hickory_proto/xfer/
retry_dns_handle.rs

1// Copyright 2015-2016 Benjamin Fry <benjaminfry@me.com>
2//
3// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
4// https://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
5// https://opensource.org/licenses/MIT>, at your option. This file may not be
6// copied, modified, or distributed except according to those terms.
7
8//! `RetryDnsHandle` allows for DnsQueries to be reattempted on failure
9
10use std::pin::Pin;
11use std::task::{Context, Poll};
12
13use futures_util::stream::{Stream, StreamExt};
14
15use crate::error::{ProtoError, ProtoErrorKind};
16use crate::xfer::{DnsRequest, DnsResponse};
17use crate::DnsHandle;
18
19/// Can be used to reattempt queries if they fail
20///
21/// Note: this does not reattempt queries that fail with a negative response.
22/// For example, if a query gets a `NODATA` response from a name server, the
23/// query will not be retried. It only reattempts queries that effectively
24/// failed to get a response, such as queries that resulted in IO or timeout
25/// errors.
26///
27/// Whether an error is retryable by the [`RetryDnsHandle`] is determined by the
28/// [`RetryableError`] trait.
29///
30/// *note* Current value of this is not clear, it may be removed
31#[derive(Clone)]
32#[must_use = "queries can only be sent through a ClientHandle"]
33pub struct RetryDnsHandle<H>
34where
35    H: DnsHandle + Unpin + Send,
36    H::Error: RetryableError,
37{
38    handle: H,
39    attempts: usize,
40}
41
42impl<H> RetryDnsHandle<H>
43where
44    H: DnsHandle + Unpin + Send,
45    H::Error: RetryableError,
46{
47    /// Creates a new Client handler for reattempting requests on failures.
48    ///
49    /// # Arguments
50    ///
51    /// * `handle` - handle to the dns connection
52    /// * `attempts` - number of attempts before failing
53    pub fn new(handle: H, attempts: usize) -> Self {
54        Self { handle, attempts }
55    }
56}
57
58impl<H> DnsHandle for RetryDnsHandle<H>
59where
60    H: DnsHandle + Send + Unpin + 'static,
61    H::Error: RetryableError,
62{
63    type Response = Pin<Box<dyn Stream<Item = Result<DnsResponse, Self::Error>> + Send + Unpin>>;
64    type Error = <H as DnsHandle>::Error;
65
66    fn send<R: Into<DnsRequest>>(&self, request: R) -> Self::Response {
67        let request = request.into();
68
69        // need to clone here so that the retry can resend if necessary...
70        //  obviously it would be nice to be lazy about this...
71        let stream = self.handle.send(request.clone());
72
73        Box::pin(RetrySendStream {
74            request,
75            handle: self.handle.clone(),
76            stream,
77            remaining_attempts: self.attempts,
78        })
79    }
80}
81
82/// A stream for retrying (on failure, for the remaining number of times specified)
83struct RetrySendStream<H>
84where
85    H: DnsHandle,
86{
87    request: DnsRequest,
88    handle: H,
89    stream: <H as DnsHandle>::Response,
90    remaining_attempts: usize,
91}
92
93impl<H: DnsHandle + Unpin> Stream for RetrySendStream<H>
94where
95    <H as DnsHandle>::Error: RetryableError,
96{
97    type Item = Result<DnsResponse, <H as DnsHandle>::Error>;
98
99    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
100        // loop over the stream, on errors, spawn a new stream
101        //  on ready and not ready return.
102        loop {
103            match self.stream.poll_next_unpin(cx) {
104                Poll::Ready(Some(Err(e))) => {
105                    if self.remaining_attempts == 0 || !e.should_retry() {
106                        return Poll::Ready(Some(Err(e)));
107                    }
108
109                    if e.attempted() {
110                        self.remaining_attempts -= 1;
111                    }
112
113                    // TODO: if the "sent" Message is part of the error result,
114                    //  then we can just reuse it... and no clone necessary
115                    let request = self.request.clone();
116                    self.stream = self.handle.send(request);
117                }
118                poll => return poll,
119            }
120        }
121    }
122}
123
124/// What errors should be retried
125pub trait RetryableError {
126    /// Whether the query should be retried after this error
127    fn should_retry(&self) -> bool;
128    /// Whether this error should count as an attempt
129    fn attempted(&self) -> bool;
130}
131
132impl RetryableError for ProtoError {
133    fn should_retry(&self) -> bool {
134        true
135    }
136
137    fn attempted(&self) -> bool {
138        !matches!(self.kind(), ProtoErrorKind::Busy)
139    }
140}
141
142#[cfg(test)]
143mod test {
144    use super::*;
145    use crate::error::*;
146    use crate::op::*;
147    use crate::xfer::FirstAnswer;
148    use futures_executor::block_on;
149    use futures_util::future::*;
150    use futures_util::stream::*;
151    use std::sync::{
152        atomic::{AtomicU16, Ordering},
153        Arc,
154    };
155    use DnsHandle;
156
157    #[derive(Clone)]
158    struct TestClient {
159        last_succeed: bool,
160        retries: u16,
161        attempts: Arc<AtomicU16>,
162    }
163
164    impl DnsHandle for TestClient {
165        type Response = Box<dyn Stream<Item = Result<DnsResponse, ProtoError>> + Send + Unpin>;
166        type Error = ProtoError;
167
168        fn send<R: Into<DnsRequest>>(&self, _: R) -> Self::Response {
169            let i = self.attempts.load(Ordering::SeqCst);
170
171            if (i > self.retries || self.retries - i == 0) && self.last_succeed {
172                let mut message = Message::new();
173                message.set_id(i);
174                return Box::new(once(ok(DnsResponse::from_message(message).unwrap())));
175            }
176
177            self.attempts.fetch_add(1, Ordering::SeqCst);
178            Box::new(once(err(ProtoError::from("last retry set to fail"))))
179        }
180    }
181
182    #[test]
183    fn test_retry() {
184        let handle = RetryDnsHandle::new(
185            TestClient {
186                last_succeed: true,
187                retries: 1,
188                attempts: Arc::new(AtomicU16::new(0)),
189            },
190            2,
191        );
192        let test1 = Message::new();
193        let result = block_on(handle.send(test1).first_answer()).expect("should have succeeded");
194        assert_eq!(result.id(), 1); // this is checking the number of iterations the TestClient ran
195    }
196
197    #[test]
198    fn test_error() {
199        let client = RetryDnsHandle::new(
200            TestClient {
201                last_succeed: false,
202                retries: 1,
203                attempts: Arc::new(AtomicU16::new(0)),
204            },
205            2,
206        );
207        let test1 = Message::new();
208        assert!(block_on(client.send(test1).first_answer()).is_err());
209    }
210}
hickory_proto/xfer/retry_dns_handle.rs

hickory_proto/xfer/
retry_dns_handle.rs
