packages/flutter_tools/lib/src/devfs.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 // @dart = 2.8

 import 'dart:async';

 import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;

 import 'asset.dart';
 import 'base/context.dart';
 import 'base/file_system.dart';
 import 'base/io.dart';
 import 'base/logger.dart';
 import 'base/net.dart';
 import 'base/os.dart';
 import 'build_info.dart';
 import 'compile.dart';
 import 'convert.dart' show base64, utf8;
 import 'vmservice.dart';

 class DevFSConfig {
   /// Should DevFS assume that symlink targets are stable?
   bool cacheSymlinks = false;
   /// Should DevFS assume that there are no symlinks to directories?
   bool noDirectorySymlinks = false;
 }

 DevFSConfig get devFSConfig => context.get<DevFSConfig>();

 /// Common superclass for content copied to the device.
 abstract class DevFSContent {
   /// Return true if this is the first time this method is called
   /// or if the entry has been modified since this method was last called.
   bool get isModified;

   /// Return true if this is the first time this method is called
   /// or if the entry has been modified after the given time
   /// or if the given time is null.
   bool isModifiedAfter(DateTime time);

   int get size;

   Future<List<int>> contentsAsBytes();

   Stream<List<int>> contentsAsStream();

   Stream<List<int>> contentsAsCompressedStream(
     OperatingSystemUtils osUtils,
   ) {
     return osUtils.gzipLevel1Stream(contentsAsStream());
   }
 }

 // File content to be copied to the device.
 class DevFSFileContent extends DevFSContent {
   DevFSFileContent(this.file);

   final FileSystemEntity file;
   File _linkTarget;
   FileStat _fileStat;

   File _getFile() {
     if (_linkTarget != null) {
       return _linkTarget;
     }
     if (file is Link) {
       // The link target.
       return file.fileSystem.file(file.resolveSymbolicLinksSync());
     }
     return file as File;
   }

   void _stat() {
     if (_linkTarget != null) {
       // Stat the cached symlink target.
       final FileStat fileStat = _linkTarget.statSync();
       if (fileStat.type == FileSystemEntityType.notFound) {
         _linkTarget = null;
       } else {
         _fileStat = fileStat;
         return;
       }
     }
     final FileStat fileStat = file.statSync();
     _fileStat = fileStat.type == FileSystemEntityType.notFound ? null : fileStat;
     if (_fileStat != null && _fileStat.type == FileSystemEntityType.link) {
       // Resolve, stat, and maybe cache the symlink target.
       final String resolved = file.resolveSymbolicLinksSync();
       final File linkTarget = file.fileSystem.file(resolved);
       // Stat the link target.
       final FileStat fileStat = linkTarget.statSync();
       if (fileStat.type == FileSystemEntityType.notFound) {
         _fileStat = null;
         _linkTarget = null;
       } else if (devFSConfig.cacheSymlinks) {
         _linkTarget = linkTarget;
       }
     }
   }

   @override
   bool get isModified {
     final FileStat _oldFileStat = _fileStat;
     _stat();
     if (_oldFileStat == null && _fileStat == null) {
       return false;
     }
     return _oldFileStat == null || _fileStat == null || _fileStat.modified.isAfter(_oldFileStat.modified);
   }

   @override
   bool isModifiedAfter(DateTime time) {
     final FileStat _oldFileStat = _fileStat;
     _stat();
     if (_oldFileStat == null && _fileStat == null) {
       return false;
     }
     return time == null
         || _oldFileStat == null
         || _fileStat == null
         || _fileStat.modified.isAfter(time);
   }

   @override
   int get size {
     if (_fileStat == null) {
       _stat();
     }
     // Can still be null if the file wasn't found.
     return _fileStat?.size ?? 0;
   }

   @override
   Future<List<int>> contentsAsBytes() => _getFile().readAsBytes();

   @override
   Stream<List<int>> contentsAsStream() => _getFile().openRead();
 }

 /// Byte content to be copied to the device.
 class DevFSByteContent extends DevFSContent {
   DevFSByteContent(this._bytes);

   List<int> _bytes;

   bool _isModified = true;
   DateTime _modificationTime = DateTime.now();

   List<int> get bytes => _bytes;

   set bytes(List<int> value) {
     _bytes = value;
     _isModified = true;
     _modificationTime = DateTime.now();
   }

   /// Return true only once so that the content is written to the device only once.
   @override
   bool get isModified {
     final bool modified = _isModified;
     _isModified = false;
     return modified;
   }

   @override
   bool isModifiedAfter(DateTime time) {
     return time == null || _modificationTime.isAfter(time);
   }

   @override
   int get size => _bytes.length;

   @override
   Future<List<int>> contentsAsBytes() async => _bytes;

   @override
   Stream<List<int>> contentsAsStream() =>
       Stream<List<int>>.fromIterable(<List<int>>[_bytes]);
 }

 /// String content to be copied to the device.
 class DevFSStringContent extends DevFSByteContent {
   DevFSStringContent(String string)
     : _string = string,
       super(utf8.encode(string));

   String _string;

   String get string => _string;

   set string(String value) {
     _string = value;
     super.bytes = utf8.encode(_string);
   }

   @override
   set bytes(List<int> value) {
     string = utf8.decode(value);
   }
 }

