Create iso file in pure go

mkiso.go

package main

import (
	"flag"
	"fmt"
	diskfs "github.com/diskfs/go-diskfs"
	"github.com/diskfs/go-diskfs/disk"
	"github.com/diskfs/go-diskfs/filesystem"
	"github.com/diskfs/go-diskfs/filesystem/iso9660"
	"log"
	"os"
	"regexp"
	"sort"
	"strconv"
	"strings"
)

func check(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

var debug bool

func dlog(s string) {
	if debug {
		fmt.Fprintf(os.Stderr, "DEBUG:  %v\n", s)
	}
}

func mkIso(isoname, volumelabel string, files map[string][]byte) (string, error) {
	var err error
	var storageSize int64
	var diskSize int64
	var blockSize int64 = 2048
	volLabel := volumelabel

	for file := range files {
		storageSize += int64(len(files[file])) + blockSize // for each file filelength + blocksize
	}
	diskImg := fmt.Sprintf("%v.iso", isoname)
	diskSize = storageSize + (1024 * 1024) // storagesize plus 1 MB; to be on the safe side
	mydisk, err := diskfs.Create(diskImg, diskSize, diskfs.Raw)
	check(err)

	// the following line is required for an ISO, which may have logical block sizes
	// only of 2048, 4096, 8192
	mydisk.LogicalBlocksize = blockSize
	fspec := disk.FilesystemSpec{
		Partition:   0,
		FSType:      filesystem.TypeISO9660,
		VolumeLabel: volLabel}

	fs, err := mydisk.CreateFilesystem(fspec)
	check(err)
	for file := range files {
		dest, err := fs.OpenFile(file, os.O_CREATE|os.O_RDWR)
		check(err)
		_, err = dest.Write(files[file])
		check(err)
		dlog(fmt.Sprintf("Wrote file: %v/%v", isoname, file))
	}

	iso, ok := fs.(*iso9660.FileSystem)
	if !ok {
		check(fmt.Errorf("not an iso9660 filesystem"))
	}
	err = iso.Finalize(iso9660.FinalizeOptions{
		RockRidge:        true,      // RockRidge to allow dashes in filenames
		VolumeIdentifier: volLabel}, // Volumelabel for mounting
	)
	check(err)
	return diskImg, err
}