Google Cloud Function to stream a file from multipart/form-data to Google Cloud Storage

gcp-function-storage-file-stream.js

/**
 * Copyright (c) 2022 Zentered OÛ, patrick@zentered.co
 * This code is licensed under the terms of the MIT license
 *
 * This code demonstrates how to create a Google Cloud Function to receive
 * a file sent via `multipart/form-data`. The file is then streamed directly
 * to Google Cloud Storage, without using a temporary file.
 *
 * The function returns any `fields` sent as FormData
 *
 *
 * Useful links:
 * - https://googleapis.dev/nodejs/storage/latest/File.html#createWriteStream
 * - https://github.com/mscdex/busboy#readme
 *
 * Inspiration:
 * - https://gist.github.com/msukmanowsky/c8daf3720c2839d3c535afc69234ab9e
 * - https://stackoverflow.com/a/68666478/459329
 * - https://stackoverflow.com/a/65749616/459329
 */

'use strict'

import Busboy from 'busboy'
import { Storage } from '@google-cloud/storage'

function asyncBusboy(req, res) {
  return new Promise((resolve, reject) => {
    const storage = new Storage()
    const bucket = storage.bucket(process.env.BUCKET)

    const fields = []
    const busboy = Busboy({
      headers: req.headers,
      limits: {
        fileSize: 10 * 1024 * 1024
      }
    })

    busboy.on('field', (key, value) => {
      fields[key] = value
    })

    busboy.on('file', (name, file, fileInfo) => {
      const { mimeType } = fileInfo
      const destFile = bucket.file(fileName)
      const writeStream = destFile.createWriteStream({
        metadata: {
          contentType: fileInfo.mimeType,
          metadata: {
            originalFileName: fileInfo.filename
          }
        }
      })
      file.pipe(writeStream)
    })

    busboy.on('close', function () {
      return resolve({ fields })
    })

    if (req.rawBody) {
      busboy.end(req.rawBody)
    } else {
      req.pipe(busboy)
    }
  })
}

export const multipartForm = async (req, res) => {
  if (req.method !== 'POST') {
    return res.status(405).end()
  }

  try {
    const { fields } = await bb(req, res, myBucket)
    console.log(fields)
  } catch (err) {
    console.error(err)
    return res.status(500).send(err)
  }

  return res.status(200).send()
}