retrieveFile method

Implementation

Future<void> retrieveFile(String filename) async {
  if (!await openDataConnection()) {
    return;
  }

  try {
    transferInProgress = true;

    if (!fileOperations.exists(filename)) {
      sendResponse('550 File not found $filename');
      transferInProgress = false;
      await _closeDataSocket();
      return;
    }
    String fullPath = fileOperations.resolvePath(filename);

    File file = File(fullPath);
    if (await file.exists()) {
      Stream<List<int>> fileStream = file.openRead();

      // Handle potential socket errors during file transfer
      StreamSubscription<List<int>>? subscription;
      subscription = fileStream.listen(
        (data) {
          if (transferInProgress && dataSocket != null) {
            try {
              dataSocket!.add(data);
            } catch (e) {
              logger.generalLog('Error writing to data socket: $e');
              transferInProgress = false;
              subscription?.cancel();
              _closeDataSocket();
            }
          }
        },
        onDone: () async {
          if (transferInProgress) {
            transferInProgress = false;
            await _closeDataSocket();
            sendResponse('226 Transfer complete');
          }
        },
        onError: (error) async {
          logger.generalLog('Error reading from file: $error');
          if (transferInProgress) {
            sendResponse('426 Connection closed; transfer aborted');
            transferInProgress = false;
            await _closeDataSocket();
          }
        },
        cancelOnError: true,
      );
    } else {
      sendResponse('550 File not found $fullPath');
      transferInProgress = false;
      await _closeDataSocket();
    }
  } catch (e) {
    logger.generalLog('Exception in retrieveFile: $e');
    sendResponse('550 File transfer failed');
    transferInProgress = false;
    await _closeDataSocket();
  }
}