How to get width / height of a base64 image in deno?

This is a repeat of this question: Get image width and height from the Base64 code in JavaScript but I am asking with regards to deno. Deno does not have the new Image() that is used in all the solutions I have read. I intend on doing this in an edge function so reduced dependencies is important. A few things I have considered:

https://github.com/DjDeveloperr/skia_canvas But the edge enviornment I'm working in does not allow write access which is required to use this.
https://github.com/matmen/ImageScript But I don't know the relevant deno http address to import it from

Is there a way to do this without a package or to do it simply using some built-in package?

Solution

In order to get image width & height without external libraries, you need to parse the image header. If you're only dealing with few image type you could easly avoid using third-party libs.

For example for parsing a png image width & height from a base64 encoded image you could do it like this:

import { decode } from "https://deno.land/std/encoding/base64.ts"

const pngImageb64 = /* some png image in base64 */

const pngImage = decode(pngImageb64);
const dataView = new DataView(pngImage.buffer);
// The width and height are 4-byte integers starting 
// at byte offset 16 and 20, respectively.
const width = dataView.getUint32(16);
const height = dataView.getUint32(20);

Ref: http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html

Width and height give the image dimensions in pixels. They are 4-byte integers. Zero is an invalid value. The maximum for each is 2^31

For jpeg it's a bit harder since the dimensions are stored in the Start of Frame (SOF) markers. The following should work for most cases (only tested it in a few jpegs)

const jpegImageb64 = /* some jpeg image in base64 */

const jpegImage = decode(jpegImageb64);
const dataView = new DataView(jpegImage.buffer);

let width, height;
for (let i = 0; i < dataView.byteLength - 9; i++) {  // - 9 prevent out-of-bounds access
    if (dataView.getUint16(i) === 0xFFC0 || dataView.getUint16(i) === 0xFFC2) {
      height = dataView.getUint16(i + 5);
      width = dataView.getUint16(i + 7);
      break;
  }
}