sockets - (recv()== 0)表示断开连接或超时？ (套接字，Linux和Windows)

Question

我在阻塞套接字上设置了超时。

DWORD to = 1200;
if (setsockopt (soc, SOL_SOCKET, SO_RCVTIMEO, (char *)&to, sizeof(to))) {
    ...
}

在recv()然后返回零的情况下，我怎么知道这是链接断开或读取超时？如果不是，我想阅读更多，如果不满意，我想采取其他行动。我意识到我可以删除t/o，然后知道这是不合理的，但是我还需要定期监视读取过程的进度。

任何帮助，不胜感激。干杯-丰富

Answer 1

在SO_RCVTIMEO的手册页的socket部分中:

...if no data has been transferred and the time‐out has been reached,
then -1 is returned with errno set to EAGAIN or EWOULDBLOCK, or
EINPROGRESS (for connect(2)) just as if the socket was specified to
be non‐blocking.

在 recv的手册页中:

These calls return the number of bytes received, or -1 if an error
occurred.  In the event of an error, errno is set to indicate the
error.

When a stream socket peer has performed an orderly shutdown, the
return value will be 0 (the traditional "end-of-file" return).

Datagram sockets in various domains (e.g., the UNIX and Internet
domains) permit zero-length datagrams.  When such a datagram is
received, the return value is 0.

The value 0 may also be returned if the requested number of bytes to
receive from a stream socket was 0.

断开连接，或者接收到长度为零的数据报，或者请求的字节数为 recv时，对 0的调用将返回 0。

调用 recv会在出现任何错误(包括超时)时返回 -1。您需要检查 errno来区分超时和其他错误。