Flexible socket application - sockets

Question

I'm writing a game wich playing on LAN with socket. I use 4 bytes length prefix to know how many data in the rest like this:
void trust_recv(int sock, int length, char *buffer)
{
int recved = 0;
int justRecv;
while(recved < length) {
justRecv = recv(sock, buffer + recved, length - recved, 0);
if (justRecv < 0) return;
recved += justRecv;
}
}
void onDataArrival(int sock)
{
int length;
char *data;
trust_recv(sock, 4, (char *) &length);
data = new char[length];
trust_recv(sock, length, data);
do_somethings_with_data(data);
}
The problem is if someone (an intruder or hacker for example) sends data with other format (maybe only 2 bytes or the length of the rest lower than 4 bytes prefix value) or an network problem, my application will be go to "not responding" state and have to close (because I use blocking socket). How to make my socket application more flexible but don't swith socket to non-blocking mode to pass this issue? (Or any ideas for organize data or algorithms as well)

Answer 1

You can set a receive timeout, during the socket setup phase, with setsockopt() call and SO_RCVTIMEO parameter;
struct timeval tv;
tv.tv_sec =8;
tv.tv_usec = 0 ;
if (setsockopt (your_sock_fd, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv, sizeof tv)
perror(“setsockopt error”);
then test the return of recv() and his errno
if (justRecv < 0)
{
if (errno == EAGAIN)
perror("TIMEOUT!");
return;
}