How to handle the Linux socket revents POLLERR, POLLHUP and POLLNVAL?

linux, network-programming, poll-syscall, sockets

Solution

A `POLLHUP` means the socket is no longer connected. In TCP, this means FIN has been received and sent.

A `POLLERR` means the socket got an asynchronous error. In TCP, this typically means a RST has been received or sent. If the file descriptor is not a socket, `POLLERR` might mean the device does not support polling.

For both of the conditions above, the socket file descriptor is still open, and has not yet been closed (but `shutdown()` may have already been called). A `close()` on the file descriptor will release resources that are still being reserved on behalf of the socket. In theory, it should be possible to reuse the socket immediately (e.g., with another `connect()` call).

A `POLLNVAL` means the socket file descriptor is not open. It would be an error to `close()` it.

Problem

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