SRI-poly:: Adapted from http://tenzer.dk/generating-subresource-integrity-checksums/

sri.go

package sri

import (
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io/ioutil"
)

func Generate256(file string) (string, error) {
	body, err := ioutil.ReadFile(file)

	if err != nil {
		return "", err
	}

	hash := sha256.Sum256(body)
	sha := base64.StdEncoding.EncodeToString(hash[:])

	return fmt.Sprintf("sha256-%s", sha), nil
}

// package main
//
// import (
//     "fmt"
//     "sri"
// )
//
// func main() {
//     sha, err := sri.Generate256("./src/sri.go")
//
//     if err != nil {
//         panic(err)
//     }
//
//     fmt.Println(sha)
// }
//

sri.js

var crypto = require('crypto');
var fs     = require('fs');

module.exports = function (file) {
    var enc  = 'utf8';
    var body = fs.readFileSync(file, { encoding: enc });
    var hash = crypto.createHash('sha256').update(body, enc);
    var sha  = hash.digest('base64');

    return 'sha256-' + sha;
}

// > var generate256 = require('./sri.js');
// undefined
// > generate256("./sri.js");
// 'sha256-U+9zwgl5Wcs2X0IzBnN/4Ri016f8lkdtvmPZuIytt8Y='
// >

sri.php

<?php
function generate256($path) {
  $file = fopen($path, "r");
  $body = fread($file, filesize($path));
  $hash = hash('sha256', $body, true);
  $sha  = base64_encode($hash);

  return "sha256-$sha";
}

// php > include './sri.php';
// php > echo generate256("./sri.php");
// sha256-wdToXd37ShQdyh8ljZAJoqvPXdQEiyqGv/IBnbKkg3A=
// php >
?>

sri.py

import base64
import hashlib

def generate256(file):
    with open(file, 'r') as f:
        body = f.read()
        hash = hashlib.sha256(body).digest()
        sha  = base64.b64encode(hash).decode()
        return 'sha256-{}'.format(sha)

# Python 2.7.10 (default, Oct 14 2015, 16:09:02)
# [GCC 5.2.1 20151010] on linux2
# Type "help", "copyright", "credits" or "license" for more information.
# >>> from sri import generate256
# >>> generate256("sri.py")
# 'sha256-ZDTvTHvqQDypoPxKGrkYPNVeXQPvKqnZeAFvRZ1l+ik='
# >>>

sri.rb

require 'digest'
require 'base64'

def generate256(file)
  body = File.read(file)
  hash = Digest::SHA256.digest(body)
  sha  = Base64.encode64(hash).strip

  "sha256-#{sha}"
end

# irb(main):001:0> require './sri'
# => true
# irb(main):002:0> generate256("sri.rb")
# => "sha256-zna8a/EB5hMXmiyjg+iSy5/Xar/+Cv0EDF1STWr+Mwo="

sri.sh

function generate256 {
  echo "sha256-`cat $1 | openssl dgst -sha256 -binary | openssl enc -base64 -A`"
}

# jmervine@laptop:~/sri $ source sri.sh
# jmervine@laptop:~/sri $ generate256 "sri.sh"
# sha256-wS2IFRvHJO0XSkrEvudmfw2nBnNz+E1o4AJ2Cf/HpZs=