fix proxy to handle other image extensions instead of only jpeg

main.go

@@ -24,7 +24,7 @@ func main() {
 	r.Use(securityHeaders)
 
 	r.HandleFunc("/{id}-lyrics", lyricsHandler)
-	r.HandleFunc("/images/{filename}.jpg", proxyHandler)
+	r.HandleFunc("/images/{filename}.{ext}", proxyHandler)
 	r.PathPrefix("/static/").Handler(http.StripPrefix("/static/", http.FileServer(http.Dir("static"))))
 
 	server := &http.Server{

proxy.go

@@ -4,13 +4,33 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 
 	"github.com/gorilla/mux"
 )
 
+func isValidExt(ext string) bool {
+	valid := []string{"jpg", "jpeg", "png", "gif"}
+	for _, c := range valid {
+		if strings.ToLower(ext) == c {
+			return true
+		}
+	}
+
+	return false
+}
+
 func proxyHandler(w http.ResponseWriter, r *http.Request) {
-	f := mux.Vars(r)["filename"]
-	url := fmt.Sprintf("https://images.genius.com/%s.jpg", f)
+	v := mux.Vars(r)
+	f := v["filename"]
+	ext := v["ext"]
+
+	if !isValidExt(ext) {
+		write(w, http.StatusBadRequest, []byte("not an image :/"))
+		return
+	}
+
+	url := fmt.Sprintf("https://images.genius.com/%s.%s", f, ext)
 
 	res, err := http.Get(url)
 	if err != nil {
@@ -23,6 +43,6 @@ func proxyHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Header().Add("Content-type", "image/jpeg")
+	w.Header().Add("Content-type", fmt.Sprintf("image/%s", ext))
 	io.Copy(w, res.Body)
 }