index.js

'use strict';
const execBuffer = require('exec-buffer');
const isJpg = require('is-jpg');
const jpegtran = require('jpegtran-changba');

module.exports = options => buf => {
  options = {...options};

  if (!Buffer.isBuffer(buf)) {
    return Promise.reject(new TypeError('Expected a buffer'));
  }

  if (!isJpg(buf)) {
    return Promise.resolve(buf);
  }

  const args = ['-copy', 'none'];

  if (options.progressive) {
    args.push('-progressive');
  }

  if (options.arithmetic) {
    args.push('-arithmetic');
  } else {
    args.push('-optimize');
  }

  args.push('-outfile', execBuffer.output, execBuffer.input);

  return execBuffer({
    input: buf,
    bin: jpegtran,
    args
  }).catch(error => {
    error.message = error.stderr || error.message;
    throw error;
  });
};