Make X-Forwarded-For handling an optional flag

src/handlers.go

@@ -340,11 +340,15 @@ func (ctx *Instance) ServeHTTP(wOrig http.ResponseWriter, r *http.Request) {
 		statusCode: new(int),
 	}
 
-	clientIP := r.Header.Get("X-Forwarded-For")
-	clientIP = strings.Split(clientIP, ", ")[0]
+	clientIP := r.RemoteAddr
 
-	if clientIP == "" {
-		clientIP = r.RemoteAddr
+	if (ctx.UseXForwarded) {
+		forwardedIP := r.Header.Get("X-Forwarded-For")
+		forwardedIP = strings.Split(forwardedIP, ", ")[0]
+
+		if forwardedIP != "" {
+			clientIP = forwardedIP
+		}
 	}
 
 	ctx.mux.ServeHTTP(w, r)

src/instance.go

@@ -25,6 +25,7 @@ type Instance struct {
 	StateDir        string
 	ThemeDir        string
 	AttemptInterval time.Duration
+	UseXForwarded	bool
 
 	Runtime RuntimeConfig
 

src/mothd.go

@@ -52,6 +52,12 @@ func main() {
 		20*time.Second,
 		"Time between maintenance tasks",
 	)
+	flag.BoolVar(
+		&ctx.UseXForwarded,
+		"x-forwarded-for",
+		false,
+		"Emit IPs from the X-Forwarded-For header in logs, when available, instead of the source IP. Use this when running behind a load-balancer or proxy",
+	)
 	listen := flag.String(
 		"listen",
 		":8080",