convert-promise.js

const spawn = require('child-process-promise').spawn;

function convert(conf) {
  let promise = spawn('convert', conf.cmd);
  let proc = promise.childProcess;
  let total = [];

  proc.stdin.write(conf.bgImageStream);
  proc.stdin.end();

  proc.stdout.on('data', (data) => {
    total.push(data);
  });

  return promise.then( () => {
    conf.imageBuffer = Buffer.concat(total);
    return conf;
  });
}