ServerHttpResponse sets the response statusCode correctly

[jrhee17]

Motivation:

It seems like Armeria's spring integration response ServerHttpResponse is not always set correctly.
In detail, it seems like we can confirm that getStatusCode returns UNKNOWN unless setStatusCode is called explicitly.

1. When a successful response is returned, we refer to the response headers used. This is similar to the upstream implementation which falls back to the response which is actually returned.
   https://github.com/spring-projects/spring-framework/blob/d2ea5b444812b4c55e00fecb7b6451073677061d/spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpResponse.java#L72-L76

2. When Armeria returns a response instead of Spring, the response is never committed. Now, the doOnCancel is listened to and the response is committed accordingly.

Modifications:

• ArmeriaServerHttpResponse#getStatusCode now also checks the response headers when returning a value
• doOnCancel now also tries to set the response code and commit the ArmeriaServerHttpResponse

Result:

• HTTP 200 is UNKNOWN in actuator metrics #5882

[github-actions]

🔍 Build Scan® (commit: 1bc9e18)

Job name	Status	Build Scan®
build-self-hosted-unsafe-jdk-8	✅	https://ge.armeria.dev/s/lm2bst6b3gzxi
build-self-hosted-unsafe-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/yckh6clz4no44
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/symaycwweo3dy
build-self-hosted-unsafe-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/efy7biagwuxvg
build-self-hosted-unsafe-jdk-17-leak	✅	https://ge.armeria.dev/s/v5mphigbhth32
build-self-hosted-unsafe-jdk-11	✅	https://ge.armeria.dev/s/kcjqfbjztymne
build-macos-12-jdk-21	✅	https://ge.armeria.dev/s/ib3qgxmklvfqs

[minwoox]

👍 👍 👍

[minwoox]

nit: We can do:

final RequestLog requestLog = ctx.log().getIfAvailable(RESPONSE_HEADERS);
if (requestLog != null) {...}

[ikhoon]

👍👍