 /// A string compressing DevFSContent.
 ///
 /// A specialized DevFSContent similar to DevFSByteContent where the contents
 /// are the compressed bytes of a string. Its difference is that the original
 /// uncompressed string can be compared with directly without the indirection
 /// of a compute-expensive uncompress/decode and compress/encode to compare
 /// the strings.
 ///
 /// The `hintString` parameter is a zlib dictionary hinting mechanism to suggest
 /// the most common string occurrences to potentially assist with compression.
 class DevFSStringCompressingBytesContent extends DevFSContent {
   DevFSStringCompressingBytesContent(this._string, { String hintString })
     : _compressor = ZLibEncoder(
       dictionary: hintString == null
           ? null
           : utf8.encode(hintString),
       gzip: true,
       level: 9,
     );

   final String _string;
   final ZLibEncoder _compressor;
   final DateTime _modificationTime = DateTime.now();

   List<int> _bytes;
   bool _isModified = true;

   List<int> get bytes => _bytes ??= _compressor.convert(utf8.encode(_string));

   /// Return true only once so that the content is written to the device only once.
   @override
   bool get isModified {
     final bool modified = _isModified;
     _isModified = false;
     return modified;
   }

   @override
   bool isModifiedAfter(DateTime time) {
     return time == null || _modificationTime.isAfter(time);
   }

   @override
   int get size => bytes.length;

   @override
   Future<List<int>> contentsAsBytes() async => bytes;

   @override
   Stream<List<int>> contentsAsStream() => Stream<List<int>>.value(bytes);

   /// This checks the source string with another string.
   bool equals(String string) => _string == string;
 }

 class DevFSException implements Exception {
   DevFSException(this.message, [this.error, this.stackTrace]);
   final String message;
   final dynamic error;
   final StackTrace stackTrace;

   @override
   String toString() => 'DevFSException($message, $error, $stackTrace)';
 }

 /// Interface responsible for syncing asset files to a development device.
 abstract class DevFSWriter {
   /// Write the assets in [entries] to the target device.
   ///
   /// The keys of the map are relative from the [baseUri].
   ///
   /// Throws a [DevFSException] if the process fails to complete.
   Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, DevFSWriter parent);
 }

 class _DevFSHttpWriter implements DevFSWriter {
   _DevFSHttpWriter(
     this.fsName,
     FlutterVmService serviceProtocol, {
     @required OperatingSystemUtils osUtils,
     @required HttpClient httpClient,
     @required Logger logger,
     Duration uploadRetryThrottle,
   })
     : httpAddress = serviceProtocol.httpAddress,
       _client = httpClient,
       _osUtils = osUtils,
       _uploadRetryThrottle = uploadRetryThrottle,
       _logger = logger;

   final HttpClient _client;
   final OperatingSystemUtils _osUtils;
   final Logger _logger;
   final Duration _uploadRetryThrottle;

   final String fsName;
   final Uri httpAddress;

   // 3 was chosen to try to limit the variance in the time it takes to execute
   // `await request.close()` since there is a known bug in Dart where it doesn't
   // always return a status code in response to a PUT request:
   // https://github.com/dart-lang/sdk/issues/43525.
   static const int kMaxInFlight = 3;

   int _inFlight = 0;
   Map<Uri, DevFSContent> _outstanding;
   Completer<void> _completer;

   @override
   Future<void> write(Map<Uri, DevFSContent> entries, Uri devFSBase, [DevFSWriter parent]) async {
     try {
       _client.maxConnectionsPerHost = kMaxInFlight;
       _completer = Completer<void>();
       _outstanding = Map<Uri, DevFSContent>.of(entries);
       _scheduleWrites();
       await _completer.future;
     } on SocketException catch (socketException, stackTrace) {
       _logger.printTrace('DevFS sync failed. Lost connection to device: $socketException');
       throw DevFSException('Lost connection to device.', socketException, stackTrace);
     } on Exception catch (exception, stackTrace) {
       _logger.printError('Could not update files on device: $exception');
       throw DevFSException('Sync failed', exception, stackTrace);
     }
   }

   void _scheduleWrites() {
     while ((_inFlight < kMaxInFlight) && (!_completer.isCompleted) && _outstanding.isNotEmpty) {
       final Uri deviceUri = _outstanding.keys.first;
       final DevFSContent content = _outstanding.remove(deviceUri);
       _startWrite(deviceUri, content, retry: 10);
       _inFlight += 1;
     }
     if ((_inFlight == 0) && (!_completer.isCompleted) && _outstanding.isEmpty) {
       _completer.complete();
     }
   }

   Future<void> _startWrite(
     Uri deviceUri,
     DevFSContent content, {
     int retry = 0,
   }) async {
     while(true) {
       try {
         final HttpClientRequest request = await _client.putUrl(httpAddress);
         request.headers.removeAll(HttpHeaders.acceptEncodingHeader);
         request.headers.add('dev_fs_name', fsName);
         request.headers.add('dev_fs_uri_b64', base64.encode(utf8.encode('$deviceUri')));
         final Stream<List<int>> contents = content.contentsAsCompressedStream(
           _osUtils,
         );
         await request.addStream(contents);
         // Once the bug in Dart is solved we can remove the timeout
         // (https://github.com/dart-lang/sdk/issues/43525).
         try {
           final HttpClientResponse response = await request.close().timeout(
             const Duration(seconds: 60));
           response.listen((_) {},
             onError: (dynamic error) {
               _logger.printTrace('error: $error');
             },
             cancelOnError: true,
           );
         } on TimeoutException {
           request.abort();
           // This should throw "HttpException: Request has been aborted".
           await request.done;
           // Just to be safe we rethrow the TimeoutException.
           rethrow;
         }
         break;
       } on Exception catch (error, trace) {
         if (!_completer.isCompleted) {
           _logger.printTrace('Error writing "$deviceUri" to DevFS: $error');
           if (retry > 0) {
             retry--;
             _logger.printTrace('trying again in a few - $retry more attempts left');
             await Future<void>.delayed(_uploadRetryThrottle ?? const Duration(milliseconds: 500));
             continue;
           }
           _completer.completeError(error, trace);
         }
       }
     }
     _inFlight -= 1;
     _scheduleWrites();
   }
 }

