c-ares 12.0.0

A Rust wrapper for the c-ares library, for asynchronous DNS requests.
Documentation 
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// Most of our lookups follow the same pattern - macro out the repetition.
macro_rules! ares_call {
    (
        $ares_call:ident,
        $channel:expr,
        $name:expr,
        $dns_class:expr,
        $query_type:expr,
        $callback:expr,
        $handler:expr
    ) => {{
        let c_name = CString::new($name).unwrap();
        let c_arg = Box::into_raw(Box::new($handler));
        unsafe {
            c_ares_sys::$ares_call(
                $channel,
                c_name.as_ptr(),
                $dns_class as c_int,
                $query_type as c_int,
                Some($callback),
                c_arg.cast(),
            );
        }
        panic::propagate();
    }};
}

macro_rules! ares_query {
    ($($arg:tt)*) => { ares_call!(ares_query, $($arg)*) }
}

macro_rules! ares_search {
    ($($arg:tt)*) => { ares_call!(ares_search, $($arg)*) }
}

// Most of our `ares_callback` implementations are much the same - macro out the repetition.
macro_rules! ares_callback {
    ($arg:expr, $status:expr, $abuf:expr, $alen:expr, $parser:expr) => {{
        let result = if $status == c_ares_sys::ares_status_t::ARES_SUCCESS as i32 {
            let data = unsafe { slice::from_raw_parts($abuf, $alen as usize) };
            $parser(data)
        } else {
            Err(Error::from($status))
        };
        let handler = unsafe { Box::from_raw($arg) };
        panic::catch(|| handler(result));
    }};
}