SFTP Client

sftp-client.js

const crypto = require('crypto');
const fs = require('fs');
const path = require('path');
const Client = require('ssh2-sftp-client');

// Host public key e.g. /etc/ssh/ssh_host_ecdsa_key.pub
const fingerprint = process.env.HOST_FINGERPRINT;
const hostConfig = {
  host: process.env.HOST,
  port: process.env.PORT || 22,
  username: process.env.USER,
  privateKey: process.env.KEY,
  hostHash: 'md5',
  hostVerifier: (keyHash) => serverHash === keyHash,
};

const serverHash = hostHash(fingerprint, 'md5');

async function main() {
  try {
    let client = new Client();
    await client.connect(hostConfig)
    console.log('Connected to', hostConfig.host);
    
    const dir = '/sftpuser';
    const files = await client.list(dir);
    const downloadList = files.filter(f => f.name.endsWith('.txt')).map(f => `${dir}/${f.name}`);
    await downloadFiles(client, downloadList);
    
    await client.end();
    console.log('Connection closed');
  } catch (error) {
    console.log(error, 'catch error');
  }
}

function hostHash(fingerprint, algorithm) {
  const key = Buffer.from(fingerprint, 'base64');
  var hasher = crypto.createHash(algorithm);
  hasher.update(key);
  return hasher.digest('hex');
}

async function downloadFiles(client, downloadList) {
  const downloadFileAsync = async (f) => {
    try {
      process.stdout.write(`Downloading ${f}...`);
      const buffer = await retry(client.get(f));
      fs.writeFileSync(`T:/${path.basename(f)}`, buffer);
      console.log('Done');
      
      process.stdout.write(`Writing acknowledgement for ${f}...`);
      const ackFile = `${path.dirname(f)}/${path.basename(f, '.txt')}.ack`;
      await retry(client.put(Buffer.from('OK\n', 'utf-8'), ackFile));
      console.log('Done');
      
      process.stdout.write(`Deleting ${f}...`);
      await retry(client.delete(f));
      console.log('Done'); 
    } catch (error) {
      console.error(`Failed to process ${f}`, error);
    }
  }
  
  return downloadList.reduce(async (prevPromise, nextFile) => {
    await prevPromise;
    return downloadFileAsync(nextFile);
  }, Promise.resolve());
}

function retry(promise, retries=3, err=null) {
  if (!retries) {
    return Promise.reject(err);
  }
  return promise.catch(err => {
    console.error(err);
    console.log('Error occurred. Retrying...');
    return retry(promise, (retries - 1), err);
  });
}

main();