shove stuff in a Buffer, hand it to a callback when it's done

StreamBuffer.js

var events = require('events')
  , util   = require('util')
  ;

function StreamBuffer(callback) {
  events.EventEmitter.call(this);

  this.writable = true;

  var self = this;

  this.on('data', function (data) {
    if (!self.buffer) {
      self.buffer = new Buffer(data);
    }
    else {
      self.buffer = Buffer.concat([self.buffer, data]);
    }
  });

  this.on('error', function (exception) {
    self.writable = false;
    return callback(exception);
  });

  this.on('end', function () {
    return callback(null, self.buffer);
  });
}
util.inherits(StreamBuffer, events.EventEmitter);

module.exports = StreamBuffer;