Only remove trailing slash from URI value

This commit upgrades the algorithm when trailing slash are to be
ignored. Previously a root URI (i.e. "/") would result to to empty
string which is an issue for monitoring system that requires tag values
to be non empty. If the URI is a single character, the trailing is not
applied and "/" is left as is.

Closes gh-20536

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

@@ -107,7 +107,7 @@ public final class WebFluxTags {
 		PathPattern pathPattern = exchange.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
 		if (pathPattern != null) {
 			String patternString = pathPattern.getPatternString();
-			if (ignoreTrailingSlash) {
+			if (ignoreTrailingSlash && patternString.length() > 1) {
 				patternString = TRAILING_SLASH_PATTERN.matcher(patternString).replaceAll("");
 			}
 			return Tag.of("uri", patternString);

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/servlet/WebMvcTags.java

@@ -112,7 +112,7 @@ public final class WebMvcTags {
 		if (request != null) {
 			String pattern = getMatchingPattern(request);
 			if (pattern != null) {
-				if (ignoreTrailingSlash) {
+				if (ignoreTrailingSlash && pattern.length() > 1) {
 					pattern = TRAILING_SLASH_PATTERN.matcher(pattern).replaceAll("");
 				}
 				return Tag.of("uri", pattern);

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/WebMvcTagsTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -52,12 +52,26 @@ class WebMvcTagsTests {
 
 	@Test
 	void uriTagValueIsBestMatchingPatternWhenAvailable() {
-		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "/spring");
+		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "/spring/");
 		this.response.setStatus(301);
 		Tag tag = WebMvcTags.uri(this.request, this.response);
+		assertThat(tag.getValue()).isEqualTo("/spring/");
+	}
+
+	@Test
+	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashRemoveTrailingSlash() {
+		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "/spring/");
+		Tag tag = WebMvcTags.uri(this.request, this.response, true);
 		assertThat(tag.getValue()).isEqualTo("/spring");
 	}
 
+	@Test
+	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashKeepSingleSlash() {
+		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "/");
+		Tag tag = WebMvcTags.uri(this.request, this.response, true);
+		assertThat(tag.getValue()).isEqualTo("/");
+	}
+
 	@Test
 	void uriTagValueIsRootWhenRequestHasNoPatternOrPathInfo() {
 		assertThat(WebMvcTags.uri(this.request, null).getValue()).isEqualTo("root");

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

@@ -39,12 +39,13 @@ import static org.mockito.Mockito.mock;
  * @author Brian Clozel
  * @author Michael McFadyen
  * @author Madhura Bhave
+ * @author Stephane Nicoll
  */
 class WebFluxTagsTests {
 
 	private MockServerWebExchange exchange;
 
-	private PathPatternParser parser = new PathPatternParser();
+	private final PathPatternParser parser = new PathPatternParser();
 
 	@BeforeEach
 	void setup() {
@@ -53,12 +54,28 @@ class WebFluxTagsTests {
 
 	@Test
 	void uriTagValueIsBestMatchingPatternWhenAvailable() {
-		this.exchange.getAttributes().put(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, this.parser.parse("/spring"));
+		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
+	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashRemoveTrailingSlash() {
+		this.exchange.getAttributes().put(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE,
+				this.parser.parse("/spring/"));
+		Tag tag = WebFluxTags.uri(this.exchange, true);
 		assertThat(tag.getValue()).isEqualTo("/spring");
 	}
 
+	@Test
+	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashKeepSingleSlash() {
+		this.exchange.getAttributes().put(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, this.parser.parse("/"));
+		Tag tag = WebFluxTags.uri(this.exchange, true);
+		assertThat(tag.getValue()).isEqualTo("/");
+	}
+
 	@Test
 	void uriTagValueIsRedirectionWhenResponseStatusIs3xx() {
 		this.exchange.getResponse().setStatusCode(HttpStatus.MOVED_PERMANENTLY);