Proof of concept for creating .ico files in JS

.gitignore

node_modules/

index.js

// Reference for encoding
// http://en.wikipedia.org/wiki/ICO_%28file_format%29#Outline
var fs = require('fs');
var file = fs.createWriteStream('out.ico');

// Write out the .ico header
// Reserved space
var buff = new Buffer(2);
buff.writeUInt8(0, 0);
file.write(buff, 'binary');

// Indiciate ico file
buff = new Buffer(2);
buff.writeUInt8(1, 0);
file.write(buff, 'binary');

// Indiciate 1 image
buff = new Buffer(2);
buff.writeUInt8(1, 0);
file.write(buff, 'binary');

// Create the image
var pngparse = require('pngparse');
var image = fs.readFileSync('sprite1.png');
pngparse.parse(image, function (err, data) {
  // If there was an error, throw it
  if (err) { throw err; }

  // Image is 50 px wide
  buff = new Buffer(1);
  buff.writeUInt8(50, 0);
  file.write(buff, 'binary');

  // Image is 50 px tall
  buff = new Buffer(1);
  buff.writeUInt8(50, 0);
  file.write(buff, 'binary');

  // Specify no color palette
  // TODO: Not sure if this is appropriate
  buff = new Buffer(1);
  buff.writeUInt8(0, 0);
  file.write(buff, 'binary');

  // Reserved space
  // TODO: Not sure if this is appropriate
  buff = new Buffer(1);
  buff.writeUInt8(0, 0);
  file.write(buff, 'binary');

  // Specify no color planes
  // TODO: Not sure if this is appropriate
  buff = new Buffer(1);
  buff.writeUInt8(1, 0);
  file.write(buff, 'binary');

  // Specify 8 bits per pixel (bit depth)
  // TODO: Quite confident in this one
  buff = new Buffer(2);
  buff.writeUInt8(8, 0);
  file.write(buff, 'binary');

  // Specify image size in bytes
  // DEV: Assuming LE means little endian
  // TODO: Semi-confident in this one
  buff = new Buffer(4);
  buff.writeUInt32LE(image.length, 0);
  file.write(buff, 'binary');

  // Specify image size in bytes
  // TODO: Not that confident in this one
  buff = new Buffer(4);
  buff.writeUInt32LE(file._writableState.length, 0);
  file.write(buff, 'binary');

  // Dump the .png
  file.write(image, 'binary');

  // Close the image
  file.end();
});

out.ico

package.json

{
  "name": "gist-ico-poc",
  "version": "0.1.0",
  "description": "Proof of concept to encode a PNG to an ICO",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "repository": {
    "type": "git",
    "url": "git@gist.github.com:7656254.git"
  },
  "keywords": [
    "png",
    "ico"
  ],
  "author": "Todd Wolfson <todd@twolfson.com>",
  "license": "UNLICENSE",
  "bugs": {
    "url": "https://gist.github.com/7656254"
  },
  "dependencies": {
    "pngparse": "~2.0.1"
  }
}

sprite1.png