【Netty源码分析】客户端connect服务端过程

上一篇博客【Netty源码分析】Netty服务端bind端口过程 我们介绍了服务端绑定端口的过程，这一篇博客我们介绍一下客户端连接服务端的过程。

ChannelFuture future = boostrap.connect("127.0.0.1", 8080).sync();  

调用BootStrap的connect函数

public ChannelFuture connect(String inetHost, int inetPort) {
        return connect(InetSocketAddress.createUnresolved(inetHost, inetPort));
}

public ChannelFuture connect(SocketAddress remoteAddress) {
        if (remoteAddress == null) {
            throw new NullPointerException("remoteAddress");
        }

        validate();
        return doResolveAndConnect(remoteAddress, config.localAddress());
    }

调用doResolveAndConnect函数

 private ChannelFuture doResolveAndConnect(final SocketAddress remoteAddress, final SocketAddress localAddress) {
    ........
    return doResolveAndConnect0(channel, remoteAddress, localAddress, channel.newPromise());
    ........
}

private ChannelFuture doResolveAndConnect0(final Channel channel, SocketAddress remoteAddress,
                                               final SocketAddress localAddress, final ChannelPromise promise)
	........

    doConnect(remoteAddress, localAddress, promise);

	........

}

调用doConnect函数时会同时开启一个线程，用来处理客户端的操作。

 private static void doConnect(
            final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise connectPromise) {

        // This method is invoked before channelRegistered() is triggered.  Give user handlers a chance to set up
        // the pipeline in its channelRegistered() implementation.
        final Channel channel = connectPromise.channel();
        channel.eventLoop().execute(new Runnable() {
            @Override
            public void run() {
                if (localAddress == null) {
                    channel.connect(remoteAddress, connectPromise);
                } else {
                    channel.connect(remoteAddress, localAddress, connectPromise);
                }
                connectPromise.addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            }
        });
    }

AbstractChannel的connect函数

@Override
public ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
        return pipeline.connect(remoteAddress, localAddress, promise);
}

@Override
public final ChannelFuture connect(
            SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
        return tail.connect(remoteAddress, localAddress, promise);
}

private void invokeConnect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
        if (invokeHandler()) {
            try {
                ((ChannelOutboundHandler) handler()).connect(this, remoteAddress, localAddress, promise);
            } catch (Throwable t) {
                notifyOutboundHandlerException(t, promise);
            }
        } else {
            connect(remoteAddress, localAddress, promise);
        }
    }

HeadContext的connect函数

@Override
public void connect(
                ChannelHandlerContext ctx,
           SocketAddress remoteAddress, SocketAddress localAddress,
                ChannelPromise promise) throws Exception {
  unsafe.connect(remoteAddress, localAddress, promise);
}

AbstractUnsafe函数的connect函数

@Override
public final void connect(
                final SocketAddress remoteAddress, final SocketAddress localAddress, final ChannelPromise promise) {
    .......

    if (doConnect(remoteAddress, localAddress)) {
        fulfillConnectPromise(promise, wasActive);
    }

	.......
}

调用NioSocketChannle的doConnect函数

 @Override
    protected boolean doConnect(SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
        if (localAddress != null) {
            doBind0(localAddress);
        }

        boolean success = false;
        try {
            boolean connected = javaChannel().connect(remoteAddress);
            if (!connected) {
                selectionKey().interestOps(SelectionKey.OP_CONNECT);
            }
            success = true;
            return connected;
        } finally {
            if (!success) {
                doClose();
            }
        }
    }

或许执行doBind0函数

private void doBind0(SocketAddress localAddress) throws Exception {
        if (PlatformDependent.javaVersion() >= 7) {
            javaChannel().bind(localAddress);
        } else {
            javaChannel().socket().bind(localAddress);
        }
    }

javaChannle()函数获得的就是SocketChannle对象，这样就完成了客户端连接服务端的操作。