序

本文主要研究一下reactor-netty中HttpClient对TcpClien的封装

maven

<dependency>
            <groupId>io.projectreactor.ipc</groupId>
            <artifactId>reactor-netty</artifactId>
            <version>0.7.3.RELEASE</version>
        </dependency>

实例

HttpClient client = HttpClient.create();
        Mono<HttpClientResponse> mono = client.get("http://baidu.com");
        //NOTE reactor.ipc.netty.http.client.MonoHttpClientResponse
        LOGGER.info("mono resp:{}",mono.getClass());
        mono.subscribe();

HttpClient.request

reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/http/client/HttpClient.java

/**
     * Use the passed HTTP method to send to the given URL. When connection has been made,* the passed handler is invoked and can be used to tune the request and
     * write data to it.
     *
     * @param method the HTTP method to send
     * @param url the target remote URL
     * @param handler the {@link Function} to invoke on opened TCP connection
     * @return a {@link Mono} of the {@link HttpServerResponse} ready to consume for
     * response
     */
    public Mono<HttpClientResponse> request(HttpMethod method,String url,Function<? super HttpClientRequest,? extends Publisher<Void>> handler) {

        if (method == null || url == null) {
            throw new IllegalArgumentException("Method && url cannot be both null");
        }

        return new MonoHttpClientResponse(this,url,method,handler(handler,options));
    }

Mono.subscribe

reactor-core-3.1.3.RELEASE-sources.jar!/reactor/core/publisher/Mono.java

/**
     * Subscribe to this {@link Mono} and request unbounded demand.
     * <p>
     * This version doesn't specify any consumption behavior for the events from the
     * chain,especially no error handling,so other variants should usually be preferred.
     *
     * <p>
     * <img width="500" src="https://raw.githubusercontent.com/reactor/reactor-core/v3.1.3.RELEASE/src/docs/marble/unbounded1.png" alt="">
     * <p>
     *
     * @return a new {@link Disposable} that can be used to cancel the underlying {@link Subscription}
     */
    public final Disposable subscribe() {
        if(this instanceof MonoProcessor){
            MonoProcessor<T> s = (MonoProcessor<T>)this;
            s.connect();
            return s;
        }
        else{
            return subscribeWith(new LambdaMonoSubscriber<>(null,null,null));
        }
    }

这里调用了subscribeWith，创建了一个LambdaMonoSubscriber

/**
     * Subscribe the given {@link Subscriber} to this {@link Mono} and return said
     * {@link Subscriber} (eg. a {@link MonoProcessor}).
     *
     * @param subscriber the {@link Subscriber} to subscribe with
     * @param <E> the reified type of the {@link Subscriber} for chaining
     *
     * @return the passed {@link Subscriber} after subscribing it to this {@link Mono}
     */
    public final <E extends Subscriber<? super T>> E subscribeWith(E subscriber) {
        subscribe(subscriber);
        return subscriber;
    }
    public final void subscribe(Subscriber<? super T> actual) {
        onLastAssembly(this).subscribe(Operators.toCoreSubscriber(actual));
    }

这个onLastAssembly(this).subscribe调用的是子类的方法

MonoHttpClientResponse.subscribe

reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/http/client/MonoHttpClientResponse.java

public void subscribe(final CoreSubscriber<? super HttpClientResponse> subscriber) {
        ReconnectableBridge bridge = new ReconnectableBridge();
        bridge.activeURI = startURI;

        Mono.defer(() -> parent.client.newHandler(new HttpClientHandler(this,bridge),parent.options.getRemoteAddress(bridge.activeURI),HttpClientOptions.isSecure(bridge.activeURI),bridge))
            .retry(bridge)
            .cast(HttpClientResponse.class)
            .subscribe(subscriber);
    }

这里使用Mono.defer又对client.newHandler包装了下，defer的英文原意是 Defers the creation of the actual Publisher the Subscriber will be subscribed to.，也就是延迟publisher的创建

这里的subscriber便是Operators.toCoreSubscriber(lambdaMonoSubscriber)

