refactor image generation

}

func blackHandler(w http.ResponseWriter, r *http.Request) {

	// prepare

	m := image.NewRGBA(image.Rect(0, 0, 240, 240))

	blue := color.RGBA{0, 0, 0, 255}

	draw.Draw(m, m.Bounds(), &image.Uniform{blue}, image.ZP, draw.Src)

	black := color.RGBA{0, 0, 0, 255}

	draw.Draw(m, m.Bounds(), &image.Uniform{black}, image.ZP, draw.Src)

	// encode

	buf := new(bytes.Buffer)

	_ = jpeg.Encode(buf, m, nil)

	// write

	w.Header().Set("Content-Type", "image/jpeg")

	w.Header().Set("Content-Length", strconv.Itoa(len(buf.Bytes())))

	w.Write(buf.Bytes())

	var img image.Image = m

	writeImage(w, &img)

}

func greenHandler(w http.ResponseWriter, r *http.Request) {

	// prepare

	m := image.NewRGBA(image.Rect(0, 0, 240, 240))

	blue := color.RGBA{0, 128, 0, 255}

	draw.Draw(m, m.Bounds(), &image.Uniform{blue}, image.ZP, draw.Src)

	// encode

	buf := new(bytes.Buffer)

	_ = jpeg.Encode(buf, m, nil)

	green := color.RGBA{0, 128, 0, 255}

	draw.Draw(m, m.Bounds(), &image.Uniform{green}, image.ZP, draw.Src)

	// write

	w.Header().Set("Content-Type", "image/jpeg")

	w.Header().Set("Content-Length", strconv.Itoa(len(buf.Bytes())))

	w.Write(buf.Bytes())

	var img image.Image = m

	writeImage(w, &img)

}

func blueHandler(w http.ResponseWriter, r *http.Request) {

	// prepare

	m := image.NewRGBA(image.Rect(0, 0, 240, 240))

	blue := color.RGBA{0, 0, 255, 255}

	draw.Draw(m, m.Bounds(), &image.Uniform{blue}, image.ZP, draw.Src)

	// encode

	buf := new(bytes.Buffer)

	_ = jpeg.Encode(buf, m, nil)

	var img image.Image = m

	writeImage(w, &img)

}

func writeImage(w http.ResponseWriter, img *image.Image) {

	buffer := new(bytes.Buffer)

	if err := jpeg.Encode(buffer, *img, nil); err != nil {

		log.Fatalln("unable to encode image")

	}

	// write

	w.Header().Set("Content-Type", "image/jpeg")

	w.Header().Set("Content-Length", strconv.Itoa(len(buf.Bytes())))

	w.Write(buf.Bytes())

	w.Header().Set("Content-Length", strconv.Itoa(len(buffer.Bytes())))

	if _, err := w.Write(buffer.Bytes()); err != nil {

		log.Fatalln("unable to write image")

	}

}