domain/resolv/stub/mod.rs
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//! A stub resolver.
//!
//! The most simple resolver possible simply relays all messages to one of a
//! set of pre-configured resolvers that will do the actual work. This is
//! equivalent to what the resolver part of the C library does. This module
//! provides such a stub resolver that emulates this C resolver as closely
//! as possible, in particular in the way it is being configured.
//!
//! The main type is [`StubResolver`] that implements the [`Resolver`] trait
//! and thus can be used with the various lookup functions.
use self::conf::{
ResolvConf, ResolvOptions, SearchSuffix, ServerConf, Transport,
};
use crate::base::iana::Rcode;
use crate::base::message::Message;
use crate::base::message_builder::{AdditionalBuilder, MessageBuilder};
use crate::base::name::{ToName, ToRelativeName};
use crate::base::question::Question;
use crate::net::client::dgram_stream;
use crate::net::client::multi_stream;
use crate::net::client::protocol::{TcpConnect, UdpConnect};
use crate::net::client::redundant;
use crate::net::client::request::{
ComposeRequest, Error, RequestMessage, SendRequest,
};
use crate::resolv::lookup::addr::{lookup_addr, FoundAddrs};
use crate::resolv::lookup::host::{lookup_host, search_host, FoundHosts};
use crate::resolv::lookup::srv::{lookup_srv, FoundSrvs, SrvError};
use crate::resolv::resolver::{Resolver, SearchNames};
use bytes::Bytes;
use futures_util::stream::{FuturesUnordered, StreamExt};
use octseq::array::Array;
use std::boxed::Box;
use std::fmt::Debug;
use std::future::Future;
use std::net::IpAddr;
use std::pin::Pin;
use std::string::ToString;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::vec::Vec;
use std::{io, ops};
#[cfg(feature = "resolv-sync")]
use tokio::runtime;
use tokio::sync::Mutex;
use tokio::time::timeout;
//------------ Sub-modules ---------------------------------------------------
pub mod conf;
//------------ Module Configuration ------------------------------------------
//------------ StubResolver --------------------------------------------------
/// A DNS stub resolver.
///
/// This type collects all information making it possible to start DNS
/// queries. You can create a new resolver using the system’s configuration
/// using the [`new`] associate function or using your own configuration with
/// [`from_conf`].
///
/// Stub resolver values can be cloned relatively cheaply as they keep all
/// information behind an arc.
///
/// If you want to run a single query or lookup on a resolver synchronously,
/// you can do so simply by using the [`run`] or [`run_with_conf`] associated
/// functions.
///
/// [`new`]: #method.new
/// [`from_conf`]: #method.from_conf
/// [`query`]: #method.query
/// [`run`]: #method.run
/// [`run_with_conf`]: #method.run_with_conf
#[derive(Debug)]
pub struct StubResolver {
transport: Mutex<Option<redundant::Connection<RequestMessage<Vec<u8>>>>>,
/// Resolver options.
options: ResolvOptions,
servers: Vec<ServerConf>,
}
impl StubResolver {
/// Creates a new resolver using the system’s default configuration.
pub fn new() -> Self {
Self::from_conf(ResolvConf::default())
}
/// Creates a new resolver using the given configuraiton.
pub fn from_conf(conf: ResolvConf) -> Self {
StubResolver {
transport: None.into(),
options: conf.options,
servers: conf.servers,
}
}
pub fn options(&self) -> &ResolvOptions {
&self.options
}
pub async fn query<N: ToName, Q: Into<Question<N>>>(
&self,
question: Q,
) -> Result<Answer, io::Error> {
Query::new(self)?
.run(Query::create_message(question.into()))
.await
}
async fn query_message(
&self,
message: QueryMessage,
) -> Result<Answer, io::Error> {
Query::new(self)?.run(message).await
}
async fn setup_transport<
CR: Clone + Debug + ComposeRequest + Send + Sync + 'static,
>(
&self,
) -> Result<redundant::Connection<CR>, Error> {
// Create a redundant transport and fill it with the right transports
let (redun, transp) = redundant::Connection::new();
// Start the run function on a separate task.
let redun_run_fut = transp.run();
// It would be nice to have just one task. However redun.run() has to
// execute before we can call redun.add(). However, we need to know
// the type of the elements we add to FuturesUnordered. For the moment
// we have two tasks.
tokio::spawn(async move {
redun_run_fut.await;
});
let fut_list_tcp = FuturesUnordered::new();
let fut_list_udp_tcp = FuturesUnordered::new();
// Start the tasks with empty base transports. We need redun to be
// running before we can add transports.
