add fix from golang/go

caddyhttp/staticfiles/fileserver.go

@@ -56,6 +56,9 @@ func (fs FileServer) serveFile(w http.ResponseWriter, r *http.Request, name stri
 
 	f, err := fs.Root.Open(name)
 	if err != nil {
+		// TODO: remove when http.Dir handles this
+		// Go issue #18984
+		err = mapFSRootOpenErr(err)
 		if os.IsNotExist(err) {
 			return http.StatusNotFound, nil
 		} else if os.IsPermission(err) {
@@ -230,3 +233,35 @@ var staticEncodingPriority = []string{
 	"br",
 	"gzip",
 }
+
+// mapFSRootOpenErr maps the provided non-nil error
+// to a possibly better non-nil error. In particular, it turns OS-specific errors
+// about opening files in non-directories into os.ErrNotExist.
+//
+// TODO: remove when http.Dir handles this
+// Go issue #18984
+func mapFSRootOpenErr(originalErr error) error {
+	if os.IsNotExist(originalErr) || os.IsPermission(originalErr) {
+		return originalErr
+	}
+
+	perr, ok := originalErr.(*os.PathError)
+	if !ok {
+		return originalErr
+	}
+	name := perr.Path
+	parts := strings.Split(name, string(filepath.Separator))
+	for i := range parts {
+		if parts[i] == "" {
+			continue
+		}
+		fi, err := os.Stat(strings.Join(parts[:i+1], string(filepath.Separator)))
+		if err != nil {
+			return originalErr
+		}
+		if !fi.IsDir() {
+			return os.ErrNotExist
+		}
+	}
+	return originalErr
+}

caddyhttp/staticfiles/fileserver_test.go

@@ -178,6 +178,11 @@ func TestServeHTTP(t *testing.T) {
 			expectedBodyContent: testFiles[filepath.Join("webroot", "sub", "brotli.html.br")],
 			expectedEtag:        `W/"1e240-e"`,
 		},
+		// Test 20 - treat existing file as a directory.
+		{
+			url:            "https://foo/file1.html/other",
+			expectedStatus: http.StatusNotFound,
+		},
 	}
 
 	for i, test := range tests {