Optimize 7z extraction performance and fix UTF-16LE filename handling

ios/flutter_7zip.podspec

@@ -23,6 +23,6 @@ A new Flutter FFI plugin project.
   s.platform = :ios, '12.0'
 
   # Flutter.framework does not contain a i386 slice.
-  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }
+  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386', 'CLANG_CXX_LANGUAGE_STANDARD' => 'c++20' }
   s.swift_version = '5.0'
 end

lib/flutter_7zip.dart

@@ -28,13 +28,42 @@ final Flutter7zipBindings _bindings = Flutter7zipBindings(_dylib);
 final _nativeFreeDataFunc =
     _dylib.lookup<NativeFunction<Void Function(Pointer<Void>)>>('freeReadData');
 
+/// Timing statistics for a single extraction operation.
+class FileExtractStat {
+  /// Index of the file in the archive.
+  final int fileIndex;
+
+  /// Whether this entry was a directory.
+  final bool isDirectory;
+
+  /// Elapsed milliseconds for this single file extraction.
+  final int elapsedMs;
+
+  const FileExtractStat(this.fileIndex, this.isDirectory, this.elapsedMs);
+}
+
+/// Wrapper around [SZArchive.extract] return value.
+class ArchiveExtractResult {
+  /// Total elapsed milliseconds for the entire extraction.
+  final int totalElapsedMs;
+
+  /// Number of files extracted.
+  final int totalFiles;
+
+  const ArchiveExtractResult(this.totalElapsedMs, this.totalFiles);
+
+  @override
+  String toString() => '${totalFiles}files/${totalElapsedMs}ms';
+}
+
 class SZArchive {
   final Pointer<Void> _archive;
+  final _pointers = <Pointer>[];
+  final Stopwatch _stopwatch = Stopwatch();
+  final List<FileExtractStat> _fileStats = [];
 
   SZArchive._(this._archive);
 
-  final _pointers = <Pointer>[];
-
   /// Dispose the archive and free all resources.
   void dispose() {
     _bindings.closeArchive(_archive);
@@ -43,6 +72,18 @@ class SZArchive {
     }
   }
 
+  /// Total elapsed milliseconds spent extracting files from this archive.
+  int get elapsedMs => _stopwatch.elapsedMilliseconds;
+
+  /// Per-file extraction statistics collected since opening.
+  List<FileExtractStat> get fileStats => List.unmodifiable(_fileStats);
+
+  /// Reset timing counters.
+  void resetTiming() {
+    _stopwatch.reset();
+    _fileStats.clear();
+  }
+
   /// Get the number of files in the archive.
   int get numFiles => _bindings.getArchiveFileCount(_archive);
 
@@ -107,9 +148,8 @@ class SZArchive {
   /// Extract the file at the given [index] to a file at the given [path].
   void extractToFile(int index, String path) {
     var p = path.toNativeUtf8();
-    var file = File(path);
-    if (!file.existsSync()) {
-      file.createSync(recursive: true);
+    if (!File(path).parent.existsSync()) {
+      File(path).parent.createSync(recursive: true);
     }
     final status = _bindings.extractArchiveToFile(_archive, index, p.cast());
     malloc.free(p);
@@ -118,6 +158,24 @@ class SZArchive {
     }
   }
 
+  /// Extract file by [index] to [outputDir], creating subdirs as needed.
+  /// Returns true if entry was a directory (already created).
+  /// Throws on error.
+  bool extractToDir(int index, String outputDir) {
+    _stopwatch.start();
+    final before = _stopwatch.elapsedMilliseconds;
+    var p = outputDir.toNativeUtf8();
+    final result = _bindings.extractFileToDir(_archive, index, p.cast());
+    malloc.free(p);
+    if (result < 0 || result > 1) {
+      _stopwatch.stop();
+      throw Exception('Failed to extract file index $index (code=$result)');
+    }
+    final after = _stopwatch.elapsedMilliseconds;
+    _fileStats.add(FileExtractStat(index, result == 1, after - before));
+    return result == 1;
+  }
+
   /// Open an archive at the given [path].
   static SZArchive open(String path) {
     var p = path.toNativeUtf8();
@@ -133,30 +191,29 @@ class SZArchive {
   }
 
