Stream node requests to the cloud with file metadata - node.js

Question

Im using koa in order to build a web app, and I want to allow users to upload files to it. The files need to be streamed to the cloud, but I would like to avoid saving the file locally.
The problem is that I need some file metadata before I pipe the upload stream to the writeable stream. I want to have the mime-type and optionally attach other data like the original file name etc.
I tried sending the binary data with the request's "content-type" header set to the file's type, but I would like the request to have the content type application/octet-stream so I can know in the back-end how to handle the request.
I read somewhere that the better option would be to use multipart/form-data but I'm not sure how to structure the request, and how to parse the metadata in order to notify the cloud before I pipe to its write stream.
Here is the code im currently using. Basically, it just pipes the request as is, and I use the request header to know the type of the file:
module.exports = async ctx => {
// Generate a random id that will be part of the filename.
const id = pushid();
// Get the content type from the header.
const contentType = ctx.header['content-type'];
// Get the extension for the file from the content type
const ext = contentType.split('/').pop();
// This is the configuration for the upload stream to the cloud.
const uploadConfig = {
// I must specify a content type, or know the file extension.
contentType
// there is some other stuff here but its not relevant.
};
// Create a upload stream for the cloud storage.
const uploadStream = bucket
.file(`assets/${id}/original.${ext}`)
.createWriteStream(uploadConfig);
// Here is what took me hours to get to work... dev life is hard
ctx.req.pipe(uploadStream);
// return a promise so Koa doesn't shut down the request before its finished uploading.
return new Promise((resolve, reject) =>
uploadStream.on('finish', resolve).on('error', reject)
);
};
Please assume I don't know much about the uploading protocols and managing streams.

Answer 1

Ok so after a lot of searching I found out that there is a parser that works with streams called busboy. It is pretty easy to use, but before jumping into the code I highly suggest everyone dealing with multipart/form-data requests to read this article.
Here is how I solved it:
const Busboy = require('busboy');
module.exports = async ctx => {
// Init busboy with the headers of the "raw" request.
const busboy = new Busboy({ headers: ctx.req.headers });
busboy.on('file', (fieldname, stream, filename, encoding, contentType) => {
const id = pushid();
const ext = path.extname(filename);
const uploadStream = bucket
.file(`assets/${id}/original${ext}`)
.createWriteStream({
contentType,
resumable: false,
metadata: {
cacheControl: 'public, max-age=3600'
}
});
stream.pipe(uploadStream);
});
// Pipe the request to busboy.
ctx.req.pipe(busboy);
// return a promise that resolves to whatever you want
ctx.body = await new Promise(resolve => {
busboy.on('finish', () => {
resolve('done');
});
});
};