Exceptions thrown by middleware.process_response don't get to middleware.process_exception

[bob84123]

If I have a custom exception handler, implemented as a middleware class with a process_exception method, this handler does not receive an exception that is thrown during another middleware's process_response method. This mainly happens with django.middleware.transaction.TransactionMiddleware; if a view executes a query that violates a PostgreSQL constraint, an exception isn't thrown until the transaction is committed, which is inside the middleware, and so my exception logger can't catch that.

I have a patch that fixes the issue and doesn't break anything else (according to the test suite). I can't see any downsides of applying this, but I may be missing something, so let me know.

[Aymeric Augustin]

Exception middleware currently works as advertised.

​https://docs.djangoproject.com/en/dev/topics/http/middleware/#process-exception:

Django calls process_exception() when a view raises an exception.

You're proposing to change its behavior, so that it will also be called if an exception happens in a middleware.

This requires a decision by a core developer.

[anonymous]

It would to be great to have process_exception called for exceptions that happen in a middleware. Hope there is progress on this bug soon.

[Aymeric Augustin]

Overall, the design of Django's middleware assumes that middleware is reliable and will not throw exceptions under normal circumstances.

Besides, the current behavior is documented.

Since TransactionMiddleware is now deprecated (it's basically impossible to implement this feature reliable as a middleware), the original use case has disappeared, and I'm going to close this ticket.