 // Basic statistics for DevFS update operation.
 class UpdateFSReport {
   UpdateFSReport({
     bool success = false,
     int invalidatedSourcesCount = 0,
     int syncedBytes = 0,
     this.fastReassembleClassName,
   }) : _success = success,
        _invalidatedSourcesCount = invalidatedSourcesCount,
        _syncedBytes = syncedBytes;

   bool get success => _success;
   int get invalidatedSourcesCount => _invalidatedSourcesCount;
   int get syncedBytes => _syncedBytes;

   bool _success;
   String fastReassembleClassName;
   int _invalidatedSourcesCount;
   int _syncedBytes;

   void incorporateResults(UpdateFSReport report) {
     if (!report._success) {
       _success = false;
     }
     fastReassembleClassName ??= report.fastReassembleClassName;
     _invalidatedSourcesCount += report._invalidatedSourcesCount;
     _syncedBytes += report._syncedBytes;
   }
 }

 class DevFS {
   /// Create a [DevFS] named [fsName] for the local files in [rootDirectory].
   ///
   /// Failed uploads are retried after [uploadRetryThrottle] duration, defaults to 500ms.
   DevFS(
     FlutterVmService serviceProtocol,
     this.fsName,
     this.rootDirectory, {
     @required OperatingSystemUtils osUtils,
     @required Logger logger,
     @required FileSystem fileSystem,
     HttpClient httpClient,
     Duration uploadRetryThrottle,
   }) : _vmService = serviceProtocol,
        _logger = logger,
        _fileSystem = fileSystem,
        _httpWriter = _DevFSHttpWriter(
         fsName,
         serviceProtocol,
         osUtils: osUtils,
         logger: logger,
         uploadRetryThrottle: uploadRetryThrottle,
         httpClient: httpClient ?? ((context.get<HttpClientFactory>() == null)
           ? HttpClient()
           : context.get<HttpClientFactory>()())
       );

   final FlutterVmService _vmService;
   final _DevFSHttpWriter _httpWriter;
   final Logger _logger;
   final FileSystem _fileSystem;

   final String fsName;
   final Directory rootDirectory;
   final Set<String> assetPathsToEvict = <String>{};

   List<Uri> sources = <Uri>[];
   DateTime lastCompiled;
   DateTime _previousCompiled;
   PackageConfig lastPackageConfig;
   File _widgetCacheOutputFile;

   Uri _baseUri;
   Uri get baseUri => _baseUri;

   Uri deviceUriToHostUri(Uri deviceUri) {
     final String deviceUriString = deviceUri.toString();
     final String baseUriString = baseUri.toString();
     if (deviceUriString.startsWith(baseUriString)) {
       final String deviceUriSuffix = deviceUriString.substring(baseUriString.length);
       return rootDirectory.uri.resolve(deviceUriSuffix);
     }
     return deviceUri;
   }

   Future<Uri> create() async {
     _logger.printTrace('DevFS: Creating new filesystem on the device ($_baseUri)');
     try {
       final vm_service.Response response = await _vmService.createDevFS(fsName);
       _baseUri = Uri.parse(response.json['uri'] as String);
     } on vm_service.RPCError catch (rpcException) {
       if (rpcException.code == RPCErrorCodes.kServiceDisappeared) {
         // This can happen if the device has been disconnected, so translate to
         // a DevFSException, which the caller will handle.
         throw DevFSException('Service disconnected', rpcException);
       }
       // 1001 is kFileSystemAlreadyExists in //dart/runtime/vm/json_stream.h
       if (rpcException.code != 1001) {
         // Other RPCErrors are unexpected. Rethrow so it will hit crash
         // logging.
         rethrow;
       }
       _logger.printTrace('DevFS: Creating failed. Destroying and trying again');
       await destroy();
       final vm_service.Response response = await _vmService.createDevFS(fsName);
       _baseUri = Uri.parse(response.json['uri'] as String);
     }
     _logger.printTrace('DevFS: Created new filesystem on the device ($_baseUri)');
     return _baseUri;
   }

   Future<void> destroy() async {
     _logger.printTrace('DevFS: Deleting filesystem on the device ($_baseUri)');
     await _vmService.deleteDevFS(fsName);
     _logger.printTrace('DevFS: Deleted filesystem on the device ($_baseUri)');
   }

   /// Mark the [lastCompiled] time to the previous successful compile.
   ///
   /// Sometimes a hot reload will be rejected by the VM due to a change in the
   /// structure of the code not supporting the hot reload. In these cases,
   /// the best resolution is a hot restart. However, the resident runner
   /// will not recognize this file as having been changed since the delta
   /// will already have been accepted. Instead, reset the compile time so
   /// that the last updated files are included in subsequent compilations until
   /// a reload is accepted.
   void resetLastCompiled() {
     lastCompiled = _previousCompiled;
   }


   /// If the build method of a single widget was modified, return the widget name.
   ///
   /// If any other changes were made, or there is an error scanning the file,
   /// return `null`.
   String _checkIfSingleWidgetReloadApplied() {
     if (_widgetCacheOutputFile != null && _widgetCacheOutputFile.existsSync()) {
       final String widget = _widgetCacheOutputFile.readAsStringSync().trim();
       if (widget.isNotEmpty) {
         return widget;
       }
     }
     return null;
   }

