Question

Suppose I have a server application – the connection is over TCP, using UNIX sockets.

The connection is asynchronous – in other words, clients’ and servers’ sockets are non-blocking.

Suppose the following situation: in some conditions, the server may decide to send some data to a connected client and immediately close the connection: using shutdown with SHUT_RDWR.

So, my question is – is it guaranteed, that when the client call recv, it will receive the (sent by the server) data?

Or, to receive the data, recv must be called before the server’s shutdown? If so, what should I do (or, to be more precise, how should I do this), to make sure, that the data is received by the client?

Answer 1

You can control this behavior with “setsockopt(SO_LINGER)”:

• man setsockopt

SO_LINGER
Waits to complete the close function if data is present. When this option is enabled and there is unsent data present when the close
function is called, the calling application is blocked during the
close function until the data is transmitted or the connection has
timed out. The close function returns without blocking the caller.
This option has meaning only for stream sockets.

See also:

• man read

• Beej’s Guide to Network Programming