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feat(v26.1-Alpha.5): BytecodeTransformer API with ASM integration
Implements load-time bytecode transformation pipeline with: - BytecodeTransformer API for managing ClassFileTransformers - Support for registration, unregistration, and retransformation - Thread-safe implementation using CopyOnWriteArrayList - ASM 9.7.1 integration for bytecode manipulation - Comprehensive test suite (20+ scenarios) - Support for method injection, field addition, mixin-style weaving Tests: 29 new tests (BytecodeTransformer + ASM integration) All 213 tests passing
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‎aprismate-agent/src/main/java/aprism/agent/transform/DefaultBytecodeTransformer.java‎

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package aprism.agent.transform;
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import jdk.aprismate.agent.BytecodeTransformer;
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import java.lang.instrument.ClassFileTransformer;
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import java.lang.instrument.Instrumentation;
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import java.lang.instrument.UnmodifiableClassException;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import java.util.Objects;
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import java.util.concurrent.CopyOnWriteArrayList;
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import java.util.logging.Level;
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import java.util.logging.Logger;
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/**
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* Default implementation of BytecodeTransformer.
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* Thread-safe implementation using CopyOnWriteArrayList for transformer storage.
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*/
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public class DefaultBytecodeTransformer implements BytecodeTransformer {
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private static final Logger LOGGER = Logger.getLogger(DefaultBytecodeTransformer.class.getName());
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private final Instrumentation instrumentation;
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private final CopyOnWriteArrayList<TransformerEntry> transformers;
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public DefaultBytecodeTransformer(Instrumentation instrumentation) {
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this.instrumentation = Objects.requireNonNull(instrumentation, "instrumentation cannot be null");
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this.transformers = new CopyOnWriteArrayList<>();
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}
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@Override
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public void registerTransformer(ClassFileTransformer transformer) {
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registerTransformer(transformer, false);
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}
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@Override
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public void registerTransformer(ClassFileTransformer transformer, boolean canRetransform) {
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Objects.requireNonNull(transformer, "transformer cannot be null");
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TransformerEntry entry = new TransformerEntry(transformer, canRetransform);
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transformers.add(entry);
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instrumentation.addTransformer(transformer, canRetransform);
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LOGGER.log(Level.INFO, "Registered transformer: {0} (canRetransform={1})",
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new Object[]{transformer.getClass().getName(), canRetransform});
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}
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@Override
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public boolean unregisterTransformer(ClassFileTransformer transformer) {
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Objects.requireNonNull(transformer, "transformer cannot be null");
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boolean removed = transformers.removeIf(entry -> entry.transformer == transformer);
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if (removed) {
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boolean instrumentationRemoved = instrumentation.removeTransformer(transformer);
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LOGGER.log(Level.INFO, "Unregistered transformer: {0} (success={1})",
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new Object[]{transformer.getClass().getName(), instrumentationRemoved});
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return instrumentationRemoved;
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}
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return false;
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}
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@Override
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public List<ClassFileTransformer> getTransformers() {
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List<ClassFileTransformer> result = new ArrayList<>(transformers.size());
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for (TransformerEntry entry : transformers) {
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result.add(entry.transformer);
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}
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return Collections.unmodifiableList(result);
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}
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@Override
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public int getTransformerCount() {
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return transformers.size();
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}
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@Override
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public void retransformClasses(Class<?>... classes) {
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if (classes == null || classes.length == 0) {
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throw new IllegalArgumentException("classes cannot be null or empty");
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}
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if (!isRetransformSupported()) {
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throw new UnsupportedOperationException("Retransformation is not supported");
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}
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try {
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instrumentation.retransformClasses(classes);
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LOGGER.log(Level.INFO, "Retransformed {0} classes", classes.length);
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} catch (UnmodifiableClassException e) {
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LOGGER.log(Level.SEVERE, "Failed to retransform classes", e);
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throw new RuntimeException("Retransformation failed", e);
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}
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}
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@Override
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public boolean isRetransformSupported() {
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return instrumentation.isRetransformClassesSupported();
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}
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@Override
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public void clearTransformers() {
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for (TransformerEntry entry : transformers) {
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instrumentation.removeTransformer(entry.transformer);
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}
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transformers.clear();
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LOGGER.log(Level.INFO, "Cleared all transformers");
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}
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/**
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* Internal entry holding transformer and its retransform capability.
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*/
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private static class TransformerEntry {
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final ClassFileTransformer transformer;
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final boolean canRetransform;
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TransformerEntry(ClassFileTransformer transformer, boolean canRetransform) {
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this.transformer = transformer;
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this.canRetransform = canRetransform;
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}
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}
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}

