setting timeout for socket recv TCP - c

Question

I found some hints on how to do it but I dont understand how to use setsockopt. I have an infinite while loop calling recv, I want to timeout and close(cli_socket) if client doesnt send anything in 5 seconds.
If client sends only part of the whole expected message I want to reset timer and give him another 5 seconds.
currentry I have this:
while((cut = buffer.find("\r\n")) == -1)
{
struct timeval tv;
tv.tv_sec = 5;
setsockopt(cli_socket, SOL_SOCKET, SO_RCVTIMEO,(struct timeval *)&tv,sizeof(struct timeval));
recv(cli_socket, tmpBuffer, 100, 0);
buffer += tmpBuffer;
memset(tmpBuffer, 0, 100);
}

Answer 1

You should test the return of recv and break your loop if it is EAGAIN or EWOULDBLOCK:
EAGAIN or EWOULDBLOCK
The socket is marked nonblocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received
struct timeval tv = {5, 0};
setsockopt(cli_socket, SOL_SOCKET, SO_RCVTIMEO, (struct timeval *)&tv, sizeof(struct timeval));
while((cut = buffer.find("\r\n")) == -1)
{
int numBytes = recv(cli_socket, tmpBuffer, 100, 0));
/// Edit: recv does not return EAGAIN else, it return -1 on error.
/// and in case of timeout, errno is set to EAGAIN or EWOULDBLOCK
if (numBytes <= 0)
{
// nothing received from client in last 5 seconds
break;
}
buffer.append(tmpBuffer, numBytes);
}
You can also use select function which is not so complicated to use:
while((cut = buffer.find("\r\n")) == -1)
{
timeval timeout = { 5, 0 };
fd_set in_set;
FD_ZERO(&in_set);
FD_SET(cli_socket, &in_set);
// select the set
int cnt = select(cli_socket + 1, &in_set, NULL, NULL, &timeout);
if (FD_ISSET(cli_socket, &in_set))
{
int numBytes = recv(cli_socket, tmpBuffer, 100, 0));
if (numBytes <= 0)
{
// nothing received from client
break;
}
buffer.append(tmpBuffer, numBytes);
}
else
{
// nothing received from client in last 5 seconds
break;
}
}