blob meta infos while streaming

blob_meta_infos_while_streaming.js

var url = require('url');
var http = require('http');

//var imgUrl = 'http://upload.wikimedia.org/wikipedia/commons/9/95/Big_Pine_landscape.jpg';
var imgUrl = 'http://downloads.xenproject.org/Branding/Images/Mascot/Xen%20Big%20Panda%204242x3129.png';
//var imgUrl = 'http://stackoverflow.com/questions/19934406/verify-mime-type-of-uploaded-files-in-node-js';
var options = url.parse(imgUrl);

http.get(options, function (response) {

  var metaCatcher = new MetaCatcher();

  metaCatcher.on('meta', function (meta) {
    console.log(meta);
  });

  metaCatcher.on('end', function() {
    console.log('finished');
  });
  
  response.pipe(metaCatcher).pipe(require('fs').createWriteStream('downloaded.png'));
});

var util = require('util'),
  Transform = require('stream').Transform,
  mmm = require('mmmagic'),
  Magic = mmm.Magic,
  magic = new Magic(mmm.MAGIC_MIME_TYPE),
  sizeOf = require('image-size');

function MetaCatcher (options) {
  if (!(this instanceof MetaCatcher)) {
    return new MetaCatcher(options);
  }

  Transform.call(this, options);

  this.meta = { size: 0 };
  this.chunks = [];

  var self = this;

  this.on('finish', function () {
    if (self.meta.size > 0) {
      self.emit('meta', self.meta);
    }
  });
}

util.inherits(MetaCatcher, Transform);

MetaCatcher.prototype.checkMimeType = function (callback) {
  var self = this;
  
  if (this.meta.mimeType) {
    return callback();
  }

  magic.detect(Buffer.concat(this.chunks), function (err, result) {
    if (err) {
      // self.emit('error', err);
      return callback();
    }

    self.meta.mimeType = result;
    callback();
  });
};

MetaCatcher.prototype.checkImageDimension = function (callback) {
  if (!this.meta.mimeType) {
    return callback();
  }
  
  if (this.meta.imageDimensions || (!this.meta.mimeType && this.meta.mimeType.indexOf('image') < 0)) {
    this.chunks = [];
    return callback();
  }

  try {
    this.meta.imageDimensions = sizeOf(Buffer.concat(this.chunks));
    this.chunks = [];
  } catch (e) {
//      console.log('Not ready to catch image size!!!');
  }
  callback();
};

MetaCatcher.prototype._transform = function (chunk, encoding, done) {
  this.push(chunk);
  this.chunks.push(chunk);
  this.meta.size += chunk.length;

  var self = this;
  
  this.checkMimeType(function () {
    self.checkImageDimension(done);
  });
};