work.suroh.tk/node_modules/socket.io-parser/binary.js

/*global Blob,File*/

/**
 * Module requirements
 */

var isArray = require('isarray');
var isBuf = require('./is-buffer');
var toString = Object.prototype.toString;
var withNativeBlob = typeof Blob === 'function' || (typeof Blob !== 'undefined' && toString.call(Blob) === '[object BlobConstructor]');
var withNativeFile = typeof File === 'function' || (typeof File !== 'undefined' && toString.call(File) === '[object FileConstructor]');

/**
 * Replaces every Buffer | ArrayBuffer in packet with a numbered placeholder.
 * Anything with blobs or files should be fed through removeBlobs before coming
 * here.
 *
 * @param {Object} packet - socket.io event packet
 * @return {Object} with deconstructed packet and list of buffers
 * @api public
 */

exports.deconstructPacket = function(packet) {
  var buffers = [];
  var packetData = packet.data;
  var pack = packet;
  pack.data = _deconstructPacket(packetData, buffers);
  pack.attachments = buffers.length; // number of binary 'attachments'
  return {packet: pack, buffers: buffers};
};

function _deconstructPacket(data, buffers) {
  if (!data) return data;

  if (isBuf(data)) {
    var placeholder = { _placeholder: true, num: buffers.length };
    buffers.push(data);
    return placeholder;
  } else if (isArray(data)) {
    var newData = new Array(data.length);
    for (var i = 0; i < data.length; i++) {
      newData[i] = _deconstructPacket(data[i], buffers);
    }
    return newData;
  } else if (typeof data === 'object' && !(data instanceof Date)) {
    var newData = {};
    for (var key in data) {
      newData[key] = _deconstructPacket(data[key], buffers);
    }
    return newData;
  }
  return data;
}

/**
 * Reconstructs a binary packet from its placeholder packet and buffers
 *
 * @param {Object} packet - event packet with placeholders
 * @param {Array} buffers - binary buffers to put in placeholder positions
 * @return {Object} reconstructed packet
 * @api public
 */

exports.reconstructPacket = function(packet, buffers) {
  packet.data = _reconstructPacket(packet.data, buffers);
  packet.attachments = undefined; // no longer useful
  return packet;
};

function _reconstructPacket(data, buffers) {
  if (!data) return data;

  if (data && data._placeholder) {
    return buffers[data.num]; // appropriate buffer (should be natural order anyway)
  } else if (isArray(data)) {
    for (var i = 0; i < data.length; i++) {
      data[i] = _reconstructPacket(data[i], buffers);
    }
  } else if (typeof data === 'object') {
    for (var key in data) {
      data[key] = _reconstructPacket(data[key], buffers);
    }
  }

  return data;
}

/**
 * Asynchronously removes Blobs or Files from data via
 * FileReader's readAsArrayBuffer method. Used before encoding
 * data as msgpack. Calls callback with the blobless data.
 *
 * @param {Object} data
 * @param {Function} callback
 * @api private
 */

exports.removeBlobs = function(data, callback) {
  function _removeBlobs(obj, curKey, containingObject) {
    if (!obj) return obj;

    // convert any blob
    if ((withNativeBlob && obj instanceof Blob) ||
        (withNativeFile && obj instanceof File)) {
      pendingBlobs++;

      // async filereader
      var fileReader = new FileReader();
      fileReader.onload = function() { // this.result == arraybuffer
        if (containingObject) {
          containingObject[curKey] = this.result;
        }
        else {
          bloblessData = this.result;
        }

        // if nothing pending its callback time
        if(! --pendingBlobs) {
          callback(bloblessData);
        }
      };

      fileReader.readAsArrayBuffer(obj); // blob -> arraybuffer
    } else if (isArray(obj)) { // handle array
      for (var i = 0; i < obj.length; i++) {
        _removeBlobs(obj[i], i, obj);
      }
    } else if (typeof obj === 'object' && !isBuf(obj)) { // and object
      for (var key in obj) {
        _removeBlobs(obj[key], key, obj);
      }
    }
  }

  var pendingBlobs = 0;
  var bloblessData = data;
  _removeBlobs(bloblessData);
  if (!pendingBlobs) {
    callback(bloblessData);
  }
};