FeignException contains request- or response-body

[robachmann]

While working on #912 I came across an odd behaviour:

In errorStatus a FeignException is created with the response's body:

feign/core/src/main/java/feign/FeignException.java

Line 81 in ce66205

body = Util.toByteArray(response.body().asInputStream());

In errorReading a FeignException is created with the request's body (even though the response with its body would be at hand):

feign/core/src/main/java/feign/FeignException.java

Line 72 in ce66205

request.body());

I think it's inconsistent and confusing for the user as he or she can't rely on the same data-source for all exceptions. On the other hand, I'm not sure whether it's intentional as there are unit-tests that check this behaviour, thus changing it could also be breaking-change for users:

feign/core/src/test/java/feign/FeignTest.java

Line 525 in ce66205

assertThat(e.contentUTF8()).isEqualTo("Request body");

If we agree on returning the response-body, I'd gladly create a PR for it.

[kdavisk6]

It is intentional. Feign Exception cannot depend on a Response being available when it is created or available since these exceptions can be thrown before and after a request. For example, when a request times out, a FeignException is created and there is no response. In order to provide additional context, we use the Request.

One thing we can do to clear up this potential confusion is to update the documentation and comment to code to make this intention clearer.