Will it blend ? Java agents and OSGi Slides revision : 20190923- ea 7 - - PowerPoint PPT Presentation

Will it blend? Java agents and OSGi

Slides revision: 20190923-ea7c311

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Welcome

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About me

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Outline

Quick demo Java agents primer Usage scenarios OSGi integration Integration testing Testing demo

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Quick demo

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Java agents primer

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Java instrumentation APIs

java.lang.instrument Javadoc, Java SE 8 Provides services that allow Java programming language agents to instrument programs running

• n the JVM.

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Static agents

# loaded at application startup $ java -javaagent:agent.jar -jar app.jar Premain-Class: org.example.my.Agent import java.lang.instrument.*; public class Agent { public static void premain(String args,⏎ Instrumentation inst) { inst.addTransformer(new ClassFileTransformer() { /* implementation elided */ }); } }

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Dynamic agents

// dynamically attached to a running JVM VirtualMachine vm = VirtualMachine.attach(vmPid); vm.loadAgent(agentFilePath); vm.detach(); Agent-Class: org.example.my.Agent import java.lang.instrument.*; public class Agent { public static void agentmain(String args,⏎ Instrumentation inst) { inst.addTransformer(new ClassFileTransformer() { /* implementation elided */ }); } }

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Class transformation

public interface ClassFileTransformer { byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException; }

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Java bytecode

public static void main(java.lang.String[]); Code: 0: getstatic #16⏎ // Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #22⏎ // String Hello, world 5: invokevirtual #24⏎ // Method java/io/PrintStream.println:(Ljava/lang/String; 8: return

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Bytecode generation libraries

Apache Commons BCEL ByteBuddy CGLib Javassist ObjectWeb ASM

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Bytecode generation with Javassist

public byte[] transform(...) throws ... { ClassPool classPool = ClassPool.getDefault(); CtMethod method = classPool.getMethod(⏎ Descriptor.toJavaName(className), "main"); method.insertAfter("System.out.println " + ⏎ "(\"... hello yourself!...\");"); byte[] newClass = method.getDeclaringClass()⏎ .toBytecode(); method.getDeclaringClass().detach(); return newClass; }

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Usage scenarios

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When to use agents

• 1. Code outside of your control
• 2. No better platform facilities exist
• 3. (Usually) Cross-cutting concerns

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Agent examples

• 1. Monitoring (logging, tracing, error reporting ...)
• 2. Profiling
• 3. Debugging
• 4. Mocking libraries
• 5. Code reload/Hot swap

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OSGi integration

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Mind the classloader

• ClassPool defaultPool = ClassPool.getDefault();
• CtClass cc = defaultPool.get(⏎
• Descriptor.toJavaName(className));

+ ClassPool classPool = new ClassPool(true); + classPool.appendClassPath(new LoaderClassPath(loader)); + classPool.insertClassPath(new ByteArrayClassPath(⏎ + Descriptor.toJavaName(className), classfileBuffer));

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Carefully manage dependencies

New requirements typically fail since they are not defined by the bundle Bundles can be processed at build-time Patching Import-Package DynamicImport-Package: *

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OSGi alternatives - Weaving Hooks

 Simplified deployment - OSGi bundle  Simple registration via OSGi whiteboard  Handles updated bundle package imports  OSGi-only solution

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Integration testing

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Packaging challenges

Java agents... must be packaged as a Jar file, with a specific manifest not trivially attached to the current process usually a one-way deal, no support for rolling back class changes

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Custom test launchers

"unit" tests launch Java process with custom agents attached require separate communication channel with java agent no out-of-the-box support for code coverage and

• ther tools

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Bootstrapping the test

// 1. which java? String javaHome = System.getProperty("java.home"); Path javaExe = Paths.get(javaHome, "bin", "java"); // 2. which jar? String ja = findAgentJar(); // 3. which classpath? String classPath = buildClassPath(); // 4. launch ProcessBuilder pb = new ProcessBuilder( javaExe.toString(), "-javaagent:" + ja, "-cp", classPath, TestApplication.class.getName() );

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Verifying side effects

Path stdout = Paths.get("target", "stdout.txt"); Path stderr = Paths.get("target", "stderr.txt"); pb.redirectInput(Redirect.INHERIT); pb.redirectOutput(stdout.toFile()); pb.redirectError(stderr.toFile());

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Adding code coverage

ProcessBuilder pb = new ProcessBuilder( javaExe.toString(), "-javaagent:" + codeCoverageAgent, "-javaagent:" + ja, "-cp", classPath, TestApplication.class.getName() );

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OSGi integration testing

// note - must run in a forked container @RunWith(PaxExam.class) public class OsgiIT { @Configuration public Option[] config() throws IOException { return options( junitBundles(), ⏎ vmOption("-javaagent:" + agentJar) ); } @Test public void callTimesOut() throws IOException { assertTrue(agentReallyWorks()); } }

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Testing demo

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Resources

https://docs.oracle.com/javase/8/docs/api/java/lang/instrum summary.html https://www.javassist.org/ https://sling.apache.org/documentation/bundles/connectio agent.html

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