   /// Updates files on the device.
   ///
   /// Returns the number of bytes synced.
   Future<UpdateFSReport> update({
     @required Uri mainUri,
     @required ResidentCompiler generator,
     @required bool trackWidgetCreation,
     @required String pathToReload,
     @required List<Uri> invalidatedFiles,
     @required PackageConfig packageConfig,
     @required String dillOutputPath,
     DevFSWriter devFSWriter,
     String target,
     AssetBundle bundle,
     DateTime firstBuildTime,
     bool bundleFirstUpload = false,
     bool fullRestart = false,
     String projectRootPath,
   }) async {
     assert(trackWidgetCreation != null);
     assert(generator != null);
     final DateTime candidateCompileTime = DateTime.now();
     lastPackageConfig = packageConfig;
     _widgetCacheOutputFile = _fileSystem.file('$dillOutputPath.incremental.dill.widget_cache');

     // Update modified files
     final Map<Uri, DevFSContent> dirtyEntries = <Uri, DevFSContent>{};
     int syncedBytes = 0;
     if (fullRestart) {
       generator.reset();
     }
     // On a full restart, or on an initial compile for the attach based workflow,
     // this will produce a full dill. Subsequent invocations will produce incremental
     // dill files that depend on the invalidated files.
     _logger.printTrace('Compiling dart to kernel with ${invalidatedFiles.length} updated files');

     // Await the compiler response after checking if the bundle is updated. This allows the file
     // stating to be done while waiting for the frontend_server response.
     final Future<CompilerOutput> pendingCompilerOutput = generator.recompile(
       mainUri,
       invalidatedFiles,
       outputPath: dillOutputPath,
       fs: _fileSystem,
       projectRootPath: projectRootPath,
       packageConfig: packageConfig,
     );
     if (bundle != null) {
       // The tool writes the assets into the AssetBundle working dir so that they
       // are in the same location in DevFS and the iOS simulator.
       final String assetBuildDirPrefix = _asUriPath(getAssetBuildDirectory());
       final String assetDirectory = getAssetBuildDirectory();
       bundle.entries.forEach((String archivePath, DevFSContent content) {
         // If the content is backed by a real file, isModified will file stat and return true if
         // it was modified since the last time this was called.
         if (!content.isModified || bundleFirstUpload) {
           return;
         }
         final Uri deviceUri = _fileSystem.path.toUri(_fileSystem.path.join(assetDirectory, archivePath));
         if (deviceUri.path.startsWith(assetBuildDirPrefix)) {
           archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
         }
         dirtyEntries[deviceUri] = content;
         syncedBytes += content.size;
         if (archivePath != null && !bundleFirstUpload) {
           assetPathsToEvict.add(archivePath);
         }
       });
     }
     final CompilerOutput compilerOutput = await pendingCompilerOutput;
     if (compilerOutput == null || compilerOutput.errorCount > 0) {
       return UpdateFSReport(success: false);
     }
     // Only update the last compiled time if we successfully compiled.
     _previousCompiled = lastCompiled;
     lastCompiled = candidateCompileTime;
     // list of sources that needs to be monitored are in [compilerOutput.sources]
     sources = compilerOutput.sources;
     //
     // Don't send full kernel file that would overwrite what VM already
     // started loading from.
     if (!bundleFirstUpload) {
       final String compiledBinary = compilerOutput?.outputFilename;
       if (compiledBinary != null && compiledBinary.isNotEmpty) {
         final Uri entryUri = _fileSystem.path.toUri(pathToReload);
         final DevFSFileContent content = DevFSFileContent(_fileSystem.file(compiledBinary));
         syncedBytes += content.size;
         dirtyEntries[entryUri] = content;
       }
     }
     _logger.printTrace('Updating files.');
     if (dirtyEntries.isNotEmpty) {
       await (devFSWriter ?? _httpWriter).write(dirtyEntries, _baseUri, _httpWriter);
     }
     _logger.printTrace('DevFS: Sync finished');
     return UpdateFSReport(
       success: true,
       syncedBytes: syncedBytes,
       invalidatedSourcesCount: invalidatedFiles.length,
       fastReassembleClassName: _checkIfSingleWidgetReloadApplied(),
     );
   }

   /// Converts a platform-specific file path to a platform-independent URL path.
   String _asUriPath(String filePath) => _fileSystem.path.toUri(filePath).path + '/';
 }

 /// An implementation of a devFS writer which copies physical files for devices
 /// running on the same host.
 ///
 /// DevFS entries which correspond to physical files are copied using [File.copySync],
 /// while entries that correspond to arbitrary string/byte values are written from
 /// memory.
 ///
 /// Requires that the file system is the same for both the tool and application.
 class LocalDevFSWriter implements DevFSWriter {
   LocalDevFSWriter({
     @required FileSystem fileSystem,
   }) : _fileSystem = fileSystem;

   final FileSystem _fileSystem;

   @override
   Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, [DevFSWriter parent]) async {
     try {
       for (final Uri uri in entries.keys) {
         final DevFSContent devFSContent = entries[uri];
         final File destination = _fileSystem.file(baseUri.resolveUri(uri));
         if (!destination.parent.existsSync()) {
           destination.parent.createSync(recursive: true);
         }
         if (devFSContent is DevFSFileContent) {
           final File content = devFSContent.file as File;
           content.copySync(destination.path);
           continue;
         }
         destination.writeAsBytesSync(await devFSContent.contentsAsBytes());
       }
     } on FileSystemException catch (err) {
       throw DevFSException(err.toString());
     }
   }
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	// @dart = 2.8

	import 'dart:async';

	import 'package:meta/meta.dart';
	import 'package:package_config/package_config.dart';
	import 'package:vm_service/vm_service.dart' as vm_service;

	import 'asset.dart';
	import 'base/context.dart';
	import 'base/file_system.dart';
	import 'base/io.dart';
	import 'base/logger.dart';
	import 'base/net.dart';
	import 'base/os.dart';
	import 'build_info.dart';
	import 'compile.dart';
	import 'convert.dart' show base64, utf8;
	import 'vmservice.dart';

	class DevFSConfig {
	/// Should DevFS assume that symlink targets are stable?
	bool cacheSymlinks = false;
	/// Should DevFS assume that there are no symlinks to directories?
	bool noDirectorySymlinks = false;
	}

