From d4a00ed16762d1236bbb407e16d4692d0b862d8a Mon Sep 17 00:00:00 2001
From: Camila Belo <camilaibs@gmail.com>
Date: Sun, 22 May 2022 08:53:52 +0200
Subject: [PATCH] refactor(techdocs): extract links sanitizer hook

Signed-off-by: Camila Belo <camilaibs@gmail.com>
---
 .../reader/transformers/html/hooks/links.ts   | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 plugins/techdocs/src/reader/transformers/html/hooks/links.ts

diff --git a/plugins/techdocs/src/reader/transformers/html/hooks/links.ts b/plugins/techdocs/src/reader/transformers/html/hooks/links.ts
new file mode 100644
index 0000000000..38f775cfbe
--- /dev/null
+++ b/plugins/techdocs/src/reader/transformers/html/hooks/links.ts
@@ -0,0 +1,51 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const MKDOCS_CSS = /main\.[A-Fa-f0-9]{8}\.min\.css$/;
+const GOOGLE_FONTS = /^https:\/\/fonts\.googleapis\.com/;
+const GSTATIC_FONTS = /^https:\/\/fonts\.gstatic\.com/;
+
+/**
+ * Checks whether a node is link or not.
+ * @param node - can be any element.
+ * @returns true when node is link.
+ */
+const isLink = (node: Element) => node.nodeName === 'LINK';
+
+/**
+ * Checks whether a link is safe or not.
+ * @param node - is an link element.
+ * @returns true when link is mkdocs css, google fonts or gstatic fonts.
+ */
+const isSafe = (node: Element) => {
+  const href = node?.getAttribute('href') || '';
+  const isMkdocsCss = href.match(MKDOCS_CSS);
+  const isGoogleFonts = href.match(GOOGLE_FONTS);
+  const isGstaticFonts = href.match(GSTATIC_FONTS);
+  return isMkdocsCss || isGoogleFonts || isGstaticFonts;
+};
+
+/**
+ * Function that removes unsafe link nodes.
+ * @param node - can be any element.
+ * @param hosts - list of allowed hosts.
+ */
+export const removeUnsafeLinks = (node: Element) => {
+  if (isLink(node) && !isSafe(node)) {
+    node.remove();
+  }
+  return node;
+};