minipass

A very minimal implementation of a PassThrough stream

It’s very fast for objects, strings, and buffers.

Supports pipe()ing (including multi-pipe() and backpressure transmission), buffering data until either a data event handler or pipe() is added (so you don’t lose the first chunk), and most other cases where PassThrough is a good idea.

There is a read() method, but it’s much more efficient to consume data from this stream via 'data' events or by calling pipe() into some other stream. Calling read() requires the buffer to be flattened in some cases, which requires copying memory.

There is also no unpipe() method. Once you start piping, there is no stopping it!

If you set objectMode: true in the options, then whatever is written will be emitted. Otherwise, it’ll do a minimal amount of Buffer copying to ensure proper Streams semantics when read(n) is called.

This is not a through or through2 stream. It doesn’t transform the data, it just passes it right through. If you want to transform the data, extend the class, and override the write() method. Once you’re done transforming the data however you want, call super.write() with the transform output.

For an example of a stream that extends MiniPass to provide transform capabilities, check out minizlib.

USAGE

const MiniPass = require('minipass')
const mp = new MiniPass(options) // optional: { encoding }
mp.write('foo')
mp.pipe(someOtherStream)
mp.end('bar')

collecting

mp.collect().then(all => {
  // all is an array of all the data emitted
  // encoding is supported in this case, so
  // so the result will be a collection of strings if
  // an encoding is specified, or buffers/objects if not.
  //
  // In an async function, you may do
  // const data = await stream.collect()
})

iteration

You can iterate over streams synchronously or asynchronously in platforms that support it.

Synchronous iteration will end when the currently available data is consumed, even if the end event has not been reached. In string and buffer mode, the data is concatenated, so unless multiple writes are occurring in the same tick as the read(), sync iteration loops will generally only have a single iteration.

To consume chunks in this way exactly as they have been written, with no flattening, create the stream with the { objectMode: true } option.

const mp = new Minipass({ objectMode: true })
mp.write('a')
mp.write('b')
for (let letter of mp) {
  console.log(letter) // a, b
}
mp.write('c')
mp.write('d')
for (let letter of mp) {
  console.log(letter) // c, d
}
mp.write('e')
mp.end()
for (let letter of mp) {
  console.log(letter) // e
}
for (let letter of mp) {
  console.log(letter) // nothing
}

Asynchronous iteration will continue until the end event is reached, consuming all of the data.

const mp = new Minipass({ encoding: 'utf8' })

// some source of some data
let i = 5
const inter = setInterval(() => {
  if (i --> 0)
    mp.write(Buffer.from('foo\n', 'utf8'))
  else {
    mp.end()
    clearInterval(inter)
  }
}, 100)

// consume the data with asynchronous iteration
async function consume () {
  for await (let chunk of mp) {
    console.log(chunk)
  }
  return 'ok'
}

consume().then(res => console.log(res))
// logs `foo\n` 5 times, and then `ok`