	DevFSConfig get devFSConfig => context.get<DevFSConfig>();

	/// Common superclass for content copied to the device.
	abstract class DevFSContent {
	/// Return true if this is the first time this method is called
	/// or if the entry has been modified since this method was last called.
	bool get isModified;

	/// Return true if this is the first time this method is called
	/// or if the entry has been modified after the given time
	/// or if the given time is null.
	bool isModifiedAfter(DateTime time);

	int get size;

	Future<List<int>> contentsAsBytes();

	Stream<List<int>> contentsAsStream();

	Stream<List<int>> contentsAsCompressedStream(
	OperatingSystemUtils osUtils,
	) {
	return osUtils.gzipLevel1Stream(contentsAsStream());
	}
	}

	// File content to be copied to the device.
	class DevFSFileContent extends DevFSContent {
	DevFSFileContent(this.file);

	final FileSystemEntity file;
	File _linkTarget;
	FileStat _fileStat;

	File _getFile() {
	if (_linkTarget != null) {
	return _linkTarget;
	}
	if (file is Link) {
	// The link target.
	return file.fileSystem.file(file.resolveSymbolicLinksSync());
	}
	return file as File;
	}

	void _stat() {
	if (_linkTarget != null) {
	// Stat the cached symlink target.
	final FileStat fileStat = _linkTarget.statSync();
	if (fileStat.type == FileSystemEntityType.notFound) {
	_linkTarget = null;
	} else {
	_fileStat = fileStat;
	return;
	}
	}
	final FileStat fileStat = file.statSync();
	_fileStat = fileStat.type == FileSystemEntityType.notFound ? null : fileStat;
	if (_fileStat != null && _fileStat.type == FileSystemEntityType.link) {
	// Resolve, stat, and maybe cache the symlink target.
	final String resolved = file.resolveSymbolicLinksSync();
	final File linkTarget = file.fileSystem.file(resolved);
	// Stat the link target.
	final FileStat fileStat = linkTarget.statSync();
	if (fileStat.type == FileSystemEntityType.notFound) {
	_fileStat = null;
	_linkTarget = null;
	} else if (devFSConfig.cacheSymlinks) {
	_linkTarget = linkTarget;
	}
	}
	}

	@override
	bool get isModified {
	final FileStat _oldFileStat = _fileStat;
	_stat();
	if (_oldFileStat == null && _fileStat == null) {
	return false;
	}
	return _oldFileStat == null \|\| _fileStat == null \|\| _fileStat.modified.isAfter(_oldFileStat.modified);
	}

	@override
	bool isModifiedAfter(DateTime time) {
	final FileStat _oldFileStat = _fileStat;
	_stat();
	if (_oldFileStat == null && _fileStat == null) {
	return false;
	}
	return time == null
	\|\| _oldFileStat == null
	\|\| _fileStat == null
	\|\| _fileStat.modified.isAfter(time);
	}

	@override
	int get size {
	if (_fileStat == null) {
	_stat();
	}
	// Can still be null if the file wasn't found.
	return _fileStat?.size ?? 0;
	}

	@override
	Future<List<int>> contentsAsBytes() => _getFile().readAsBytes();

	@override
	Stream<List<int>> contentsAsStream() => _getFile().openRead();
	}

	/// Byte content to be copied to the device.
	class DevFSByteContent extends DevFSContent {
	DevFSByteContent(this._bytes);

	List<int> _bytes;

	bool _isModified = true;
	DateTime _modificationTime = DateTime.now();

	List<int> get bytes => _bytes;

	set bytes(List<int> value) {
	_bytes = value;
	_isModified = true;
	_modificationTime = DateTime.now();
	}

	/// Return true only once so that the content is written to the device only once.
	@override
	bool get isModified {
	final bool modified = _isModified;
	_isModified = false;
	return modified;
	}

	@override
	bool isModifiedAfter(DateTime time) {
	return time == null \|\| _modificationTime.isAfter(time);
	}

	@override
	int get size => _bytes.length;

	@override
	Future<List<int>> contentsAsBytes() async => _bytes;

	@override
	Stream<List<int>> contentsAsStream() =>
	Stream<List<int>>.fromIterable(<List<int>>[_bytes]);
	}

	/// String content to be copied to the device.
	class DevFSStringContent extends DevFSByteContent {
	DevFSStringContent(String string)
	: _string = string,
	super(utf8.encode(string));

	String _string;

	String get string => _string;

	set string(String value) {
	_string = value;
	super.bytes = utf8.encode(_string);
	}

