net/http: redirect if the URL path is a dir & doesn't end in a slash

Fixes #13996

Change-Id: I9b2c7fba0705900aca9a70bc6a2687667a9a976c
Reviewed-on: https://go-review.googlesource.com/20128Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/fs.go

@@ -393,6 +393,15 @@ func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirec
 		}
 	}
 
+	// redirect if the directory name doesn't end in a slash
+	if d.IsDir() {
+		url := r.URL.Path
+		if url[len(url)-1] != '/' {
+			localRedirect(w, r, path.Base(url)+"/")
+			return
+		}
+	}
+
 	// use contents of index.html for directory, if present
 	if d.IsDir() {
 		index := strings.TrimSuffix(name, "/") + indexPage

src/net/http/fs_test.go

@@ -505,6 +505,24 @@ func TestServeFileFromCWD(t *testing.T) {
 	}
 }
 
+// Issue 13996
+func TestServeDirWithoutTrailingSlash(t *testing.T) {
+	e := "/testdata/"
+	defer afterTest(t)
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		ServeFile(w, r, ".")
+	}))
+	defer ts.Close()
+	r, err := Get(ts.URL + "/testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Body.Close()
+	if g := r.Request.URL.Path; g != e {
+		t.Errorf("got %s, want %s", g, e)
+	}
+}
+
 // Tests that ServeFile doesn't add a Content-Length if a Content-Encoding is
 // specified.
 func TestServeFileWithContentEncoding_h1(t *testing.T) { testServeFileWithContentEncoding(t, h1Mode) }