Dart

SFTP Upload Large File in Parts

See more SFTP Examples

Demonstrates how to split a large file into N parts and then upload each part separately. This technique can be used to potentially avoid limits a SFTP server might impose on upload file size. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  final sftp = CkSFtp();

  // Set some timeouts, in milliseconds:
  sftp.connectTimeoutMs = 5000;
  sftp.idleTimeoutMs = 10000;

  // Connect to the SSH server.  
  // The standard SSH port = 22
  // The hostname may be a hostname or IP address.
  final hostname = 'sftp.example.com';
  final port = 22;
  try {
    sftp.connect(hostname, port);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Authenticate with the SSH server.  Chilkat SFTP supports
  // both password-based authenication as well as public-key
  // authentication.  This example uses password authenication.
  try {
    sftp.authenticatePw('myLogin', 'myPassword');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // After authenticating, the SFTP subsystem must be initialized:
  try {
    sftp.initializeSftp();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Open a remote file for writing on the SSH server.
  // If the file already exists, it is overwritten.
  // (Specify "createNew" instead of "createTruncate" to
  // prevent overwriting existing files.)
  final String handle;
  try {
    handle = sftp.openFile('big.zip', 'writeOnly', 'createTruncate');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // We're going to upload the local file "qa_data/zips/big.zip" (a relative local path from our current working directory)
  // to the SFTP server.
  final localFilePath = 'qa_data/zips/big.zip';

  // Rather than uploading in one shot, we'll read the local file in chunks
  // and upload a chunk at a time.
  final fac = CkFileAccess();

  try {
    fac.openForRead(localFilePath);
  } on ChilkatException catch (e) {
    sftp.closeHandle(handle);
    print(e.lastErrorText);
    return;
  }

  // If we were to split the local file into 128K chunks, how many chunks (blocks) would
  // we have, including the last partial block?
  final blockSize = 131072;
  final numBlocks = fac.getNumBlocks(blockSize);
  print('Number of blocks = $numBlocks');

  final bd = CkBinData();
  var i = 0;
  while (i < numBlocks) {
    // Read the Nth block, which gets appended to the bd.  (which means
    // we must clear the contents of bd before the next iteration)
    try {
      fac.readBlockBd(i, blockSize, bd);
    } on ChilkatException catch (e) {
      sftp.closeHandle(handle);
      print(e.lastErrorText);
      return;
    }

    // Upload this block to the open remote file.
    try {
      sftp.writeFileBd(handle, bd);
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }

    // Clear the contents for the next iteration.
    bd.clear();

    i++;
  }

  // Close the local file.
  fac.fileClose();

  // -----------------------------------------------------------------------------
  // This is important.  You must close the handle on the server.
  // Otherwise open handles will accumulate on the server until eventually a limit
  // is reached and the server will fail on a call to OpenFile.
  // -----------------------------------------------------------------------------

  // Close the remote file handle on the server.
  try {
    sftp.closeHandle(handle);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Success.');
}