Set matching pattern in reactive server observation context

This commit fixes the observation instrumentation for the reactive HTTP
server by setting the best matching pattern determined by the web
framework into the `ServerRequestObservationContext`.

This information is required by the observation convention for creating
the expected `KeyValue` for the matching pattern. Prior to this commit,
the information was missing and resulted in an UNKNOWN key value.

Fixes gh-29422

Author: bclozel

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/support/RouterFunctionMapping.java

@@ -28,6 +28,7 @@
 import org.springframework.http.codec.ServerCodecConfigurer;
 import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
+import org.springframework.web.filter.reactive.ServerHttpObservationFilter;
 import org.springframework.web.reactive.function.server.HandlerFunction;
 import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.RouterFunctions;
@@ -170,6 +171,8 @@ private void setAttributes(
 		PathPattern matchingPattern = (PathPattern) attributes.get(RouterFunctions.MATCHING_PATTERN_ATTRIBUTE);
 		if (matchingPattern != null) {
 			attributes.put(BEST_MATCHING_PATTERN_ATTRIBUTE, matchingPattern);
+			ServerHttpObservationFilter.findObservationContext(serverRequest.exchange())
+					.ifPresent(context -> context.setPathPattern(matchingPattern));
 		}
 		Map<String, String> uriVariables =
 				(Map<String, String>) attributes.get(RouterFunctions.URI_TEMPLATE_VARIABLES_ATTRIBUTE);

spring-webflux/src/main/java/org/springframework/web/reactive/handler/AbstractUrlHandlerMapping.java

@@ -30,6 +30,7 @@
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
+import org.springframework.web.filter.reactive.ServerHttpObservationFilter;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.util.pattern.PathPattern;
 
@@ -165,6 +166,8 @@ protected Object lookupHandler(PathContainer lookupPath, ServerWebExchange excha
 
 		exchange.getAttributes().put(BEST_MATCHING_HANDLER_ATTRIBUTE, handler);
 		exchange.getAttributes().put(BEST_MATCHING_PATTERN_ATTRIBUTE, pattern);
+		ServerHttpObservationFilter.findObservationContext(exchange)
+				.ifPresent(context -> context.setPathPattern(pattern));
 		exchange.getAttributes().put(PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, pathWithinMapping);
 		exchange.getAttributes().put(URI_TEMPLATE_VARIABLES_ATTRIBUTE, matchInfo.getUriVariables());
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/RequestMappingInfoHandlerMapping.java

@@ -38,6 +38,7 @@
 import org.springframework.util.Assert;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.filter.reactive.ServerHttpObservationFilter;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.reactive.result.condition.NameValueExpression;
@@ -139,6 +140,8 @@ protected void handleMatch(RequestMappingInfo info, HandlerMethod handlerMethod,
 
 		exchange.getAttributes().put(BEST_MATCHING_HANDLER_ATTRIBUTE, handlerMethod);
 		exchange.getAttributes().put(BEST_MATCHING_PATTERN_ATTRIBUTE, bestPattern);
+		ServerHttpObservationFilter.findObservationContext(exchange)
+				.ifPresent(context -> context.setPathPattern(bestPattern));
 		exchange.getAttributes().put(URI_TEMPLATE_VARIABLES_ATTRIBUTE, uriVariables);
 		exchange.getAttributes().put(MATRIX_VARIABLES_ATTRIBUTE, matrixVariables);
 

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/support/RouterFunctionMappingTests.java

@@ -22,6 +22,8 @@
 
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.http.codec.ServerCodecConfigurer;
+import org.springframework.http.observation.reactive.ServerRequestObservationContext;
+import org.springframework.web.filter.reactive.ServerHttpObservationFilter;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.reactive.function.server.HandlerFunction;
 import org.springframework.web.reactive.function.server.RouterFunction;
@@ -34,8 +36,10 @@
 import org.springframework.web.util.pattern.PathPattern;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.web.filter.reactive.ServerHttpObservationFilter.CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE;
 
 /**
+ * Tests for {@link RouterFunctionMapping}.
  * @author Arjen Poutsma
  * @author Brian Clozel
  */
@@ -132,6 +136,8 @@ void mappedRequestShouldHoldAttributes() {
 		PathPattern matchingPattern = exchange.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
 		assertThat(matchingPattern).isNotNull();
 		assertThat(matchingPattern.getPatternString()).isEqualTo("/match");
+		assertThat(ServerHttpObservationFilter.findObservationContext(exchange))
+				.hasValueSatisfying(context -> assertThat(context.getPathPattern()).isEqualTo(matchingPattern));
 
 		ServerRequest serverRequest = exchange.getAttribute(RouterFunctions.REQUEST_ATTRIBUTE);
 		assertThat(serverRequest).isNotNull();
@@ -141,7 +147,10 @@ void mappedRequestShouldHoldAttributes() {
 	}
 
 	private ServerWebExchange createExchange(String urlTemplate) {
-		return MockServerWebExchange.from(MockServerHttpRequest.get(urlTemplate));
+		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get(urlTemplate));
+		ServerRequestObservationContext observationContext = new ServerRequestObservationContext(exchange);
+		exchange.getAttributes().put(CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE, observationContext);
+		return exchange;
 	}
 
 }

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/RequestMappingInfoHandlerMappingTests.java

@@ -36,6 +36,7 @@
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
+import org.springframework.http.observation.reactive.ServerRequestObservationContext;
 import org.springframework.lang.Nullable;
 import org.springframework.stereotype.Controller;
 import org.springframework.util.ClassUtils;
@@ -63,6 +64,7 @@
 import static org.springframework.web.bind.annotation.RequestMethod.GET;
 import static org.springframework.web.bind.annotation.RequestMethod.HEAD;
 import static org.springframework.web.bind.annotation.RequestMethod.OPTIONS;
+import static org.springframework.web.filter.reactive.ServerHttpObservationFilter.CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE;
 import static org.springframework.web.reactive.HandlerMapping.BEST_MATCHING_HANDLER_ATTRIBUTE;
 import static org.springframework.web.reactive.HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE;
 import static org.springframework.web.reactive.result.method.RequestMappingInfo.paths;
@@ -257,6 +259,18 @@ public void handleMatchBestMatchingPatternAttribute() {
 		assertThat(mapped).isSameAs(handlerMethod);
 	}
 
+	@Test
+	public void handleMatchBestMatchingPatternAttributeInObservationContext() {
+		RequestMappingInfo key = paths("/{path1}/2", "/**").build();
+		ServerWebExchange exchange = MockServerWebExchange.from(get("/1/2"));
+		ServerRequestObservationContext observationContext = new ServerRequestObservationContext(exchange);
+		exchange.getAttributes().put(CURRENT_OBSERVATION_CONTEXT_ATTRIBUTE, observationContext);
+		this.handlerMapping.handleMatch(key, handlerMethod, exchange);
+
+		assertThat(observationContext.getPathPattern()).isNotNull();
+		assertThat(observationContext.getPathPattern().toString()).isEqualTo("/{path1}/2");
+	}
+
 	@Test // gh-22543
 	public void handleMatchBestMatchingPatternAttributeNoPatternsDefined() {
 		ServerWebExchange exchange = MockServerWebExchange.from(get(""));