Logging custom facade (elastic#2390)

Author: eyalkoren

CHANGELOG.asciidoc

@@ -28,11 +28,13 @@ endif::[]
 * Exceptions that are logged using the fatal log level are now captured (log4j2 only) - {pull}2377[#2377]
 * Replaced `authorization` in the default value of `sanitize_field_names` with `*auth*` - {pull}2326[#2326]
 * Unsampled transactions are dropped and not sent to the APM-Server if the APM-Server version is 8.0+ - {pull}2329[#2329]
+* Adding agent logging capabilities to our SDK, making it available for external plugins - {pull}2390[#2390]
 
 [float]
 ===== Bug fixes
 * Fix runtime attach with some docker images - {pull}2385[#2385]
 * Restore dynamic capability to `log_level` config for plugin loggers - {pull}2384[#2384]
+* Fix slf4j-related `LinkageError` - {pull}2390[#2390]
 
 [[release-notes-1.x]]
 === Java Agent version 1.x

NOTICE

@@ -1,5 +1,5 @@
 Elastic APM Java Agent
-Copyright 2018-2019 Elasticsearch B.V.
+Copyright 2018-2022 Elasticsearch B.V.
 
 ###############################################################################
 
@@ -14,6 +14,7 @@ following sources:
  - JCTools
  - https://github.com/jvm-profiling-tools/async-profiler
  - https://github.com/real-logic/agrona
+ - Apache Log4j 2 - https://logging.apache.org/log4j/2.x/license.html
 
 ------------------------------------------------------------------------------
 stagemonitor NOTICE
@@ -130,6 +131,27 @@ information: Portions Copyright [yyyy] [name of copyright owner]
 
 CDDL HEADER END
 
+------------------------------------------------------------------------------
+Apache Log4j NOTICE
+
+Apache Log4j
+Copyright 1999-2021 Apache Software Foundation
+
+This product includes software developed at
+The Apache Software Foundation (http://www.apache.org/).
+
+ResolverUtil.java
+Copyright 2005-2006 Tim Fennell
+
+Dumbster SMTP test server
+Copyright 2004 Jason Paul Kitchen
+
+TypeUtil.java
+Copyright 2002-2012 Ramnivas Laddad, Juergen Hoeller, Chris Beams
+
+picocli (http://picocli.info)
+Copyright 2017 Remko Popma
+
 ------------------------------------------------------------------------------
 
                                  Apache License
@@ -369,7 +391,8 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 ###############################################################################
 
-This product includes code from slf4j, under MIT License
+This product includes code from slf4j, under MIT License.
+It also includes code that is based on some slf4j interfaces.
 
 Copyright (c) 2004-2011 QOS.ch
 All rights reserved.

apm-agent-core/pom.xml

@@ -69,6 +69,11 @@
             <artifactId>log4j-slf4j-impl</artifactId>
             <version>${version.log4j}</version>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>${version.slf4j}</version>
+        </dependency>
         <dependency>
             <groupId>co.elastic.logging</groupId>
             <artifactId>log4j2-ecs-layout</artifactId>

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/ElasticApmAgent.java

@@ -58,8 +58,8 @@
 import net.bytebuddy.matcher.ElementMatchers;
 import net.bytebuddy.pool.TypePool;
 import net.bytebuddy.utility.JavaModule;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 import org.stagemonitor.configuration.ConfigurationOption;
 import org.stagemonitor.configuration.source.ConfigurationSource;
 
@@ -526,12 +526,9 @@ private static void validateAdviceReturnAndParameterTypes(MethodDescription.InDe
         String adviceMethod = advice.getInternalName();
         try {
             checkNotAgentType(advice.getReturnType(), "return type", adviceClass, adviceMethod);
-            checkNotSlf4jType(advice.getReturnType(), "return type", adviceClass, adviceMethod);
 
             for (ParameterDescription.InDefinedShape parameter : advice.getParameters()) {
                 checkNotAgentType(parameter.getType(), "parameter", adviceClass, adviceMethod);
-                checkNotSlf4jType(parameter.getType(), "parameter", adviceClass, adviceMethod);
-
                 AnnotationDescription.Loadable<Advice.Return> returnAnnotation = parameter.getDeclaredAnnotations().ofType(Advice.Return.class);
                 if (returnAnnotation != null && !returnAnnotation.load().readOnly()) {
                     throw new IllegalStateException("Advice parameter must not use '@Advice.Return(readOnly=false)', use @Advice.AssignReturned.ToReturned instead");
@@ -552,15 +549,6 @@ private static void checkNotAgentType(TypeDescription.Generic type, String descr
         }
     }
 
