sockets - Determine tcp connection state

Question

In linux, how can i determine the state of a TCP socket? I searched many in this theme, but i does not finded real usable solution. I the most chases says: write something into the socket and it will fail if connection closed. But what if the content of stream is bound, and a may not write anything junk into the stream? I a other aspect the netstat can determine the socket state, but if i would like to implement the netstat based solution, it will be very expensive. I must resolv the fileDescriptor to socketID, than read all record from /proc/net/tcp, find the fitting line and test state is established. It is not so efficient if this method must be periodically called. It there some other shorthand solution for this problem?

Answer 1

您必须执行套接字 I/O 操作以确定连接是否仍然存在。如果您无法写入套接字，您仍然可以尝试读取操作（只要它不干扰任何其他读取操作）并查看它是否因连接错误而失败。

Answer 2

你不能。TCP 套接字没有动态状态；它们只有先前操作的结果。如果您不在 TCP 连接上进行操作，则故意将其设计为不更改状态。它没有“拨号音”，这是它完全取代了像 SNA 这样的网络架构的根本原因。