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Available socket bytes

May 13th, 2008 by dholm

Ever wondered how to find out how many bytes can be read from a socket? I did and it is really simple although possibly not portable.

ssize_t socket_get_available(int socket_fd)
{
        int available = -1;
        assert(0 <= socket_fd);

        if (ioctl(socket_fd, FIONREAD, &available) < 0) {
                return -1;
        }

        return (ssize_t) available;
}

4 Responses

Martin writes:

May 24th, 2008 at 21:32

Eeek! man ioctl_list:

“0×0000541B FIONREAD int *”

That you might be lucky and it happens to work on your platform is no excuse.

Martin writes:

May 24th, 2008 at 21:39

Also, since you’re returning -1 to indicate an error I think you want ssize_t. That is, if I remember correctly (take e.g. ssize_t read(…) vs size_t fread(…)).

Martin writes:

May 24th, 2008 at 21:43

Hi btw!

dholm writes:

May 26th, 2008 at 07:43

Long time, no see!
Thanks for the suggestions! I fixed the implementation, apparently I don’t have the ioctl_list man page.