聊聊sentinel的SentinelGatewayFilter

序

本文主要研究一下sentinel的SentinelGatewayFilter

SentinelGatewayFilter

Sentinel-1.6.2/sentinel-adapter/sentinel-spring-cloud-gateway-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/gateway/sc/SentinelGatewayFilter.java

public class SentinelGatewayFilter implements GatewayFilter, GlobalFilter {

    private final GatewayParamParser<ServerWebExchange> paramParser = new GatewayParamParser<>(
        new ServerWebExchangeItemParser());

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        Route route = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR);

        Mono<Void> asyncResult = chain.filter(exchange);
        if (route != null) {
            String routeId = route.getId();
            Object[] params = paramParser.parseParameterFor(routeId, exchange,
                r -> r.getResourceMode() == SentinelGatewayConstants.RESOURCE_MODE_ROUTE_ID);
            String origin = Optional.ofNullable(GatewayCallbackManager.getRequestOriginParser())
                .map(f -> f.apply(exchange))
                .orElse("");
            asyncResult = asyncResult.transform(
                new SentinelReactorTransformer<>(new EntryConfig(routeId, EntryType.IN,
                    1, params, new ContextConfig(contextName(routeId), origin)))
            );
        }

        Set<String> matchingApis = pickMatchingApiDefinitions(exchange);
        for (String apiName : matchingApis) {
            Object[] params = paramParser.parseParameterFor(apiName, exchange,
                r -> r.getResourceMode() == SentinelGatewayConstants.RESOURCE_MODE_CUSTOM_API_NAME);
            asyncResult = asyncResult.transform(
                new SentinelReactorTransformer<>(new EntryConfig(apiName, EntryType.IN, 1, params))
            );
        }

        return asyncResult;
    }

    private String contextName(String route) {
        return SentinelGatewayConstants.GATEWAY_CONTEXT_ROUTE_PREFIX + route;
    }

    Set<String> pickMatchingApiDefinitions(ServerWebExchange exchange) {
        return GatewayApiMatcherManager.getApiMatcherMap().values()
            .stream()
            .filter(m -> m.test(exchange))
            .map(WebExchangeApiMatcher::getApiName)
            .collect(Collectors.toSet());
    }
}

• SentinelGatewayFilter实现了GatewayFilter、GlobalFilter接口；其filter方法主要是获取route信息，然后对asyncResult进行transform，这里使用的是SentinelReactorTransformer

SentinelReactorTransformer

Sentinel-1.6.2/sentinel-adapter/sentinel-reactor-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/reactor/SentinelReactorTransformer.java

public class SentinelReactorTransformer<T> implements Function<Publisher<T>, Publisher<T>> {

    private final EntryConfig entryConfig;

    public SentinelReactorTransformer(String resourceName) {
        this(new EntryConfig(resourceName));
    }

    public SentinelReactorTransformer(EntryConfig entryConfig) {
        AssertUtil.notNull(entryConfig, "entryConfig cannot be null");
        this.entryConfig = entryConfig;
    }

    @Override
    public Publisher<T> apply(Publisher<T> publisher) {
        if (publisher instanceof Mono) {
            return new MonoSentinelOperator<>((Mono<T>) publisher, entryConfig);
        }
        if (publisher instanceof Flux) {
            return new FluxSentinelOperator<>((Flux<T>) publisher, entryConfig);
        }

        throw new IllegalStateException("Publisher type is not supported: " + publisher.getClass().getCanonicalName());
    }
}

• SentinelReactorTransformer使用entryConfig创建了MonoSentinelOperator或者MonoSentinelOperator

MonoSentinelOperator

Sentinel-1.6.2/sentinel-adapter/sentinel-reactor-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/reactor/MonoSentinelOperator.java

public class MonoSentinelOperator<T> extends MonoOperator<T, T> {

    private final EntryConfig entryConfig;

    public MonoSentinelOperator(Mono<? extends T> source, EntryConfig entryConfig) {
        super(source);
        AssertUtil.notNull(entryConfig, "entryConfig cannot be null");
        this.entryConfig = entryConfig;
    }

    @Override
    public void subscribe(CoreSubscriber<? super T> actual) {
        source.subscribe(new SentinelReactorSubscriber<>(entryConfig, actual, true));
    }
}

• MonoSentinelOperator在subscribe的时候，使用的是SentinelReactorSubscriber

FluxSentinelOperator

Sentinel-1.6.2/sentinel-adapter/sentinel-reactor-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/reactor/FluxSentinelOperator.java

public class FluxSentinelOperator<T> extends FluxOperator<T, T> {

    private final EntryConfig entryConfig;

    public FluxSentinelOperator(Flux<? extends T> source, EntryConfig entryConfig) {
        super(source);
        AssertUtil.notNull(entryConfig, "entryConfig cannot be null");
        this.entryConfig = entryConfig;
    }

    @Override
    public void subscribe(CoreSubscriber<? super T> actual) {
        source.subscribe(new SentinelReactorSubscriber<>(entryConfig, actual, false));
    }
}

• FluxSentinelOperator在subscribe的时候，使用的是SentinelReactorSubscriber

SentinelReactorSubscriber

Sentinel-1.6.2/sentinel-adapter/sentinel-reactor-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/reactor/SentinelReactorSubscriber.java

public class SentinelReactorSubscriber<T> extends InheritableBaseSubscriber<T> {

    private final EntryConfig entryConfig;

    private final CoreSubscriber<? super T> actual;
    private final boolean unary;

    private volatile AsyncEntry currentEntry;
    private final AtomicBoolean entryExited = new AtomicBoolean(false);

    public SentinelReactorSubscriber(EntryConfig entryConfig,
                                     CoreSubscriber<? super T> actual,
                                     boolean unary) {
        checkEntryConfig(entryConfig);
        this.entryConfig = entryConfig;
        this.actual = actual;
        this.unary = unary;
    }

    private void checkEntryConfig(EntryConfig config) {
        AssertUtil.notNull(config, "entryConfig cannot be null");
    }

