A simple web server to convert GIF from an url to compressed archive of images

gif-to-images-tar-gz.go

package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"fmt"
	"image/gif"
	"image/png"
	"io"
	"log"
	"net/http"
)

const (
	BYTE = 1 << (10 * iota) // 1 byte
	KILOBYTE
	MEGABYTE
	GIGABYTE
	TERABYTE
	PETABYTE
	EXABYTE
)

func gifToTar(name string, r io.Reader) (io.Reader, error) {
	g, err := gif.DecodeAll(r)
	if err != nil {
		return nil, err
	}

	var out bytes.Buffer
	tw := tar.NewWriter(&out)
	for i, pi := range g.Image {
		var buf bytes.Buffer
		err = png.Encode(&buf, pi)
		if err != nil {
			return nil, err
		}
		byts := buf.Bytes()
		err = tw.WriteHeader(&tar.Header{
			Name: fmt.Sprintf("%s_%d.%s", name, i, "png"),
			Size: int64(len(byts)),
			Mode: 0600,
		})
		if err != nil {
			return nil, err
		}
		_, err = tw.Write(byts)
		if err != nil {
			return nil, err
		}
	}

	if err := tw.Flush(); err != nil {
		return nil, err
	}
	if err := tw.Close(); err != nil {
		return nil, err
	}

	return &out, nil
}

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		gurl := r.URL.Query().Get("gif")
		resp, err := http.Get(gurl)
		if err != nil {
			w.WriteHeader(http.StatusBadRequest)
			fmt.Fprintf(w, "err: %s", err.Error())
			return
		}
		defer resp.Body.Close()
		ctypes := resp.Header["Content-Type"]
		switch ctypes[0] {
		// case "image/webp":
		// 	img, err = webp.Decode(resp.Body)
		case "image/gif":
		default:
			if err != nil {
				w.WriteHeader(http.StatusBadRequest)
				fmt.Fprintf(w, "err: unsupported format %s : supports image/gif alone.", ctypes[0])
				return
			}
		}

		lr := io.LimitReader(resp.Body, 100*KILOBYTE)
		br, err := gifToTar("thumb", lr)
		if err != nil {
			w.WriteHeader(http.StatusBadRequest)
			fmt.Fprintf(w, "err: %s", err.Error())
			return
		}
		w.Header().Set("Content-Disposition", "attachment; filename=images.tar.gz")
		w.Header().Set("Content-Encoding", "gzip")
		w.Header().Set("Content-Type", "application/tar+gzip")
		w.WriteHeader(http.StatusOK)
		gzw := gzip.NewWriter(w)
		io.Copy(gzw, br)
	})

	log.Fatal(http.ListenAndServe(":8080", nil))
}