#define sk_close(s) (((*s)->close) (s))
#define sk_write(s,buf,len) (((*s)->write) (s, buf, len))
#define sk_write_oob(s,buf,len) (((*s)->write_oob) (s, buf, len))
#define sk_close(s) (((*s)->close) (s))
#define sk_write(s,buf,len) (((*s)->write) (s, buf, len))
#define sk_write_oob(s,buf,len) (((*s)->write_oob) (s, buf, len))