unpipe() and resume() in _transform()

[utftu]

• Node.js Version: 13.*
• OS: mac
• Scope (install, code, runtime, meta, other?):
• Module (and version) (if relevant):

In case of synchronous pipe removal in _transform, the resume method does not resume as expected

const stream = require('stream')

const fs = require('fs');
const readStream = fs.createReadStream('big.txt')
const writeStream = fs.createWriteStream('result.txt');

const transformStream = new class extends stream.Transform {

  _transform(chunk, encoding, callback) {
    readStream.unpipe()
    readStream.resume()
  }
}

readStream.on('end', () => {
  console.log('never print')
})


readStream
  .pipe(transformStream)
  .pipe(writeStream)

Nevertheless, resume operation during an asynchronous call and removal not from the _transform method

Can someone explain this behavior why unpipe () and resume () do not work in the _transform method?

[addaleax]

/cc @ronag

[addaleax]

@ronag The only two things I could think of are a) process.exit() or equivalents being called or b) blocking JS execution that prevents the nextTick queue from running.

For debugging Node.js core, it’s sometimes a good idea to use process._rawDebug() rather than console.log(), which doesn’t use streams under the hood.

That being said, if I just add the console.log() calls like you did, it does print output for me.

[ronag]

For debugging Node.js core, it’s sometimes a good idea to use process._rawDebug() rather than console.log()

Oh, thanks for that! I'll keep digging.