-    private static void checkNotSlf4jType(TypeDescription.Generic type, String description, String adviceClass, String adviceMethod) {
-        // When trying to instrument slf4j classes from the application, advices would instead resolve the types from the agent class loader
-        // This would lead to errors on indy bootstrap, similar to the ones reported at https://github.com/elastic/apm-agent-java/issues/2163
-        String name = type.asRawType().getTypeName();
-        if (name.startsWith("org.slf4j.")) {
-            throw new IllegalStateException(String.format("Advice %s in %s#%s must not reference slf4j types: %s", description, adviceClass, adviceMethod, name));
-        }
-    }
-
     private static MatcherTimer getOrCreateTimer(Class<? extends ElasticApmInstrumentation> adviceClass) {
         final String name = adviceClass.getName();
         MatcherTimer timer = matcherTimers.get(name);

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/IndyBootstrap.java

@@ -27,8 +27,8 @@
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.dynamic.ClassFileLocator;
 import net.bytebuddy.dynamic.loading.ClassInjector;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 import org.stagemonitor.configuration.ConfigurationOptionProvider;
 import org.stagemonitor.util.IOUtils;
 

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/IndyPluginClassLoaderFactory.java

@@ -23,8 +23,8 @@
 import net.bytebuddy.dynamic.ClassFileLocator;
 import net.bytebuddy.matcher.ElementMatcher;
 import net.bytebuddy.pool.TypePool;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 
 import javax.annotation.Nullable;
 import java.io.IOException;

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/MatcherTimerLifecycleListener.java

@@ -20,8 +20,8 @@
 
 import co.elastic.apm.agent.bci.bytebuddy.MatcherTimer;
 import co.elastic.apm.agent.context.AbstractLifecycleListener;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 
 import java.util.ArrayList;
 import java.util.Collections;

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/bytebuddy/CustomElementMatchers.java

@@ -27,8 +27,8 @@
 import net.bytebuddy.description.annotation.AnnotationSource;
 import net.bytebuddy.description.method.MethodDescription;
 import net.bytebuddy.matcher.ElementMatcher;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 
 import javax.annotation.Nullable;
 import java.io.File;

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/bytebuddy/ErrorLoggingListener.java

@@ -20,8 +20,8 @@
 
 import net.bytebuddy.agent.builder.AgentBuilder;
 import net.bytebuddy.utility.JavaModule;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import co.elastic.apm.agent.sdk.logging.Logger;
+import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 
 public class ErrorLoggingListener extends AgentBuilder.Listener.Adapter {
 

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/classloading/IndyPluginClassLoader.java

@@ -59,18 +59,16 @@ private static ClassLoader getParent(@Nullable ClassLoader targetClassLoader, Cl
                 agentClassLoader, startsWith("co.elastic.apm.agent").or(startsWith("net.bytebuddy")),
                 targetClassLoader, ElementMatchers.<String>any());
         } else {
-            // in prod, always search in the agent class loader first
-            // this ensures that we're referencing the agent bundled classes in advices rather than the ones form the application
-            // (for example for slf4j, Byte Buddy, or even dependencies that are bundled in external plugins etc.)
+            // In prod, always search in the agent class loader first.
+            // This ensures that we're referencing the agent bundled classes in advices rather than the ones form the application
+            // (for example Byte Buddy, or even dependencies that are bundled in external plugins etc.)
             // However, we need to avoid looking up classes from the agent class loader that we want to instrument.
             // For example, we're instrumenting log4j2 to support ecs_log_reformatting which is also available within the agent class loader.
             // Within the context of an instrumentation plugin, referencing log4j2 should always reference the instrumented types, not the ones shipped with the agent.
             // The list of packages not to load should correspond with matching dependency exclusions from the apm-agent-core in apm-agent-plugins/pom.xml
-            // As we're using slf4j as the logging facade, plugins don't need to refer to the agent-bundled log4j2.
-            // This implies, we can't reference instrumented slf4j classes in plugins, though.
-            // We ensure this by validating that advice method signatures don't contain slf4j classes.
+            // As we're using a custom logging facade, plugins don't need to refer to the agent-bundled log4j2 or slf4j.
             return new DiscriminatingMultiParentClassLoader(
-                agentClassLoader, not(startsWith("org.apache.logging.log4j")),
+                agentClassLoader, not(startsWith("org.apache.logging.log4j").and(not(startsWith("org.slf4j")))),
                 targetClassLoader, ElementMatchers.<String>any());
         }
     }