[Backport] fix: Prevent error page recursion (#35209) #35259
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We sometimes see rendering errors in the error page itself, which then cause another attempt at rendering the error page. I'm not sure _exactly_ how the loop is occurring, but it looks something like this: 1. An error is raised in a view or middleware and is not caught by application code 2. Django catches the error and calls the registered uncaught error handler 3. Our handler tries to render an error page 4. The rendering code raises an error 5. GOTO 2 (until some sort of server limit is reached) By catching all errors raised during error-page render and substituting in a hardcoded string, we can reduce server resources, avoid logging massive sequences of recursive stack traces, and still give the user *some* indication that yes, there was a problem. This should help address openedx#35151 At least one of these rendering errors is known to be due to a translation error. There's a separate issue for restoring translation quality so that we avoid those issues in the future (openedx/openedx-translations#549) but in general we should catch all rendering errors, including unknown ones. Testing: - In `lms/envs/devstack.py` change `DEBUG` to `False` to ensure that the usual error page is displayed (rather than the debug error page). - Add line `1/0` to the top of the `student_dashboard` function in `common/djangoapps/student/views/dashboard.py` to make that view error. - In `lms/templates/static_templates/server-error.html` replace `static.get_platform_name()` with `None * 7` to make the error template itself produce an error. - Visit <http://localhost:18000/dashboard>. Without the fix, the response takes 10 seconds and produces a 6 MB, 85k line set of stack traces and the page displays "A server error occurred. Please contact the administrator." With the fix, the response takes less than a second and produces three stack traces (one of which contains the error page's rendering error).
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@cmltaWt0 thank you! I think this error has been going on for at least 5 years without an easy way to reproduce or fix. Thanks for fixing it! |
This is a backport of #35209
Fix details
We sometimes see rendering errors in the error page itself, which then cause another attempt at rendering the error page. I'm not sure exactly how the loop is occurring, but it looks something like this:
By catching all errors raised during error-page render and substituting in a hardcoded string, we can reduce server resources, avoid logging massive sequences of recursive stack traces, and still give the user some indication that yes, there was a problem.
This should help address #35151
At least one of these rendering errors is known to be due to a translation error. There's a separate issue for restoring translation quality so that we avoid those issues in the future (openedx/openedx-translations#549) but in general we should catch all rendering errors, including unknown ones.
Testing:
lms/envs/devstack.pychangeDEBUGtoFalseto ensure that the usual error page is displayed (rather than the debug error page).1/0to the top of thestudent_dashboardfunction incommon/djangoapps/student/views/dashboard.pyto make that view error.lms/templates/static_templates/server-error.htmlreplacestatic.get_platform_name()withNone * 7to make the error template itself produce an error.Without the fix, the response takes 10 seconds and produces a 6 MB, 85k line set of stack traces and the page displays "A server error occurred. Please contact the administrator."
With the fix, the response takes less than a second and produces three stack traces (one of which contains the error page's rendering error).
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