java - 如何让 netty channel.writeAndFlush() 在没有 TCP ACK 响应时抛出异常

Question

我正在使用 Netty4 框架开发一个 IM 服务器。同时，我使用名为channel.writeAndFlush() 的方法向客户端发送消息。但是，当手机端的客户端socket异常关闭时，比如关闭网络连接，或者在设备上开启飞行模式，netty4 frame找不到对应的channel inactive。此外，writeAndFlush()方法返回的ChannelGroupFuture通过ChannelGroupFuture.isSuccess()方法报告发送结果成功。那么，为什么 ChannelGroupFuture 没有返回发送失败而没有抛出任何异常？

ChannelGroupFuture future = connectionService.sendMessageToUser(msgBase, toUid).sync();

future.addListeners(new ChannelGroupFutureListener(){

@Override
                public void operationComplete(ChannelGroupFuture future)
                        throws Exception {
                    if(future.isDone() && future.isSuccess()){
                        chatMessageService.saveSentChatMessage(msgBase);
                    } else if(!future.isSuccess()){
                        chatMessageService.saveUnsentChatMessage(msgBase);
                    }
});

 public ChannelGroupFuture writeAndFlush(Object message, ChannelMatcher matcher) {
    if (message == null) {
        throw new NullPointerException("message");
    }
    if (matcher == null) {
        throw new NullPointerException("matcher");
    }
    if(matcher instanceof AttributeChannelMatcher){
        Map<Channel, ChannelFuture> futures = new LinkedHashMap<Channel, ChannelFuture>(1);
        AttributeChannelMatcher<T>  attributeMatcher = (AttributeChannelMatcher<T>) matcher;
        Channel c = nonServerChannelMap.get(attributeMatcher.getAttributeKeyValue());

        futures.put(c, c.writeAndFlush(safeDuplicate(message)));
        ReferenceCountUtil.release(message);
        return new DefaultChannelGroupFuture(this, futures, executor);
    }else{
        Map<Channel, ChannelFuture> futures = new LinkedHashMap<Channel, ChannelFuture>(size());

        for (Channel c :  nonServerChannelMap.values()) {
            if (matcher.matches(c)) {
                futures.put(c, c.writeAndFlush(safeDuplicate(message)));
            }
        }
        ReferenceCountUtil.release(message);
        return new DefaultChannelGroupFuture(this, futures, executor);
    }
}

Answer 1

你不能。 TCP 写入相对于应用程序是异步的。他们在返回之前不会等待 ACK。发送端有一个发送缓冲区，接收端有一个接收缓冲区。所有这一切意味着，在您检测到断开的连接之前，可能需要多次写入和相当多的几秒钟。