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bytekit

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Java Bytecode Kit

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## ByteKit
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bytecode kit for java.

## 目标

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
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
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

## 对比

| 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` |
| ---- | ---- |---- | :----: |:----: | :----: |:----: | :----: |
| ByteKit | `@AtEnter` `@AtExit` `@AtExceptionExit` `@AtFieldAccess` `@AtInvoke` `@AtInvokeException` `@AtLine` `@AtSyncEnter` `@AtSyncExit` `@AtThrow`| this/args/return/throw field locals 子调用入参/返回值/子调用异常 line number|✓|✓|✓|✓|✓|
| ByteBuddy | `@OnMethodEnter` `@OnMethodExit` `@OnMethodExit#onThrowable()`| this/args/return/throw field locals|✓|✗|✓|✓|✓|
| 传统AOP | `Enter` `Exit` `Exception` |this/args/return/throw|✗|✗|✗|✗|✗

## 特性

### 1. 丰富的注入点支持

* `@AtEnter` 函数入口
* `@AtExit` 函数退出
* `@AtExceptionExit` 函数抛出异常
* `@AtFieldAccess` 访问field
* `@AtInvoke` 在method里的子函数调用
* `@AtInvokeException` 在method里的子函数调用抛出异常
* `@AtLine` 在指定行号
* `@AtSyncEnter` 进入同步块，比如`synchronized`块
* `@AtSyncExit` 退出同步块
* `@AtThrow`  代码里显式`throw`异常点

### 2. 动态的Binding

* `@Binding.This` this对象
* `@Binding.Class` Class对象
* `@Binding.Method` 函数调用的 Method 对象
* `@Binding.MethodName` 函数的名字
* `@Binding.MethodDesc` 函数的desc
* `@Binding.Return` 函数调用的返回值
* `@Binding.Throwable` 函数里抛出的异常
* `@Binding.Args` 函数调用的入参
* `@Binding.ArgNames` 函数调用的入参的名字

* `@Binding.LocalVars` 局部变量
* `@Binding.LocalVarNames` 局部变量的名字
* `@Binding.Field` field对象属性字段

* `@Binding.InvokeArgs` method里的子函数调用的入参
* `@Binding.InvokeReturn` method里的子函数调用的返回值
* `@Binding.InvokeMethodName` method里的子函数调用的名字
* `@Binding.InvokeMethodOwner`  method里的子函数调用的类名
* `@Binding.InvokeMethodDeclaration` method里的子函数调用的desc

* `@Binding.Line` 行号
* `@Binding.Monitor` 同步块里监控的对象

### 3. 可编程的异常处理

* `@ExceptionHandler` 在插入的增强代码，可以用`try/catch`块包围起来

### 4. inline支持

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。

### 5. invokeOrigin 技术

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？

比如有一个 hello() 函数：

```java
    public String hello(String str) {
        return "hello " + str;
    }
```

我们想对它做增强，那么可以编写下面的代码：

```java
    public String hello(String str) {
        System.out.println("before");
        Object value = InstrumentApi.invokeOrigin();
        System.out.println("after, result: " + value);
        return object;
    }
```

增强后的结果是：

```java
    public String hello(String str) {
        System.out.println("before");
        Object value = "hello " + str;
        System.out.println("after, result: " + value);
        return object;
    }
```

**这种方式可以随意插入代码，非常灵活。**

参考增强Dubbo Filter的示例： [[查看源文件](bytekit-core/src/test/java/com/alibaba/bytekit/asm/inst/DubboFilter_APM.java)]

## 示例

以`ByteKitDemo.java`为例说明，[[查看源文件](bytekit-core/src/test/java/com/example/ByteKitDemo.java)]。

### 1. 定义注入点和Binding数据

* 在下面的 SampleInterceptor 时定义了要注入 `@AtEnter`/`@AtExit`/`@AtExceptionExit`三个地方，
* 用`@Binding`绑定了不同的数据
* 在`@AtEnter`里配置了 `inline = true`，则说明插入的`SampleInterceptor#atEnter`函数本身会被inline掉
* 配置了 `suppress = RuntimeException.class` 和 `suppressHandler = PrintExceptionSuppressHandler.class`，说明插入的代码会被 `try/catch` 包围

```java
    public static class SampleInterceptor {

@AtEnter(inline = true, suppress = RuntimeException.class, suppressHandler = PrintExceptionSuppressHandler.class)
        public static void atEnter(@Binding.This Object object, 
                @Binding.Class Object clazz,
                @Binding.Args Object[] args, 
                @Binding.MethodName String methodName,
                @Binding.MethodDesc String methodDesc) {
            System.out.println("atEnter, args[0]: " + args[0]);
        }

@AtExit(inline = true)
        public static void atExit(@Binding.Return Object returnObject) {
            System.out.println("atExit, returnObject: " + returnObject);
        }

@AtExceptionExit(inline = true, onException = RuntimeException.class)
        public static void atExceptionExit(@Binding.Throwable RuntimeException ex,
                @Binding.Field(name = "exceptionCount") int exceptionCount) {
            System.out.println("atExceptionExit, ex: " + ex.getMessage() + ", field exceptionCount: " + exceptionCount);
        }
    }
```

### 2. @ExceptionHandler

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

```java
    public static class PrintExceptionSuppressHandler {

@ExceptionHandler(inline = true)
        public static void onSuppress(@Binding.Throwable Throwable e, @Binding.Class Object clazz) {
            System.out.println("exception handler: " + clazz);
            e.printStackTrace();
        }
    }
```

### 3. 查看反编译结果

原始的Sample类是：

```java
    public static class Sample {
        private int exceptionCount = 0;

public String hello(String str, boolean exception) {
            if (exception) {
                exceptionCount++;
                throw new RuntimeException("test exception, str: " + str);
            }
            return "hello " + str;
        }
    }
```

增强后的字节码，再反编译：

```java
package com.example;

public static class ByteKitDemo.Sample {
    private int exceptionCount = 0;

public String hello(String string, boolean bl) {
 try {
 String string2 = "(Ljava/lang/String;Z)Ljava/lang/String;";
 String string3 = "hello";
 Object[] arrobject = new Object[]{string, new Boolean(bl)};
 Class<ByteKitDemo.Sample> class_ = ByteKitDemo.Sample.class;
 ByteKitDemo.Sample sample = this;
 System.out.println("atEnter, args[0]: " + arrobject[0]);
 }
 catch (RuntimeException runtimeException) {
 Class<ByteKitDemo.Sample> class_ = ByteKitDemo.Sample.class;
 RuntimeException runtimeException2 = runtimeException;
 System.out.println("exception handler: " + class_);
 runtimeException2.printStackTrace();
 }
 try {
 String string4;
 void str;
 void exception;
 if (exception != false) {
 ++this.exceptionCount;
 throw new RuntimeException("test exception, str: " + (String)str);
 }
 String string5 = string4 = "hello " + (String)str;
 System.out.println("atExit, returnObject: " + string5);
 return string4;
 }
 catch (RuntimeException runtimeException) {
 int n = this.exceptionCount;
 RuntimeException runtimeException3 = runtimeException;
 System.out.println("atExceptionExit, ex: " + runtimeException3.getMessage() + ", field exceptionCount: " + n);
 throw runtimeException;
 }
 }
}
```

## 开发相关

deploy到远程仓库：

```bash
mvn clean deploy -DskipTests -P release
```

## License
Apache License V2

bytekit

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