关于spring-cloud:SpringCloud升级之路20200x版44避免链路信息丢失做的设计2

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本系列代码地址：https://github.com/JoJoTec/sp…

咱们在这一节咱们将持续解说防止链路信息失落做的设计，次要针对获取到现有 Span 之后，如何保障每个 GlobalFilter 都能放弃链路信息。首先，咱们 自定义 Reactor 的外围 Publisher 即 Mono 和 Flux 的工厂，将链路信息封装进去，保障由这个工厂生成的 Mono 和 Flux，都是只有是这个工厂生成的 Mono 和 Flux 之间无论怎么拼接都会放弃链路信息的：

公共 Subscriber 封装，将 reactor Subscriber 的所有要害接口，都查看以后上下文是否有链路信息，即 Span，如果没有就包裹上，如果有则间接执行即可。

public class TracedCoreSubscriber<T> implements Subscriber<T>{
    private final Subscriber<T> delegate;
    private final Tracer tracer;
    private final CurrentTraceContext currentTraceContext;
    private final Span span;

    TracedCoreSubscriber(Subscriber<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) {
        this.delegate = delegate;
        this.tracer = tracer;
        this.currentTraceContext = currentTraceContext;
        this.span = span;
    }

    @Override
    public void onSubscribe(Subscription s) {executeWithinScope(() -> {delegate.onSubscribe(s);
        });
    }

    @Override
    public void onError(Throwable t) {executeWithinScope(() -> {delegate.onError(t);
        });
    }

    @Override
    public void onComplete() {executeWithinScope(() -> {delegate.onComplete();
        });
    }

    @Override
    public void onNext(T o) {executeWithinScope(() -> {delegate.onNext(o);
        });
    }

    private void executeWithinScope(Runnable runnable) {
        // 如果以后没有链路信息，强制包裹
        if (tracer.currentSpan() == null) {try (CurrentTraceContext.Scope scope = this.currentTraceContext.maybeScope(this.span.context())) {runnable.run();
            }
        } else {
            // 如果以后已有链路信息，则间接执行
            runnable.run();}
    }
}

之后别离定义所有 Flux 的代理 TracedFlux，和所有 Mono 的代理 TracedMono，其实就是在 subscribe 的时候，用 TracedCoreSubscriber 包装传入的 CoreSubscriber：

public class TracedFlux<T> extends Flux<T> {
    private final Flux<T> delegate;
    private final Tracer tracer;
    private final CurrentTraceContext currentTraceContext;
    private final Span span;

    TracedFlux(Flux<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) {
        this.delegate = delegate;
        this.tracer = tracer;
        this.currentTraceContext = currentTraceContext;
        this.span = span;
    }

    @Override
    public void subscribe(CoreSubscriber<? super T> actual) {delegate.subscribe(new TracedCoreSubscriber(actual, tracer, currentTraceContext, span));
    }
}

public class TracedMono<T> extends Mono<T> {
    private final Mono<T> delegate;
    private final Tracer tracer;
    private final CurrentTraceContext currentTraceContext;
    private final Span span;

    TracedMono(Mono<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) {
        this.delegate = delegate;
        this.tracer = tracer;
        this.currentTraceContext = currentTraceContext;
        this.span = span;
    }

    @Override
    public void subscribe(CoreSubscriber<? super T> actual) {delegate.subscribe(new TracedCoreSubscriber(actual, tracer, currentTraceContext, span));
    }
}

定义工厂类，应用申请 ServerWebExchange 和原始 Flux 创立 TracedFlux，以及应用申请 ServerWebExchange 和原始 Mono 创立 TracedMono，并且 Span 是通过 Attributes 获取的，依据前文的源码剖析咱们晓得，这个 Attribute 是通过 TraceWebFilter 放入 Attributes 的。因为咱们只在 GatewayFilter 中应用，肯定在 TraceWebFilter 之后所以这个 Attribute 肯定存在。

@Component
public class TracedPublisherFactory {protected static final String TRACE_REQUEST_ATTR = Span.class.getName();

    @Autowired
    private Tracer tracer;
    @Autowired
    private CurrentTraceContext currentTraceContext;

    public <T> Flux<T> getTracedFlux(Flux<T> publisher, ServerWebExchange exchange) {return new TracedFlux<>(publisher, tracer, currentTraceContext, (Span) exchange.getAttributes().get(TRACE_REQUEST_ATTR));
    }

    public <T> Mono<T> getTracedMono(Mono<T> publisher, ServerWebExchange exchange) {return new TracedMono<>(publisher, tracer, currentTraceContext, (Span) exchange.getAttributes().get(TRACE_REQUEST_ATTR));
    }
}

咱们编写所有咱们前面要实现的 GlobalFilter 的抽象类，这个抽象类的次要性能是：

保障继承这个抽象类的 GlobalFilter 自身以及拼接的链路中，是有链路信息的，其实就是保障它 filter 返回的 Mono<Void> 是由咱们下面实现的 Factory 生成的即可。
不同 GlobalFilter 之间须要排序，有程序的执行，这个通过实现 Ordered 接口即可

package com.github.jojotech.spring.cloud.apigateway.filter;

import com.github.jojotech.spring.cloud.apigateway.common.TraceWebFilterUtil;
import com.github.jojotech.spring.cloud.apigateway.common.TracedPublisherFactory;
import reactor.core.publisher.Mono;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.sleuth.CurrentTraceContext;
import org.springframework.cloud.sleuth.Span;
import org.springframework.cloud.sleuth.Tracer;
import org.springframework.core.Ordered;
import org.springframework.web.server.ServerWebExchange;


/**
 * 所有 filter 的子类
 * 次要保障 span 的完整性，在某些状况下，span 会半途进行，导致日志中没有 traceId 和 spanId
 * 参考：https://github.com/spring-cloud/spring-cloud-sleuth/issues/2004
 */
public abstract class AbstractTracedFilter implements GlobalFilter, Ordered {
    @Autowired
    protected Tracer tracer;
    @Autowired
    protected TracedPublisherFactory tracedPublisherFactory;
    @Autowired
    protected CurrentTraceContext currentTraceContext;

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        Mono<Void> traced;
        if (tracer.currentSpan() == null) {
            try (CurrentTraceContext.Scope scope = this.currentTraceContext
                    .maybeScope(((Span) exchange.getAttributes().get(TraceWebFilterUtil.TRACE_REQUEST_ATTR))
                            .context())) {traced = traced(exchange, chain);
            }
        }
        else {
            // 如果以后已有链路信息，则间接执行
            traced = traced(exchange, chain);
        }
        return tracedPublisherFactory.getTracedMono(traced, exchange);
    }

    protected abstract Mono<Void> traced(ServerWebExchange exchange, GatewayFilterChain chain);
}

这样，咱们就能够基于这个抽象类去实现须要定制的 GlobalFilter 了