Golang HTTP Handler to Upload Image => Resize => Convert to JPEG => Save to Disk.

gistfile1.go

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

	file, _, err := r.FormFile("file")
	if err != nil {
		log.Println(err)
		http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
		return
	}

	img, _, err := image.Decode(file)
	if err != nil {
		log.Println(err)
		http.Error(w, http.StatusText(http.StatusUnsupportedMediaType), http.StatusUnsupportedMediaType)
		return
	}

	m := resize.Resize(1000, 0, img, resize.Lanczos3)

	out, err := os.Create("test_resized.jpg")
	if err != nil {
		log.Println(err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
	defer out.Close()

	// Encode into jpeg http://blog.golang.org/go-image-package
	err = jpeg.Encode(out, m, nil)
	if err != nil {
		log.Println(err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
}