🐛 bug: Fix Static middleware browser support for subdirectories (#3673)

Author: efectn

.github/testdata/fs/css/test/style2.css

@@ -0,0 +1,3 @@
+h1 {
+  color: black;
+}

middleware/static/static.go

@@ -23,6 +23,9 @@ import (
 // It returns an error if the path attempts to traverse directories.
 func sanitizePath(p []byte, filesystem fs.FS) ([]byte, error) {
 	var s string
+
+	hasTrailingSlash := len(p) > 0 && p[len(p)-1] == '/'
+
 	if bytes.IndexByte(p, '\\') >= 0 {
 		b := make([]byte, len(p))
 		copy(b, p)
@@ -66,6 +69,10 @@ func sanitizePath(p []byte, filesystem fs.FS) ([]byte, error) {
 		s = "/" + s
 	}
 
+	if hasTrailingSlash && len(s) > 1 && s[len(s)-1] != '/' {
+		s += "/"
+	}
+
 	return utils.UnsafeBytes(s), nil
 }
 

middleware/static/static_test.go

@@ -651,6 +651,20 @@ func Test_Static_FS_Browse(t *testing.T) {
 	require.NoError(t, err, "app.Test(req)")
 	require.Contains(t, string(body), "color")
 
+	resp, err = app.Test(httptest.NewRequest(fiber.MethodGet, "/dirfs/test", nil))
+	require.NoError(t, err, "app.Test(req)")
+	require.Equal(t, 200, resp.StatusCode, "Status code")
+	require.Equal(t, fiber.MIMETextHTMLCharsetUTF8, resp.Header.Get(fiber.HeaderContentType))
+
+	resp, err = app.Test(httptest.NewRequest(fiber.MethodGet, "/dirfs/test/style2.css", nil))
+	require.NoError(t, err, "app.Test(req)")
+	require.Equal(t, 200, resp.StatusCode, "Status code")
+	require.Equal(t, fiber.MIMETextCSSCharsetUTF8, resp.Header.Get(fiber.HeaderContentType))
+
+	body, err = io.ReadAll(resp.Body)
+	require.NoError(t, err, "app.Test(req)")
+	require.Contains(t, string(body), "color")
+
 	resp, err = app.Test(httptest.NewRequest(fiber.MethodGet, "/embed", nil))
 	require.NoError(t, err, "app.Test(req)")
 	require.Equal(t, 200, resp.StatusCode, "Status code")