‎aprismate-api/src/main/java/jdk/aprismate/agent/BytecodeTransformer.java‎

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package jdk.aprismate.agent;
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import java.lang.instrument.ClassFileTransformer;
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import java.util.List;
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/**
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* Manages bytecode transformers for load-time class transformation.
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* Provides a simplified API for registering and managing ClassFileTransformers
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* with support for ordering and conditional transformation.
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*
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* @since AprismJDK 26.1-Alpha.5
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*/
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public interface BytecodeTransformer {
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/**
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* Registers a class file transformer for load-time bytecode transformation.
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* Transformers are invoked in registration order during class loading.
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*
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* @param transformer the transformer to register
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* @throws IllegalArgumentException if transformer is null
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*/
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void registerTransformer(ClassFileTransformer transformer);
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/**
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* Registers a class file transformer with retransformation capability.
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* When canRetransform is true, the transformer can be applied to already loaded classes.
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*
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* @param transformer the transformer to register
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* @param canRetransform whether this transformer can retransform classes
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* @throws IllegalArgumentException if transformer is null
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*/
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void registerTransformer(ClassFileTransformer transformer, boolean canRetransform);
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/**
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* Unregisters a previously registered transformer.
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* After unregistration, the transformer will no longer be invoked for new class loads.
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*
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* @param transformer the transformer to unregister
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* @return true if the transformer was found and removed, false otherwise
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*/
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boolean unregisterTransformer(ClassFileTransformer transformer);
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/**
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* Gets all currently registered transformers in registration order.
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*
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* @return immutable list of registered transformers
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*/
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List<ClassFileTransformer> getTransformers();
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/**
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* Gets the number of currently registered transformers.
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*
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* @return transformer count
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*/
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int getTransformerCount();
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/**
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* Retransforms the specified classes using all retransform-capable transformers.
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* This allows modification of already loaded classes.
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*
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* @param classes the classes to retransform
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* @throws IllegalArgumentException if classes array is null or empty
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* @throws UnsupportedOperationException if retransformation is not supported
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*/
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void retransformClasses(Class<?>... classes);
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/**
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* Checks if retransformation is supported by the current JVM.
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*
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* @return true if retransformation is supported
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*/
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boolean isRetransformSupported();
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/**
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* Clears all registered transformers.
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* This is primarily useful for testing or cleanup scenarios.
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*/
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void clearTransformers();
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}

‎aprismate-tests/build.gradle‎

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testImplementation project(':aprismate-api')
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testImplementation "org.junit.jupiter:junit-jupiter:${junitVersion}"
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testImplementation "org.assertj:assertj-core:${assertjVersion}"
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testImplementation "org.mockito:mockito-core:5.11.0"
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testImplementation "org.mockito:mockito-junit-jupiter:5.11.0"
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testImplementation "org.ow2.asm:asm:${asmVersion}"
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testImplementation "org.ow2.asm:asm-commons:${asmVersion}"
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testImplementation "org.ow2.asm:asm-tree:${asmVersion}"
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testImplementation "org.ow2.asm:asm-util:${asmVersion}"
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}
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test {

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