gistfile1.txt

package main

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"log"
	"os"
)

type chapter struct {
	begin int64
	end   int64
}

func main() {
	log.Printf("opening %s", os.Args[1])

	indata, err := os.ReadFile(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}

	bio := bytes.NewReader(indata)

	gzi, err := gzip.NewReader(bio)
	if err != nil {
		log.Fatal(err)
	}

	i := 0
	chapters := []chapter{}

	for {
		gzi.Multistream(false)

		pos, err := bio.Seek(0, os.SEEK_CUR)
		if err != nil {
			log.Fatal(err)
		}

		chapter := chapter{
			begin: pos - 10,
			end: int64(bio.Len()),
		}

		log.Printf("new stream! id=%d @%d", i, pos)
		if i > 0 {
			chapters[i - 1].end = pos - 10
		}

		chapters = append(chapters, chapter)

		outF, err := os.Create(fmt.Sprintf("stream-%d.tar", i))
		if err != nil {
			log.Fatal(err)
			return
		}
		defer outF.Close()

		if _, err := io.Copy(outF, gzi); err != nil {
			log.Printf("error while copying:")
			log.Fatal(err)
		}

		i++

		err = gzi.Reset(bio)
		if err == io.EOF {
			break
		}
		if err != nil {
			log.Printf("error while resetting:")
			log.Fatal(err)
		}
	}

	if err := gzi.Close(); err != nil {
		log.Fatal(err)
	}

	for i, chapter := range chapters {
		log.Printf("chapter %d, begin: %d, end: %d", i, chapter.begin, chapter.end)

		outF, err := os.Create(fmt.Sprintf("stream-%d.tar.gz", i))
		if err != nil {
			log.Fatal(err)
		}
		defer outF.Close()

		outF.Write(indata[chapter.begin:chapter.end])
	}
}