源码解读-Agent 插件体系
SkyWalkingAgent.Transformer#transform方法
private static class Transformer implements AgentBuilder.Transformer {
private PluginFinder pluginFinder;
Transformer(PluginFinder pluginFinder) {
this.pluginFinder = pluginFinder;
}
@Override
public DynamicType.Builder<?> transform(final DynamicType.Builder<?> builder,
final TypeDescription typeDescription,
final ClassLoader classLoader,
final JavaModule module) {
List<AbstractClassEnhancePluginDefine> pluginDefines = pluginFinder.find(typeDescription);
if (pluginDefines.size() > 0) {
DynamicType.Builder<?> newBuilder = builder;
EnhanceContext context = new EnhanceContext();
for (AbstractClassEnhancePluginDefine define : pluginDefines) {
DynamicType.Builder<?> possibleNewBuilder = define.define(
typeDescription, newBuilder, classLoader, context);
if (possibleNewBuilder != null) {
newBuilder = possibleNewBuilder;
}
}
if (context.isEnhanced()) {
LOGGER.debug("Finish the prepare stage for {}.", typeDescription.getName());
}
return newBuilder;
}
LOGGER.debug("Matched class {}, but ignore by finding mechanism.", typeDescription.getTypeName());
return builder;
}
}
插件结构（以dubbo-2.7.x-plugin为例）
DubboInstrumentation 代码解析
/**
* 任何XxxInstrumentation 用于定义插件拦截点的
* 拦截点：指定类的指定方法（实例方法、构造方法、静态方法）
* 一个Instrumentation 只能拦截一个类，即只能有一个enhanceClass，但是可以拦截这个类里面的多个方法，即getInstanceMethodsInterceptPoints()中可以new 多个InstanceMethodsInterceptPoint()
*/
public class DubboInstrumentation extends ClassInstanceMethodsEnhancePluginDefine {
private static final String ENHANCE_CLASS = "org.apache.dubbo.monitor.support.MonitorFilter";
private static final String INTERCEPT_CLASS = "org.apache.skywalking.apm.plugin.asf.dubbo.DubboInterceptor";
/**
* 指定插件要拦截的类
*/
@Override
protected ClassMatch enhanceClass() {
return NameMatch.byName(ENHANCE_CLASS);
}
/**
* 指定插件要拦截的方法，不拦截返回null
*/
@Override
public ConstructorInterceptPoint[] getConstructorsInterceptPoints() {
return null;
}
/**
* 指定插件要拦截的实例方法（同样会有静态方法、构造方法，最后会总结）
*/
@Override
public InstanceMethodsInterceptPoint[] getInstanceMethodsInterceptPoints() {
return new InstanceMethodsInterceptPoint[]{
new InstanceMethodsInterceptPoint() {
/**
* 返回要拦截的方法名
*/
@Override
public ElementMatcher<MethodDescription> getMethodsMatcher() {
return named("invoke");
}
/**
* 指定拦截器全类名，用于拦截到指定方法之后做具体操作的
*/
@Override
public String getMethodsInterceptor() {
//详见1.2DubboInterceptor
return INTERCEPT_CLASS;
}
/**
* 指定是否需要在拦截的时候对原方法参数进行修改
*/
@Override
public boolean isOverrideArgs() {
return false;
}
}
};
}
}
DubboInterceptor
// spring AOP 切面时，@Around注解，方法前后
public class DubboInterceptor implements InstanceMethodsAroundInterceptor {
public static final String ARGUMENTS = "arguments";
/**
* <h2>Consumer:</h2> The serialized trace context data will
* inject to the {@link RpcContext#attachments} for transport to provider side.
* <p>
* <h2>Provider:</h2> The serialized trace context data will extract from
* {@link RpcContext#attachments}. current trace segment will ref if the serialize context data is not null.