    @Override
    public Context currentContext() {
        if (currentEntry == null || entryExited.get()) {
            return actual.currentContext();
        }
        com.alibaba.csp.sentinel.context.Context sentinelContext = currentEntry.getAsyncContext();
        if (sentinelContext == null) {
            return actual.currentContext();
        }
        return actual.currentContext()
            .put(SentinelReactorConstants.SENTINEL_CONTEXT_KEY, currentEntry.getAsyncContext());
    }

    private void doWithContextOrCurrent(Supplier<Optional<com.alibaba.csp.sentinel.context.Context>> contextSupplier,
                                        Runnable f) {
        Optional<com.alibaba.csp.sentinel.context.Context> contextOpt = contextSupplier.get();
        if (!contextOpt.isPresent()) {
            // Provided context is absent, use current context.
            f.run();
        } else {
            // Run on provided context.
            ContextUtil.runOnContext(contextOpt.get(), f);
        }
    }

    private void entryWhenSubscribed() {
        ContextConfig sentinelContextConfig = entryConfig.getContextConfig();
        if (sentinelContextConfig != null) {
            // If current we're already in a context, the context config won't work.
            ContextUtil.enter(sentinelContextConfig.getContextName(), sentinelContextConfig.getOrigin());
        }
        try {
            AsyncEntry entry = SphU.asyncEntry(entryConfig.getResourceName(), entryConfig.getEntryType(),
                entryConfig.getAcquireCount(), entryConfig.getArgs());
            this.currentEntry = entry;
            actual.onSubscribe(this);
        } catch (BlockException ex) {
            // Mark as completed (exited) explicitly.
            entryExited.set(true);
            // Signal cancel and propagate the {@code BlockException}.
            cancel();
            actual.onSubscribe(this);
            actual.onError(ex);
        } finally {
            if (sentinelContextConfig != null) {
                ContextUtil.exit();
            }
        }
    }

    @Override
    protected void hookOnSubscribe(Subscription subscription) {
        doWithContextOrCurrent(() -> currentContext().getOrEmpty(SentinelReactorConstants.SENTINEL_CONTEXT_KEY),
            this::entryWhenSubscribed);
    }

    @Override
    protected void hookOnNext(T value) {
        if (isDisposed()) {
            tryCompleteEntry();
            return;
        }
        doWithContextOrCurrent(() -> Optional.ofNullable(currentEntry).map(AsyncEntry::getAsyncContext),
            () -> actual.onNext(value));

        if (unary) {
            // For some cases of unary operator (Mono), we have to do this during onNext hook.
            // e.g. this kind of order: onSubscribe() -> onNext() -> cancel() -> onComplete()
            // the onComplete hook will not be executed so we'll need to complete the entry in advance.
            tryCompleteEntry();
        }
    }

    @Override
    protected void hookOnComplete() {
        tryCompleteEntry();
        actual.onComplete();
    }

    @Override
    protected boolean shouldCallErrorDropHook() {
        // When flow control triggered or stream terminated, the incoming
        // deprecated exceptions should be dropped implicitly, so we'll not call the `onErrorDropped` hook.
        return !entryExited.get();
    }

    @Override
    protected void hookOnError(Throwable t) {
        if (currentEntry != null && currentEntry.getAsyncContext() != null) {
            // Normal requests with non-BlockException will go through here.
            Tracer.traceContext(t, 1, currentEntry.getAsyncContext());
        }
        tryCompleteEntry();
        actual.onError(t);
    }

    @Override
    protected void hookOnCancel() {

    }

    private boolean tryCompleteEntry() {
        if (currentEntry != null && entryExited.compareAndSet(false, true)) {
            currentEntry.exit(1, entryConfig.getArgs());
            return true;
        }
        return false;
    }
}

• SentinelReactorSubscriber继承了InheritableBaseSubscriber(拷贝自reactor.core.publisher.BaseSubscriber，允许子类覆盖onSubscribe、onNext、onError、onComplete方法)
• 这里hookOnSubscribe调用了entryWhenSubscribed，它在sentinelContextConfig不为null的时候会先执行ContextUtil.enter，然后使用SphU.asyncEntry创建了AsyncEntry，最后在finally里头在sentinelContextConfig不为null的时候执行ContextUtil.exit();
• 这里hookOnNext、hookOnComplete、hookOnError都调用了tryCompleteEntry方法，它主要是尝试退出AsyncEntry

小结

• SentinelGatewayFilter实现了GatewayFilter、GlobalFilter接口；其filter方法主要是获取route信息，然后对asyncResult进行transform，这里使用的是SentinelReactorTransformer
• SentinelReactorTransformer使用entryConfig创建了MonoSentinelOperator或者MonoSentinelOperator；它们在subscribe的时候，使用的是SentinelReactorSubscriber
• SentinelReactorSubscriber主要是在hookOnSubscribe的时候调用了entryWhenSubscribed方法创建AsyncEntry，在hookOnNext、hookOnComplete、hookOnError的时候调用了tryCompleteEntry方法，尝试退出AsyncEntry

doc

• SentinelGatewayFilter