Improve Error Handling

[msrd0]

This Pull Request removes all usages of the now outdated failure crate and replaces them with anyhow, the suggested successor for a generic error type.

It also aligns the API of NewMiddleware with the API of NewHandler. Since the user does not get to handle the error types but all we do is generate an error response, we don't need a concrete error type like std::io::Error but can use a generic one. This simplifies the use of non-io errors since they can now use the shorthand ? operator instead of going the considerably more elaborate io::Error::Other route.

This is a breaking API change but I expect the required changes to be minimal. Most users don't have many manual implementations of NewHandler or NewMiddleware, and for those implementations, all they have to do is change io::Result into anyhow::Result (which is re-exported by gotham).

[codecov]

Codecov Report

Merging #438 into master will decrease coverage by 0.27%.
The diff coverage is 66.95%.

@@            Coverage Diff             @@
##           master     #438      +/-   ##
==========================================
- Coverage   84.44%   84.17%   -0.28%     
==========================================
  Files         110      110              
  Lines        5479     5473       -6     
==========================================
- Hits         4627     4607      -20     
- Misses        852      866      +14     

Impacted Files	Coverage Δ
examples/handlers/async_handlers/src/main.rs	93.57% <0.00%> (ø)
examples/handlers/form_urlencoded/src/main.rs	80.55% <0.00%> (-2.78%)	⬇️
examples/handlers/multipart/src/main.rs	72.72% <0.00%> (-0.41%)	⬇️
examples/handlers/request_data/src/main.rs	85.18% <0.00%> (-1.86%)	⬇️
examples/handlers/stateful/src/main.rs	83.67% <ø> (ø)
gotham/src/lib.rs	82.75% <ø> (ø)
gotham/src/middleware/logger/mod.rs	0.00% <0.00%> (ø)
gotham/src/middleware/security/mod.rs	0.00% <0.00%> (ø)
gotham/src/middleware/timer/mod.rs	0.00% <0.00%> (ø)
gotham/src/pipeline/chain.rs	70.00% <0.00%> (ø)
... and 35 more

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[pksunkara]

Looks good. I didn't find any issues. I will wait for while to let @nyarly or @colinbankier review this.

[msrd0]

@nyarly @colinbankier @pksunkara any updates on this?

[msrd0]

Update: I have now also refactored HandlerError to have a From<E> implementation for all error types that implement Into<anyhow::Error> + Display. This allows to use all types that implement std::error::Error plus anyhow::Error itself as the error type for handlers, with ? shorthand support being completed with #450. Also, for convenience, Result<T, E> and TryFuture<T, E> have a map_err_with_status(status) method that is basically equivalent to map_err(|err| HandlerError::from(err).with_status(status)).

CC @tanriol

[sezna]

So there are two options to enable this -- we can either loosen or remove the code coverage requirement, or you can add more test coverage. Obviously the latter is preferred, but only if it is practical.

[msrd0]

Afaik, code coverage is optional and merging is blocked because this pull request has no review (and also because there were merge conflicts which I just resolved). If you think some part of this PR is poorly tested, please let me know.

[sezna]

I didn't realize the codecov check was non-blocking. I'll look at this.

[sezna]

LGTM!

[msrd0]

I resolved another merge conflict, should be good for merge now @sezna