return an error if Dir is invoked with a normal file

Author: mauri870

src/net/http/fs.go

@@ -78,11 +78,16 @@ func (d Dir) Open(name string) (File, error) {
 	if dir == "" {
 		dir = "."
 	}
+	fi, err := os.Stat(dir)
+	if err != nil || !fi.IsDir() {
+		return nil, errors.New("http: invalid directory path")
+	}
 	fullName := filepath.Join(dir, path)
 	f, err := os.Open(fullName)
 	if err != nil {
 		return nil, mapOpenError(err, fullName, filepath.Separator, os.Stat)
 	}
+
 	return f, nil
 }
 
@@ -661,7 +666,7 @@ func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirec
 				return
 			}
 		} else {
-			if url != "/" && url[len(url)-1] == '/' {
+			if url[len(url)-1] == '/' {
 				localRedirect(w, r, "../"+path.Base(url))
 				return
 			}

src/net/http/fs_test.go

@@ -475,12 +475,6 @@ func TestDirJoin(t *testing.T) {
 	test(Dir("/etc"), "/hosts")
 	test(Dir("/etc"), "hosts")
 	test(Dir("/etc"), "../../../../hosts")
-
-	// Not really directories, but since we use this trick in
-	// ServeFile, test it:
-	test(Dir("/etc/hosts"), "")
-	test(Dir("/etc/hosts"), "/")
-	test(Dir("/etc/hosts"), "../")
 }
 
 func TestEmptyDirOpenCWD(t *testing.T) {
@@ -497,6 +491,22 @@ func TestEmptyDirOpenCWD(t *testing.T) {
 	test(Dir("./"))
 }
 
+// issue 63769
+func TestDirNormalFile(t *testing.T) {
+	test := func(d Dir, filename string) {
+		f, err := d.Open(filename)
+		if err == nil {
+			f.Close()
+			t.Fatalf("got nil, want error")
+		}
+	}
+
+	test(Dir("testdata/index.html"), "")
+	test(Dir("testdata/index.html"), "/")
+	test(Dir("testdata/index.html"), "..")
+	test(Dir("testdata/index.html"), "../")
+}
+
 func TestServeFileContentType(t *testing.T) { run(t, testServeFileContentType) }
 func testServeFileContentType(t *testing.T, mode testMode) {
 	const ctype = "icecream/chocolate"
@@ -1672,24 +1682,15 @@ func (grw gzipResponseWriter) Flush() {
 // Issue 63769
 func TestFileServerDirWithRootFile(t *testing.T) { run(t, testFileServerDirWithRootFile) }
 func testFileServerDirWithRootFile(t *testing.T, mode testMode) {
-	filename := "index.html"
-	contents, err := os.ReadFile("testdata/index.html")
-	if err != nil {
-		t.Fatal(err)
-	}
 	ts := newClientServerTest(t, mode, FileServer(Dir("testdata/index.html"))).ts
 	defer ts.Close()
 
 	res, err := ts.Client().Get(ts.URL)
 	if err != nil {
 		t.Fatal(err)
 	}
-	b, err := io.ReadAll(res.Body)
-	if err != nil {
-		t.Fatal("reading Body:", err)
-	}
-	if s := string(b); s != string(contents) {
-		t.Errorf("for path %q got %q, want %q", filename, s, contents)
+	if s := res.StatusCode; s != StatusInternalServerError {
+		t.Errorf("got %q, want 500", s)
 	}
 	res.Body.Close()
 }