*/
//原方法调用前
@Override
public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes,
MethodInterceptResult result) throws Throwable {
Invoker invoker = (Invoker) allArguments[0];
Invocation invocation = (Invocation) allArguments[1];
RpcContext rpcContext = RpcContext.getContext();
boolean isConsumer = rpcContext.isConsumerSide();
URL requestURL = invoker.getUrl();
AbstractSpan span;
final String host = requestURL.getHost();
final int port = requestURL.getPort();
boolean needCollectArguments;
int argumentsLengthThreshold;
if (isConsumer) {
final ContextCarrier contextCarrier = new ContextCarrier();
span = ContextManager.createExitSpan(generateOperationName(requestURL, invocation), contextCarrier, host + ":" + port);
//invocation.getAttachments().put("contextData", contextDataStr);
//@see https://github.com/alibaba/dubbo/blob/dubbo-2.5.3/dubbo-rpc/dubbo-rpc-api/src/main/java/com/alibaba/dubbo/rpc/RpcInvocation.java#L154-L161
CarrierItem next = contextCarrier.items();
while (next.hasNext()) {
next = next.next();
rpcContext.getAttachments().put(next.getHeadKey(), next.getHeadValue());
if (invocation.getAttachments().containsKey(next.getHeadKey())) {
invocation.getAttachments().remove(next.getHeadKey());
}
}
needCollectArguments = DubboPluginConfig.Plugin.Dubbo.COLLECT_CONSUMER_ARGUMENTS;
argumentsLengthThreshold = DubboPluginConfig.Plugin.Dubbo.CONSUMER_ARGUMENTS_LENGTH_THRESHOLD;
} else {
ContextCarrier contextCarrier = new ContextCarrier();
CarrierItem next = contextCarrier.items();
while (next.hasNext()) {
next = next.next();
next.setHeadValue(rpcContext.getAttachment(next.getHeadKey()));
}
span = ContextManager.createEntrySpan(generateOperationName(requestURL, invocation), contextCarrier);
span.setPeer(rpcContext.getRemoteAddressString());
needCollectArguments = DubboPluginConfig.Plugin.Dubbo.COLLECT_PROVIDER_ARGUMENTS;
argumentsLengthThreshold = DubboPluginConfig.Plugin.Dubbo.PROVIDER_ARGUMENTS_LENGTH_THRESHOLD;
}
Tags.URL.set(span, generateRequestURL(requestURL, invocation));
collectArguments(needCollectArguments, argumentsLengthThreshold, span, invocation);
span.setComponent(ComponentsDefine.DUBBO);
SpanLayer.asRPCFramework(span);
}
//调用后
@Override
public Object afterMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes,
Object ret) throws Throwable {
Result result = (Result) ret;
if (result != null && result.getException() != null) {
dealException(result.getException());
}
ContextManager.stopSpan();
return ret;
}
//调用异常时
@Override
public void handleMethodException(EnhancedInstance objInst, Method method, Object[] allArguments,
Class<?>[] argumentsTypes, Throwable t) {
dealException(t);
}
/**
* Log the throwable, which occurs in Dubbo RPC service.
*/
private void dealException(Throwable throwable) {
AbstractSpan span = ContextManager.activeSpan();
span.log(throwable);
}
/**
* Format operation name. e.g. org.apache.skywalking.apm.plugin.test.Test.test(String)
*
* @return operation name.
*/
private String generateOperationName(URL requestURL, Invocation invocation) {
StringBuilder operationName = new StringBuilder();
operationName.append(requestURL.getPath());
operationName.append("." + invocation.getMethodName() + "(");
for (Class<?> classes : invocation.getParameterTypes()) {
operationName.append(classes.getSimpleName() + ",");
}
if (invocation.getParameterTypes().length > 0) {
operationName.delete(operationName.length() - 1, operationName.length());
}
operationName.append(")");
return operationName.toString();
}
/**
* Format request url. e.g. dubbo://127.0.0.1:20880/org.apache.skywalking.apm.plugin.test.Test.test(String).
