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

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

'use strict'


var ParserStream = require('../common').ParserStream
var str2arr = require('../common').str2arr
var sliceEq = require('../common').sliceEq


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


module.exports = function () {
  var parser = new ParserStream()

  parser._bytes(24, function (data) {
    parser._skipBytes(Infinity)

    // check PNG signature
    if (!sliceEq(data, 0, SIG_PNG)) {
      parser.push(null)
      return
    }

    // check that first chunk is IHDR
    if (!sliceEq(data, 12, SIG_IHDR)) {
      parser.push(null)
      return
    }

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

    parser.push(null)
  })

  return parser
}