Maximum buffer length for sendto?

Question

How do you get the maximum number of bytes that can be passed to a sendto(..) call for a socket opened as a UDP port?

Answer 1

On Mac OS X there are different values for sending (SO_SNDBUF) and receiving (SO_RCVBUF). This is the size of the send buffer (man getsockopt):

getsockopt(sock, SOL_SOCKET, SO_SNDBUF, (int *)&optval, &optlen);

Trying to send a bigger message (on Leopard 9216 octets on UDP sent via the local loopback) will result in "Message too long / EMSGSIZE".