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

json-protocol.js

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

util.inherits(StreamParser, events.EventEmitter);

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

  var start = 0, msg, i;
  while((i = buffer.indexOf(DELIMITER, start)) >= 0) {
    var json = buffer.slice(start, i);
    msg = null;
    try {
      msg = JSON.parse(json);         
    }                               
    catch(err){
      this.emit(ERROR, err);
    }     

    if (msg){
      this.emit(MESSAGE, msg);          
    } 
    start = i + 1;
  }
                     
  if (start < buffer.length){
    this.buffer = buffer.slice(start);  
  }
  else {
    this.buffer = '';
  }
}

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

StreamParser.prototype.serialize = serialize;


/////////////////////////////////////////////////////////////////////////////
// Events
/////////////////////////////////////////////////////////////////////////////    

var ERROR = 'error';
var MESSAGE = 'message';

StreamParser.prototype.ERROR = ERROR
StreamParser.prototype.MESSAGE = MESSAGE
                                              
/////////////////////////////////////////////////////////////////////////////
// Exports
/////////////////////////////////////////////////////////////////////////////    

var DELIMITER = '\n';
var ENCODING = 'ascii';

exports.StreamParser = StreamParser;
exports.serialize = serialize;
exports.DELIMITER = DELIMITER;
exports.ENCODING = ENCODING;

/////////////////////////////////////////////////////////////////////////////
// Testing
/////////////////////////////////////////////////////////////////////////////

function testModule(){
  var parser = new StreamParser();
  parser.on(MESSAGE, function (msg) {
    console.log('message: ', JSON.stringify(msg));
  });
  
  var msg = serialize({hi: true});
  var part1 = msg.slice(0, 4);
  var part2 = msg.slice(4);
  console.log('serialized json: ' +  JSON.stringify(msg));
  console.log('part1: ' + part1);
  console.log('part2: ' + part2);
  
  parser.read(part1);
  parser.read(part2);
  
}

if (require.main === module){
  testModule();
}