// We have 3 modes of operation: use_vc: only use TCP, ign_tc: only
// UDP no fallback to TCP, and normal with is UDP falling back to TCP.
for s in &self.servers {
// This assumes that Transport only has UdpTcp and Tcp. Sadly, a
// match doesn’t work here because of the use_cv flag.
if self.options.use_vc || matches!(s.transport, Transport::Tcp) {
let (conn, tran) =
multi_stream::Connection::new(TcpConnect::new(s.addr));
// Start the run function on a separate task.
fut_list_tcp.push(tran.run());
redun.add(Box::new(conn)).await?;
} else {
let udp_connect = UdpConnect::new(s.addr);
let tcp_connect = TcpConnect::new(s.addr);
let (conn, tran) =
dgram_stream::Connection::new(udp_connect, tcp_connect);
// Start the run function on a separate task.
fut_list_udp_tcp.push(tran.run());
redun.add(Box::new(conn)).await?;
}
}
tokio::spawn(async move {
run(fut_list_tcp, fut_list_udp_tcp).await;
});
Ok(redun)
}
async fn get_transport(
&self,
) -> Result<redundant::Connection<RequestMessage<Vec<u8>>>, Error> {
let mut opt_transport = self.transport.lock().await;
match &*opt_transport {
Some(transport) => Ok(transport.clone()),
None => {
let transport = self.setup_transport().await?;
*opt_transport = Some(transport.clone());
Ok(transport)
}
}
}
}
async fn run<TcpFut: Future, UdpTcpFut: Future>(
mut fut_list_tcp: FuturesUnordered<TcpFut>,
mut fut_list_udp_tcp: FuturesUnordered<UdpTcpFut>,
) {
loop {
let tcp_empty = fut_list_tcp.is_empty();
let udp_tcp_empty = fut_list_udp_tcp.is_empty();
if tcp_empty && udp_tcp_empty {
break;
}
tokio::select! {
_ = fut_list_tcp.next(), if !tcp_empty => {
// Nothing to do
}
_ = fut_list_udp_tcp.next(), if !udp_tcp_empty => {
// Nothing to do
}
}
}
}
impl StubResolver {
pub async fn lookup_addr(
&self,
addr: IpAddr,
) -> Result<FoundAddrs<&Self>, io::Error> {
lookup_addr(&self, addr).await
}
pub async fn lookup_host(
&self,
qname: impl ToName,
) -> Result<FoundHosts<&Self>, io::Error> {
lookup_host(&self, qname).await
}
pub async fn search_host(
&self,
qname: impl ToRelativeName,
) -> Result<FoundHosts<&Self>, io::Error> {
search_host(&self, qname).await
}
/// Performs an SRV lookup using this resolver.
///
/// See the documentation for the [`lookup_srv`] function for details.
pub async fn lookup_srv(
&self,
service: impl ToRelativeName,
name: impl ToName,
fallback_port: u16,
) -> Result<Option<FoundSrvs>, SrvError> {
lookup_srv(&self, service, name, fallback_port).await
}
}
#[cfg(feature = "resolv-sync")]
#[cfg_attr(docsrs, doc(cfg(feature = "resolv-sync")))]
impl StubResolver {
/// Synchronously perform a DNS operation atop a standard resolver.
///
/// This associated functions removes almost all boiler plate for the
/// case that you want to perform some DNS operation, either a query or
/// lookup, on a resolver using the system’s configuration and wait for
/// the result.
///
/// The only argument is a closure taking a reference to a [`StubResolver`]
/// and returning a future. Whatever that future resolves to will be
/// returned.
pub fn run<R, T, E, F>(op: F) -> R::Output
where
R: Future<Output = Result<T, E>> + Send + 'static,
E: From<io::Error>,
F: FnOnce(StubResolver) -> R + Send + 'static,
{
Self::run_with_conf(ResolvConf::default(), op)
}
/// Synchronously perform a DNS operation atop a configured resolver.
///
/// This is like [`run`] but also takes a resolver configuration for
/// tailor-making your own resolver.
///
/// [`run`]: Self::run
pub fn run_with_conf<R, T, E, F>(conf: ResolvConf, op: F) -> R::Output
where
R: Future<Output = Result<T, E>> + Send + 'static,
E: From<io::Error>,
F: FnOnce(StubResolver) -> R + Send + 'static,
{
let resolver = Self::from_conf(conf);
let runtime = runtime::Builder::new_current_thread()
.enable_all()
.build()?;
runtime.block_on(op(resolver))
}
}
impl Default for StubResolver {
fn default() -> Self {
Self::new()
}
}
impl<'a> Resolver for &'a StubResolver {
type Octets = Bytes;
type Answer = Answer;
type Query =
Pin<Box<dyn Future<Output = Result<Answer, io::Error>> + Send + 'a>>;
fn query<N, Q>(&self, question: Q) -> Self::Query
where
N: ToName,
Q: Into<Question<N>>,
{
let message = Query::create_message(question.into());
Box::pin(self.query_message(message))
}
}
impl<'a> SearchNames for &'a StubResolver {
type Name = SearchSuffix;
type Iter = SearchIter<'a>;
fn search_iter(&self) -> Self::Iter {
SearchIter {
resolver: self,
pos: 0,
}
}
}
//------------ Query ---------------------------------------------------------
pub struct Query<'a> {
/// The resolver whose configuration we are using.
resolver: &'a StubResolver,
edns: Arc<AtomicBool>,
/// The preferred error to return.
