Available socket bytes

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 to “Available socket bytes”

  1. Martin Says:

    Eeek! man ioctl_list:

    “0×0000541B FIONREAD int *”

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

  2. Martin Says:

    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(…)).

  3. Martin Says:

    Hi btw! :)

  4. dholm Says:

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

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