net/http: skip redirecting in ServeMux when URL path for CONNECT is empty

In 1.21 ServeMux, we had a special-case to skip redirection when a given
path is empty for CONNECT requests:
https://go.googlesource.com/go/+/refs/tags/go1.24.4/src/net/http/servemux121.go#205.

This special case seems to not have been carried over to 1.22 ServeMux.
This causes needless redirection, which this CL fixes.

Fixes #74422

Change-Id: I3cc5b4d195ab0591a9139225b632cbe17f4290db
Reviewed-on: https://go-review.googlesource.com/c/go/+/699915
Reviewed-by: Sean Liao <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

Author: nicholashusin

src/net/http/server.go

@@ -2759,9 +2759,12 @@ func (mux *ServeMux) matchOrRedirect(host, method, path string, u *url.URL) (_ *
 	defer mux.mu.RUnlock()
 
 	n, matches := mux.tree.match(host, method, path)
-	// If we have an exact match, or we were asked not to try trailing-slash redirection,
-	// or the URL already has a trailing slash, then we're done.
-	if !exactMatch(n, path) && u != nil && !strings.HasSuffix(path, "/") {
+	// We can terminate here if any of the following is true:
+	// - We have an exact match already.
+	// - We were asked not to try trailing slash redirection.
+	// - The URL already has a trailing slash.
+	// - The URL is an empty string.
+	if !exactMatch(n, path) && u != nil && !strings.HasSuffix(path, "/") && path != "" {
 		// If there is an exact match with a trailing slash, then redirect.
 		path += "/"
 		n2, _ := mux.tree.match(host, method, path)

src/net/http/server_test.go

@@ -97,6 +97,7 @@ func TestFindHandler(t *testing.T) {
 		{"GET", "/foo/x", "&http.handler{i:2}"},
 		{"GET", "/bar/x", "&http.handler{i:4}"},
 		{"GET", "/bar", `&http.redirectHandler{url:"/bar/", code:301}`},
+		{"CONNECT", "", "(http.HandlerFunc)(.*)"},
 		{"CONNECT", "/", "&http.handler{i:1}"},
 		{"CONNECT", "//", "&http.handler{i:1}"},
 		{"CONNECT", "//foo", "&http.handler{i:5}"},
@@ -112,7 +113,7 @@ func TestFindHandler(t *testing.T) {
 		r.URL = &url.URL{Path: test.path}
 		gotH, _, _, _ := mux.findHandler(&r)
 		got := fmt.Sprintf("%#v", gotH)
-		if got != test.wantHandler {
+		if !regexp.MustCompile(test.wantHandler).MatchString(got) {
 			t.Errorf("%s %q: got %q, want %q", test.method, test.path, got, test.wantHandler)
 		}
 	}