检测 TCP 客户端断开连接
假设我正在运行一个简单的服务器并且 accept() 从客户端建立了一个连接.
Let's say I'm running a simple server and have accept()ed a connection from a client.
判断客户端何时断开连接的最佳方法是什么?通常，客户端应该发送关闭命令，但是如果它手动断开连接或完全失去网络连接怎么办?服务器如何检测或处理这种情况?
What is the best way to tell when the client has disconnected? Normally, a client is supposed to send a close command, but what if it disconnects manually or loses network connection altogether? How can the server detect or handle this?
推荐答案
select (with the read mask set) will return with the handle signalled, 但是当你使用 ioctl* 检查等待读取的字节数时，它会返回将为零.这是套接字已断开连接的标志.
select (with the read mask set) will return with the handle signalled, but when you use ioctl* to check the number of bytes pending to be read, it will be zero. This is a sign that the socket has been disconnected.
这是关于检查客户端是否断开连接的各种方法的精彩讨论:Stephen Cleary，检测半开(丢弃)连接.
This is a great discussion on the various methods of checking that the client has disconnected: Stephen Cleary, Detection of Half-Open (Dropped) Connections.
* Windows 使用 ioctlsocket.
* for Windows use ioctlsocket.
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