gistfile1.txt

const createGallery = (imageName) => {
  const prefix = 'gallery_';
  const imagePath = './images/';
  const readableStream = fs.createReadStream(imagePath + imageName);
  const writableStream = fs.createWriteStream(imagePath + prefix + imageName);
  const transformer = sharp()
    .resize(1110, 600)
    .crop(sharp.strategy.entropy)
    .on('error', function(err) {
      console.log('sharp ', err);
    });
  pump(readableStream, transformer, writableStream, function(err) {
    if (err) {
      console.log('pipe sharp finished', err);
    }
  });
  return prefix + imageName;
};

exports.gallery = (req, res, next) => {
  const url = getUrl(req);
  const imageName = createGallery(req.file.filename);
  const imagePath = url + '/images/' + imageName;
  const src = imagePath;
  const name = req.file.originalname;
  const data = {src: src, name: name};
  // Hack
  setInterval(function() {
    res.status(200).json(data);
  }, 1000);
};

https://medium.freecodecamp.org/node-js-streams-everything-you-need-to-know-c9141306be93 This would point in the direction that I just said. :)
Just try with readableStream.pipe(transformer).pipe(writableStream).pipe(res.status(200).json(data)); as well

const createGallery = (req, res) => {
  const prefix = 'gallery_';
  const imagePath = './images/';
  const readableStream = fs.createReadStream(imagePath + req.file.filename);
  const writableStream = fs.createWriteStream(imagePath + prefix + req.file.filename);
  const transformer = sharp()
    .resize(1110, 600)
    .crop(sharp.strategy.entropy)
    .on('error', function(err) {
      console.log('sharp ', err);
    });
  pump(readableStream, transformer, writableStream, function(err) {
    if (err) {
      console.log('pipe sharp finished', err);
      res.status(500);
    }
    const imageName = prefix + req.file.filename;
    const url = getUrl(req);
    const imagePath = url + '/images/' + imageName;
    const src = imagePath;
    const name = req.file.originalname;
    const data = {src: src, name: name};
    res.status(200).json(data);
  });
};
exports.gallery = (req, res, next) => {
  createGallery(req, res);
};