    final List<String> definitions =
        (request[_definitionsString] as List<dynamic>).cast<String>();
    final List<String> definitionTypes =
        (request[_definitionTypesString] as List<dynamic>).cast<String>();
    final List<String> typeDefinitions =
        (request[_typeDefinitionsString] as List<dynamic>).cast<String>();
    final List<String> typeBounds =
        (request[_typeBoundsString] as List<dynamic>).cast<String>();
    final List<String> typeDefaults =
        (request[_typeDefaultsString] as List<dynamic>).cast<String>();
    final String libraryUri = request[_libraryUriString];
    final String? klass = request[_classString];
    final String? method = request[_methodString];
    final int offset = request[_offsetString];
    final String? scriptUri = request[_scriptUriString];
    final bool isStatic = request[_isStaticString];

    // [residentCompiler.compile] must be called before
    // [residentCompiler.compileExpression] can be called. See the
    // documentation of [ResidentCompiler.compile] for more information.
    await residentCompiler.compile();
    return await residentCompiler.compileExpression(
      expression,
      definitions,
      definitionTypes,
      typeDefinitions,
      typeBounds,
      typeDefaults,
      libraryUri,
      klass,
      method,
      offset,
      scriptUri,
      isStatic,
    );
  }

  /// Takes in JSON [input] from the socket and compiles the request,
  /// using incremental compilation if possible. Returns a JSON string to be
  /// sent back to the client socket containing either an error message or the
  /// kernel file to be used.
  ///
  /// If the command is compile, paths the source file, package_config.json,
  /// and the output-dill file must be provided via "executable", "packages",
  /// and "output-dill".
  static Future<String> handleRequest(String input) async {
    Map<String, dynamic> request;
    try {
      request = jsonDecode(input);
    } on FormatException {
      return _encodeErrorMessage('$input is not valid JSON.');
    }

    switch (request[_commandString]) {
      case _replaceCachedDillString:
        return _handleReplaceCachedDillRequest(request);
      case _compileString:
        return _handleCompileRequest(request);
      case _compileExpressionString:
        return _handleCompileExpressionRequest(request);
      case _shutdownString:
        return _shutdownJsonResponse;
      default:
        return _encodeErrorMessage(
            'Unsupported command: ${request[_commandString]}.');
    }
  }

  /// Generates the compiler options needed to handle the [request].
  static ArgResults _generateCompilerOptions({
    required Map<String, dynamic> request,

    /// The compiled kernel file will be stored at this path, and not at
    /// [request['--output-dill']].
    required String outputDillOverride,
    required String initializeFromDillPath,
  }) {
    return argParser.parse(<String>[
      '--sdk-root=${_sdkUri.toFilePath()}',
      if (!(request['aot'] ?? false)) '--incremental',
      '--platform=${_platformKernelUri.path}',
      '--output-dill=$outputDillOverride',
      '--initialize-from-dill=$initializeFromDillPath',
      // We can assume that the cached dill is up-to-date when handling
      // 'compileExpression' requests because if dartdev was given a source file
      // to run, then it must have compiled it with the resident frontend
      // compiler, guaranteeing that the cached dill is up-to-date, and if
      // dartdev was given a dill file to run, then it must have used the
      // resident frontend compiler's 'replaceCachedDill' endpoint to update the
      // dill cache.
      if (request[_commandString] == _compileExpressionString)
        '--assume-initialize-from-dill-up-to-date',
      '--target=vm',
      '--filesystem-scheme',
      'org-dartlang-root',
      if (request.containsKey(_packageString))
        '--packages=${request[_packageString]}',
      if (request['support-mirrors'] ?? false) '--support-mirrors',
      if (request['enable-asserts'] ?? false) '--enable-asserts',
      if (request['sound-null-safety'] ?? false) '--sound-null-safety',
      if (request['verbosity'] != null) '--verbosity=${request["verbosity"]}',
      if (request['verbose'] ?? false) '--verbose',
      if (request['aot'] ?? false) '--aot',
      if (request['tfa'] ?? false) '--tfa',
      if (request['rta'] ?? false) '--rta',
      if (request['tree-shake-write-only-fields'] ?? false)
        '--tree-shake-write-only-fields',
      if (request['protobuf-tree-shaker-v2'] ?? false)
        '--protobuf-tree-shaker-v2',
      if (request['define'] != null)
        for (String define in request['define']) define,
      if (request['enable-experiment'] != null)
        for (String experiment in request['enable-experiment']) experiment,
    ]);
  }

  /// Encodes the [message] in JSON to be sent over the socket.
  static String _encodeErrorMessage(String message) => jsonEncode(
        <String, Object>{_successString: false, 'errorMessage': message},
      );

