A simple carriage-return, line-feed delimited JSON protocol.

json-protocol.js

/*
   A simple carriage-return, line-feed delimited JSON protocol.

   Receiving Usage:

     protocol = require('./json-protocol');

     // parsing data
     parser = protocol.StreamParser();

     parser.on('message', function (msg) {
       // handle message
     });

     socket.on('data', function (data) {
       parser.read(data);
     });


   Sending Usage:

     protocol = require('./frame-protocol');
     socket.write(protocol.serialize({"hello": "world"}));

  Based on code from:
    https://gist.github.com/880514    
    https://github.com/joyent/node/blob/f44d0b90442d9a1dc7457924f827722fc3a7c440/lib/child_process.js#L71-141

*/

var util = require('util');
var events = require('events');
                     
var CR = '\r'.charCodeAt(0);
var LF = '\n'.charCodeAt(0);
var DELIMITER = '\r\n';
var ENCODING = 'ascii';
var ERROR = 'error';
var MESSAGE = 'message';

function StreamParser(){
  if (!(this instanceof StreamParser)){
    return new StreamParser();
  }                           
  events.EventEmitter.call(this);
  this.buffer = '';
}

util.inherits(StreamParser, events.EventEmitter);

function read(data){
  this.buffer += data.toString(ENCODING);
  var buffer = this.buffer;

  var start = 0, len = buffer.length;
  for(i = 0; i + 1 < len; ++i){
    var charCode = buffer.charCodeAt(i);
    var nextCharCode = buffer.charCodeAt(i + 1);
    if (charCode === CR && nextCharCode === LF){
        var json = buffer.slice(start, i);
        try {
          var message = JSON.parse(json);         
          this.emit(MESSAGE, message);          
        }                               
        catch(err){
          this.emit(ERROR, err);
        }
        start = i + 2;
        ++i;
    }
  }
                     
  if (i < len){
    this.buffer = buffer.slice(start);  
  }
  else {
    this.buffer = '';
  }
}

function serialize(message){
  return JSON.stringify(message) + DELIMITER;
}

StreamParser.prototype.read = read;
StreamParser.prototype.serialize = serialize;

exports.StreamParser = StreamParser;
exports.serialize = serialize;