nscd_lookup/
sync.rs

1//! Synchronous / blocking host name look up
2
3use std::ops::ControlFlow;
4use std::os::fd::{AsFd, OwnedFd};
5use std::time::{Duration, Instant};
6
7use rustix::event::{PollFd, PollFlags, Timespec, poll};
8use rustix::io::Errno;
9
10use crate::protocol::{
11    AiResponseHeader, DataError, HeaderError, IoState, IpAddrIterator, IsEmpty, IsWouldblock,
12    RequestError, SocketError, interpret_data, open_socket, read_data, read_header, write_request,
13};
14
15/// Look up a host name, synchronously.
16///
17/// This function looks up `host` using [nscd](https://man7.org/linux/man-pages/man8/nscd.8.html),
18/// stores the response in `buf`, and returns an iterator over the data.
19/// The result is `None` if there were no IP addresses associated with domain name.
20///
21/// If the timeout is `None`, then [`DEFAULT_TIMEOUT`] is used.
22#[inline]
23pub fn lookup(
24    host: impl AsRef<[u8]>,
25    buf: &mut Vec<u8>,
26    timeout: Option<Duration>,
27) -> Result<Option<IpAddrIterator<'_>>, Error> {
28    do_lookup(host.as_ref(), buf, timeout.unwrap_or(DEFAULT_TIMEOUT))
29}
30
31fn do_lookup<'a>(
32    host: &[u8],
33    buf: &'a mut Vec<u8>,
34    timeout: Duration,
35) -> Result<Option<IpAddrIterator<'a>>, Error> {
36    let deadline = Instant::now() + timeout;
37
38    let sock = open_socket().map_err(Error::Socket)?;
39
40    let mut io = IoState::default();
41    loop {
42        match write_request(sock.as_fd(), &mut io, host) {
43            Ok(ControlFlow::Continue(())) => continue,
44            Ok(ControlFlow::Break(())) => break,
45            Err(err) if err.is_wouldblock() => await_writable(&sock, deadline)?,
46            Err(err) => return Err(Error::Request(err)),
47        }
48    }
49
50    io = IoState::default();
51    let mut resp = AiResponseHeader::default();
52    let data_len = loop {
53        await_readable(&sock, deadline)?;
54        match read_header(sock.as_fd(), &mut io, &mut resp) {
55            Ok(ControlFlow::Continue(())) => continue,
56            Ok(ControlFlow::Break(IsEmpty::Empty)) => return Ok(None),
57            Ok(ControlFlow::Break(IsEmpty::HasData(data_len))) => break data_len,
58            Err(err) if err.is_wouldblock() => await_readable(&sock, deadline)?,
59            Err(err) => return Err(Error::Header(err)),
60        }
61    };
62    buf.resize(data_len, 0);
63
64    io = IoState::default();
65    loop {
66        match read_data(sock.as_fd(), &mut io, buf) {
67            Ok(ControlFlow::Continue(())) => continue,
68            Ok(ControlFlow::Break(())) => break,
69            Err(err) if err.is_wouldblock() => await_readable(&sock, deadline)?,
70            Err(err) => return Err(Error::Data(err)),
71        }
72    }
73
74    Ok(Some(interpret_data(&resp, buf)?))
75}
76
77fn await_writable(sock: &OwnedFd, deadline: Instant) -> Result<(), Error> {
78    let events = PollFlags::IN
79        | PollFlags::OUT
80        | PollFlags::WRNORM
81        | PollFlags::WRBAND
82        | PollFlags::ERR
83        | PollFlags::HUP;
84    await_io(sock, deadline, events)
85}
86
87fn await_readable(sock: &OwnedFd, deadline: Instant) -> Result<(), Error> {
88    let events = PollFlags::IN
89        | PollFlags::PRI
90        | PollFlags::RDNORM
91        | PollFlags::RDBAND
92        | PollFlags::ERR
93        | PollFlags::HUP;
94    await_io(sock, deadline, events)
95}
96
97fn await_io(sock: &OwnedFd, deadline: Instant, events: PollFlags) -> Result<(), Error> {
98    let Some(remaining) = deadline.checked_duration_since(Instant::now()) else {
99        return Err(Error::Timeout(None));
100    };
101
102    let timeout = Timespec::try_from(remaining).map_err(|_| Error::Timeout(None))?;
103    let mut fds = [PollFd::new(sock, events)];
104    if poll(&mut fds, Some(&timeout)).map_err(|err| Error::Timeout(Some(err)))? == 0 {
105        return Err(Error::Timeout(None));
106    }
107
108    Ok(())
109}
110
111#[derive(Debug, Clone, Copy, thiserror::Error, displaydoc::Display)]
112/// An error returned by [`lookup()`]
113pub enum Error {
114    /// Could not use socket
115    Socket(#[from] SocketError),
116    /// Could not send request
117    Request(#[from] RequestError),
118    /// Could not receive response header
119    Header(#[from] HeaderError),
120    /// Could not receive response data
121    Data(#[from] DataError),
122    /// Timeout while waiting for response
123    Timeout(#[source] Option<Errno>),
124}
125
126/// Default timeout for [`lookup()`]'s `timeout` parameter.
127pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(5);
nscd_lookup/sync.rs

nscd_lookup/
sync.rs
