Now let us consider what the server process must do to accept
connections on a socket. First it must use the listen
function
to enable connection requests on the socket, and then accept each
incoming connection with a call to accept
(see section Accepting Connections). Once connection requests are enabled on a server socket,
the select
function reports when the socket has a connection
ready to be accepted (see section Waiting for Input or Output).
The listen
function is not allowed for sockets using
connectionless communication styles.
You can write a network server that does not even start running until a
connection to it is requested. See section inetd
Servers.
In the Internet namespace, there are no special protection mechanisms for controlling access to a port; any process on any machine can make a connection to your server. If you want to restrict access to your server, make it examine the addresses associated with connection requests or implement some other handshaking or identification protocol.
In the local namespace, the ordinary file protection bits control who has access to connect to the socket.
listen
function enables the socket socket to accept
connections, thus making it a server socket.
The argument n specifies the length of the queue for pending
connections. When the queue fills, new clients attempting to connect
fail with ECONNREFUSED
until the server calls accept
to
accept a connection from the queue.
The listen
function returns 0
on success and -1
on failure. The following errno
error conditions are defined
for this function:
EBADF
ENOTSOCK
EOPNOTSUPP
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