可以看到这里调用了parent的client.newHandler，这里的parent便是HttpClient，里头的client是TcpClient

retry使用的是ReconnectableBridge，handler使用的是HttpClientHandler

MonoHttpClientResponse#ReconnectableBridge

static final class ReconnectableBridge
            implements Predicate<Throwable>,Consumer<Channel> {

        volatile URI      activeURI;
        volatile String[] redirectedFrom;

        ReconnectableBridge() {
        }

        void redirect(String to) {
            String[] redirectedFrom = this.redirectedFrom;
            URI from = activeURI;
            try {
                activeURI = new URI(to);
            }
            catch (URISyntaxException e) {
                throw Exceptions.propagate(e);
            }
            if (redirectedFrom == null) {
                this.redirectedFrom = new String[]{from.toString()};
            }
            else {
                String[] newRedirectedFrom = new String[redirectedFrom.length + 1];
                System.arraycopy(redirectedFrom,newRedirectedFrom,redirectedFrom.length);
                newRedirectedFrom[redirectedFrom.length] = from.toString();
                this.redirectedFrom = newRedirectedFrom;
            }
        }

        @Override
        public void accept(Channel channel) {
            String[] redirectedFrom = this.redirectedFrom;
            if (redirectedFrom != null) {
                channel.attr(HttpClientOperations.REDIRECT_ATTR_KEY)
                       .set(redirectedFrom);
            }
        }

        @Override
        public boolean test(Throwable throwable) {
            if (throwable instanceof RedirectClientException) {
                RedirectClientException re = (RedirectClientException) throwable;
                redirect(re.location);
                return true;
            }
            if (AbortedException.isConnectionReset(throwable)) {
                redirect(activeURI.toString());
                return true;
            }
            return false;
        }
    }

这里看好像是处理redirect的，并不是真正意义上的retry，比如retry多少次之类的

MonoHttpClientResponse#HttpClientHandler

reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/http/client/MonoHttpClientResponse.java

static final class HttpClientHandler
            implements BiFunction<NettyInbound,NettyOutbound,Publisher<Void>> {

        final MonoHttpClientResponse parent;
        final ReconnectableBridge    bridge;

        HttpClientHandler(MonoHttpClientResponse parent,ReconnectableBridge bridge) {
            this.bridge = bridge;
            this.parent = parent;
        }

        @Override
        public Publisher<Void> apply(NettyInbound in,NettyOutbound out) {
            try {
                URI uri = bridge.activeURI;
                HttpClientOperations ch = (HttpClientOperations) in;
                String host = uri.getHost();
                int port = uri.getPort();
                if (port != -1 && port != 80 && port != 443) {
                    host = host + ':' + port;
                }
                ch.getNettyRequest()
                  .setUri(uri.getRawPath() + (uri.getQuery() == null ? "" :
                          "?" + uri.getRawQuery()))
                  .setMethod(parent.method)
                  .setProtocolVersion(HttpVersion.HTTP_1_1)
                  .headers()
                  .add(HttpHeaderNames.HOST,host)
                  .add(HttpHeaderNames.ACCEPT,ALL);

                if (parent.method == HttpMethod.GET
                        || parent.method == HttpMethod.HEAD
                        || parent.method == HttpMethod.DELETE) {
                    ch.chunkedTransfer(false);
                }

                if (parent.handler != null) {
                    return parent.handler.apply(ch);
                }
                else {
                    return ch.send();
                }
            }
            catch (Throwable t) {
                return Mono.error(t);
            }
        }

        @Override
        public String toString() {
            return "HttpClientHandler{" + "startURI=" + bridge.activeURI + ",method=" + parent.method + ",handler=" + parent.handler + '}';
        }

    }

这里的handler可以看到netty的痕迹，最后是直接调用HttpClientOperations.send方法

reactor-netty-0.7.3.RELEASE-sources.jar!/reactor/ipc/netty/http/client/HttpClientOperations.java

public Mono<Void> send() {
        if (markSentHeaderAndBody()) {
            HttpMessage request = newFullEmptyBodyMessage();
            return FutureMono.deferFuture(() -> channel().writeAndFlush(request));
        }
        else {
            return Mono.empty();
        }
    }

最后调用netty的channel().writeAndFlush(request)将请求发送出去

小结

reactor-netty中的HttpClient对TcpClient进行了桥接，而TcpClient则是基于netty来实现。