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本文主要研究一下AsyncHttpClient的KeepAliveStrategy

KeepAliveStrategy

org/asynchttpclient/channel/KeepAliveStrategy.java

public interface KeepAliveStrategy {/*** Determines whether the connection should be kept alive after this HTTP message exchange.** @param ahcRequest    the Request, as built by AHC* @param nettyRequest  the HTTP request sent to Netty* @param nettyResponse the HTTP response received from Netty* @return true if the connection should be kept alive, false if it should be closed.*/boolean keepAlive(Request ahcRequest, HttpRequest nettyRequest, HttpResponse nettyResponse);
}

KeepAliveStrategy接口定義了keepAlive方法用于決定是否對該connection進行keep alive

DefaultKeepAliveStrategy

org/asynchttpclient/channel/DefaultKeepAliveStrategy.java

/*** Connection strategy implementing standard HTTP 1.0/1.1 behavior.*/
public class DefaultKeepAliveStrategy implements KeepAliveStrategy {/*** Implemented in accordance with RFC 7230 section 6.1 https://tools.ietf.org/html/rfc7230#section-6.1*/@Overridepublic boolean keepAlive(Request ahcRequest, HttpRequest request, HttpResponse response) {return HttpUtil.isKeepAlive(response)&& HttpUtil.isKeepAlive(request)// support non standard Proxy-Connection&& !response.headers().contains("Proxy-Connection", CLOSE, true);}
}

DefaultKeepAliveStrategy實現了KeepAliveStrategy接口，其keepAlive方法判根據HTTP 1.0/1.1協議的規定進行判斷，需要request、response都是keep alive，且response header不包含Proxy-Connection: close才返回true

HttpUtil

io/netty/handler/codec/http/HttpUtil.java

    /*** Returns {@code true} if and only if the connection can remain open and* thus 'kept alive'.  This methods respects the value of the.** {@code "Connection"} header first and then the return value of* {@link HttpVersion#isKeepAliveDefault()}.*/public static boolean isKeepAlive(HttpMessage message) {return !message.headers().containsValue(HttpHeaderNames.CONNECTION, HttpHeaderValues.CLOSE, true) &&(message.protocolVersion().isKeepAliveDefault() ||message.headers().containsValue(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE, true));}

isKeepAlive方法在HttpMessage沒有connection: close的header，且http協議默認keep alive或者header包含了connection: keep-alive才返回true

handleHttpResponse

org/asynchttpclient/netty/handler/HttpHandler.java

  private void handleHttpResponse(final HttpResponse response, final Channel channel, final NettyResponseFuture<?> future, AsyncHandler<?> handler) throws Exception {HttpRequest httpRequest = future.getNettyRequest().getHttpRequest();logger.debug("\n\nRequest {}\n\nResponse {}\n", httpRequest, response);future.setKeepAlive(config.getKeepAliveStrategy().keepAlive(future.getTargetRequest(), httpRequest, response));NettyResponseStatus status = new NettyResponseStatus(future.getUri(), response, channel);HttpHeaders responseHeaders = response.headers();if (!interceptors.exitAfterIntercept(channel, future, handler, response, status, responseHeaders)) {boolean abort = abortAfterHandlingStatus(handler, status) || //abortAfterHandlingHeaders(handler, responseHeaders) || //abortAfterHandlingReactiveStreams(channel, future, handler);if (abort) {finishUpdate(future, channel, true);}}}

HttpHandler的handleHttpResponse方法會通過KeepAliveStrategy的keepAlive來判斷是否需要keep alive，然后寫入到NettyResponseFuture中

exitAfterHandlingConnect

org/asynchttpclient/netty/handler/intercept/ConnectSuccessInterceptor.java

  public boolean exitAfterHandlingConnect(Channel channel,NettyResponseFuture<?> future,Request request,ProxyServer proxyServer) {if (future.isKeepAlive())future.attachChannel(channel, true);Uri requestUri = request.getUri();LOGGER.debug("Connecting to proxy {} for scheme {}", proxyServer, requestUri.getScheme());channelManager.updatePipelineForHttpTunneling(channel.pipeline(), requestUri);future.setReuseChannel(true);future.setConnectAllowed(false);requestSender.drainChannelAndExecuteNextRequest(channel, future, new RequestBuilder(future.getTargetRequest()).build());return true;}

exitAfterHandlingConnect方法在NettyResponseFuture的keep alive為true時執行future.attachChannel(channel, true)

attachChannel

org/asynchttpclient/netty/NettyResponseFuture.java

  public void attachChannel(Channel channel, boolean reuseChannel) {// future could have been cancelled firstif (isDone()) {Channels.silentlyCloseChannel(channel);}this.channel = channel;this.reuseChannel = reuseChannel;}public boolean isReuseChannel() {return reuseChannel;}  

attachChannel這里維護了reuseChannel屬性

getOpenChannel

org/asynchttpclient/netty/request/NettyRequestSender.java

  private Channel getOpenChannel(NettyResponseFuture<?> future, Request request, ProxyServer proxyServer,AsyncHandler<?> asyncHandler) {if (future != null && future.isReuseChannel() && Channels.isChannelActive(future.channel())) {return future.channel();} else {return pollPooledChannel(request, proxyServer, asyncHandler);}}private Channel pollPooledChannel(Request request, ProxyServer proxy, AsyncHandler<?> asyncHandler) {try {asyncHandler.onConnectionPoolAttempt();} catch (Exception e) {LOGGER.error("onConnectionPoolAttempt crashed", e);}Uri uri = request.getUri();String virtualHost = request.getVirtualHost();final Channel channel = channelManager.poll(uri, virtualHost, proxy, request.getChannelPoolPartitioning());if (channel != null) {LOGGER.debug("Using pooled Channel '{}' for '{}' to '{}'", channel, request.getMethod(), uri);}return channel;}  

getOpenChannel先判斷NettyResponseFuture是否是reuse的，以及是否active，若是則直接返回future.channel()，否則通過pollPooledChannel從連接池中獲取

小結

AsyncHttpClient的KeepAliveStrategy定義了keepAlive方法用于決定是否對該connection進行keep alive；HttpHandler的handleHttpResponse方法會通過KeepAliveStrategy的keepAlive來判斷是否需要keep alive，然后寫入到NettyResponseFuture中；getOpenChannel先判斷NettyResponseFuture是否是reuse的，以及是否active，若是則直接返回future.channel()，否則通過pollPooledChannel從連接池中獲取。