man 7 socket

You can change the size of the receive and the send buffer as follows (send buffer shown):

int buffersize = 64*1024; // 64k
setsockopt(socket, SOL_SOCKET, SO_SNDBUF, (char *) &buffersize, sizeof(buffersize));

and to get the current size, use:

getsockopt(socket, SOL_SOCKET, SO_SNDBUF, (char &) &buffersize, sizeof(buffersize));


ret1 = recv(fd, buffer, 32, MSG_PEEK | MSG_DONTWAIT);

MSG_PEEK
This flag causes the receive operation to return data from the beginning of the receive queue without removing that data
from the queue. Thus, a subsequent receive call will return the same data.