Adds 'errorResponseHandler' to HBApplication to allow HBHTTPResponseErrors to be intercepted and a custom response returned

[SoftwareEngineerChris]

As promised, this is the second PR. It introduces the ability to handle a HBHTTPResponseError and provide a custom response, falling back to the default implementation in HTTPResponder using HBHTTPResponseError if the errorResponseHandler is not provided.

The reason for this PR is that I wanted to continue using standard HBHTTPErrors e.g. HBHTTPError(.notFound) at the higher-levels of the application, but have the ability to create/manipulate a custom response in-place of the ones provided by HBHTTPResponseError itself at a global level.

[codecov]

Codecov Report

Merging #61 (3042783) into main (438ab21) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
+ Coverage   83.17%   83.19%   +0.01%     
==========================================
  Files          47       47              
  Lines        2372     2374       +2     
==========================================
+ Hits         1973     1975       +2     
  Misses        399      399              

Impacted Files	Coverage Δ
Sources/Hummingbird/Application.swift	92.45% <ø> (ø)
...Hummingbird/Server/Application+HTTPResponder.swift	86.11% <100.00%> (+0.81%)	⬆️

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[adam-fowler]

Hi can I ask how you are using Hummingbird. Are you using hummingbird-core or are you just using the router elements of Hummingbird?

If it is the latter I have a minor change which will resolve this for you. The only reason I catch errors in HTTPResponder.respond is for a logging. Instead of converting them to an HBHTTPResponse at the that point I can return them as an error.

If it is the former you could use a Middleware to catch all the errors and process them eg

struct ErrorMiddleware: HBMiddleware {
    public func apply(to request: HBRequest, next: HBResponder) -> EventLoopFuture<HBResponse> {
        return next.respond(to: request).flatMapErrorThrowing { error in
            try processError(error)
        }
    }
}

See the ErrorMiddleware I setup for hummingbird-lambda https://github.com/hummingbird-project/hummingbird-lambda/blob/main/Sources/HummingbirdLambda/ErrorMiddleware.swift

[SoftwareEngineerChris]

Thanks Adam, I think the middleware might do the trick. I’m effectively using Hummingbird to proxy requests elsewhere that aren’t matched by the router (whilst still having some paths matched and handled by the router).

[adam-fowler]

Thanks Adam, I think the middleware might do the trick. I’m effectively using Hummingbird to proxy requests elsewhere that aren’t matched by the router (whilst still having some paths matched and handled by the router).

Make sure it is the first middleware you add to ensure you catch errors from any other middleware

[SoftwareEngineerChris]

I think LambdaErrorMiddleware definitively points me in the right direction - thanks again!

[SoftwareEngineerChris]

The middleware approach worked perfectly - didn’t even need to change any of the code, just shifted it into the middleware. Thanks again Adam.