gistfile1.txt

package main

import (
  "bufio"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"

	"github.com/eikeon/gzip"
)

type byteCounter struct {
	r      *bufio.Reader
	offset int64
}

func (b *byteCounter) Read(p []byte) (int, error) {
	n, err := b.r.Read(p)
	b.offset += int64(n)
	return n, err
}

func (b *byteCounter) ReadByte() (byte, error) {
	c, err := b.r.ReadByte()
	if err == nil {
		b.offset++
	}
	return c, err
}

func foo() error {
	f, err := os.Open("test.gz")
	if err != nil {
		log.Fatal(err)
	}
	bc := &byteCounter{r: bufio.NewReader(f)}
	gz, err := gzip.NewReader(bc)
	if err != nil {
		log.Fatal(err)
	}
	gz.StopAtBoundary(true)
	var off int64
	for {
		n, err := io.Copy(ioutil.Discard, gz)
		if err != nil {
			log.Fatalf("@%d: %d bytes + error: %v", off, n, err)
		}
		if off == bc.offset {
			fmt.Printf("@%d: EOF\n", off)
			break
		}
		fmt.Printf("@%d: %d bytes uncompressed\n", off, n)
		off = bc.offset
	}
	return err
}

func bar(off int64) error {
	f, _ := os.Open("test.gz")
	_, err := f.Seek(off, 0)
	if err != nil {
		return err
	}
	bc := &byteCounter{r: bufio.NewReader(f)}
	bc.offset = off
	gz, err := gzip.NewReader(bc)
	if err != nil {
		log.Fatal(err)
	}
	gz.StopAtBoundary(true)

	n, err := io.Copy(ioutil.Discard, gz)
	if err != nil {
		log.Fatalf("@%d: %d bytes + error: %v", off, n, err)
	}
	if off == bc.offset {
		fmt.Printf("@%d: EOF\n", off)
	}
	fmt.Printf("@%d,%d: %d bytes uncompressed\n", off, bc.offset, n)
	off = bc.offset

	return err
}

func main() {
	fmt.Printf("foo() -> err: %v\n", foo())
	fmt.Println("---")
	fmt.Printf("bar(417) -> err: %v\n", bar(417))
	fmt.Printf("bar(12846) -> err: %v\n", bar(12846))
}