feign 获取请求真实目的ip地址

需求

最近小编的项目中出现了很多feign 调用出现 Read Time out 的异常，但因为没有集成链路追踪的第三方框架，查不到原因。所以想到打印请求的ip地址，判断是指定的服务器出现的问题还是所有服务器都有这个问题，但是feign 打印异常日志不会显示目的端地址，这就很难受了没办法只能自己改装下

大致想法

需要改装肯定需要知道feign 具体请求调用的源码，大致需要知道下面几个问题

• feign 集成了ribbon 如何在负载均衡之后获取真实的ip地址
• feign 实际请求 http 源码在哪
• 能否替换 feign http 请求的组件

源码解析

之前小编有两篇文章分析过 feign相关的源码

自定义 feign 调用实现 hystrix 超时、异常熔断
Feign 集成 Hystrix实现不同的调用接口不同的设置

这其中有个关键的源码位置在于 InvocationHandler 的 invoke 方法，在feign 组件中大致有两个类实现了此接口
FeignInvocationHandler
HystrixInvocationHandler
如果 项目中使用了 Hystrix 那么会用到HystrixInvocationHandler那个，否则一般是FeignInvocationHandler（自定义组件的除外）
那么此时只需要在invoke 方法中打个断点就行

此时跟踪到 feign.SynchronousMethodHandler#executeAndDecode

Object executeAndDecode(RequestTemplate template) throws Throwable {
    Request request = targetRequest(template);
	.......
    Response response;
    long start = System.nanoTime();
    try {
      // 真正执行请求 
      response = client.execute(request, options);
      
      response.toBuilder().request(request).build();
    } catch (IOException e) {
      ....
      throw errorExecuting(request, e);
    }
    .....
  }

通过debug就知道这个 client 是 LoadBalancerFeignClient
org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient#execute

public Response execute(Request request, Request.Options options) throws IOException {
		try {
			URI asUri = URI.create(request.url());
			String clientName = asUri.getHost();
			URI uriWithoutHost = cleanUrl(request.url(), clientName);
			
			// 封装 ribbon 请求组件
			FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
					this.delegate, request, uriWithoutHost);

			IClientConfig requestConfig = getClientConfig(options, clientName);
			// 这行是关键
			return 
					// 获取 FeignLoadBalancer
					lbClient(clientName)
					// 负载之后请求真实的url
					// com.netflix.client.AbstractLoadBalancerAwareClient#executeWithLoadBalancer(....)
					.executeWithLoadBalancer(ribbonRequest,requestConfig)
					.toResponse();
		}
		catch (ClientException e) {
			....
			throw new RuntimeException(e);
		}
	}

com.netflix.client.AbstractLoadBalancerAwareClient#executeWithLoadBalancer(....)

public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
        LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);

        try {
        	// 在com.netflix.loadbalancer.reactive.LoadBalancerCommand#submit 中会根据 负载均衡算法之后获取到真实的ip地址

            return command.submit(
                new ServerOperation<T>() {
                    @Override
                    // 传入的server 就是真实的ip
                    public Observable<T> call(Server server) {

                        URI finalUri = reconstructURIWithServer(server, request.getUri());
                        // 路径替换把原本 http://client-name/xxxx 地址改为 http://127.0.0.1:9090/xxxx
                        S requestForServer = (S) request.replaceUri(finalUri);
                        try {
                        	// 请求父类中的 execute 方法，也就是 上面 lbClient(clientName) 返回的 FeignLoadBalancer
                            return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                        } 
                        catch (Exception e) {
                            return Observable.error(e);
                        }
                    }
                })
                .toBlocking()
                .single();
        } catch (Exception e) {
            Throwable t = e.getCause();
            if (t instanceof ClientException) {
                throw (ClientException) t;
            } else {
                throw new ClientException(e);
            }
        }
        
    }

org.springframework.cloud.openfeign.ribbon.FeignLoadBalancer#execute

@Override
	public RibbonResponse execute(RibbonRequest request, IClientConfig configOverride)
			throws IOException {
		Request.Options options;
		.....
		// 这里的 request 就是 `org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient#execute` 
		// 封装的FeignLoadBalancer.RibbonRequest
		// request.client() 返回就是 feign.Client.Default
		
		Response response = request.client().execute(request.toRequest(), options);
		return new RibbonResponse(request.getUri(), response);
	}

feign.Client.Default#execute

 @Override
    public Response execute(Request request, Options options) throws IOException {
      HttpURLConnection connection = convertAndSend(request, options);
      return convertResponse(connection).toBuilder().request(request).build();
    }

这里的request 中 url 就是真实的url资源路径了
现在屡屡逻辑

org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient和feign.Client.Default
都实现了 feign.Client 接口，但是 LoadBalancerFeignClient 实际上调用的还是 feign.Client.Default，无非做了自己处理（负载），有些类似于静态代理

那么上面的问题就只剩下能否替换的问题了

@Configuration
class DefaultFeignLoadBalancedConfiguration {
	@Bean
	@ConditionalOnMissingBean
	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
							  SpringClientFactory clientFactory) {
		return new LoadBalancerFeignClient(new Client.Default(null, null),
				cachingFactory, clientFactory);
	}
}

这就不需要我来过多解释了，我们只需要自定义一个 LoadBalancerFeignClient 或者 实现Client的类就行 然后注入就行

实现代码

我选择的是 自定义实现一个 Client,去继承 feign.Client.Default

@Slf4j
public class InFeignClient extends Client.Default {
    /**
     */
    public InFeignClient(SSLSocketFactory sslContextFactory, HostnameVerifier hostnameVerifier) {
        super(sslContextFactory, hostnameVerifier);
    }

    @Override
    public Response execute(Request request, Request.Options options) throws IOException {
        try {
            return super.execute(request, options);
        } catch (IOException e) {
            log.warn(" 请求 {} 异常 ======> {}", request.url(), e.getMessage());
            throw e;
        }
    }
}

然后将这个类替换

@Component
public class RestConfig {

    public CachingSpringLoadBalancerFactory cachingLBClientFactory(
            SpringClientFactory factory) {
        return new CachingSpringLoadBalancerFactory(factory);
    }

    @Bean
    public Client feignClient(SpringClientFactory clientFactory) {
        CachingSpringLoadBalancerFactory bean = cachingLBClientFactory(clientFactory);
        return new LoadBalancerFeignClient(new InFeignClient(null, null), bean, clientFactory);
    }
    
}