Calippo

Binary stream parser for node

Callipo is a more modern implementation of an existing binary stream parser for node called node-strtok. The biggest difference is that with node 0.10 we can leverage the more modern Streams2 API which provides us with out of the box methods for consuming and transforming streams of binary data.

Calippo is not intended to be a high level DSL for parsing binary streams ala node-binary, this sits lower in the stack, capable of implementing more novel abstractions on top of callipo.

Installation

Install via npm:

npm install calippo

Usage

Pulls out the data in an int32 prefixed message stream: [int32][data][int32][data]...

var Calippo = require('calippo')

var pos

var parser = Calippo(function (value) {
  if (value === undefined) {
    pos = 0
    return this.readUInt32LE
  }
  if (pos === 0) {
    pos = 1
    return this.Buffer(value)
  }
  if (pos === 1) {
    this.push(value)
    pos = 0
    return this.readUInt32LE
  }
})

parser.on('readable', function () {
  while (console.log(parser.read())) {}
})

somestream.pipe(parser)

API

Calippo(callback, options)

callback takes a single argument, the value just read from the stream, and is expected to return the type of value to read next, e.g. this.Buffer(len). It is this callback that ultimately implements the application protocol, you are expected to manage state yourself.

options is an object passed down into the node Transform api, pass {objectMode: true} if you want to output non binary data with this.push()

All expected values are returned from the callback, and and the types of values available are all attached to the this scope within the callback:

this.Buffer(len)

this.String(len, encoding)

this.Skip(len) - skip (len) bytes, calls callback with null

Calippo also implements all the standard node buffer readXXX methods for parsing numbers, see http://nodejs.org/api/buffer.html

this.readUInt32LE

this.readUInt8

...

We also implement one special type, DEFER and one method defer. These are used together for when you don't yet know what type of value you want to read next, perhaps you need to wait on some network event:

var parser = Calippo(function (value) {
  if (value === undefined) {
    var self = this
    makeSomeWebRequest(function () {
      self.defer(self.Buffer(2))
    })
    return this.DEFER
  }
})

this.defer takes one argument, the next expected type, you must return this.DEFER before your callback is called.

Licence

MIT