image-transformer/main.go

// vi:ts=4:sts=4:sw=4:noet:tw=72

package main

import (
	"flag"
	"fmt"
	"log"
	"net/http"
	"strconv"
	"strings"

	"github.com/davidbyttow/govips/pkg/vips"
)

var (
	imgServer  = flag.String("s", "https://images.example.com/", "URL prefix")
	listenAddr = flag.String("l", "0.0.0.0:8080", "Listen address")
)

func init() {
	flag.Parse()
}

func resizeHandler(w http.ResponseWriter, r *http.Request) {
	// Get the query parameters from the request URL
	path := r.URL.EscapedPath()
	parm := strings.Split(path, "/")
	if len(parm) < 4 {
		writeError(w, "", "", "error in arguments", http.StatusBadRequest)
		return
	}

	method := parm[1]
	args := parm[2]
	imgPath := strings.Join(parm[3:], "/")

	// Start fetching the image from the given url
	resp, err := http.Get(*imgServer + imgPath)
	if err != nil {
		writeError(w, imgPath, method, "failed to fetch image", http.StatusNotFound)
		return
	}
	defer resp.Body.Close()

	switch method {
	case "resize":
		size := strings.Split(args, "x")
		if len(size) < 2 {
			writeError(w, imgPath, method, "url, width, and height are required", http.StatusBadRequest)
			return
		}
		width := size[0]
		height := size[1]

		// Validate that all three required fields are present
		if imgPath == "" || width == "" || height == "" {
			writeError(w, imgPath, method, "url, width, and height are required", http.StatusBadRequest)
			return
		}

		// Convert width and height to integers
		iw, errW := strconv.Atoi(width)
		ih, errH := strconv.Atoi(height)
		if errW != nil || errH != nil {
			writeError(w, imgPath, method, "width and height must be integers", http.StatusBadRequest)
			return
		}

		// Ensure that a valid response was given
		if resp.StatusCode/100 != 2 {
			writeError(w, imgPath, method, fmt.Sprintf("failed to fetch image (%v)", resp.StatusCode), http.StatusBadRequest)
			return
		}

		// govips returns the output of the image as a []byte object. We don't need
		// it since we are directly piping it to the ResponseWriter
		_, _, err = vips.NewTransform().
			Load(resp.Body).
			ResizeStrategy(vips.ResizeStrategyEmbed).
			Resize(iw, ih).
			Output(w).
			Apply()

		if err != nil {
			writeError(w, imgPath, method, "failed to resize", http.StatusInternalServerError)
			return
		}

	default:
		writeError(w, imgPath, method, "unknown method", http.StatusBadRequest)
		return
	}

}

func writeError(w http.ResponseWriter, imgPath, method, err string, status int) {
	w.WriteHeader(status)
	w.Write([]byte(fmt.Sprintf("Error [%s %s]: %s", method, imgPath, err)))
}

func main() {
	// Start vips with the default configuration
	vips.Startup(nil)
	defer vips.Shutdown()

	http.HandleFunc("/", resizeHandler)
	log.Fatal(http.ListenAndServe(*listenAddr, nil))
}