Prior to this commit, `WebClient` would throw `IllegalArgumentException`
when receiving an HTTP response with an unknown HTTP status code.
This commit is a follow up of SPR-16748 (supporting non-standard HTTP
status codes on the reactive `ClientHttpResponse`), and is mirroring
SPR-15978 (supporting non-standard HTTP status codes in `RestTemplate`).
With this change, `WebClient` now tolerates unknown status codes in some
cases, while not offering that choice as a first class citizen:
`HttpStatus` is still the preferred way to deal with HTTP status codes.
Here's how `WebClient` will behave when fetching the full response:
```
// Given a remote endpoint returning a "123" HTTP status code
Mono<ClientResponse> result = this.webClient.get()
.uri("/status/123")
.exchange();
// will still throw an IllegalArgumentException
HttpStatus status = result.block().statusCode();
// is safe and will return 123
int statusCode = result.block().rawStatusCode();
```
Resolving directly the response body with `retrieve()` is different.
```
// will send an error signal with a UnknownHttpStatusCodeException
Mono<String> result = this.webClient.get()
.uri("/status/123")
.retrieve()
.bodyToMono(String.class);
```
In general, `WebClient` will provide high-level support
for well-known HTTP status codes, like error handling with
`WebClient.ResponseSpec#onStatus`.
For such support with unknown status codes, it is better to rely
on lower level constructs such as `ExchangeFilterFunction`.
Issue: SPR-16819
038af9a303