React Native

Read Text at a 32-bit Offset from a Remote SFTP File

Demonstrates the Chilkat SFtp.ReadFileText32 method, which reads up to a number of bytes from a specific 32-bit byte offset of an open handle and decodes them to text. The arguments are the handle, the offset, the maximum number of bytes, and the charset.

Background: Reading from an explicit offset lets you fetch just the part of a file you need — a header, a record at a known position, a slice of a large log — without downloading everything before it. As with offset writes, the offset counts bytes rather than characters, so it must respect the encoded width of any multibyte content.

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React Native

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

async function chilkatExample() {
  // Demonstrates the SFtp.ReadFileText32 method, which reads up to a number of bytes from a
  // specific 32-bit byte offset of an open handle and decodes them to text.  The 1st argument is
  // the handle, the 2nd is the offset, the 3rd is the maximum number of bytes, and the 4th is the
  // charset.

  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/record.dat', 'readOnly', 'openExisting');
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  // Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
  const offset = 10;
  const numBytes = 5;
  let text: string;
  try {
    text = await sftp.readFileText32Async(handle, offset, numBytes, 'utf-8');
  } catch {
    console.log(sftp.lastErrorText);
    return;
  }

  console.log(text);

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

  sftp.disconnect();
}