getsockopt

/*
 * Document-method: getsockopt
 * call-seq: getsockopt(level, optname)
 *
 * Gets a socket option. These are protocol and system specific, see your
 * local sytem documentation for details. The option is returned as
 * a String with the data being the binary value of the socket option.
 *
 * === Parameters
 * * +level+ is an integer, usually one of the SOL_ constants such as
 *   Socket::SOL_SOCKET, or a protocol level.
 * * +optname+ is an integer, usually one of the SO_ constants, such
 *   as Socket::SO_REUSEADDR.
 *
 * === Examples
 *
 * Some socket options are integers with boolean values, in this case
 * #getsockopt could be called like this:
 *   optval = sock.getsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR)
 *   optval = optval.unpack "i"
 *   reuseaddr = optval[0] == 0 ? false : true
 *
 * Some socket options are integers with numeric values, in this case
 * #getsockopt could be called like this:
 *   optval = sock.getsockopt(Socket::IPPROTO_IP, Socket::IP_TTL)
 *   ipttl = optval.unpack("i")[0]
 *
 * Option values may be structs. Decoding them can be complex as it involves
 * examining your system headers to determine the correct definition. An
 * example is a +struct linger+, which may be defined in your system headers
 * as:
 *   struct linger {
 *     int l_onoff;
 *     int l_linger;
 *   };
 * 
 * In this case #getsockopt could be called like this:
 *   optval =  sock.getsockopt(Socket::SOL_SOCKET, Socket::SO_LINGER)
 *   onoff, linger = optval.unpack "ii"
*/
static VALUE
bsock_getsockopt(sock, lev, optname)
    VALUE sock, lev, optname;
{
#if !defined(__BEOS__)
    int level, option;
    socklen_t len;
    char *buf;
    rb_io_t *fptr;

    level = NUM2INT(lev);
    option = NUM2INT(optname);
    len = 256;
    buf = ALLOCA_N(char,len);
    GetOpenFile(sock, fptr);

    GetOpenFile(sock, fptr);
    if (getsockopt(fileno(fptr->f), level, option, buf, &len) < 0)
        rb_sys_fail(fptr->path);

    return rb_str_new(buf, len);
#else
    rb_notimplement();
#endif
}