stream-parser

node-stream-parser
==================

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This module offers the stream-parser mixin, which provides an easy-to-use API
for parsing bytes from Writable and/or Transform stream instances. This module
is great for implementing streaming parsers for standardized file formats.

For Writable streams, the parser takes control over the _write callback
function. For Transform streams, the parser controls the _transform callback
function.

Installation
------------

`` bash
$ npm install stream-parser
`


Example
-------

Let's create a quick Transform stream subclass that utilizes the parser's
_bytes() and _passthrough() functions to parse a theoretical file format that
has an 8-byte header we want to parse, and then pass through the rest of the data.

` javascript
var Parser = require('stream-parser');
var inherits = require('util').inherits;
var Transform = require('stream').Transform;

// create a Transform stream subclass
function MyParser () {
Transform.call(this);

// buffer the first 8 bytes written
this._bytes(8, this.onheader);
}
inherits(MyParser, Transform);

// mixin stream-parser into MyParser's prototype
Parser(MyParser.prototype);

// invoked when the first 8 bytes have been received
MyParser.prototype.onheader = function (buffer, output) {
// parse the "buffer" into a useful "header" object
var header = {};
header.type = buffer.readUInt32LE(0);
header.name = buffer.toString('utf8', 4);
this.emit('header', header);

// it's usually a good idea to queue the next "piece" within the callback
this._passthrough(Infinity);
};


// now we can use it!
var parser = new MyParser();
parser.on('header', function (header) {
console.error('got "header"', header);
});
process.stdin.pipe(parser).pipe(process.stdout);
`

Here's an example of manually creating a Transform stream and turning it into a
"pass through" stream equivalent to the one built into node core:

` javascript
var Parser = require('stream-parser');
var Transform = require('stream').Transform;

// create a Transform instance and extend it with "stream-parser"
var p = new Transform();
Parser(p);

// pass through Infinity bytes... forever...
p._passthrough(Infinity);

// now p is equivalent to a stream.PassThrough instance
process.stdin.pipe(p).pipe(process.stdout);
`

See the test directory for some more example code in the test cases.

A list of known concrete implementations is here (send pull requests for more!):

* [node-icecast][]
* [node-throttle][]
* [node-flv][]
* [node-wav][]

API
---

- Parser()
- ._bytes(n, cb)
- ._skipBytes(n, cb)
- ._passthrough(n, cb)

Parser()

The Parser stream mixin works with either Writable or Transform stream
instances/subclasses. Provides a convenient generic "parsing" API:

`js
_bytes(n, cb) - buffers "n" bytes and then calls "cb" with the "chunk"
_skipBytes(n, cb) - skips "n" bytes and then calls "cb" when done
`

If you extend a Transform stream, then the _passthrough() function is also
added:

`js
_passthrough(n, cb) - passes through "n" bytes untouched and then calls "cb"
`

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Buffers n bytes and then invokes cb once that amount has been collected.

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Skips over the next n bytes and then invokes cb once that amount has been
discarded.

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Passes through n bytes to the readable side of this stream untouched,
then invokes cb once that amount has been passed through. This function is only defined
when stream-parser is extending a Transform` stream.

[node-icecast]: https://github.com/TooTallNate/node-icecast
[node-throttle]: https://github.com/TooTallNate/node-throttle
[node-flv]: https://github.com/TooTallNate/node-flv
[node-wav]: https://github.com/TooTallNate/node-wav