Function q_send 

pub unsafe extern "C" fn q_send(
    fd: c_int,
    msg: *mut ray_t,
    err: *mut c_char,
    errlen: usize,
) -> *mut ray_t

Encode + exchange + decode: send msg and return the decoded response (possibly a RAY_ERROR), or null on a transport/serialization failure with a short reason written to err.