Align WebFluxTags uri support on WebMvcTags

This commit ensures that `WebFluxTags` not only relies on
`BEST_MATCHING_PATTERN_ATTRIBUTE` or request URI to provide the "uri"
tag information.

To avoid cardinality explosion, HTTP not found and redirects are
assigned fixed uri tags.

Closes gh-12685

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

@@ -19,7 +19,6 @@ package org.springframework.boot.actuate.metrics.web.reactive.server;
 import io.micrometer.core.instrument.Tag;
 
 import org.springframework.http.HttpStatus;
-import org.springframework.util.StringUtils;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.util.pattern.PathPattern;
@@ -34,6 +33,10 @@ import org.springframework.web.util.pattern.PathPattern;
  */
 public final class WebFluxTags {
 
+	private static final Tag URI_NOT_FOUND = Tag.of("uri", "NOT_FOUND");
+
+	private static final Tag URI_REDIRECTION = Tag.of("uri", "REDIRECTION");
+
 	private WebFluxTags() {
 	}
 
@@ -70,14 +73,25 @@ public final class WebFluxTags {
 	 * @return the uri tag derived from the exchange
 	 */
 	public static Tag uri(ServerWebExchange exchange) {
-		PathPattern pathPattern = exchange.getAttributeOrDefault(
-				HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, null);
-		String uri = pathPattern == null ? exchange.getRequest().getURI().toString()
-				: pathPattern.getPatternString();
-		if (!StringUtils.hasText(uri)) {
-			uri = "/";
+		if (exchange != null) {
+			PathPattern pathPattern = exchange.getAttribute(
+					HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
+			if (pathPattern != null) {
+				return Tag.of("uri", pathPattern.getPatternString());
+			}
+			else {
+				HttpStatus status = exchange.getResponse().getStatusCode();
+				if (status != null && status.is3xxRedirection()) {
+					return URI_REDIRECTION;
+				}
+				if (status != null && status.equals(HttpStatus.NOT_FOUND)) {
+					return URI_NOT_FOUND;
+				}
+			}
+			String path = exchange.getRequest().getPath().value();
+			return Tag.of("uri", path.isEmpty() ? "root" : path);
 		}
-		return Tag.of("uri", uri.isEmpty() ? "root" : uri);
+		return Tag.of("uri", "UNKNOWN");
 	}
 
 	/**

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

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2012-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.web.reactive.server;
+
+import io.micrometer.core.instrument.Tag;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.web.reactive.HandlerMapping;
+import org.springframework.web.util.pattern.PathPatternParser;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link WebFluxTags}.
+ * @author Brian Clozel
+ */
+public class WebFluxTagsTests {
+
+	private MockServerWebExchange exchange;
+
+	private PathPatternParser parser = new PathPatternParser();
+
+	@Before
+	public void setup() {
+		this.exchange = MockServerWebExchange
+				.from(MockServerHttpRequest.get(""));
+	}
+
+	@Test
+	public void uriTagValueIsBestMatchingPatternWhenAvailable() {
+		this.exchange.getAttributes().put(
+				HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, this.parser.parse("/spring"));
+		this.exchange.getResponse().setStatusCode(HttpStatus.MOVED_PERMANENTLY);
+		Tag tag = WebFluxTags.uri(this.exchange);
+		assertThat(tag.getValue()).isEqualTo("/spring");
+	}
+
+	@Test
+	public void uriTagValueIsRedirectionWhenResponseStatusIs3xx() {
+		this.exchange.getResponse().setStatusCode(HttpStatus.MOVED_PERMANENTLY);
+		Tag tag = WebFluxTags.uri(this.exchange);
+		assertThat(tag.getValue()).isEqualTo("REDIRECTION");
+	}
+
+	@Test
+	public void uriTagValueIsNotFoundWhenResponseStatusIs404() {
+		this.exchange.getResponse().setStatusCode(HttpStatus.NOT_FOUND);
+		Tag tag = WebFluxTags.uri(this.exchange);
+		assertThat(tag.getValue()).isEqualTo("NOT_FOUND");
+	}
+
+	@Test
+	public void uriTagToleratesCustomResponseStatus() {
+		this.exchange.getResponse().setStatusCodeValue(601);
+		Tag tag = WebFluxTags.uri(this.exchange);
+		assertThat(tag.getValue()).isEqualTo("root");
+	}
+
+	@Test
+	public void uriTagIsUnknownWhenRequestIsNull() {
+		Tag tag = WebFluxTags.uri(null);
+		assertThat(tag.getValue()).isEqualTo("UNKNOWN");
+	}
+
+}