	@override
	set bytes(List<int> value) {
	string = utf8.decode(value);
	}
	}

	/// A string compressing DevFSContent.
	///
	/// A specialized DevFSContent similar to DevFSByteContent where the contents
	/// are the compressed bytes of a string. Its difference is that the original
	/// uncompressed string can be compared with directly without the indirection
	/// of a compute-expensive uncompress/decode and compress/encode to compare
	/// the strings.
	///
	/// The `hintString` parameter is a zlib dictionary hinting mechanism to suggest
	/// the most common string occurrences to potentially assist with compression.
	class DevFSStringCompressingBytesContent extends DevFSContent {
	DevFSStringCompressingBytesContent(this._string, { String hintString })
	: _compressor = ZLibEncoder(
	dictionary: hintString == null
	? null
	: utf8.encode(hintString),
	gzip: true,
	level: 9,
	);

	final String _string;
	final ZLibEncoder _compressor;
	final DateTime _modificationTime = DateTime.now();

	List<int> _bytes;
	bool _isModified = true;

	List<int> get bytes => _bytes ??= _compressor.convert(utf8.encode(_string));

	/// Return true only once so that the content is written to the device only once.
	@override
	bool get isModified {
	final bool modified = _isModified;
	_isModified = false;
	return modified;
	}

	@override
	bool isModifiedAfter(DateTime time) {
	return time == null \|\| _modificationTime.isAfter(time);
	}

	@override
	int get size => bytes.length;

	@override
	Future<List<int>> contentsAsBytes() async => bytes;

	@override
	Stream<List<int>> contentsAsStream() => Stream<List<int>>.value(bytes);

	/// This checks the source string with another string.
	bool equals(String string) => _string == string;
	}

	class DevFSException implements Exception {
	DevFSException(this.message, [this.error, this.stackTrace]);
	final String message;
	final dynamic error;
	final StackTrace stackTrace;

	@override
	String toString() => 'DevFSException($message, $error, $stackTrace)';
	}

	/// Interface responsible for syncing asset files to a development device.
	abstract class DevFSWriter {
	/// Write the assets in [entries] to the target device.
	///
	/// The keys of the map are relative from the [baseUri].
	///
	/// Throws a [DevFSException] if the process fails to complete.
	Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, DevFSWriter parent);
	}

	class _DevFSHttpWriter implements DevFSWriter {
	_DevFSHttpWriter(
	this.fsName,
	FlutterVmService serviceProtocol, {
	@required OperatingSystemUtils osUtils,
	@required HttpClient httpClient,
	@required Logger logger,
	Duration uploadRetryThrottle,
	})
	: httpAddress = serviceProtocol.httpAddress,
	_client = httpClient,
	_osUtils = osUtils,
	_uploadRetryThrottle = uploadRetryThrottle,
	_logger = logger;

	final HttpClient _client;
	final OperatingSystemUtils _osUtils;
	final Logger _logger;
	final Duration _uploadRetryThrottle;

	final String fsName;
	final Uri httpAddress;

	// 3 was chosen to try to limit the variance in the time it takes to execute
	// `await request.close()` since there is a known bug in Dart where it doesn't
	// always return a status code in response to a PUT request:
	// https://github.com/dart-lang/sdk/issues/43525.
	static const int kMaxInFlight = 3;

	int _inFlight = 0;
	Map<Uri, DevFSContent> _outstanding;
	Completer<void> _completer;

	@override
	Future<void> write(Map<Uri, DevFSContent> entries, Uri devFSBase, [DevFSWriter parent]) async {
	try {
	_client.maxConnectionsPerHost = kMaxInFlight;
	_completer = Completer<void>();
	_outstanding = Map<Uri, DevFSContent>.of(entries);
	_scheduleWrites();
	await _completer.future;
	} on SocketException catch (socketException, stackTrace) {
	_logger.printTrace('DevFS sync failed. Lost connection to device: $socketException');
	throw DevFSException('Lost connection to device.', socketException, stackTrace);
	} on Exception catch (exception, stackTrace) {
	_logger.printError('Could not update files on device: $exception');
	throw DevFSException('Sync failed', exception, stackTrace);
	}
	}

	void _scheduleWrites() {
	while ((_inFlight < kMaxInFlight) && (!_completer.isCompleted) && _outstanding.isNotEmpty) {
	final Uri deviceUri = _outstanding.keys.first;
	final DevFSContent content = _outstanding.remove(deviceUri);
	_startWrite(deviceUri, content, retry: 10);
	_inFlight += 1;
	}
	if ((_inFlight == 0) && (!_completer.isCompleted) && _outstanding.isEmpty) {
	_completer.complete();
	}
	}

	Future<void> _startWrite(
	Uri deviceUri,
	DevFSContent content, {
	int retry = 0,
	}) async {
	while(true) {
	try {
	final HttpClientRequest request = await _client.putUrl(httpAddress);
	request.headers.removeAll(HttpHeaders.acceptEncodingHeader);
	request.headers.add('dev_fs_name', fsName);
	request.headers.add('dev_fs_uri_b64', base64.encode(utf8.encode('$deviceUri')));
	final Stream<List<int>> contents = content.contentsAsCompressedStream(
	_osUtils,
	);
	await request.addStream(contents);
	// Once the bug in Dart is solved we can remove the timeout
	// (https://github.com/dart-lang/sdk/issues/43525).
	try {
	final HttpClientResponse response = await request.close().timeout(
	const Duration(seconds: 60));
	response.listen((_) {},
	onError: (dynamic error) {
	_logger.printTrace('error: $error');
	},
	cancelOnError: true,
	);
	} on TimeoutException {
	request.abort();
	// This should throw "HttpException: Request has been aborted".
	await request.done;
	// Just to be safe we rethrow the TimeoutException.
	rethrow;
	}
	break;
	} on Exception catch (error, trace) {
	if (!_completer.isCompleted) {
	_logger.printTrace('Error writing "$deviceUri" to DevFS: $error');
	if (retry > 0) {
	retry--;
	_logger.printTrace('trying again in a few - $retry more attempts left');
	await Future<void>.delayed(_uploadRetryThrottle ?? const Duration(milliseconds: 500));
	continue;
	}
	_completer.completeError(error, trace);
	}
	}
	}
	_inFlight -= 1;
	_scheduleWrites();
	}
	}

