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@ -0,0 +1,222 @@
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## ByteKit
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## 目标
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1. 之前的Arthas里的字节码增强，是通过asm来处理的，代码逻辑不好修改，理解困难
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1. 基于ASM提供更高层的字节码处理能力，面向诊断/APM领域，不是通用的字节码库
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1. ByteKit期望能提供一套简洁的API，让开发人员可以比较轻松的完成字节码增强
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## 对比
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| 功能 | 函数Enter/Exit注入点 | 绑定数据 | inline | 防止重复增强 | 避免装箱/拆箱开销 |origin调用替换 | `@ExceptionHandler` |
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| ---- | ---- |---- | :----: |:----: | :----: |:----: | :----: |
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| ByteKit | `@AtEnter` <br> `@AtExit` <br>`@AtExceptionExit` <br> `@AtFieldAccess` <br> `@AtInvoke`<br>`@AtInvokeException`<br>`@AtLine`<br>`@AtSyncEnter`<br>`@AtSyncExit`<br>`@AtThrow`| this/args/return/throw<br>field<br>locals<br>子调用入参/返回值/子调用异常<br>line number|✓|✓|✓|✓|✓|
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| ByteBuddy | `OnMethodEnter`<br>`@OnMethodExit`<br> `@OnMethodExit#onThrowable()`| this/args/return/throw<br>field<br>locals|✓|✗|✓|✓|✓|
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| 传统AOP | `Enter`<br>`Exit`<br>`Exception` |this/args/return/throw|✗|✗|✗|✗|✗
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## 特性
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### 1. 丰富的注入点支持
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* `@AtEnter` 函数入口
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* `@AtExit` 函数退出
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* `@AtExceptionExit` 函数抛出异常
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* `@AtFieldAccess` 访问field
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* `@AtInvoke` 在method里的子函数调用
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* `@AtInvokeException` 在method里的子函数调用抛出异常
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* `@AtLine` 在指定行号
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* `@AtSyncEnter` 进入同步块，比如`synchronized`块
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* `@AtSyncExit` 退出同步块
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* `@AtThrow` 代码里显式`throw`异常点
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### 2. 动态的Binding
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* `@Binding.This` this对象
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* `@@Binding.Class` Class对象
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* `@Binding.Method` 函数调用的 Method 对象
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* `@Binding.MethodName` 函数的名字
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* `@Binding.MethodDesc` 函数的desc
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* `@Binding.Return` 函数调用的返回值
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* `@Binding.Throwable` 函数里抛出的异常
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* `@Binding.Args` 函数调用的入参
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* `@Binding.ArgNames` 函数调用的入参的名字
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* `@Binding.LocalVars` 局部变量
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* `@Binding.LocalVarNames` 局部变量的名字
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* `@Binding.Field` field对象属性字段
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* `@Binding.InvokeArgs` method里的子函数调用的入参
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* `@Binding.InvokeReturn` method里的子函数调用的返回值
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* `@Binding.InvokeMethodName` method里的子函数调用的名字
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* `@Binding.InvokeMethodOwner` method里的子函数调用的类名
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* `@Binding.InvokeMethodDeclaration` method里的子函数调用的desc
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* `@Binding.Line` 行号
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* `@Binding.Monitor` 同步块里监控的对象
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### 3. 可编程的异常处理
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* `@ExceptionHandler` 在插入的增强代码，可以用`try/catch`块包围起来
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### 4. inline支持
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增强的代码 和 异常处理代码都可以通过 inline技术内联到原来的类里，达到最理想的增强效果。
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### 5. invokeOrigin 技术
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通常，我们要增强一个类，就想要办法在函数前后插入一个static的回调函数，但这样子局限太大。那么有没有更灵活的方式呢？
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比如有一个 hello() 函数：
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```java
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public String hello(String str) {
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return "hello " + str;
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}
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```
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我们想对它做增强，那么可以编写下面的代码：
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```java
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public String hello(String str) {
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System.out.println("before");
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Object value = InstrumentApi.invokeOrigin();
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System.out.println("after, result: " + value);
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return object;
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}
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```
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增强后的结果是：
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```java
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public String hello(String str) {
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System.out.println("before");
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Object value = "hello " + str;
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System.out.println("after, result: " + value);
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return object;
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}
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```
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**这种方式可以随意插入代码，非常灵活。**
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## 示例
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以`ByteKitDemo.java`为例说明，[[查看源文件](src/test/java/com/example/ByteKitDemo.java)]。
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### 1. 定义注入点和Binding数据
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* 在下面的 SampleInterceptor 时定义了要注入 `@AtEnter`/`@AtExit`/`@AtExceptionExit`三个地方，
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* 用`@Binding`绑定了不同的数据
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* 在`@AtEnter`里配置了 `inline = true`，则说明插入的`SampleInterceptor#atEnter`函数本身会被inline掉
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* 配置了 `suppress = RuntimeException.class` 和 `suppressHandler = PrintExceptionSuppressHandler.class`，说明插入的代码会被 `try/catch` 包围
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```java
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public static class SampleInterceptor {
