Add missing outcome tag for WebClient metrics

On error cases, the "outcome" tag would be missing from recorded metrics
for the `WebClient`.

This commit fixes this issue and improves the reference documentation by
mentioning the tag values used for error cases, when the client response
is not received (I/O errors, client error, etc).

Fixes gh-17219

Author: bclozel

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/reactive/client/DefaultWebClientExchangeTagsProvider.java

@@ -37,13 +37,9 @@ public Iterable<Tag> tags(ClientRequest request, ClientResponse response, Throwa
 		Tag method = WebClientExchangeTags.method(request);
 		Tag uri = WebClientExchangeTags.uri(request);
 		Tag clientName = WebClientExchangeTags.clientName(request);
-		if (response != null) {
-			return Arrays.asList(method, uri, clientName, WebClientExchangeTags.status(response),
-					WebClientExchangeTags.outcome(response));
-		}
-		else {
-			return Arrays.asList(method, uri, clientName, WebClientExchangeTags.status(throwable));
-		}
+		return Arrays.asList(method, uri, clientName,
+				(response != null) ? WebClientExchangeTags.status(response) : WebClientExchangeTags.status(throwable),
+				WebClientExchangeTags.outcome(response));
 	}
 
 }

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/reactive/client/DefaultWebClientExchangeTagsProviderTests.java

@@ -77,14 +77,14 @@ void tagsWhenNoUriTemplateShouldProvideUriPath() {
 	void tagsWhenIoExceptionShouldReturnIoErrorStatus() {
 		Iterable<Tag> tags = this.tagsProvider.tags(this.request, null, new IOException());
 		assertThat(tags).containsExactlyInAnyOrder(Tag.of("method", "GET"), Tag.of("uri", "/projects/{project}"),
-				Tag.of("clientName", "example.org"), Tag.of("status", "IO_ERROR"));
+				Tag.of("clientName", "example.org"), Tag.of("status", "IO_ERROR"), Tag.of("outcome", "UNKNOWN"));
 	}
 
 	@Test
 	void tagsWhenExceptionShouldReturnClientErrorStatus() {
 		Iterable<Tag> tags = this.tagsProvider.tags(this.request, null, new IllegalArgumentException());
 		assertThat(tags).containsExactlyInAnyOrder(Tag.of("method", "GET"), Tag.of("uri", "/projects/{project}"),
-				Tag.of("clientName", "example.org"), Tag.of("status", "CLIENT_ERROR"));
+				Tag.of("clientName", "example.org"), Tag.of("status", "CLIENT_ERROR"), Tag.of("outcome", "UNKNOWN"));
 	}
 
 }

spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -1981,10 +1981,11 @@ following information:
 |`outcome`
 |Request's outcome based on the status code of the response. 1xx is
 `INFORMATIONAL`, 2xx is `SUCCESS`, 3xx is `REDIRECTION`, 4xx `CLIENT_ERROR`, and 5xx is
-`SERVER_ERROR`
+`SERVER_ERROR`, `UNKNOWN` otherwise
 
 |`status`
-|Response's HTTP status code (for example, `200` or `500`)
+|Response's HTTP status code if available (for example, `200` or `500`),
+or `IO_ERROR` in case or I/O issues, `CLIENT_ERROR` otherwise
 
 |`uri`
 |Request's URI template prior to variable substitution, if possible (for example,