fix: Wrap weasyprint to catch exceptions (ietf-tools#6324)

ietf/doc/tests.py

@@ -2843,6 +2843,12 @@ def test_pdfized(self):
                 self.should_succeed(dict(name=rfc.name,rev=f'{r:02d}',ext=ext))
         self.should_404(dict(name=rfc.name,rev='02'))
 
+        import socket
+        socket.socket = lambda *args, **kwargs: None
+        url = urlreverse(self.view, kwargs=dict(name=rfc.name))
+        r = self.client.get(url)
+        self.assertEqual(r.status_code, 504)
+
 class NotifyValidationTests(TestCase):
     def test_notify_validation(self):
         valid_values = [

ietf/doc/views_doc.py

@@ -51,6 +51,7 @@
 from django import forms
 from django.contrib.staticfiles import finders
 
+from weasyprint.urls import URLFetchingError
 
 import debug                            # pyflakes:ignore
 
@@ -974,7 +975,16 @@ def document_pdfized(request, name, rev=None, ext=None):
     if not os.path.exists(doc.get_file_name()):
         raise Http404("File not found: %s" % doc.get_file_name())
 
-    pdf = doc.pdfized()
+    try:
+        pdf = doc.pdfized()
+    except URLFetchingError:
+        # retry once, then give up
+        try:
+            pdf = doc.pdfized()
+        except URLFetchingError as exception:
+            return render(request, "doc/weasyprint_failed.html",
+                          dict(error=f'{type(exception).__name__}: {exception}'),
+                          status=504)
     if pdf:
         return HttpResponse(pdf,content_type='application/pdf')
     else:

ietf/templates/doc/weasyprint_failed.html

@@ -0,0 +1,17 @@
+{# Copyright The IETF Trust 2023, All Rights Reserved #}
+{% extends "base.html" %}
+{% load origin %}
+{% block title %}Network error while rendering PDF{% endblock %}
+{% block content %}
+    {% origin %}
+    <h1>Network error while rendering PDF</h1>
+    <p>
+        A network error was encountered while trying to render your document as PDF.
+    </p>
+    <p>
+        We have retried the operation, and it failed again. You may want to wait a bit, and try again.
+    </p>
+    <p>
+        The error was: <code>{{ error }}</code>
+    </p>
+{% endblock %}