net/http: make ServeMux preserve query string during redirects

Ensure that the implicitly created redirect
for
  "/route"
after
  "/route/"
has been registered doesn't lose the query string information.

Fixes #17841.

Change-Id: Ib7df9242fab8c9368a18fc0da678003d6bec63b8
Reviewed-on: https://go-review.googlesource.com/43779
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/net/http/server.go b/src/net/http/server.go
index 45f8e1b16a..71f46a74f9 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -1963,6 +1963,7 @@ func StripPrefix(prefix string, h Handler) Handler {
 // The provided code should be in the 3xx range and is usually
 // StatusMovedPermanently, StatusFound or StatusSeeOther.
 func Redirect(w ResponseWriter, r *Request, urlStr string, code int) {
+	queryAlreadySet := false
 	if u, err := url.Parse(urlStr); err == nil {
 		// If url was relative, make absolute by
 		// combining with request path.
@@ -2005,9 +2006,17 @@ func Redirect(w ResponseWriter, r *Request, urlStr string, code int) {
 				urlStr += "/"
 			}
 			urlStr += query
+			queryAlreadySet = len(query) != 0
 		}
 	}
 
+	// We should make sure not to lose the query string of
+	// the original request when doing a redirect, if not already set.
+	// See Issue 17841.
+	if !queryAlreadySet && len(r.URL.RawQuery) != 0 {
+		urlStr += "?" + r.URL.RawQuery
+	}
+
 	w.Header().Set("Location", hexEscapeNonASCII(urlStr))
 	w.WriteHeader(code)