Make external iframe render work (#35730)

Fix #35729, #17635, #21098

web_src/js/standalone/external-render-iframe.ts

@@ -0,0 +1,43 @@
+/* To manually test:
+
+[markup.in-iframe]
+ENABLED = true
+FILE_EXTENSIONS = .in-iframe
+RENDER_CONTENT_MODE = iframe
+RENDER_COMMAND = `echo '<div style="width: 100%; height: 2000px; border: 10px solid red; box-sizing: border-box;"><a href="/">a link</a> <a target="_blank" href="//gitea.com">external link</a></div>'`
+
+;RENDER_COMMAND = cat /path/to/file.pdf
+;RENDER_CONTENT_SANDBOX = disabled
+
+*/
+
+function mainExternalRenderIframe() {
+  const u = new URL(window.location.href);
+  const iframeId = u.searchParams.get('gitea-iframe-id');
+
+  // iframe is in different origin, so we need to use postMessage to communicate
+  const postIframeMsg = (cmd: string, data: Record<string, any> = {}) => {
+    window.parent.postMessage({giteaIframeCmd: cmd, giteaIframeId: iframeId, ...data}, '*');
+  };
+
+  const updateIframeHeight = () => postIframeMsg('resize', {iframeHeight: document.documentElement.scrollHeight});
+  updateIframeHeight();
+  window.addEventListener('DOMContentLoaded', updateIframeHeight);
+  // the easiest way to handle dynamic content changes and easy to debug, can be fine-tuned in the future
+  setInterval(updateIframeHeight, 1000);
+
+  //  no way to open an absolute link with CSP frame-src, it also needs some tricks like "postMessage" or "copy the link to clipboard"
+  const openIframeLink = (link: string, target: string) => postIframeMsg('open-link', {openLink: link, anchorTarget: target});
+  document.addEventListener('click', (e) => {
+    const el = e.target as HTMLAnchorElement;
+    if (el.nodeName !== 'A') return;
+    const href = el.getAttribute('href') || '';
+    // safe links: "./any", "../any", "/any", "//host/any", "http://host/any", "https://host/any"
+    if (href.startsWith('.') || href.startsWith('/') || href.startsWith('http://') || href.startsWith('https://')) {
+      e.preventDefault();
+      openIframeLink(href, el.getAttribute('target'));
+    }
+  });
+}
+
+mainExternalRenderIframe();