Webservice: Support foreground/background color.

service/placeholder.go

@@ -1,37 +1,92 @@
 package main
 
 import (
+	"errors"
 	"image/color"
 	"image/png"
 	"net/http"
 	"strconv"
+	"strings"
 
 	log "github.com/Sirupsen/logrus"
 
 	"github.com/gorilla/mux"
 	"github.com/michiwend/goplaceholder"
 )
 
+func hexToRGB(h string) (uint8, uint8, uint8, error) {
+	rgb, err := strconv.ParseUint(string(h), 16, 32)
+	if err == nil {
+		return uint8(rgb >> 16), uint8((rgb >> 8) & 0xFF), uint8(rgb & 0xFF), nil
+	}
+	return 0, 0, 0, err
+}
+
+func normalizeHex(h string) string {
+	h = strings.TrimPrefix(h, "#")
+	if len(h) != 3 && len(h) != 6 {
+		return ""
+	}
+	if len(h) == 3 {
+		h = h[:1] + h[:1] + h[1:2] + h[1:2] + h[2:] + h[2:]
+	}
+	return h
+}
+
+func paramToColor(param, defaultValue string) (color.RGBA, error) {
+
+	if len(param) == 0 {
+		param = defaultValue
+	}
+
+	hexColor := normalizeHex(param)
+	if len(hexColor) == 0 {
+		return color.RGBA{}, errors.New("bad hex color format")
+	}
+
+	R, G, B, err := hexToRGB(hexColor)
+	if err != nil {
+		return color.RGBA{}, err
+	}
+
+	return color.RGBA{R, G, B, 255}, nil
+}
+
 func serveImage(w http.ResponseWriter, r *http.Request) {
 
 	params := mux.Vars(r)
 	r.ParseForm()
-	text := r.FormValue("text")
+
 	width, _ := strconv.ParseInt(params["width"], 10, 32)
 	height, _ := strconv.ParseInt(params["height"], 10, 32)
 	// FIXME err handling
 
+	text := r.FormValue("text")
+
 	if width > 4000 || height > 4000 {
 		w.Header().Set("Content-Type", "text/html")
 		w.Write([]byte("image too large"))
+
+	foregroundValue := r.FormValue("fg")
+	backgroundValue := r.FormValue("bg")
+
+	fg, err := paramToColor(foregroundValue, "969696")
+	if err != nil {
+		http.Error(w, "Bad value for foreground color", http.StatusBadRequest)
+		log.WithField("color", foregroundValue).Error(err)
+		return
+	}
+	bg, err := paramToColor(backgroundValue, "CCCCCC")
+	if err != nil {
+		http.Error(w, "Bad value for background color", http.StatusBadRequest)
+		log.WithField("color", backgroundValue).Error(err)
 		return
 	}
 
 	img, err := goplaceholder.Placeholder(
 		text,
 		"/usr/share/fonts/TTF/DejaVuSans-Bold.ttf",
-		color.RGBA{150, 150, 150, 255},
-		color.RGBA{204, 204, 204, 255},
+		fg, bg,
 		int(width), int(height))
 
 	if err != nil {