fix: mark sftp mission as completed when dispose

lib/data/model/sftp/req.dart

@@ -58,13 +58,18 @@ class SftpReqStatus {
   @override
   int get hashCode => id ^ super.hashCode;
 
+  void dispose() {
+    // ignore: deprecated_member_use_from_same_package
+    worker.dispose();
+    completer?.complete();
+  }
+
   void onNotify(dynamic event) {
     switch (event.runtimeType) {
       case SftpWorkerStatus:
         status = event;
         if (status == SftpWorkerStatus.finished) {
-          worker.dispose();
-          completer?.complete();
+          dispose();
         }
         break;
       case double:

lib/data/model/sftp/worker.dart

@@ -20,6 +20,13 @@ class SftpWorker {
     required this.req,
   });
 
+  /// Use [@Deprecated] to prevent calling [SftpWorker.dispose] directly
+  ///
+  /// Don't delete this method
+  @Deprecated(
+    "Use [SftpWorkerStatus.dispose] to dispose the worker, "
+    "instead of [SftpWorker.dispose]",
+  )
   void dispose() {
     worker.dispose();
   }
@@ -77,24 +84,27 @@ Future<void> _download(
     final client = await genClient(req.spi, privateKey: req.privateKey);
     mainSendPort.send(SftpWorkerStatus.sshConnectted);
 
-    await Directory(req.localPath.substring(0, req.localPath.lastIndexOf('/')))
-        .create(recursive: true);
-    final local = File(req.localPath);
-    if (await local.exists()) {
-      await local.delete();
-    }
-    final localFile = local.openWrite(mode: FileMode.append);
+    /// Create the directory if not exists
+    final dirPath = req.localPath.substring(0, req.localPath.lastIndexOf('/'));
+    await Directory(dirPath).create(recursive: true);
+
+    /// Use [FileMode.write] to overwrite the file
+    final localFile = File(req.localPath).openWrite(mode: FileMode.write);
     final file = await (await client.sftp()).open(req.remotePath);
     final size = (await file.stat()).size;
     if (size == null) {
-      mainSendPort.send(Exception('can not get file size'));
+      mainSendPort.send(Exception('can\'t get file size: ${req.remotePath}'));
       return;
     }
-    // Read 10m each time
-    const defaultChunkSize = 1024 * 1024 * 10;
-    final chunkSize = size > defaultChunkSize ? defaultChunkSize : size;
+
     mainSendPort.send(size);
     mainSendPort.send(SftpWorkerStatus.loading);
+
+    // Read 2m each time
+    // Issue #161
+    // The download speed is about 2m/s may due to single core performance
+    const defaultChunkSize = 1024 * 1024 * 2;
+    final chunkSize = size > defaultChunkSize ? defaultChunkSize : size;
     for (var i = 0; i < size; i += chunkSize) {
       final fileData = file.read(length: chunkSize);
       await for (var form in fileData) {
@@ -102,8 +112,10 @@ Future<void> _download(
         mainSendPort.send((i + form.length) / size * 100);
       }
     }
+
     await localFile.close();
     await file.close();
+
     mainSendPort.send(watch.elapsed);
     mainSendPort.send(SftpWorkerStatus.finished);
   } catch (e) {