From 8ee3b8c848f055955b282e580d0e047bc53afd94 Mon Sep 17 00:00:00 2001
From: Julius Volz <julius.volz@gmail.com>
Date: Thu, 14 Nov 2019 14:58:22 +0100
Subject: [PATCH] React UI: Fix "<path-prefix>/new" -> "<path-prefix>/new/"
 redirect (#6319)

Fixes https://github.com/prometheus/prometheus/issues/6163

Signed-off-by: Julius Volz <julius.volz@gmail.com>
---
 web/web.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/web/web.go b/web/web.go
index d8e7fcbb2..c2fcb24db 100644
--- a/web/web.go
+++ b/web/web.go
@@ -347,6 +347,15 @@ func New(logger log.Logger, o *Options) *Handler {
 		fs.ServeHTTP(w, r)
 	})
 
+	// Make sure that "<path-prefix>/new" is redirected to "<path-prefix>/new/" and
+	// not just the naked "/new/", which would be the default behavior of the router
+	// with the "RedirectTrailingSlash" option (https://godoc.org/github.com/julienschmidt/httprouter#Router.RedirectTrailingSlash),
+	// and which breaks users with a --web.route-prefix that deviates from the path derived
+	// from the external URL.
+	router.Get("/new", func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "new")+"/", http.StatusFound)
+	})
+
 	router.Get("/new/*filepath", func(w http.ResponseWriter, r *http.Request) {
 		p := route.Param(r.Context(), "filepath")