stream-headerfooter

This module provides the ability to attach JSON headers and footers into any standard node/io.js stream pipeline to be consumed downstream. More specifically, this module provides:

• The ability to pass JSON objects along streams when they first start (headers) and when they end (footers).
• Header and Footer receivers are evented with 'header' and 'footer' events.
• A simple, easy to use interface using stream piping.
• Automatic stream sanitation after events are captured (headers and footers are removed from the pipeline after being consumed).
• Flexible header/footer typing (string, number, object or array).

Installation

npm install --save stream-headerfooter

Basic usage

Include

var headerfooter = require('stream-headerfooter')

Attach Headers and Footers to an Outgoing Stream

You can attach JSON headers/footers to a special stream (headerfooter.Out) that encodes your headers and footers and sends them to be recieved later down your pipeline.

Make sure to add your header before your stream begins, and add your footer before your stream ends. This outgoing stream is a duplex transform stream, so it can be piped to AND from.

var outgoing = new headerfooter.Out()
outgoing.header = { name: "streamA", metadata:[23, 33, 221, 222] }
outgoing.footer = { exit_code: 2 }

Receive and Handle Incoming Headers and Footers

You'll need to create a special stream headerfooter.In to listen for headers and footers. This stream will emit header and footer events as they are received.

Just create event handlers to handle headers and footers from your stream. The incoming stream is also a duplex transform stream, so it can be piped to AND from.

var receiver = new headerfooter.In()
 
receiver.on('header', function(header) {
    console.log('Stream Header:', header)
})
 
receiver.on('footer', function(footer) {
    console.log('Stream Footer:', footer)
})
 
receiver.on('data', function(data) {
    console.log('Stream Data:', data) // sanitized stream data without header and footer data in buffer
})

Write and Receive!

Plug both these streams into your stream pipeline. The outgoing stream that has the headers on one end, and the receiver on the other end. header and footer events, as well as all other native node/io.js stream events can be captured (if they have handlers) on the receiving end.

var passthroughA = new PassThrough() // dummy
var passthroughB = new PassThrough() // dummy
 
passthroughA.pipe(outgoing).pipe(passthroughB)
passthroughB.pipe(receiver)
 
passthroughA.write('Testing... 123')
passthroughA.end("...Ending")
 
//=> Stream Header: { name: "streamA", metadata:[23, 33, 221, 222] }
//=> Stream Data: Testing... 123
//=> Stream Data: ...Ending
//=> Stream Footer: { exit_code: 2 }

License

The MIT License (MIT)
Copyright (c) 2015 Arjun Mehta