erikng/convert.go

## convert.go
package main

import (
	"fmt"
	"image"
	"image/draw"
	"image/jpeg"
	"image/png"
	"io"
	"log"
	"net/http"
)

func handleUpload(w http.ResponseWriter, r *http.Request) {
	err := r.ParseMultipartForm(100000)
	if err != nil {
		respondErr(err, w)
		return
	}

	file, header, err := r.FormFile("wallpaper")
	if err != nil {
		respondErr(err, w)
		return
	}
	defer file.Close()
	ct := header.Header.Get("Content-Type")
	img, err := convert(file, ct)
	if err != nil {
		respondErr(err, w)
		return
	}

	w.Header().Set("Content-Disposition", "attachment; filename=com.apple.desktop.admin.png")
	w.Header().Set("Content-Type", "image/png")
	if err := png.Encode(w, img); err != nil {
		respondErr(err, w)
		return
	}
}

type decodeFunc func(io.Reader) (image.Image, error)

func convert(file io.Reader, contentType string) (image.Image, error) {
	var decode decodeFunc
	switch contentType {
	case "image/jpeg":
		decode = jpeg.Decode
	case "image/png":
		decode = png.Decode
	default:
		return nil, fmt.Errorf("unrecognized image format: %s", contentType)
	}
	src, err := decode(file)
	if err != nil {
		return nil, err
	}

	img := image.NewRGBA(src.Bounds())
	draw.Draw(img, img.Bounds(), src, image.ZP, draw.Src)
	// lower the alpha of one of the pixels by 1, to ensure
	// that alpha is set
	t := img.RGBAAt(0, 0)
	t.A = t.A - 1
	img.Set(0, 0, t)

	return img, nil
}

func respondErr(err error, w http.ResponseWriter) {
	log.Println(err)
	http.Error(w, err.Error(), http.StatusInternalServerError)
	return
}

func index(w http.ResponseWriter, r *http.Request) {
	uploadTmpl := `
	<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Mac LoginWindow image.</title>
  </head>
  <body>
    <div class="container">
      <h1>Convert LoginWindow Picture</h1>
	  <p>submit either a jpeg or a png. It will be converted to a png file with alpha channel set.</p>
      <form class="form-upload" method="post" action="/upload" enctype="multipart/form-data">
          <fieldset>
            <input type="file" name="wallpaper" id="wallpaper">
            <input type="submit" name="submit" value="Submit">
        </fieldset>
      </form>
  </body>
</html>`
	w.Write([]byte(uploadTmpl))
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/upload", handleUpload)
	mux.HandleFunc("/", index)
	http.ListenAndServe(":8080", mux)
}
	package main

	import (
	"fmt"
	"image"
	"image/draw"
	"image/jpeg"
	"image/png"
	"io"
	"log"
	"net/http"
	)

	func handleUpload(w http.ResponseWriter, r *http.Request) {
	err := r.ParseMultipartForm(100000)
	if err != nil {
	respondErr(err, w)
	return
	}

	file, header, err := r.FormFile("wallpaper")
	if err != nil {
	respondErr(err, w)
	return
	}
	defer file.Close()
	ct := header.Header.Get("Content-Type")
	img, err := convert(file, ct)
	if err != nil {
	respondErr(err, w)
	return
	}

	w.Header().Set("Content-Disposition", "attachment; filename=com.apple.desktop.admin.png")
	w.Header().Set("Content-Type", "image/png")
	if err := png.Encode(w, img); err != nil {
	respondErr(err, w)
	return
	}
	}

	type decodeFunc func(io.Reader) (image.Image, error)

	func convert(file io.Reader, contentType string) (image.Image, error) {
	var decode decodeFunc
	switch contentType {
	case "image/jpeg":
	decode = jpeg.Decode
	case "image/png":
	decode = png.Decode
	default:
	return nil, fmt.Errorf("unrecognized image format: %s", contentType)
	}
	src, err := decode(file)
	if err != nil {
	return nil, err
	}

	img := image.NewRGBA(src.Bounds())
	draw.Draw(img, img.Bounds(), src, image.ZP, draw.Src)
	// lower the alpha of one of the pixels by 1, to ensure
	// that alpha is set
	t := img.RGBAAt(0, 0)
	t.A = t.A - 1
	img.Set(0, 0, t)

	return img, nil
	}

	func respondErr(err error, w http.ResponseWriter) {
	log.Println(err)
	http.Error(w, err.Error(), http.StatusInternalServerError)
	return
	}

	func index(w http.ResponseWriter, r *http.Request) {
	uploadTmpl := `
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<title>Mac LoginWindow image.</title>
	</head>
	<body>
	<div class="container">
	<h1>Convert LoginWindow Picture</h1>
	<p>submit either a jpeg or a png. It will be converted to a png file with alpha channel set.</p>
	<form class="form-upload" method="post" action="/upload" enctype="multipart/form-data">
	<fieldset>
	<input type="file" name="wallpaper" id="wallpaper">
	<input type="submit" name="submit" value="Submit">
	</fieldset>
	</form>
	</body>
	</html>`
	w.Write([]byte(uploadTmpl))
	}

	func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/upload", handleUpload)
	mux.HandleFunc("/", index)
	http.ListenAndServe(":8080", mux)
	}