Attaches error to Observation

without this change when there is no response and the observation closing web exception handler stops the observation we've forgotten to attach an error to it
with this change we're attaching the error

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/observation/DefaultGatewayObservationConvention.java

@@ -50,7 +50,8 @@ public class DefaultGatewayObservationConvention implements GatewayObservationCo
 			return keyValues;
 		}
 		Route route = context.getServerWebExchange().getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR);
-		keyValues = keyValues.and(ROUTE_URI.withValue(route.getUri().toString()),
+		keyValues = keyValues
+				.and(ROUTE_URI.withValue(route.getUri().toString()),
 						METHOD.withValue(context.getRequest().getMethod().name()))
 				.and(ROUTE_ID.withValue(route.getId()));
 		ServerHttpResponse response = context.getResponse();

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/observation/GatewayContext.java

@@ -53,4 +53,5 @@ public class GatewayContext extends RequestReplySenderContext<HttpHeaders, Serve
 	public ServerWebExchange getServerWebExchange() {
 		return serverWebExchange;
 	}
+
 }

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/observation/ObservationClosingWebExceptionHandler.java

@@ -41,6 +41,7 @@ public class ObservationClosingWebExceptionHandler implements WebExceptionHandle
 			Observation observation = exchange.getAttribute(ObservedRequestHttpHeadersFilter.CHILD_OBSERVATION);
 			if (observation != null) {
 				log.debug(() -> "Observation was not previously stopped, will stop it.");
+				observation.error(ex);
 				observation.stop();
 			}
 		}

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/B3BraveObservedHttpHeadersFilterTests.java

@@ -104,9 +104,8 @@ class B3BraveObservedHttpHeadersFilterTests {
 			assertThat(headers.get("b3").get(0)).matches("^" + context.traceId() + "-(.*)-1-" + context.spanId() + "$");
 			List<FinishedSpan> finishedSpans = testSpanHandler.spans().stream().map(BraveFinishedSpan::new)
 					.collect(Collectors.toList());
-			SpansAssert.then(finishedSpans).hasASpanWithName("HTTP GET", spanAssert -> spanAssert
-					.hasTag("spring.cloud.gateway.route.id", "foo")
-					.hasTag("http.method", "GET")
+			SpansAssert.then(finishedSpans).hasASpanWithName("HTTP GET",
+					spanAssert -> spanAssert.hasTag("spring.cloud.gateway.route.id", "foo").hasTag("http.method", "GET")
 							.hasTag("http.status_code", "200")
 							.hasTag("spring.cloud.gateway.route.uri", "http://localhost:8080/")
 							.hasTag("http.uri", "http://localhost:8080/get"));

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/ObservationClosingWebExceptionHandlerTests.java

@@ -52,8 +52,10 @@ class ObservationClosingWebExceptionHandlerTests {
 	void shouldStopTheObservationIfItWasNotStoppedPreviouslyAndThereWasAnError() {
 		Observation observation = Mockito.mock(Observation.class);
 		exchange.getAttributes().put(ObservedRequestHttpHeadersFilter.CHILD_OBSERVATION, observation);
+		RuntimeException runtimeException = new RuntimeException();
 
-		assertThatNoException().isThrownBy(() -> handler.handle(exchange, new RuntimeException()));
+		assertThatNoException().isThrownBy(() -> handler.handle(exchange, runtimeException));
+		Mockito.verify(observation).error(runtimeException);
 		Mockito.verify(observation).stop();
 	}
 

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/observation/ObservedHttpHeadersFilterTests.java

@@ -84,17 +84,16 @@ public class ObservedHttpHeadersFilterTests extends SampleTestRunner {
 					.containsEntry("X-B3-TraceId", Collections.singletonList(context.traceId()))
 					.doesNotContainEntry("X-B3-SpanId", Collections.singletonList(context.spanId()))
 					.containsKey("X-B3-SpanId");
-			SpansAssert.then(bb.getFinishedSpans()).hasASpanWithName("HTTP GET", spanAssert -> spanAssert
-					.hasTag("http.method", "GET").hasTag("http.status_code", "200")
+			SpansAssert.then(bb.getFinishedSpans()).hasASpanWithName("HTTP GET",
+					spanAssert -> spanAssert.hasTag("http.method", "GET").hasTag("http.status_code", "200")
 							.hasTag("http.uri", "http://localhost:8080/get")
 							.hasTag("spring.cloud.gateway.route.uri", "http://localhost:8080/")
 							.hasTag("spring.cloud.gateway.route.id", "foo"));
-			MeterRegistryAssert.then(meterRegistry)
-					.hasTimerWithNameAndTags("http.client.requests",
-							Tags.of("spring.cloud.gateway.route.id", "foo", "error", "none", "http.method", "GET", "http.status_code", "200", "spring.cloud.gateway.route.uri",
-									"http://localhost:8080/"))
-					.hasMeterWithNameAndTags("http.client.requests.active",
-							Tags.of("spring.cloud.gateway.route.id", "foo", "http.method", "GET", "spring.cloud.gateway.route.uri", "http://localhost:8080/"));
+			MeterRegistryAssert.then(meterRegistry).hasTimerWithNameAndTags("http.client.requests",
+					Tags.of("spring.cloud.gateway.route.id", "foo", "error", "none", "http.method", "GET",
+							"http.status_code", "200", "spring.cloud.gateway.route.uri", "http://localhost:8080/"))
+					.hasMeterWithNameAndTags("http.client.requests.active", Tags.of("spring.cloud.gateway.route.id",
+							"foo", "http.method", "GET", "spring.cloud.gateway.route.uri", "http://localhost:8080/"));
 		};
 	}