  /// Used to create compile requests for the ResidentFrontendServer.
  /// Returns a JSON string that the resident compiler will be able to
  /// interpret.
  static String createCompileJSON(
      {required String executable,
      String? packages,
      required String outputDill,
      bool? supportMirrors,
      bool? enableAsserts,
      bool? soundNullSafety,
      String? verbosity,
      bool? aot,
      bool? tfa,
      bool? rta,
      bool? treeShakeWriteOnlyFields,
      bool? protobufTreeShakerV2,
      List<String>? define,
      List<String>? enableExperiment,
      bool verbose = false}) {
    return jsonEncode(<String, Object>{
      "command": "compile",
      "executable": executable,
      "output-dill": outputDill,
      if (aot != null) "aot": true,
      if (define != null) "define": define,
      if (enableAsserts != null) "enable-asserts": true,
      if (enableExperiment != null) "enable-experiment": enableExperiment,
      if (packages != null) "packages": packages,
      if (protobufTreeShakerV2 != null) "protobuf-tree-shaker-v2": true,
      if (rta != null) "rta": true,
      if (soundNullSafety != null) "sound-null-safety": soundNullSafety,
      if (supportMirrors != null) "support-mirrors": true,
      if (tfa != null) "tfa": true,
      if (treeShakeWriteOnlyFields != null)
        "tree-shaker-write-only-fields": true,
      if (verbosity != null) "verbosity": verbosity,
      "verbose": verbose,
    });
  }
}

/// Closes the ServerSocket and removes the [serverInfoFile] that is used
/// to access this instance of the Resident Frontend Server.
Future<void> residentServerCleanup(
    ServerSocket server, File serverInfoFile) async {
  try {
    if (_cleanupHandler != null) {
      await _cleanupHandler!.cancel();
    }
  } catch (_) {
  } finally {
    try {
      if (serverInfoFile.existsSync()) {
        serverInfoFile.deleteSync();
      }
    } catch (_) {}
  }

  await server.close();
}

/// Starts a timer that will shut down the resident frontend server in
/// the amount of time specified by [timerDuration], if it is not cancelled.
Timer startShutdownTimer(
    Duration timerDuration, ServerSocket server, File serverInfoFile) {
  return new Timer(timerDuration, () async {
    await residentServerCleanup(server, serverInfoFile);
  });
}

/// Listens for compilation commands from socket connections on the
/// provided [address] and [port].
/// If the last request exceeds the amount of time specified by
/// [inactivityTimeout], the server will bring itself down
Future<StreamSubscription<Socket>?> residentListenAndCompile(
    InternetAddress address, int port, File serverInfoFile,
    {Duration inactivityTimeout = const Duration(minutes: 30)}) async {
  ServerSocket server;
  try {
    try {
      serverInfoFile.createSync(exclusive: true);
    } catch (e) {
      throw new StateError('A server is already running.');
    }
    server = await ServerSocket.bind(address, port);
    // There are particular aspects of the info file format that must be
    // preserved to ensure backwards compatibility with the original versions
    // of the utilities for parsing this file.
    //
    // The aspects of the info file format that must be preserved are:
    // 1. The file must begin with 'address:$address '. Note that $address IS
    //    NOT preceded by a space and IS followed by a space.
    // 2. The file must end with 'port:$port'. Note that $port IS NOT preceded
    //    by a space. $port may be followed by zero or more whitespace
    //    characters.
    serverInfoFile.writeAsStringSync(
      'address:${server.address.address} '
      'sdkHash:${expectedSdkHash} '
      'port:${server.port} ',
    );
  } on StateError catch (e) {
    print('Error: $e\n');
    return null;
  } catch (e) {
    // If we created a file, but bind or writing failed, clean up.
    try {
      serverInfoFile.deleteSync();
    } catch (_) {}
    print('Error: $e\n');
    return null;
  }

  _cleanupHandler = ProcessSignal.sigint.watch().listen((signal) async {
    await residentServerCleanup(server, serverInfoFile);
    exit(1);
  });
  Timer shutdownTimer =
      startShutdownTimer(inactivityTimeout, server, serverInfoFile);
  // TODO: This should be changed to print to stderr so we don't change the
  // stdout text for regular apps.
  print('The Resident Frontend Compiler is listening at '
      '${server.address.address}:${server.port}');

  return server.listen((client) {
    client.listen((Uint8List data) async {
      String result = await ResidentFrontendServer.handleRequest(
          new String.fromCharCodes(data));
      client.write(result);
      shutdownTimer.cancel();
      if (result == ResidentFrontendServer._shutdownJsonResponse) {
        await residentServerCleanup(server, serverInfoFile);
      } else {
        shutdownTimer =
            startShutdownTimer(inactivityTimeout, server, serverInfoFile);
      }
    }, onError: (error) {
      client.close();
    }, onDone: () {
      client.close();
    });
  }, onError: (_) async {
    shutdownTimer.cancel();
    await residentServerCleanup(server, serverInfoFile);
  });
}