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

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

'use strict'


var readUInt16LE = require('../common').readUInt16LE

var HEADER = 0
var TYPE_ICO = 1
var INDEX_SIZE = 16

// Format specification:
// https://en.wikipedia.org/wiki/ICO_(file_format)#Icon_resource_structure
module.exports = function (data) {
  var header = readUInt16LE(data, 0)
  var type = readUInt16LE(data, 2)
  var numImages = readUInt16LE(data, 4)

  if (header !== HEADER || type !== TYPE_ICO || !numImages) {
    return
  }

  if (data.length < 6 + numImages * INDEX_SIZE) return

  var variants = []
  var maxSize = { width: 0, height: 0 }

  for (var i = 0; i < numImages; i++) {
    var width = data[6 + INDEX_SIZE * i] || 256
    var height = data[6 + INDEX_SIZE * i + 1] || 256
    var size = { width: width, height: height }
    variants.push(size)

    if (width > maxSize.width || height > maxSize.height) {
      maxSize = size
    }
  }

  return {
    width: maxSize.width,
    height: maxSize.height,
    variants: variants,
    type: 'ico',
    mime: 'image/x-icon',
    wUnits: 'px',
    hUnits: 'px'
  }
}