///
/// Every time we finish a single query, we see if we can update this with
/// a better one. If we finally have to fail, we return this result. This
/// is a result so we can return a servfail answer if that is the only
/// answer we get. (Remember, SERVFAIL is returned for a bogus answer, so
/// you might want to know.)
error: Result<Answer, io::Error>,
}
impl<'a> Query<'a> {
pub fn new(resolver: &'a StubResolver) -> Result<Self, io::Error> {
Ok(Query {
resolver,
edns: Arc::new(AtomicBool::new(true)),
error: Err(io::Error::new(
io::ErrorKind::TimedOut,
"all timed out",
)),
})
}
pub async fn run(
mut self,
mut message: QueryMessage,
) -> Result<Answer, io::Error> {
loop {
match self.run_query(&mut message).await {
Ok(answer) => {
if answer.header().rcode() == Rcode::FORMERR
&& self.does_edns()
{
// FORMERR with EDNS: turn off EDNS and try again.
self.disable_edns();
continue;
} else if answer.header().rcode() == Rcode::SERVFAIL {
// SERVFAIL: go to next server.
self.update_error_servfail(answer);
} else {
// I guess we have an answer ...
return Ok(answer);
}
}
Err(err) => self.update_error(err),
}
return self.error;
}
}
fn create_message(question: Question<impl ToName>) -> QueryMessage {
let mut message = MessageBuilder::from_target(Default::default())
.expect("MessageBuilder should not fail");
message.header_mut().set_rd(true);
let mut message = message.question();
message.push(question).expect("push should not fail");
message.additional()
}
async fn run_query(
&mut self,
message: &mut QueryMessage,
) -> Result<Answer, io::Error> {
let msg = Message::from_octets(message.as_target().to_vec())
.expect("Message::from_octets should not fail");
let request_msg = RequestMessage::new(msg).map_err(|e| {
io::Error::new(io::ErrorKind::Other, e.to_string())
})?;
let transport = self.resolver.get_transport().await.map_err(|e| {
io::Error::new(io::ErrorKind::Other, e.to_string())
})?;
let mut gr_fut = transport.send_request(request_msg);
let reply =
timeout(self.resolver.options.timeout, gr_fut.get_response())
.await?
.map_err(|e| {
io::Error::new(io::ErrorKind::Other, e.to_string())
})?;
Ok(Answer { message: reply })
}
fn update_error(&mut self, err: io::Error) {
// We keep the last error except for timeouts or if we have a servfail
// answer already. Since we start with a timeout, we still get a that
// if everything times out.
if err.kind() != io::ErrorKind::TimedOut && self.error.is_err() {
self.error = Err(err)
}
}
fn update_error_servfail(&mut self, answer: Answer) {
self.error = Ok(answer)
}
pub fn does_edns(&self) -> bool {
self.edns.load(Ordering::Relaxed)
}
pub fn disable_edns(&self) {
self.edns.store(false, Ordering::Relaxed);
}
}
//------------ QueryMessage --------------------------------------------------
// XXX This needs to be re-evaluated if we start adding OPTions to the query.
pub(super) type QueryMessage = AdditionalBuilder<Array<512>>;
//------------ Answer --------------------------------------------------------
/// The answer to a question.
///
/// This type is a wrapper around the DNS [`Message`] containing the answer
/// that provides some additional information.
#[derive(Clone)]
pub struct Answer {
message: Message<Bytes>,
}
impl Answer {
/// Returns whether the answer is a final answer to be returned.
pub fn is_final(&self) -> bool {
(self.message.header().rcode() == Rcode::NOERROR
|| self.message.header().rcode() == Rcode::NXDOMAIN)
&& !self.message.header().tc()
}
/// Returns whether the answer is truncated.
pub fn is_truncated(&self) -> bool {
self.message.header().tc()
}
pub fn into_message(self) -> Message<Bytes> {
self.message
}
}
impl From<Message<Bytes>> for Answer {
fn from(message: Message<Bytes>) -> Self {
Answer { message }
}
}
impl ops::Deref for Answer {
type Target = Message<Bytes>;
fn deref(&self) -> &Self::Target {
&self.message
}
}
impl AsRef<Message<Bytes>> for Answer {
fn as_ref(&self) -> &Message<Bytes> {
&self.message
}
}
//------------ SearchIter ----------------------------------------------------
#[derive(Clone, Debug)]
pub struct SearchIter<'a> {
resolver: &'a StubResolver,
pos: usize,
}
impl<'a> Iterator for SearchIter<'a> {
type Item = SearchSuffix;
fn next(&mut self) -> Option<Self::Item> {
if let Some(res) = self.resolver.options().search.get(self.pos) {
self.pos += 1;
Some(res.clone())
} else {
None
}
}
}