event-transmitter/lib/Listener.js

Transmit events over any stream pipeline.

var util = require('util');
var stream = require('stream');
var crypto = require('crypto');

var Transform = stream.Transform || require('readable-stream').Transform;

util.inherits(Listener, Transform);


// main constructor

function Listener(opts) {
  var hash;

  Transform.call(this);
  opts = opts || {};

  hash = crypto.createHash('sha1', opts.delimiter || 'jambalaya');
  hash.setEncoding('hex');
  hash.end();

  this.buffer = new Buffer('');
  this.delimiter = new Buffer('<' + hash.read().substr(0, 10) + '>');
  this.tag_open = false;
}


// transform stream methods

Listener.prototype._transform = function(chunk, enc, cb) {
  this.buffer = Buffer.concat([this.buffer, chunk]);
  parseStreamTags(this, cb);
};

Listener.prototype._flush = function(cb) {
  this.push(this.buffer);
  cb();
};


// parse methods

function parseStreamTags(stream, cb) {
  var delimiter = stream.delimiter;
  var idx = stream.buffer.indexOf(delimiter);

  if (idx !== -1) {
    handleTag(stream, delimiter, idx, cb);
  } else {
    testPartial(stream, delimiter, cb);
  }
}

function handleTag(stream, delimiter, idx, cb) {
  var tag;

  if (stream.tag_open === false) {
    stream.tag_open = true;
    stream.push(stream.buffer.slice(0, idx));
    stream.buffer = stream.buffer.slice(idx + delimiter.length);

    parseStreamTags(stream, cb);
  } else {
    try {
      tag = JSON.parse(stream.buffer.slice(0, idx).toString());
    } catch (e) {
      stream.emit('error', new Error(e));
    }

    stream.emit.apply(stream, tag);
    stream.tag_open = false;
    stream.buffer = stream.buffer.slice(idx + delimiter.length);

    parseStreamTags(stream, cb);
  }
}

function testPartial(stream, delimiter, cb) {
  var possible = false;
  var i;
  var j;

  for (i = stream.buffer.length - delimiter.length; i < stream.buffer.length; i++) {
    for (j = 0; j < delimiter.length; j++) {
      if (stream.buffer[i + j] !== delimiter[j]) {
        break;
      } else if (i + j >= stream.buffer.length - 1) {
        possible = true;
        break;
      }
    }

    if (possible === true) {
      break;
    }
  }

  if (stream.tag_open === false) {
    if (possible === true) {
      stream.push(stream.buffer.slice(0, i));
      stream.buffer = stream.buffer.slice(i);
    } else {
      stream.push(stream.buffer);
      stream.buffer = new Buffer('');
    }
  }

  cb();
}


module.exports = exports = Listener;