gzread.go

package main

import (
	"compress/gzip"
	"flag"
	"io"
	"log"
	"net/http"
	"os"
)

func main() {
	url := flag.String("url", "", "gz file URL")
	saveName := flag.String("save", "", "location to save original file")
	flag.Parse()

	if *url == "" {
		log.Fatal("URL is not set")
	}

	resp, err := http.Get(*url)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()

	var writePipes []*io.PipeWriter

	gr, gw := io.Pipe()
	writePipes = append(writePipes, gw)

	var saveFile io.Writer
	if *saveName != "" {
		saveFile, err = os.Create(*saveName)
		if err != nil {
			log.Fatal(err)
		}
		defer saveFile.Close()
		sr, sw := io.Pipe()
		writePipes = append(writePipes, sw)

		go func() {
			if _, err := io.Copy(saveFile, sr); err != nil {
				log.Fatal(err)
			}
		}()
	}

	wr := make([]io.Writer, len(writePipes))
	for i := range writePipes {
		wr[i] = writePipes[i]
	}

	mw := io.MultiWriter(wr...)
	go func() {
		if _, err := io.Copy(mw, resp.Body); err != nil {
			log.Fatal(err)
		}
		for i := range writePipes {
			writePipes[i].Close()
		}
	}()

	g, err := gzip.NewReader(gr)
	if err != nil {
		log.Fatal(err)
	}
	defer g.Close()

	if _, err := io.Copy(os.Stdout, g); err != nil {
		log.Fatal(err)
	}
}