*
* @return request url.
*/
private String generateRequestURL(URL url, Invocation invocation) {
StringBuilder requestURL = new StringBuilder();
requestURL.append(url.getProtocol() + "://");
requestURL.append(url.getHost());
requestURL.append(":" + url.getPort() + "/");
requestURL.append(generateOperationName(url, invocation));
return requestURL.toString();
}
private void collectArguments(boolean needCollectArguments, int argumentsLengthThreshold, AbstractSpan span, Invocation invocation) {
if (needCollectArguments && argumentsLengthThreshold > 0) {
Object[] parameters = invocation.getArguments();
if (parameters != null && parameters.length > 0) {
StringBuilder stringBuilder = new StringBuilder();
boolean first = true;
for (Object parameter : parameters) {
if (!first) {
stringBuilder.append(",");
}
stringBuilder.append(parameter);
if (stringBuilder.length() > argumentsLengthThreshold) {
stringBuilder.append("...");
break;
}
first = false;
}
span.tag(ARGUMENTS, stringBuilder.toString());
}
}
}
}
总结一下
拦截实例方法
XxxImplInstrumentation 继承 ClassInstanceMethodsEnhancePluginDefine
重写 getInstanceMethodsInterceptPoints（）来定义实例方法拦截点
XxxInterceptor implements InstanceMethodsAroundInterceptor
重写 beforeMethod afterMethod handleMethodException 方法实现拦截增强
拦截构造方法
XxxImplInstrumentation 继承 ClassInstanceMethodsEnhancePluginDefine
重写 getConstructorsInterceptPoints（）来定义构造方法拦截点
XxxInterceptor implements InstanceConstructorInterceptor
重写 onConstruct 方法实现拦截增强
拦截静态方法
XxxImplInstrumentation 继承 ClassStaticMethodsEnhancePluginDefine
重写 getStaticMethodsInterceptPoints（）来定义静态方法拦截点
XxxInterceptor implements StaticMethodsAroundInterceptor
重写 beforeMethod afterMethod handleMethodException 方法实现拦截增强
对于实例方法和静态方法拦截点里的三个接口
getMethodsMatcher() 定义拦截哪个方法
getMethodsInterceptor() 定义拦截到方法之后要使用那个拦截器
isOverrideArgs() 指定在拦截器工作的时候是否可以对原方法入参进行修改
源码解读-WitnessClass 机制
AbstractClassEnhancePluginDefine#witnessClasses（）
AbstractClassEnhancePluginDefine是所有插件的父类
/*
* Witness classname。为什么需要Witness classname？
* 比如：一个库存在两个发行的版本（例如1.0、2.0），
* 它们包含相同的目标类，但是由于版本迭代器的缘故，
* 它们可能具有相同的名称，但方法不同，或者方法参数列表不同。
* 因此，如果我要针对特定的版本（例如1.0），显然版本号没法判断；
* 这时需要“WitnessClasses”。您可以仅在此特定发行版本中添加任何类
* （类似于 com.company.1.x.A，仅在1.0中），您可以实现目标。
*/
protected String[] witnessClasses() {
//数组的判断逻辑是 && ，有多个类时，必须全部满足，才可以使用。
return new String[] {};
}
示例
mysql5.x
public class Constants {
public static final String WITNESS_MYSQL_5X_CLASS = "com.mysql.jdbc.ConnectionImpl";
}
mysql6.x
public class Constants {
public static final String WITNESS_MYSQL_6X_CLASS = "com.mysql.cj.api.MysqlConnection";
}
mysql8.x
public class Constants {
public static final String WITNESS_MYSQL_8X_CLASS = "com.mysql.cj.interceptors.QueryInterceptor";
}
解决了什么问题
解决了 我们拿不到业务系统所有用的组件版本号时，可以准确匹配所使用的agent增强插件。
