separate-stream

separate-stream

Separates the chunks of one writable stream into multiple readable streams.

Usage

The package exports the SeparateStream class. It can be imported like this:

const SeparateStream = require('separate-stream')

SeparateStream ({ change, map, split })

Creates a new instance of SeparateStream that implements a Writable stream interface. All chunks written to the Writable interface are forwarded to a Readable stream that is given as an argument to the change callback function. Every chunk after the first chunk is handed over to the split function that must return a boolean value which must be true if a new stream should be started. The map callback allows translating incoming chunks before they are forwarded.

The following options are supported:

• async change(stream, chunk): A callback function that is called whenever a new stream is started. It will be called at least once for the first chunk. Stream processing will wait until the function returned. (default: () => {})
• split(chunk): A callback function that controls when to change to the next output stream. A new output stream is started if the function returns true. (default: () => false)
• map(chunk): A callback function that translates incoming chunks. (default: v => v)

Example

This example splits the incoming stream whenever there is an o in the chunk. The chunks are translated to upper case.

const { promisify } = require('util')
const { finished, Readable } = require('readable-stream')
const SeparateStream = require('..')

async function main () {
  const input = new Readable({ objectMode: true, read: () => {} })
  const separateStream = new SeparateStream({
    change: stream => {
      console.log('new stream!')
      stream.on('data', chunk => console.log(chunk))
    },
    split: chunk => {
      return chunk.includes('o')
    },
    map: v => v.toUpperCase()
  })

  input.push('this')
  input.push('stream')
  input.push('is')
  input.push('separated')
  input.push('to')
  input.push('multiple')
  input.push('output')
  input.push('streams')
  input.push(null)

  input.pipe(separateStream)

  await promisify(finished)(separateStream)
}

main()