React Native

Check Whether the Last SFTP Read Failed

Demonstrates the Chilkat SFtp.LastReadFailed method, which returns whether the most recent read for a handle failed. The only argument is the handle. A normal end-of-file is not a failure.

Background: A chunked read loop needs to tell three outcomes apart: more data, a clean end-of-file, and an actual error such as a dropped connection or a revoked handle. LastReadFailed isolates the error case — it is false on a normal EOF read (which succeeds with zero bytes) and true for an empty, malformed, or already-closed handle — so the loop can stop cleanly on EOF but bail out with an error message on a genuine failure.

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import { BinData, SFtp } from '@chilkat/react-native'

async function chilkatExample() {
  // Demonstrates the SFtp.LastReadFailed method, which returns whether the most recent read for a
  // handle failed.  The only argument is the handle.  A normal end-of-file is NOT a failure.

  const sftp = new SFtp();

  // Connect, authenticate, and initialize the SFTP subsystem.
  const port = 22;
  try {
    await sftp.connectAsync('sftp.example.com', port);
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  // Normally you would not hard-code the password in source.  You should instead obtain it
  // from an interactive prompt, environment variable, or a secrets vault.
  const password = 'mySshPassword';

  try {
    await sftp.authenticatePwAsync('mySshLogin', password);
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  try {
    await sftp.initializeSftpAsync();
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  let handle: string;
  try {
    handle = await sftp.openFileAsync('subdir/data.txt', 'readOnly', 'openExisting');
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  let reading = true;
  const chunkSize = 4096;
  const bd = new BinData();
  while (reading) {
    await sftp.readFileBdAsync(handle, chunkSize, bd);

    // Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
    // zero bytes, and LastReadFailed is false.
    if (sftp.lastReadFailed(handle)) {
      console.log(`Read failed: ${sftp.lastErrorText}`);
      return;
    }

    reading = !sftp.eof(handle);
  }

  try {
    await sftp.closeHandleAsync(handle);
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  console.log(`Read ${bd.numBytes} bytes with no read failures.`);

  sftp.disconnect();
}