From: Jonathan Amsterdam <jba@google.com>
Date: Sat, 17 May 2025 23:36:06 +0000 (-0400)
Subject: net/http: fix ServeMux.Handler on trailing-slash redirect
X-Git-Tag: go1.25rc1~230
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=3602cec3af6083d095729f3db8493a226b9273c3;p=gostls13.git

net/http: fix ServeMux.Handler on trailing-slash redirect

When a match involves a trailing-slash redirect,  ServeMux.Handler now
returns the pattern that matched.

Fixes #73688.

Change-Id: I682d9cc9a3628bed8bf21139b98369ffa6c53792
Reviewed-on: https://go-review.googlesource.com/c/go/+/673815
Reviewed-by: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
---

diff --git a/src/net/http/serve_test.go b/src/net/http/serve_test.go
index 5d2a29a6fc..84d383ccfa 100644
--- a/src/net/http/serve_test.go
+++ b/src/net/http/serve_test.go
@@ -391,6 +391,19 @@ func TestServeMuxHandler(t *testing.T) {
 	}
 }
 
+// Issue 73688
+func TestServeMuxHandlerTrailingSlash(t *testing.T) {
+	setParallel(t)
+	mux := NewServeMux()
+	const original = "/{x}/"
+	mux.Handle(original, NotFoundHandler())
+	r, _ := NewRequest("POST", "/foo", nil)
+	_, p := mux.Handler(r)
+	if p != original {
+		t.Errorf("got %q, want %q", p, original)
+	}
+}
+
 // Issue 24297
 func TestServeMuxHandleFuncWithNilHandler(t *testing.T) {
 	setParallel(t)
diff --git a/src/net/http/server.go b/src/net/http/server.go
index 5dd21bdf3f..921b42b59e 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -2714,7 +2714,7 @@ func (mux *ServeMux) findHandler(r *Request) (h Handler, patStr string, _ *patte
 		var u *url.URL
 		n, matches, u = mux.matchOrRedirect(host, r.Method, path, r.URL)
 		if u != nil {
-			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path, nil, nil
+			return RedirectHandler(u.String(), StatusMovedPermanently), n.pattern.String(), nil, nil
 		}
 		if path != escapedPath {
 			// Redirect to cleaned path.
@@ -2760,7 +2760,11 @@ func (mux *ServeMux) matchOrRedirect(host, method, path string, u *url.URL) (_ *
 		path += "/"
 		n2, _ := mux.tree.match(host, method, path)
 		if exactMatch(n2, path) {
-			return nil, nil, &url.URL{Path: cleanPath(u.Path) + "/", RawQuery: u.RawQuery}
+			// It is safe to return n2 here: it is used only in the second RedirectHandler case
+			// of findHandler, and that method returns before it does the "n == nil" check where
+			// the first return value matters. We return it here only to make the pattern available
+			// to findHandler.
+			return n2, nil, &url.URL{Path: cleanPath(u.Path) + "/", RawQuery: u.RawQuery}
 		}
 	}
 	return n, matches, nil