	// Basic statistics for DevFS update operation.
	class UpdateFSReport {
	UpdateFSReport({
	bool success = false,
	int invalidatedSourcesCount = 0,
	int syncedBytes = 0,
	this.fastReassembleClassName,
	}) : _success = success,
	_invalidatedSourcesCount = invalidatedSourcesCount,
	_syncedBytes = syncedBytes;

	bool get success => _success;
	int get invalidatedSourcesCount => _invalidatedSourcesCount;
	int get syncedBytes => _syncedBytes;

	bool _success;
	String fastReassembleClassName;
	int _invalidatedSourcesCount;
	int _syncedBytes;

	void incorporateResults(UpdateFSReport report) {
	if (!report._success) {
	_success = false;
	}
	fastReassembleClassName ??= report.fastReassembleClassName;
	_invalidatedSourcesCount += report._invalidatedSourcesCount;
	_syncedBytes += report._syncedBytes;
	}
	}

	class DevFS {
	/// Create a [DevFS] named [fsName] for the local files in [rootDirectory].
	///
	/// Failed uploads are retried after [uploadRetryThrottle] duration, defaults to 500ms.
	DevFS(
	FlutterVmService serviceProtocol,
	this.fsName,
	this.rootDirectory, {
	@required OperatingSystemUtils osUtils,
	@required Logger logger,
	@required FileSystem fileSystem,
	HttpClient httpClient,
	Duration uploadRetryThrottle,
	}) : _vmService = serviceProtocol,
	_logger = logger,
	_fileSystem = fileSystem,
	_httpWriter = _DevFSHttpWriter(
	fsName,
	serviceProtocol,
	osUtils: osUtils,
	logger: logger,
	uploadRetryThrottle: uploadRetryThrottle,
	httpClient: httpClient ?? ((context.get<HttpClientFactory>() == null)
	? HttpClient()
	: context.get<HttpClientFactory>()())
	);

	final FlutterVmService _vmService;
	final _DevFSHttpWriter _httpWriter;
	final Logger _logger;
	final FileSystem _fileSystem;

	final String fsName;
	final Directory rootDirectory;
	final Set<String> assetPathsToEvict = <String>{};

	List<Uri> sources = <Uri>[];
	DateTime lastCompiled;
	DateTime _previousCompiled;
	PackageConfig lastPackageConfig;
	File _widgetCacheOutputFile;

	Uri _baseUri;
	Uri get baseUri => _baseUri;

	Uri deviceUriToHostUri(Uri deviceUri) {
	final String deviceUriString = deviceUri.toString();
	final String baseUriString = baseUri.toString();
	if (deviceUriString.startsWith(baseUriString)) {
	final String deviceUriSuffix = deviceUriString.substring(baseUriString.length);
	return rootDirectory.uri.resolve(deviceUriSuffix);
	}
	return deviceUri;
	}

	Future<Uri> create() async {
	_logger.printTrace('DevFS: Creating new filesystem on the device ($_baseUri)');
	try {
	final vm_service.Response response = await _vmService.createDevFS(fsName);
	_baseUri = Uri.parse(response.json['uri'] as String);
	} on vm_service.RPCError catch (rpcException) {
	if (rpcException.code == RPCErrorCodes.kServiceDisappeared) {
	// This can happen if the device has been disconnected, so translate to
	// a DevFSException, which the caller will handle.
	throw DevFSException('Service disconnected', rpcException);
	}
	// 1001 is kFileSystemAlreadyExists in //dart/runtime/vm/json_stream.h
	if (rpcException.code != 1001) {
	// Other RPCErrors are unexpected. Rethrow so it will hit crash
	// logging.
	rethrow;
	}
	_logger.printTrace('DevFS: Creating failed. Destroying and trying again');
	await destroy();
	final vm_service.Response response = await _vmService.createDevFS(fsName);
	_baseUri = Uri.parse(response.json['uri'] as String);
	}
	_logger.printTrace('DevFS: Created new filesystem on the device ($_baseUri)');
	return _baseUri;
	}

	Future<void> destroy() async {
	_logger.printTrace('DevFS: Deleting filesystem on the device ($_baseUri)');
	await _vmService.deleteDevFS(fsName);
	_logger.printTrace('DevFS: Deleted filesystem on the device ($_baseUri)');
	}

	/// Mark the [lastCompiled] time to the previous successful compile.
	///
	/// Sometimes a hot reload will be rejected by the VM due to a change in the
	/// structure of the code not supporting the hot reload. In these cases,
	/// the best resolution is a hot restart. However, the resident runner
	/// will not recognize this file as having been changed since the delta
	/// will already have been accepted. Instead, reset the compile time so
	/// that the last updated files are included in subsequent compilations until
	/// a reload is accepted.
	void resetLastCompiled() {
	lastCompiled = _previousCompiled;
	}


	/// If the build method of a single widget was modified, return the widget name.
	///
	/// If any other changes were made, or there is an error scanning the file,
	/// return `null`.
	String _checkIfSingleWidgetReloadApplied() {
	if (_widgetCacheOutputFile != null && _widgetCacheOutputFile.existsSync()) {
	final String widget = _widgetCacheOutputFile.readAsStringSync().trim();
	if (widget.isNotEmpty) {
	return widget;
	}
	}
	return null;
	}

