Image placeholder microservice

server.go

package main

import (
	"bytes"
	"fmt"
	"image"
	"image/color"
	"image/draw"
	"image/jpeg"
	"log"
	"net/http"
	"strconv"
	"time"

	"golang.org/x/image/font"
	"golang.org/x/image/font/inconsolata"
	"golang.org/x/image/math/fixed"
)

func Logger(inner http.HandlerFunc, name string) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		inner.ServeHTTP(w, r)

		log.Printf(
			"%s\t%s\t%s\t%s",
			r.Method,
			r.RequestURI,
			name,
			time.Since(start),
		)
	})
}

func addLabel(img *image.RGBA, x, y int, label string) {
	col := color.RGBA{64, 64, 64, 255}

	d := &font.Drawer{
		Dst:  img,
		Src:  image.NewUniform(col),
		Face: inconsolata.Bold8x16,
	}
	l := d.MeasureString(label)
	d.Dot = fixed.P(x - int(l) / 128, y)
	d.DrawString(label)
}

func ImagePlaceholderHandler(w http.ResponseWriter, r *http.Request) {
	width, err := strconv.Atoi(r.FormValue("w"))
	if err != nil {
		width = 512
	}
	height, err := strconv.Atoi(r.FormValue("h"))
	if err != nil {
		height = 512
	}

	m := image.NewRGBA(image.Rect(0, 0, width, height))
	grey := color.RGBA{200, 200, 200, 255}
	draw.Draw(m, m.Bounds(), &image.Uniform{grey}, image.ZP, draw.Src)
	addLabel(m, width/2, height/2, fmt.Sprintf("%v x %v", width, height))

	var img image.Image = m
	buffer := new(bytes.Buffer)
	if err := jpeg.Encode(buffer, img, nil); err != nil {
		log.Println("unable to encode image.")
	}

	w.Header().Set("Content-Type", "image/jpeg")
	w.Header().Set("Content-Length", strconv.Itoa(len(buffer.Bytes())))
	w.WriteHeader(http.StatusOK)
	if _, err := w.Write(buffer.Bytes()); err != nil {
		log.Println("unable to write image.")
	}
}

func main() {
	http.HandleFunc("/", Logger(ImagePlaceholderHandler, "image#placeholder"))

	log.Printf("Service listening on port 8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}