Detect closed connection on non blocking socket

Question

I'm really sorry if my question is a duplicate, but I didn't find useful infos in the site.

I'm using non blocking sockets and a select(). How can I detect if a client closed the connection on non-blocking socket? I saw that a read() returns -1 with errno = EWOULDBLOCK when no datas are available to be read and also when a connection is closed.

How can I discriminate above cases?

Answer 1

When the peer has closed the connection:

1. select() will return the socket as readable.
2. A recv() or read() on the socket will return zero.

I saw that a read() returns -1 with errno = EWOULDBLOCK when no datas are available to be read

Correct, but the connection isn't closed.

and also when a connection is closed.

No you didn't. That's not correct. It returns zero.

How can I discriminate above cases?

They aren't the same, and they don't manifest themselves in the same way.