stream-parser

Generic interruptible "parser" mixin for Transform & Writable streams

node-stream-parser

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.

$ npm install stream-parser

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.

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 (bufferoutput) {
  // 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:

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!):

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

_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:

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

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

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

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.