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@AtEnter(inline = true, suppress = RuntimeException.class, suppressHandler = PrintExceptionSuppressHandler.class)
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public static void atEnter(@Binding.This Object object,
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@Binding.Class Object clazz,
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@Binding.Args Object[] args,
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@Binding.MethodName String methodName,
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@Binding.MethodDesc String methodDesc) {
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System.out.println("atEnter, args[0]: " + args[0]);
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}
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@AtExit(inline = true)
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public static void atExit(@Binding.Return Object returnObject) {
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System.out.println("atExit, returnObject: " + returnObject);
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}
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@AtExceptionExit(inline = true, onException = RuntimeException.class)
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public static void atExceptionExit(@Binding.Throwable RuntimeException ex,
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@Binding.Field(name = "exceptionCount") int exceptionCount) {
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System.out.println("atExceptionExit, ex: " + ex.getMessage() + ", field exceptionCount: " + exceptionCount);
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}
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}
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```
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### 2. @ExceptionHandler
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在上面的 `@AtEnter`配置里，生成的代码会被 try/catch 包围，那么具体的内容是在`PrintExceptionSuppressHandler`里
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```java
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public static class PrintExceptionSuppressHandler {
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@ExceptionHandler(inline = true)
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public static void onSuppress(@Binding.Throwable Throwable e, @Binding.Class Object clazz) {
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System.out.println("exception handler: " + clazz);
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e.printStackTrace();
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}
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}
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```
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### 3. 查看反编译结果
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原始的Sample类是：
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```java
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public static class Sample {
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private int exceptionCount = 0;
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public String hello(String str, boolean exception) {
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if (exception) {
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exceptionCount++;
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throw new RuntimeException("test exception, str: " + str);
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}
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return "hello " + str;
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}
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}
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```
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增强后的字节码，再反编译：
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```java
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package com.example;
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public static class ByteKitDemo.Sample {
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private int exceptionCount = 0;
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public String hello(String string, boolean bl) {
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try {
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String string2 = "(Ljava/lang/String;Z)Ljava/lang/String;";
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String string3 = "hello";
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Object[] arrobject = new Object[]{string, new Boolean(bl)};
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Class<ByteKitDemo.Sample> class_ = ByteKitDemo.Sample.class;
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ByteKitDemo.Sample sample = this;
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System.out.println("atEnter, args[0]: " + arrobject[0]);
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}
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catch (RuntimeException runtimeException) {
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Class<ByteKitDemo.Sample> class_ = ByteKitDemo.Sample.class;
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RuntimeException runtimeException2 = runtimeException;
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System.out.println("exception handler: " + class_);
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runtimeException2.printStackTrace();
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}
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try {
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String string4;
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void str;
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void exception;
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if (exception != false) {
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++this.exceptionCount;
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throw new RuntimeException("test exception, str: " + (String)str);
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}
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String string5 = string4 = "hello " + (String)str;
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System.out.println("atExit, returnObject: " + string5);
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return string4;
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}
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catch (RuntimeException runtimeException) {
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int n = this.exceptionCount;
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RuntimeException runtimeException3 = runtimeException;
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System.out.println("atExceptionExit, ex: " + runtimeException3.getMessage() + ", field exceptionCount: " + n);
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throw runtimeException;
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}
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}
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}
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```
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gongdewei
5 years ago
