Avoid uri tag explosion when use of path variable is undetected

Previously, WebMvcTags would fall back to using the request’s path
info if Spring MVC’s best matching path pattern attribute was not
available. For non-Spring MVC web frameworks that support path
variables, such as Jersey, this led to an explosion of URI tags that
could exhaust the heap.

Closes gh-12447

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

@@ -77,8 +77,9 @@ public final class WebMvcTags {
 	/**
 	 * Creates a {@code uri} tag based on the URI of the given {@code request}. Uses the
 	 * {@link HandlerMapping#BEST_MATCHING_PATTERN_ATTRIBUTE} best matching pattern if
-	 * available, falling back to the request's {@link HttpServletRequest#getPathInfo()
-	 * path info} if necessary.
+	 * available. Falling back to {@code REDIRECTION} for 3xx responses, {@code NOT_FOUND}
+	 * for 404 responses, {@code root} for requests with no path info, and {@code UNKNOWN}
+	 * for all other requests.
 	 * @param request the request
 	 * @param response the response
 	 * @return the uri tag derived from the request
@@ -102,7 +103,6 @@ public final class WebMvcTags {
 			if (pathInfo.isEmpty()) {
 				return URI_ROOT;
 			}
-			return Tag.of("uri", pathInfo);
 		}
 		return URI_UNKNOWN;
 	}

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

@@ -38,12 +38,6 @@ public class WebMvcTagsTests {
 
 	private final MockHttpServletResponse response = new MockHttpServletResponse();
 
-	@Test
-	public void uriTrailingSlashesAreSuppressed() {
-		this.request.setPathInfo("//spring/");
-		assertThat(WebMvcTags.uri(this.request, null).getValue()).isEqualTo("/spring");
-	}
-
 	@Test
 	public void uriTagValueIsBestMatchingPatternWhenAvailable() {
 		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE,
@@ -53,6 +47,23 @@ public class WebMvcTagsTests {
 		assertThat(tag.getValue()).isEqualTo("/spring");
 	}
 
+	@Test
+	public void uriTagValueIsRootWhenRequestHasNoPatternOrPathInfo() {
+		assertThat(WebMvcTags.uri(this.request, null).getValue()).isEqualTo("root");
+	}
+
+	@Test
+	public void uriTagValueIsRootWhenRequestHasNoPatternAndSlashPathInfo() {
+		this.request.setPathInfo("/");
+		assertThat(WebMvcTags.uri(this.request, null).getValue()).isEqualTo("root");
+	}
+
+	@Test
+	public void uriTagValueIsUnknownWhenRequestHasNoPatternAndNonRootPathInfo() {
+		this.request.setPathInfo("/example");
+		assertThat(WebMvcTags.uri(this.request, null).getValue()).isEqualTo("UNKNOWN");
+	}
+
 	@Test
 	public void uriTagValueIsRedirectionWhenResponseStatusIs3xx() {
 		this.response.setStatus(301);