fix(pages): Let the 500 page's links escape their iframe (backport #585)

agent/pages/internal_server_error.html

@@ -121,15 +121,21 @@
         <h1>The application returned an error</h1>
         <p>Error: 500 Internal Server Error</p>
       </div>
+      <!-- nginx serves this page inside an iframe. A link with no target loads
+           into that frame, and both destinations send X-Frame-Options:
+           SAMEORIGIN, so the browser refuses to render them. _blank opens a new
+           top-level tab, which is never framed, and leaves this page up. -->
       <a
         class="button"
+        target="_blank"
         href="https://docs.frappe.io/cloud/performance-error-debugging#500-internal-server-error"
         >View troubleshooting guide</a
       >
     </div>
     <p class="footer">
       Site owner? Review the
       <a
+        target="_blank"
         href="https://frappecloud.com/dashboard/benches/__BENCH_NAME__/logs/web.error.log"
         >error logs</a
       >

agent/tests/test_pages.py

@@ -2,6 +2,7 @@
 
 import glob
 import os
+import re
 import unittest
 
 PAGES_DIRECTORY = os.path.join(os.path.dirname(__file__), "..", "pages")
@@ -37,6 +38,21 @@ def test_placeholder_dashboard_links_are_rewritten(self):
             if "dashboard-url" in html:
                 self.assertIn("dashboard/sites/${window.location.hostname}", html, name)
 
+    def test_iframed_pages_escape_the_frame(self):
+        # nginx injects the 500 page as an iframe. A link with no target loads into
+        # that frame, and every destination sends X-Frame-Options: SAMEORIGIN.
+        escaping_targets = ('target="_blank"', 'target="_top"')
+        with open(BENCH_NGINX_TEMPLATE) as f:
+            template = f.read()
+
+        for name, html in read_pages():
+            if f'iframe src="/{name}"' not in template:
+                continue
+            for tag in re.findall(r"<a\b[^>]*>", html):
+                if 'href="http' in tag:
+                    escapes = any(target in tag for target in escaping_targets)
+                    self.assertTrue(escapes, f"{name}: {tag}")
+
     def test_bench_name_placeholder_is_substituted_by_nginx(self):
         # an unsubstituted __BENCH_NAME__ ships a dead link to the site owner
         with open(BENCH_NGINX_TEMPLATE) as f: