Node.js thesubdb.com hash implementation

getHash.js

const fs = require('fs'),
			crypto = require('crypto')

function getHash(pathToFile) {
	let readSize = 64 * 1024 // 64kb
  
	return new Promise((resolve, reject) => {
		let fd = fs.openSync(pathToFile, 'r')
		
    let buffer = new Buffer(readSize * 2)
		let r1 = fs.read(fd, buffer, 0, readSize, 0)
		let r2 = fs.stat(pathToFile).then(s => {
			return fs.read(fd, buffer, readSize, readSize, s.size - readSize)
		})

		Promise.all([r1, r2])
			.then(() => {
				let hash = crypto.createHash('md5').update(buffer).digest('hex')
				resolve(hash)
			})
	});
}