handle error inside serveFile

src/net/http/fs.go

@@ -78,15 +78,11 @@ func (d Dir) Open(name string) (File, error) {
 	if dir == "" {
 		dir = "."
 	}
-	if fi, _ := os.Stat(dir); fi != nil && !fi.IsDir() {
-		return nil, errors.New("http: attempting to traverse a non-directory")
-	}
 	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
 }
 
@@ -664,11 +660,16 @@ func serveFile(w ResponseWriter, r *Request, fs FileSystem, name string, redirec
 				localRedirect(w, r, path.Base(url)+"/")
 				return
 			}
-		} else {
-			if url[len(url)-1] == '/' {
-				localRedirect(w, r, "../"+path.Base(url))
+		} else if url[len(url)-1] == '/' {
+			base := path.Base(url)
+			if base == "/" || base == "." {
+				// The FileSystem maps a path like "/" or "/./" to a file instead of a directory.
+				msg := "http: attempting to traverse a non-directory"
+				Error(w, msg, StatusInternalServerError)
 				return
 			}
+			localRedirect(w, r, "../"+base)
+			return
 		}
 	}
 

src/net/http/fs_test.go

@@ -475,6 +475,12 @@ 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) {
@@ -491,22 +497,6 @@ 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"
@@ -1682,15 +1672,25 @@ func (grw gzipResponseWriter) Flush() {
 // Issue 63769
 func TestFileServerDirWithRootFile(t *testing.T) { run(t, testFileServerDirWithRootFile) }
 func testFileServerDirWithRootFile(t *testing.T, mode testMode) {
-	ts := newClientServerTest(t, mode, FileServer(Dir("testdata/index.html"))).ts
-	defer ts.Close()
+	testDirFile := func(t *testing.T, h Handler) {
+		ts := newClientServerTest(t, mode, h).ts
+		defer ts.Close()
 
-	res, err := ts.Client().Get(ts.URL)
-	if err != nil {
-		t.Fatal(err)
+		res, err := ts.Client().Get(ts.URL)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if g, w := res.StatusCode, StatusInternalServerError; g != w {
+			t.Errorf("StatusCode mismatch: got %d, want: %d", g, w)
+		}
+		res.Body.Close()
 	}
-	if g, w := res.StatusCode, StatusInternalServerError; g != w {
-		t.Errorf("StatusCode mismatch: got %d, want: %d", g, w)
-	}
-	res.Body.Close()
+
+	t.Run("FileServer", func(t *testing.T) {
+		testDirFile(t, FileServer(Dir("testdata/index.html")))
+	})
+
+	t.Run("FileServerFS", func(t *testing.T) {
+		testDirFile(t, FileServerFS(os.DirFS("testdata/index.html")))
+	})
 }