sha256 CLI tool

sha256sum.go

package main

import (
	"crypto/sha256"
	"fmt"
	"hash"
	"io/ioutil"
	"os"
)

// Gets the first cli argument as a string, or a empty string when no arguments are given
func getArg() (result string) {
	result = ""
	if len(os.Args) < 2 {
		fmt.Println("Missing expected argument")
	} else {
		result = os.Args[1]
	}
	return result
}

type fileHasher interface {
	hashFile(string) string
}

type sha256FileHasher struct {
	hash.Hash
}

func (self *sha256FileHasher) hashFile(filePath string) (hash string) {
	hash = "unknown"
	data, err := ioutil.ReadFile(filePath)
	if err != nil {
		fmt.Printf("Cannot hash: %v\n", err)
		return hash
	}

	self.Write(data)
	hashBytes := self.Sum(nil)
	self.Reset()

	hash = fmt.Sprintf("%x", hashBytes)
	return hash
}

func newSHA256FileHasher() (hasher fileHasher) {
	return &sha256FileHasher{sha256.New()}
}

func main() {
	filePath := getArg()
	if filePath == "" {
		return
	}
	hasher := newSHA256FileHasher()
	hash := hasher.hashFile(filePath)
	fmt.Printf("SHA256 hash of file at %v is %s\n", filePath, hash)
}