Generate checksum for a file in Go

With billions of files being downloaded and transferred across Internet everyday. Generating checksum is important component in proramming today to ensure that the files are not being tempered with. In this tutorial, we will learn how to generate MD5 checksum for a sample file in Go

checksum.go

 package main

 import (
 "fmt"
 "io"
 "os"
 "math"
 "crypto/md5"
 )

 const filechunk = 8192 // we settle for 8KB

 func main() {

 file, err := os.Open("utf8.txt")

 if err != nil {
 panic(err.Error())
 }

 defer file.Close()

 // calculate the file size  
 info, _ := file.Stat()

 filesize := info.Size()  

 blocks := uint64(math.Ceil(float64(filesize) / float64(filechunk)))

 hash := md5.New()

 for i := uint64(0); i < blocks; i++ {
 blocksize := int(math.Min(filechunk, float64(filesize-int64(i*filechunk))))
 buf := make([] byte, blocksize)

 file.Read(buf)
 io.WriteString(hash, string(buf)) // append into the hash
 }

 fmt.Printf("%s checksum is %x\n",file.Name(), hash.Sum(nil)) 

 }

Output : >go run checksum.go

utf8.txt checksum is c3882b3e45e88ba87617f44ce1e7611d

This example uses the md5 crypto and of course you can just replace it with SHA1, SHA256 easily by changing the crypto package.

References :

http://golang.org/pkg/crypto/md5/

Write file in Go

Get file size in Go