liner.js

module.exports = Liner

var Transform = require('stream').Transform;
var util = require('util');

util.inherits(Liner, Transform);
function Liner(options) {
  Transform.call(this, options);

  // We're only objectMode on the readable side, not writable.
  this._readableState.objectMode = true;

  // since we operate on utf8, and usually get that first, anyway,
  // just do the decode in the transform if necessary.
  this._writableState.decodeStrings = false;

  this._partial = '';
}

Liner.prototype._transform = function(chunk, encoding, cb) {
  switch (encoding) {
    case 'hex':
    case 'base64':
    case 'binary':
      chunk = new Buffer(chunk, encoding);
      break;
  }
  if (Buffer.isBuffer(chunk))
    chunk = chunk.toString('utf8');

  var chunks = (this._partial + chunk).split(/\r?\n/);
  this._partial = chunks.pop();
  chunks.forEach(function(line, i, chunks) {
    this.push(line);
  }, this);

  cb();
}

if (module === require.main) {
  require('fs').createReadStream(__filename).pipe(new Liner).on('data', function(c) {
    console.error('LINE:', c);
  });
}