Catch synchronous panics in NewHandlerService
#60
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`NewHandlerService::call` is gaining more logic, so some of the existing logic needs tidying up to keep things sane.
When something panics in a Gotham application, we can trap the panic at the `NewHandlerService` level and respond with a blank 500 error response. This is intended to be a last-ditch attempt at stopping the application falling over, and panics should instead be handled in a couple of more intelligent ways: 1. Applications should not cause a panic for anything but the most dire of runtime errors; and 2. A panic-catching middleware will be introduced which attempts to handle these panics more gracefully. Notably, this logic **does not** prevent panics occurring if the returned `Future` panics. Ref #17
bradleybeddoes
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Oct 24, 2017
smangelsdorf
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Dec 5, 2017
After #60, the OrderedRegex was refactored into ConstrainedSegmentRegex to be unwind-safe, and so the original `#[derive(Clone)]` no longer works.
smangelsdorf
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The changes in #60 require unwind safety in the pipeline and handlers used in the router builder API.
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This is part 1 of solving #17:
A few notes about this:
RefUnwindSafein quite a few places. The need for this originated fromNewHandler: RefUnwindSafe, which has transitively required the trait bound elsewhere;regex::Regextype (which we use for segment constraints) isn't unwind safe due to interior mutability. We work around this by:is_matchfunction, via ourConstrainedSegmentRegexwrapper; andRegex.catch_unwindto theNewHandlerServicelogic, which is intended to be a last resort effort to stop the application server falling over. Future work will hopefully see a more graceful panic-catching middleware which gives theResponseExtendertime to intervene before theResponseis sent. There's no ability, nor any intention, to be able to customise the response which is sent at theNewHandlerServicelevel.