Question

I’m writing a custom tunnel (first there’s a custom hello and then the connection becomes a tunnel), but it’s pretty slow.

I’m wondering if there is anything I can do to increase speed.

One way to increase speed for connections that use short messages for instance would be to disable the nagle algorithm (TCP_NODELAY).

What would you recommend for tunneling?
I am tunneling RTSP and HTTP if that helps.

EDIT: The code is as simple as it could possibly be:

int remote_fd;
int local_fd;
int fdmax;
char buf[1 << 10];

fdset master_set, read_set;
FD_ZERO(&master_set);
FD_ZERO(&read_set);
FD_SET(remote_fd, &master_set);
FD_SET(local_fd, &master_set);

fdmax = remote_fd > local_fd ? remote_fd : local_fd;

//Connect both remote_fd and local_fd
...

while (1) {
    read_set = master_set;
    select(fdmax + 1, &read_set, NULL, NULL, NULL);
    if (FD_ISSET(local_fd, &read_set)) {
        int n = recv(local_fd, buf, sizeof(buf), 0);
        send(remote_fd, buf, n, 0);
    }
    if (FD_ISSET(remote_fd, &read_set)) {
        int n = recv(remote_fd, buf, sizeof(buf), 0);
        send(local_fd, buf, n, 0);
    }
}

I have omitted error handling and the code connecting the sockets to make it more readable.

Answer 1

The problem may be in your code rathar than the socket options. TCP_NODELAY may or may not help. Large socket and and receive huffers may help. Your code may be introducing latency. Show us some code.