	/// Updates files on the device.
	///
	/// Returns the number of bytes synced.
	Future<UpdateFSReport> update({
	@required Uri mainUri,
	@required ResidentCompiler generator,
	@required bool trackWidgetCreation,
	@required String pathToReload,
	@required List<Uri> invalidatedFiles,
	@required PackageConfig packageConfig,
	@required String dillOutputPath,
	DevFSWriter devFSWriter,
	String target,
	AssetBundle bundle,
	DateTime firstBuildTime,
	bool bundleFirstUpload = false,
	bool fullRestart = false,
	String projectRootPath,
	}) async {
	assert(trackWidgetCreation != null);
	assert(generator != null);
	final DateTime candidateCompileTime = DateTime.now();
	lastPackageConfig = packageConfig;
	_widgetCacheOutputFile = _fileSystem.file('$dillOutputPath.incremental.dill.widget_cache');

	// Update modified files
	final Map<Uri, DevFSContent> dirtyEntries = <Uri, DevFSContent>{};
	int syncedBytes = 0;
	if (fullRestart) {
	generator.reset();
	}
	// On a full restart, or on an initial compile for the attach based workflow,
	// this will produce a full dill. Subsequent invocations will produce incremental
	// dill files that depend on the invalidated files.
	_logger.printTrace('Compiling dart to kernel with ${invalidatedFiles.length} updated files');

	// Await the compiler response after checking if the bundle is updated. This allows the file
	// stating to be done while waiting for the frontend_server response.
	final Future<CompilerOutput> pendingCompilerOutput = generator.recompile(
	mainUri,
	invalidatedFiles,
	outputPath: dillOutputPath,
	fs: _fileSystem,
	projectRootPath: projectRootPath,
	packageConfig: packageConfig,
	);
	if (bundle != null) {
	// The tool writes the assets into the AssetBundle working dir so that they
	// are in the same location in DevFS and the iOS simulator.
	final String assetBuildDirPrefix = _asUriPath(getAssetBuildDirectory());
	final String assetDirectory = getAssetBuildDirectory();
	bundle.entries.forEach((String archivePath, DevFSContent content) {
	// If the content is backed by a real file, isModified will file stat and return true if
	// it was modified since the last time this was called.
	if (!content.isModified \|\| bundleFirstUpload) {
	return;
	}
	final Uri deviceUri = _fileSystem.path.toUri(_fileSystem.path.join(assetDirectory, archivePath));
	if (deviceUri.path.startsWith(assetBuildDirPrefix)) {
	archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
	}
	dirtyEntries[deviceUri] = content;
	syncedBytes += content.size;
	if (archivePath != null && !bundleFirstUpload) {
	assetPathsToEvict.add(archivePath);
	}
	});
	}
	final CompilerOutput compilerOutput = await pendingCompilerOutput;
	if (compilerOutput == null \|\| compilerOutput.errorCount > 0) {
	return UpdateFSReport(success: false);
	}
	// Only update the last compiled time if we successfully compiled.
	_previousCompiled = lastCompiled;
	lastCompiled = candidateCompileTime;
	// list of sources that needs to be monitored are in [compilerOutput.sources]
	sources = compilerOutput.sources;
	//
	// Don't send full kernel file that would overwrite what VM already
	// started loading from.
	if (!bundleFirstUpload) {
	final String compiledBinary = compilerOutput?.outputFilename;
	if (compiledBinary != null && compiledBinary.isNotEmpty) {
	final Uri entryUri = _fileSystem.path.toUri(pathToReload);
	final DevFSFileContent content = DevFSFileContent(_fileSystem.file(compiledBinary));
	syncedBytes += content.size;
	dirtyEntries[entryUri] = content;
	}
	}
	_logger.printTrace('Updating files.');
	if (dirtyEntries.isNotEmpty) {
	await (devFSWriter ?? _httpWriter).write(dirtyEntries, _baseUri, _httpWriter);
	}
	_logger.printTrace('DevFS: Sync finished');
	return UpdateFSReport(
	success: true,
	syncedBytes: syncedBytes,
	invalidatedSourcesCount: invalidatedFiles.length,
	fastReassembleClassName: _checkIfSingleWidgetReloadApplied(),
	);
	}

	/// Converts a platform-specific file path to a platform-independent URL path.
	String _asUriPath(String filePath) => _fileSystem.path.toUri(filePath).path + '/';
	}

	/// An implementation of a devFS writer which copies physical files for devices
	/// running on the same host.
	///
	/// DevFS entries which correspond to physical files are copied using [File.copySync],
	/// while entries that correspond to arbitrary string/byte values are written from
	/// memory.
	///
	/// Requires that the file system is the same for both the tool and application.
	class LocalDevFSWriter implements DevFSWriter {
	LocalDevFSWriter({
	@required FileSystem fileSystem,
	}) : _fileSystem = fileSystem;

	final FileSystem _fileSystem;

	@override
	Future<void> write(Map<Uri, DevFSContent> entries, Uri baseUri, [DevFSWriter parent]) async {
	try {
	for (final Uri uri in entries.keys) {
	final DevFSContent devFSContent = entries[uri];
	final File destination = _fileSystem.file(baseUri.resolveUri(uri));
	if (!destination.parent.existsSync()) {
	destination.parent.createSync(recursive: true);
	}
	if (devFSContent is DevFSFileContent) {
	final File content = devFSContent.file as File;
	content.copySync(destination.path);
	continue;
	}
	destination.writeAsBytesSync(await devFSContent.contentsAsBytes());
	}
	} on FileSystemException catch (err) {
	throw DevFSException(err.toString());
	}
	}
	}