shasum.go

/*
  Read Stdin and compute SHA1|SHA256|SHA384|SHA512 digest
*/
package main

import (
	"flag"
	"fmt"
	"hash"
	"io"
	"os"
	"strings"

	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
)

var (
	flag1, flag256, flag384, flag512 bool // hash sizes
	flagColon, flagSpace             bool // print summ as a colon/space delemited string
	flagUpper                        bool // print hex nums in upper case
)

func init() {
	flag.BoolVar(&flag1, "1", true, "SHA1")
	flag.BoolVar(&flag256, "256", false, "SHA256")
	flag.BoolVar(&flag384, "384", false, "SHA384")
	flag.BoolVar(&flag512, "512", false, "SHA512")
	flag.BoolVar(&flagColon, "c", false, "as a colon delimited string")
	flag.BoolVar(&flagSpace, "s", false, "as a space delimited string")
	flag.BoolVar(&flagUpper, "X", false, "print hex nums in upper case")
}

func main() {
	// command line flags processing
	flag.Parse()
	// choose a digest size
	var h hash.Hash
	if flag512 {
		h = sha512.New()
	} else if flag384 {
		h = sha512.New384()
	} else if flag256 {
		h = sha256.New()
	} else {
		h = sha1.New()
	}
	// choose a delimiter
	var delimiter string
	if flagColon {
		delimiter = ":"
	} else if flagSpace {
		delimiter = " "
	}

	// compute and print out
	_, err := io.Copy(h, os.Stdin)
	if err != nil {
		fmt.Println("Error:", err)
		os.Exit(1)
	}
	fmt.Println(byteSlice2Str(h.Sum(nil), delimiter))
}

// convert a slice of bytes to a delimited hexs string
func byteSlice2Str(sl []byte, delimiter string) string {
	format := "%0.2x"
	if flagUpper {
		format = "%0.2X"
	}

	// convert bytes to sring representation
	strArr := make([]string, len(sl))
	for i, b := range sl {
		strArr[i] = fmt.Sprintf(format, b)
	}

	return strings.Join(strArr, delimiter)
}