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

Get image size without full download (JPG, GIF, PNG, WebP, BMP, TIFF, PSD)

'use strict'


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'
  }
}