How to wait for the result of writeHandler in a formidable file upload request?

[Hagen Hübel]

I want to use formidable to upload files directly to S3. Following the official example it works just fine. However, I want to await the upload process and return the final URL of the uploaded file inside of the Http-Request to my client. And this seems to be a a challenge due to the limited nature of how fileWriteStreamHandler needs to be typed.:

const s3Client = new AWS.S3({
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID,
    secretAccessKey: process.env.AWS_SECRET_KEY,
  },
});

const uploadStream = (file) => {
  const pass = new PassThrough();
  s3Client.upload(
    {
      Bucket: 'demo-bucket',
      Key: file.newFilename,
      Body: pass,
    },
    (err, data) => {
      console.log(err, data);
    },
  );

  return pass;
};

const server = http.createServer((req, res) => {
  if (req.url === '/api/upload' && req.method.toLowerCase() === 'post') {
    // parse a file upload
    const form = formidable({
      fileWriteStreamHandler: uploadStream,
    });

    form.parse(req, () => {
      res.writeHead(200);
      res.end();
    });

    return;
  }

form.parse returns immediately, no matter how long the S3-upload process works under the hood.

I tried to use a promise and await but the function type of uploadStream must not return a promise.

Type '(file: any) => Promise<any>' is not assignable to type '(file?: VolatileFile | undefined) => Writable'.

I want to achieve something like that:

form.parse(req, (uploadedFile: string) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ url: uploadedFile }, null, 2));
  res.end();
});

In order to do that, I need something like a return value from the uploadStream function where I would be able to receive the final information eventually. But since it is only returning a PassThrough-object, it seems to be very limited in that case for further approaches like mine.

Do you guys know how I can do that?

[GrosSacASacs]

Have you tried to res.end inside the s3Client.upload callback (you need to have a ref to res there)