Add mixed-classpath scenario and Tomcat http.headers collection

Two related follow-ups to the #812 servlet-commons unification, both about HTTP
request-tag collection on the Tomcat/servlet path.

1. spring-6.x-mixed-servlet-scenario — an end-to-end repro of the #13938 field
   condition: a Jakarta Spring 6 WAR that ALSO carries javax.servlet-api:4.0.1 at
   compile scope, so both javax.servlet.* (from WEB-INF/lib) and jakarta.servlet.*
   (from the Tomcat 10.1 container) are loadable in the deployed webapp at once. The
   scenario asserts http.headers and http.params are still collected on the jakarta
   entry span, proving servlet-commons' runtime instanceof dispatch resolves the live
   request under a mixed classpath — previously only covered by the
   HttpRequestWrappersTest unit test. One version by design (the resolution is
   version-independent; version compatibility is already covered by spring-6.x-scenario).

2. Tomcat http.headers — http.headers was emitted only by the Spring MVC plugin, so
   plugin.http.include_http_headers was a no-op for plain servlet apps served by the
   Tomcat plugin. Add INCLUDE_HTTP_HEADERS + HTTP_HEADERS_LENGTH_THRESHOLD to
   TomcatPluginConfig.Plugin.Http — the shared plugin.http.* namespace already used by
   the Spring MVC and HttpClient plugins, so no new config key and no agent.config
   change — and collect the configured request headers in TomcatInvokeInterceptor,
   guarded no-op when the config is empty. Proven on the dedicated Tomcat scenarios,
   where the Tomcat plugin owns the entry span: tomcat-9x (javax, Tomcat 9) and
   tomcat-10x (jakarta, Tomcat 10) now carry a mock_header header and a q1 query param
   on their internal self-call and assert http.headers + http.params, which also fills
   the previously-missing jakarta http.params coverage.

Author: wu-sheng

.github/workflows/plugins-jdk17-test.1.yaml

@@ -71,6 +71,7 @@ jobs:
       matrix:
         case:
           - spring-6.x-scenario
+          - spring-6.x-mixed-servlet-scenario
           - spring-boot-3.x-scenario
           - struts2.7-scenario
           - resteasy-6.x-scenario

CHANGES.md

@@ -6,6 +6,7 @@ Release Notes.
 ------------------
 
 * Fix `plugin.http.include_http_headers` not working on Spring Boot 3.x / Jakarta EE (apache/skywalking#13938).
+* Support `plugin.http.include_http_headers` in the Tomcat plugin, collecting the configured request headers as the `http.headers` tag on Tomcat entry spans (e.g. RESTEasy on Tomcat), consistent with the Spring MVC plugin. Honors the shared `plugin.http.http_headers_length_threshold`.
 * Unify the Tomcat plugins into a single `tomcat` plugin (Tomcat 7 - 10) and the Jetty server plugins into a single `jetty-server` plugin (Jetty 9 - 11), each supporting both `javax.servlet` and `jakarta.servlet`. Breaking change: plugin names `tomcat-7.x/8.x` and `tomcat-10.x` are replaced by `tomcat`, and `jetty-server-9.x` and `jetty-server-11.x` by `jetty-server`; update `plugin.exclude_plugins` if you reference the old names.
 * Add a Jetty 12 server plugin (`jetty-server-12.x`). Jetty 12 removed the `HttpChannel` handle target and moved request handling to the async `Server#handle(Request, Response, Callback)` core API, so it needs a separate plugin from the merged `jetty-server`.
 * Add a Struts 7 plugin (`struts2-7.x`) for Jakarta Struts, whose `DefaultActionInvocation` moved to `org.apache.struts2`.

apm-sniffer/apm-sdk-plugin/tomcat-plugin/src/main/java/org/apache/skywalking/apm/plugin/tomcat/TomcatInvokeInterceptor.java

@@ -37,8 +37,11 @@
 import org.apache.tomcat.util.http.Parameters;
 
 import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 public class TomcatInvokeInterceptor implements InstanceMethodsAroundInterceptor {
@@ -64,6 +67,10 @@ public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allAr
         if (TomcatPluginConfig.Plugin.Tomcat.COLLECT_HTTP_PARAMS) {
             collectHttpParam(request, span);
         }
+
+        if (!CollectionUtil.isEmpty(TomcatPluginConfig.Plugin.Http.INCLUDE_HTTP_HEADERS)) {
+            collectHttpHeaders(request, span);
+        }
     }
 
     @Override
@@ -115,4 +122,25 @@ private void collectHttpParam(Request request, AbstractSpan span) {
             Tags.HTTP.PARAMS.set(span, tagValue);
         }
     }
+
+    private void collectHttpHeaders(Request request, AbstractSpan span) {
+        final List<String> headersList = new ArrayList<>(TomcatPluginConfig.Plugin.Http.INCLUDE_HTTP_HEADERS.size());
+        TomcatPluginConfig.Plugin.Http.INCLUDE_HTTP_HEADERS.stream()
+            .filter(headerName -> request.getHeaders(headerName) != null)
+            .forEach(headerName -> {
+                Enumeration<String> headerValues = request.getHeaders(headerName);
+                List<String> valueList = Collections.list(headerValues);
+                if (!CollectionUtil.isEmpty(valueList)) {
+                    headersList.add(headerName + "=" + valueList);
+                }
+            });
+
+        if (!headersList.isEmpty()) {
+            String tagValue = String.join("\n", headersList);
+            tagValue = TomcatPluginConfig.Plugin.Http.HTTP_HEADERS_LENGTH_THRESHOLD > 0 ?
+                StringUtil.cut(tagValue, TomcatPluginConfig.Plugin.Http.HTTP_HEADERS_LENGTH_THRESHOLD) :
+                tagValue;
+            Tags.HTTP.HEADERS.set(span, tagValue);
+        }
+    }
 }

apm-sniffer/apm-sdk-plugin/tomcat-plugin/src/main/java/org/apache/skywalking/apm/plugin/tomcat/TomcatPluginConfig.java

@@ -18,6 +18,7 @@
 
 package org.apache.skywalking.apm.plugin.tomcat;
 
+import java.util.List;
 import org.apache.skywalking.apm.agent.core.boot.PluginConfig;
 
 public class TomcatPluginConfig {
@@ -38,6 +39,19 @@ public static class Http {
              * for the sake of performance
              */
             public static int HTTP_PARAMS_LENGTH_THRESHOLD = 1024;
+
+            /**
+             * When {@link Http#INCLUDE_HTTP_HEADERS} declares header names, this threshold controls the length
+             * limitation of all header values. use negative values to keep and send the complete headers.
+             * Note. this config item is added for the sake of performance.
+             */
+            public static int HTTP_HEADERS_LENGTH_THRESHOLD = 2048;
+
+            /**
+             * It controls what header data should be collected, this is for security purpose, values must be in lower
+             * case. Shares the {@code plugin.http.include_http_headers} config key with the other HTTP server plugins.
+             */
+            public static List<String> INCLUDE_HTTP_HEADERS;
         }
     }
 }