   /// Extract the archive at the given [archivePath] to the given [outputPath].
-  /// 
-  /// The method is synchronous and will block the main thread.
-  static void extract(String archivePath, String outputPath) {
+  ///
+  /// Returns [ArchiveExtractResult] with total timing and file count.
+  static ArchiveExtractResult extract(String archivePath, String outputPath) {
+    final sw = Stopwatch()..start();
     var archive = open(archivePath);
-    for (var i = 0; i < archive.numFiles; i++) {
-      var file = archive.getFile(i);
-      var outPath = outputPath + Platform.pathSeparator + file.name;
-      if (file.isDirectory) {
-        Directory(outPath).createSync(recursive: true);
-      } else {
-        archive.extractToFile(i, outPath);
-      }
+    var total = archive.numFiles;
+    for (var i = 0; i < total; i++) {
+      archive.extractToDir(i, outputPath);
     }
     archive.dispose();
+    sw.stop();
+    return ArchiveExtractResult(sw.elapsedMilliseconds, total);
   }
 
   /// Extract the archive at the given [archivePath] to the given [outputPath] with [isolatesCount] isolates.
-  /// 
+  ///
   /// The method is asynchronous and will not block the main thread.
-  static Future<void> extractIsolates(
+  static Future<ArchiveExtractResult> extractIsolates(
     String archivePath,
     String outputPath,
     int isolatesCount,
   ) async {
+    final sw = Stopwatch()..start();
     var archive = open(archivePath);
     var total = archive.numFiles;
     var filesPerIsolate = total ~/ isolatesCount;
@@ -172,6 +229,8 @@ class SZArchive {
       ));
     }
     await Future.wait(futures);
+    sw.stop();
+    return ArchiveExtractResult(sw.elapsedMilliseconds, total);
   }
 
   static Future<void> _extractIsolate(
@@ -183,13 +242,7 @@ class SZArchive {
     return Isolate.run(() {
       var archive = open(archivePath);
       for (var i = start; i < end; i++) {
-        var file = archive.getFile(i);
-        var outPath = outputPath + Platform.pathSeparator + file.name;
-        if (file.isDirectory) {
-          Directory(outPath).createSync(recursive: true);
-        } else {
-          archive.extractToFile(i, outPath);
-        }
+        archive.extractToDir(i, outputPath);
       }
       archive.dispose();
     });

lib/src/flutter_7zip_bindings_generated.dart

@@ -164,6 +164,25 @@ class Flutter7zipBindings {
               ffi.Pointer<ffi.Char>)>>('extractArchiveToFile');
   late final _extractArchiveToFile = _extractArchiveToFilePtr.asFunction<
       int Function(ffi.Pointer<ffi.Void>, int, ffi.Pointer<ffi.Char>)>();
+
+  int extractFileToDir(
+    ffi.Pointer<ffi.Void> archive,
+    int index,
+    ffi.Pointer<ffi.Char> outputDir,
+  ) {
+    return _extractFileToDir(
+      archive,
+      index,
+      outputDir,
+    );
+  }
+
+  late final _extractFileToDirPtr = _lookup<
+      ffi.NativeFunction<
+          ffi.Int Function(ffi.Pointer<ffi.Void>, ffi.Uint32,
+              ffi.Pointer<ffi.Char>)>>('extractFileToDir');
+  late final _extractFileToDir = _extractFileToDirPtr.asFunction<
+      int Function(ffi.Pointer<ffi.Void>, int, ffi.Pointer<ffi.Char>)>();
 }
 
 final class ArchiveFile extends ffi.Struct {

macos/flutter_7zip.podspec

@@ -29,6 +29,6 @@ A new Flutter FFI plugin project.
   s.dependency 'FlutterMacOS'
 
   s.platform = :osx, '10.11'
-  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES' }
+  s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'CLANG_CXX_LANGUAGE_STANDARD' => 'c++20' }
   s.swift_version = '5.0'
 end