c-ares 12.0.0

A Rust wrapper for the c-ares library, for asynchronous DNS requests.
Documentation 
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use std::fmt;
use std::os::raw::{c_int, c_uchar, c_void};
use std::ptr;
use std::slice;

use itertools::Itertools;

use crate::error::{Error, Result};
use crate::panic;
use crate::utils::hostname_as_str;

/// The result of a successful SRV lookup.
#[derive(Debug)]
pub struct SRVResults {
    srv_reply: *mut c_ares_sys::ares_srv_reply,
}

/// The contents of a single SRV record.
#[derive(Clone, Copy)]
pub struct SRVResult<'a> {
    // A single result - reference into an `SRVResults`.
    srv_reply: &'a c_ares_sys::ares_srv_reply,
}

impl SRVResults {
    /// Obtain an `SRVResults` from the response to an SRV lookup.
    pub fn parse_from(data: &[u8]) -> Result<SRVResults> {
        let mut srv_reply: *mut c_ares_sys::ares_srv_reply = ptr::null_mut();
        let parse_status = unsafe {
            c_ares_sys::ares_parse_srv_reply(data.as_ptr(), data.len() as c_int, &mut srv_reply)
        };
        if parse_status == c_ares_sys::ares_status_t::ARES_SUCCESS as i32 {
            let srv_result = SRVResults::new(srv_reply);
            Ok(srv_result)
        } else {
            Err(Error::from(parse_status))
        }
    }

    fn new(srv_reply: *mut c_ares_sys::ares_srv_reply) -> Self {
        SRVResults { srv_reply }
    }

    /// Returns an iterator over the `SRVResult` values in this `SRVResults`.
    pub fn iter(&self) -> SRVResultsIter<'_> {
        SRVResultsIter {
            next: unsafe { self.srv_reply.as_ref() },
        }
    }
}

impl fmt::Display for SRVResults {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let results = self.iter().format("}, {");
        write!(fmt, "[{{{results}}}]")
    }
}

/// Iterator of `SRVResult`s.
#[derive(Clone, Copy)]
pub struct SRVResultsIter<'a> {
    next: Option<&'a c_ares_sys::ares_srv_reply>,
}

impl<'a> Iterator for SRVResultsIter<'a> {
    type Item = SRVResult<'a>;
    fn next(&mut self) -> Option<Self::Item> {
        let opt_reply = self.next;
        self.next = opt_reply.and_then(|reply| unsafe { reply.next.as_ref() });
        opt_reply.map(|reply| SRVResult { srv_reply: reply })
    }
}

impl<'a> IntoIterator for &'a SRVResults {
    type Item = SRVResult<'a>;
    type IntoIter = SRVResultsIter<'a>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

impl Drop for SRVResults {
    fn drop(&mut self) {
        unsafe { c_ares_sys::ares_free_data(self.srv_reply.cast()) }
    }
}

unsafe impl Send for SRVResults {}
unsafe impl Sync for SRVResults {}
unsafe impl Send for SRVResult<'_> {}
unsafe impl Sync for SRVResult<'_> {}
unsafe impl Send for SRVResultsIter<'_> {}
unsafe impl Sync for SRVResultsIter<'_> {}

impl<'a> SRVResult<'a> {
    /// Returns the hostname in this `SRVResult`.
    pub fn host(self) -> &'a str {
        unsafe { hostname_as_str(self.srv_reply.host) }
    }

    /// Returns the weight in this `SRVResult`.
    pub fn weight(self) -> u16 {
        self.srv_reply.weight
    }

    /// Returns the priority in this `SRVResult`.
    pub fn priority(self) -> u16 {
        self.srv_reply.priority
    }

    /// Returns the port in this `SRVResult`.
    pub fn port(self) -> u16 {
        self.srv_reply.port
    }
}

impl fmt::Display for SRVResult<'_> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        write!(fmt, "Host: {}, ", self.host())?;
        write!(fmt, "Port: {}, ", self.port())?;
        write!(fmt, "Priority: {}, ", self.priority())?;
        write!(fmt, "Weight: {}", self.weight())
    }
}

pub(crate) unsafe extern "C" fn query_srv_callback<F>(
    arg: *mut c_void,
    status: c_int,
    _timeouts: c_int,
    abuf: *mut c_uchar,
    alen: c_int,
) where
    F: FnOnce(Result<SRVResults>) + Send + 'static,
{
    ares_callback!(arg.cast::<F>(), status, abuf, alen, SRVResults::parse_from);
}