Javascript AWS SDK S3 upload method with Body stream generating empty file

Question

I'm trying to use the method upload from s3 using a ReadableStream from the module fs.

The documentation says that a ReadableStream can be used at Bodyparam:

Body — (Buffer, Typed Array, Blob, String, ReadableStream) Object data.

Also the upload method description is:

Uploads an arbitrarily sized buffer, blob, or stream, using intelligent concurrent handling of parts if the payload is large enough.

Also, here: Upload pdf generated to AWS S3 using nodejs aws sdk the @shivendra says he can use a ReadableStream and it works.

This is my code:

const fs = require('fs')
const S3 = require('aws-sdk/clients/s3')

const s3 = new S3()

const send = async () => {
  const rs = fs.createReadStream('/home/osman/Downloads/input.txt')
  rs.on('open', () => {
    console.log('OPEN')
  })
  rs.on('end', () => {
    console.log('END')
  })
  rs.on('close', () => {
    console.log('CLOSE')
  })
  rs.on('data', (chunk) => {
    console.log('DATA: ', chunk)
  })

  console.log('START UPLOAD')

  const response = await s3.upload({
    Bucket: 'test-bucket',
    Key: 'output.txt',
    Body: rs,
  }).promise()

  console.log('response:')
  console.log(response)
}

send().catch(err => { console.log(err) })

It's getting this output:

START UPLOAD
OPEN
DATA: <Buffer 73 6f 6d 65 74 68 69 6e 67>
END
CLOSE
response:
{ ETag: '"d41d8cd98f00b204e9800998ecf8427e"',
  Location: 'https://test-bucket.s3.amazonaws.com/output.txt',
  key: 'output.txt',
  Key: 'output.txt',
  Bucket: 'test-bucket' }

The problem is that my file generated at S3 (output.txt) has 0 Bytes.

Someone know what am I doing wrong?

If I pass a buffer on Body it works.

Body: Buffer.alloc(8 * 1024 * 1024, 'something'), 

But it's not what I want to do. I'd like to do this using a stream to generate a file and pipe a stream to S3 as long as I generate it.

Answer 1

It's an API interface issue using NodeJS ReadableStreams. Just comment the code related to listen event 'data', solves the problem.

const fs = require('fs')
const S3 = require('aws-sdk/clients/s3')

const s3 = new S3()

const send = async () => {
  const rs = fs.createReadStream('/home/osman/Downloads/input.txt')
  rs.on('open', () => {
    console.log('OPEN')
  })
  rs.on('end', () => {
    console.log('END')
  })
  rs.on('close', () => {
    console.log('CLOSE')
  })
  // rs.on('data', (chunk) => {
  //   console.log('DATA: ', chunk)
  // })

  console.log('START UPLOAD')

  const response = await s3.upload({
    Bucket: 'test-bucket',
    Key: 'output.txt',
    Body: rs,
  }).promise()

  console.log('response:')
  console.log(response)
}

send().catch(err => { console.log(err) })

Though it's an strange API, when we listen to 'data' event, the ReadableStream starts the flowing mode (listening to an event changing publisher/EventEmitter state? Yes, very error prone...). For some reason the S3 need a paused ReadableStream. If whe put rs.on('data'...) after await s3.upload(...) it works. If we put rs.pause() after rs.on('data'...) and befote await s3.upload(...), it works too.

Now, what does it happen? I don't know yet...

But the problem was solved, even it isn't completely explained.