pngSize.js

const fs = require('fs')

const file = path => new Promise((res, err) => {
	fs.open(path, 'r', (e, fd) => {
		if(e != null) return err(e)
		const b = Buffer.alloc(24)
		fs.read(fd, b, 0, 24, 0, (e, _, buf) => {
			fs.close(fd, () => {})
			if(e == null) res(buf)
			else err(e)
		})
	})
})

const getSize = buf => {
	const b = buf.slice(0, 16).equals(Buffer.from(
		[0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0, 0, 0, 0x0d, 0x49, 0x48, 0x44, 0x52]
	))
	if(!b) return null
	return {width: buf.readUInt32BE(16), height: buf.readUInt32BE(20)}
}

const getFileSize = path => file(path).then(getSize)

module.exports = {getSize, getFileSize}