Preview mode with WSGI

Issue Summary

When I’ve used Wagtail on localhost in development mode - all works fine. But when I moved it to production with uWSGI server - Preview mode is broken now.

Steps to Reproduce

I used new-style middleware classes:

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'wagtail.wagtailcore.middleware.SiteMiddleware',
    'wagtail.wagtailredirects.middleware.RedirectMiddleware',
]

My server setup is: nginx -> uwsgi -> django wsgi application. All pages works fine (including admin panel). But when I press “Preview” button in editor, I get exception:

[2017-01-15 16:02:37.411] [ERROR     ] [django.request] [exception/handle_uncaught_exception] [p:21|t:140140641003264] || Internal Server Error: /wagtail/pages/15/edit/preview/
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 39, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 217, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 215, in _get_response
    response = response.render()
  File "/usr/local/lib/python3.6/site-packages/django/template/response.py", line 109, in render
    self.content = self.rendered_content
  File "/usr/local/lib/python3.6/site-packages/django/template/response.py", line 86, in rendered_content
    content = template.render(context, self._request)
  File "/usr/local/lib/python3.6/site-packages/django/template/backends/django.py", line 66, in render
    return self.template.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 208, in render
    return self._render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 199, in _render
    return self.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/loader_tags.py", line 174, in render
    return compiled_parent._render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 199, in _render
    return self.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/loader_tags.py", line 174, in render
    return compiled_parent._render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 199, in _render
    return self.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/loader_tags.py", line 70, in render
    result = block.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/loader_tags.py", line 70, in render
    result = block.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/loader_tags.py", line 70, in render
    result = block.nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/defaulttags.py", line 315, in render
    return nodelist.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 994, in render
    bit = node.render_annotated(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/defaulttags.py", line 209, in render
    nodelist.append(node.render_annotated(context))
  File "/usr/local/lib/python3.6/site-packages/django/template/base.py", line 961, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.6/site-packages/django/template/library.py", line 203, in render
    output = self.func(*resolved_args, **resolved_kwargs)
  File "/usr/local/lib/python3.6/site-packages/wagtail/wagtailcore/templatetags/wagtailcore_tags.py", line 21, in pageurl
    return page.relative_url(context['request'].site)
AttributeError: 'WSGIRequest' object has no attribute 'site'

Technical details

• Python version: Python 3.5.1
• Django version: Django (1.10.4)
• Wagtail version: wagtail (1.8)

[gasman]

Hi @soar,

From the stack trace, it looks like something is failing during the middleware handling - it then tries to render the 500 error template, and fails on a {% pageurl %} tag because request.site is not defined.

Please can you try simplifying your 500 error template as much as possible (e.g. leave out any menu includes) so that the original error is revealed?

Also: please check that the site record under Settings -> Sites is accurate (including setting the port to 443, if you’re using HTTPS), as that seems to be a common cause of preview failures.

[an0o0nym]

Also: please check that the site record under Settings -> Sites is accurate (including setting the port to 443, if you’re using HTTPS), as that seems to be a common cause of preview failures.

Setting port to 443 in Settings -> Sites helped me! Thanks!