The three requests needed to upload a file to S3 using a Rails API backend

s3_heroku_rails_04_requests.js

import { fileChecksum } from 'utils/checksum'

const createPresignedUrl = async(file, byte_size, checksum) => {
  let options = {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      file: {
        filename: file.name,
        byte_size: byte_size,
        checksum: checksum,
        content_type: 'application/pdf',
        metadata: {
          'message': 'resume for parsing'
        }
      }
    })
  }
  let res = await fetch(PRESIGNED_URL_API_ENDPOINT, options)
  if (res.status !== 200) return res
  return await res.json()
}

export const createUser = async(userInfo) => {
  const {pdf, email, first_name, last_name} = userInfo

  // To upload pdf file to S3, we need to do three steps:
  // 1) request a pre-signed PUT request (for S3) from the backend

  const checksum = await fileChecksum(pdf)
  const presignedFileParams = await createPresignedUrl(pdf, pdf.size, checksum)
  
  // 2) send file to said PUT request (to S3)
  const s3PutOptions = {
    method: 'PUT',
    headers: presignedFileParams.direct_upload.headers,
    body: pdf,
  }
  let awsRes = await fetch(presignedFileParams.direct_upload.url, s3PutOptions)
  if (awsRes.status !== 200) return awsRes

  // 3) confirm & create user with backend
  let usersPostOptions = {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      email: email,
      first_name: first_name,
      last_name: last_name,
      pdf: presignedFileParams.blob_signed_id,
    })
  }
  let res = await fetch(USERS_API_ENDPOINT, usersPostOptions)
  if (res.status !== 200) return res 
  return await res.json()
}