refactor(techdocs): extract iframes sanitizer hook

Signed-off-by: Camila Belo <camilaibs@gmail.com>

plugins/techdocs/src/reader/transformers/html/hooks/iframes.ts

@@ -0,0 +1,50 @@
+/*
+ * 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.
+ */
+
+/**
+ * Checks whether a node is iframe or not.
+ * @param node - can be any element.
+ * @returns true when node is iframe.
+ */
+const isIframe = (node: Element) => node.nodeName === 'IFRAME';
+
+/**
+ * Checks whether a iframe is safe or not.
+ * @param node - is an iframe element.
+ * @param hosts - list of allowed hosts.
+ * @returns true when iframe is included in hosts.
+ */
+const isSafe = (node: Element, hosts: string[]) => {
+  const src = node.getAttribute('src') || '';
+  try {
+    const { host } = new URL(src);
+    return hosts.includes(host);
+  } catch {
+    return false;
+  }
+};
+
+/**
+ * Returns a function that removes unsafe iframe nodes.
+ * @param node - can be any element.
+ * @param hosts - list of allowed hosts.
+ */
+export const removeUnsafeIframes = (hosts: string[]) => (node: Element) => {
+  if (isIframe(node) && !isSafe(node, hosts)) {
+    node.remove();
+  }
+  return node;
+};