probe-image-size/lib/parse_sync/png.js

'use strict';

/* eslint-disable consistent-return */

var str2arr      = require('../common').str2arr;
var sliceEq      = require('../common').sliceEq;
var readUInt32BE = require('../common').readUInt32BE;


var SIG_PNG  = str2arr('\x89PNG\r\n\x1a\n');
var SIG_IHDR = str2arr('IHDR');


module.exports = function (data) {
  if (data.length < 24) return;

  // check PNG signature
  if (!sliceEq(data, 0, SIG_PNG)) return;

  // check that first chunk is IHDR
  if (!sliceEq(data, 12, SIG_IHDR)) return;

  return {
    width:  readUInt32BE(data, 16),
    height: readUInt32BE(data, 20),
    type: 'png',
    mime: 'image/png',
    wUnits: 'px',
    hUnits: 'px'
  };
};