Add support for custom error pages

Author: hons82

errors.go

@@ -4,12 +4,24 @@
 
 package tunnel
 
-import "errors"
+import (
+	"errors"
+	"io/ioutil"
+)
 
 var (
-	errClientNotSubscribed    = errors.New("client not subscribed")
-	errClientNotConnected     = errors.New("client not connected")
-	errClientAlreadyConnected = errors.New("client already connected")
+	errClientNotSubscribed    = newError("clientNotSubscribed.html", "client not subscribed")
+	errClientNotConnected     = newError("clientNotConnected.html", "client not connected")
+	errClientAlreadyConnected = newError("clientAlreadyConnected.html", "client already connected")
 
-	errUnauthorised = errors.New("unauthorised")
+	errUnauthorised = newError("unauthorised.html", "unauthorised")
 )
+
+func newError(fileName string, defaultMsg string) error {
+	content, err := ioutil.ReadFile("html/errors/" + fileName)
+	if err != nil {
+		// handle the case where the file doesn't exist
+		return errors.New(defaultMsg)
+	}
+	return errors.New(string(content))
+}

server.go

@@ -564,22 +564,26 @@ func (s *Server) listen(l net.Listener, identifier id.ID) {
 // ServeHTTP proxies http connection to the client.
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	resp, err := s.RoundTrip(r)
-	if err == errUnauthorised {
-		w.Header().Set("WWW-Authenticate", "Basic realm=\"User Visible Realm\"")
-		http.Error(w, err.Error(), http.StatusUnauthorized)
-		return
-	}
 	if err != nil {
+		code := http.StatusBadGateway
+		if err == errUnauthorised {
+			w.Header().Set("WWW-Authenticate", "Basic realm=\"User Visible Realm\"")
+			code = http.StatusUnauthorized
+		} else if err == errClientNotSubscribed {
+			code = http.StatusNotFound
+		}
 		s.logger.Log(
 			"level", 0,
 			"action", "round trip failed",
 			"addr", r.RemoteAddr,
 			"host", r.Host,
 			"url", r.URL,
-			"err", err,
+			"code", code,
 		)
-
-		http.Error(w, err.Error(), http.StatusBadGateway)
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		w.WriteHeader(code)
+		fmt.Fprintln(w, err.Error())
 		return
 	}
 	defer resp.Body.Close()