pngsize-steam.js

var util = require('util');
var Transform = require('stream').Transform;
util.inherits(SizeStream, Transform);
 
function SizeStream() {
  if (!(this instanceof SizeStream))
    return new SizeStream()
  Transform.call(this)
}

SizeStream.prototype._transform = function(chunk, encoding, done) {

  try {
    var s = pngsize(chunk)
    if (s) {
      this.emit('size', s)
      done()
    }
  }

  catch(e) {
    this.emit('error', new Error('problem with the whole sizing thing'));
    return;
  }

  // send data to next stream
  this.push('downstream \n')
 
}