stil WIP

.gitignore

@@ -0,0 +1,35 @@
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### IntelliJ IDEA ###
+.idea/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

README.md

@@ -0,0 +1 @@
+Experiment with java22 and Rust to monitor exceptions in a JVM

pom.xml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.example</groupId>
+    <artifactId>Exceptional</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>22</source>
+                    <target>22</target>
+                    <compilerArgs>--enable-preview</compilerArgs>
+                </configuration>
+            </plugin>
+            <plugin>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.1.0</version>
+                <configuration>
+                    <archive>
+                        <manifestEntries>
+                            <Premain-Class>com.github.shautvast.exceptional.Agent</Premain-Class>
+                            <Can-Retransform-Classes>true</Can-Retransform-Classes>
+                            <Can-Redefine-Classes>true</Can-Redefine-Classes>
+                        </manifestEntries>
+                    </archive>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

src/main/java/com/github/shautvast/exceptional/Agent.java

@@ -0,0 +1,73 @@
+package com.github.shautvast.exceptional;
+
+import java.io.InputStream;
+import java.lang.classfile.*;
+import java.lang.constant.ClassDesc;
+import java.lang.constant.MethodTypeDesc;
+import java.lang.instrument.ClassDefinition;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+
+@SuppressWarnings("ALL")
+public class Agent {
+
+    private static final String MESSAGE = "--- Exceptional agent active";
+
+    public static void premain(String agentArgs, Instrumentation instrumentation) throws Exception {
+        instrumentation.addTransformer(new ClassFileTransformer() {
+            @Override
+            public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
+                return instrumentTheThrowable(className, classfileBuffer);
+            }
+
+            @Override
+            public byte[] transform(Module module, ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
+                return instrumentTheThrowable(className, classfileBuffer);
+            }
+        }, true);
+
+        InputStream stream = Agent.class.getResourceAsStream("/java/lang/Throwable.class");
+        byte[] b = new byte[stream.available()];
+        stream.read(b);
+
+        instrumentation.redefineClasses(new ClassDefinition(Throwable.class, b));
+    }
+
+    private static byte[] instrumentTheThrowable(String className, byte[] classfileBuffer) {
+        if (className.equals("java/lang/Throwable")) {
+
+            ClassFile classFile = ClassFile.of();
+            ClassModel classModel = classFile.parse(classfileBuffer);
+
+            return classFile.build(classModel.thisClass().asSymbol(), classBuilder -> {
+                for (ClassElement ce : classModel) {
+                    if (ce instanceof MethodModel mm) {
+                        String signature = mm.methodName() + "." + mm.methodType().stringValue();
+                        if (signature.equals("<init>.()V")) {
+                            classBuilder.withMethod(mm.methodName(), mm.methodType(), 1,
+                                    methodBuilder -> methodBuilder.withCode(
+                                            codebuilder ->
+//                                                codebuilder.invokeInstruction(Opcode.LDC, );
+                                                codebuilder.invokeInstruction(Opcode.INVOKESTATIC,
+                                                        ClassDesc.of("com.github.shautvast.exceptional.Agent"), "foo",
+                                                        MethodTypeDesc.ofDescriptor("()V"),
+                                                        false)
+                                            ));
+                            continue;
+                        }
+                    }
+                    classBuilder.with(ce);
+                }
+            });
+        } else {
+            return classfileBuffer;
+        }
+    }
+
+    public static void foo() {
+        System.out.println("foo");
+    }
+
+}