What can make a writeStream to emit close without writing to file?

Question

I want to merge chucks of file to another file but writeStream is emitting close without writing or appending the readStream content to the output file.

I have an async function with a for-of loop that iterates through the array and within the loop I created a writableStream with flag write truncate/write w flag if iteration index is 0 else append w then create a readStream then pipe it into writeStream.

 async function mergeBlocks(op) {
  for (const [index, block] of op.blockObjects.entries()) {
    const flags = index === 0? 'w' : 'a'
    const w = createWriteStream(op.output, { start: block.start, flags }),
      r = createReadStream(block.path, { start: block.start, end: block.end })
    console.log(index)
    r.pipe(w)
    await new Promise(res =>
      w.on('finish', () => {
        console.log('close')
        res()
      })
    )
  }
}

But it only write the first block and close the writeStream without writing to output file for on every other iteration. Please what am I doing wrong?

EDIT Check answer below.

Answer 1

The start and end I was setting to the createReadStream options was not necessary I only have to set those if I am reading from on file by setting those only the first block will match the chunk start and end position which explains why is only to first chunk that's being written to file while other are just empty contents. And as for code I ended up using promisify stream.pipeline which simplifies my code more.

async function mergeBlocks() {
  for (const [index, block] of op.blockObjects.entries()) {
    await pipeline(
      createReadStream(join(block.bucket, block.hash)),
      createWriteStream(op.output, { flags: index === 0 ? 'w' : 'a', start: block.start })
    )
  }
}