Calculate md5 from file chunk using golang

file-chunk-md5-calculator.go

package main

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

const (
	bufferSize = int64(8 * 1024 * 1024)
)

func main() {
	var filePath string
	var chunkSize int64

	flag.StringVar(&filePath, "filepath", "", "file path")
	flag.Int64Var(&chunkSize, "chunksize", -1, "chunk size in bytes")

	flag.Parse()

	if len(filePath) <= 0 {
		println("No filepath")
		os.Exit(1)
	}

	fileInfo, err := os.Stat(filePath)
	if err != nil {
		println("Cannot find file,", filePath, ", error:", err.Error())
		os.Exit(1)
	}

	chunkCount := int64(1)
	if chunkSize > 0 {
		chunkCount = (fileInfo.Size() / chunkSize) + 1
	} else {
		chunkSize = fileInfo.Size()
	}

	file, err := os.Open(filePath)
	if err != nil {
		println("Cannot open file,", filePath, ", error:", err.Error())
		os.Exit(1)
	}
	defer file.Close()

	hash := md5.New()
	buff := make([]byte, bufferSize)
	for i := int64(0); i < chunkCount; i++ {
		hash.Reset()
		for chunkReaded := int64(0); chunkReaded < chunkSize; {
			m := bufferSize
			if chunkReaded+m > chunkSize {
				m = chunkSize - chunkReaded
			}

			n, err := file.Read(buff[0:m])
			if err != nil {
				if err == io.EOF {
					break
				}

				println("Cannot read file,", filePath, ", error:", err.Error())
				os.Exit(1)
			}
			hash.Write(buff[0:n])
			chunkReaded += int64(n)
		}

		if chunkCount > 1 {
			fmt.Printf("Chunk[%d] md5 = %x\r\n", i, hash.Sum(nil))
		} else {
			fmt.Printf("md5 = %x\r\n", hash.Sum(nil))
		}
	}
}