Handling exceptions in Spring 5 Reactive kotlin - exception

Question

I've been hitting the wall and haven't came up with any reasonable solution, so maybe someone will give it a try. I wrote simple service integrating with github, and having hard time to understand how should I work with exceptions in reactive word properly. Once I got expected 404 status error from Github I would like to throw my custom exception and present it to the client instead of valid response, I'm checking code statuses of response from github and the only thing I receive on my site is:
2018-06-26 21:45:08.286 WARN 8336 --- [ctor-http-nio-2]
.a.w.r.e.DefaultErrorWebExceptionHandler : Failed to handle request
[GET http://localhost:8080/repositories/sh1nen/no-exist]: Response
status 404
Here is my simple method responsible for making requests and handling error codes appropriately.
fun findSpecificOwnerRepository(owner: String, repositoryName: String) = webClient
.get()
.uri("/repos/$owner/$repositoryName")
.retrieve()
.onStatus({ httpStatus -> HttpStatus.NOT_FOUND == httpStatus }, { Mono.error(RepositoryNotFoundException(reason = "Repository $repositoryName not found.")) })
.onStatus({ httpStatus -> HttpStatus.SERVICE_UNAVAILABLE == httpStatus }, { Mono.error(RepositoryNotFoundException(reason = "Service unavailable.")) })
.bodyToMono(GithubRepositoryResponse::class.java)
Here is my custom exception which basically represents no resources on my site to represent:
internal class RepositoryNotFoundException(
status: HttpStatus = HttpStatus.NOT_FOUND,
reason: String? = null,
throwable: Throwable? = null) : ResponseStatusException(status, reason, throwable)
And the endpoint itself which I'm hitting to get the response:
#GetMapping("{owner}/{repositoryName}")
fun findSpecificOwnerRepository(#PathVariable owner: String, #PathVariable repositoryName: String) = githubClient
.findSpecificOwnerRepository(owner, repositoryName)
I would like to get 404 with a message which is hardcoded. Do I need any special #ExceptionHandler in controller to handle my custom exception ?
Is there any chance of implementing situation when for example github is not able to keep up with requests I am serving and throw in that case also some exception? How could it be implemented?

Answer 1

I'm not sure if you are actually missing anything for point 1), as the exception you extend should naturally result in 404 to your clients, if I recall correctly.
About point 2, it all depends on how your source handles rate limiting. In the case of GitHub, it will return a 403 once you hit rate limits, but you can be extra careful and check the custom headers as well. See https://developer.github.com/v3/#rate-limiting
So the simplest way it would be implemented is with onStatus. Alternatively, you can inspect the whole response and act accordingly by using exchange instead of retrieve, and flatMaping on the resulting Mono (that emits the whole server response).