hash multiple files in Go

hashtool.go

package main

import (
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"encoding/hex"
	"flag"
	"fmt"
	"log"
	"os"
)

type Hasher func([]byte) ([]byte, int)

func (h Hasher) Size() int {
	_, size := h(nil)
	return size
}

func sha256Hasher(data []byte) ([]byte, int) {
	sum := sha256.Sum256(data)
	return sum[:], sha256.Size
}

func md5Hasher(data []byte) ([]byte, int) {
	sum := md5.Sum(data)
	return sum[:], md5.Size
}

func sha224Hasher(data []byte) ([]byte, int) {
	sum := sha256.Sum224(data)
	return sum[:], sha256.Size224
}

func sha512Hasher(data []byte) ([]byte, int) {
	sum := sha512.Sum512(data)
	return sum[:], sha512.Size
}

func sha384Hasher(data []byte) ([]byte, int) {
	sum := sha512.Sum384(data)
	return sum[:], sha512.Size384
}

func sha1Hasher(data []byte) ([]byte, int) {
	sum := sha1.Sum(data)
	return sum[:], sha1.Size
}

var algoMap = map[string]Hasher{
	"sha256": sha256Hasher,
	"md5":    md5Hasher,
	"sha224": sha224Hasher,
	"sha512": sha512Hasher,
	"sha384": sha384Hasher,
	"sha1":   sha1Hasher,
}

var algo = flag.String("a", "sha256", ""+
	"hashing algorithm\n"+
	"available algorithms:\n"+
	"  sha256\n"+
	"  md5\n"+
	"  sha224\n"+
	"  sha512\n"+
	"  sha384\n"+
	"  sha1\n",
)

func main() {
	flag.Parse()
	log.SetFlags(0)

	hasher, ok := algoMap[*algo]
	if !ok {
		log.Fatal("algorithm not available: ", *algo)
	}

	combined := make([]byte, hasher.Size())
	for _, input := range flag.Args() {
		data, err := os.ReadFile(input)
		if err != nil {
			log.Fatal(err)
		}

		sum, _ := hasher(data)
		for i, b := range sum {
			combined[i] ^= b
		}
	}

	fmt.Println(hex.EncodeToString(combined))
}