qcs_api_client_common/
backoff.rs

1//! Exponential backoff for use with QCS.
2//!
3//! This re-exports types from [`backoff`](::backoff) and provides a [`default_backoff`] function
4//! to create a more useful default [`ExpontentialBackoff`].
5
6use std::time::Duration;
7
8use http::StatusCode;
9
10use ::backoff::backoff::Backoff;
11pub use ::backoff::*;
12
13/// Create a default [`ExponentialBackoff`] for use with QCS.
14///
15/// This backoff will retry for up to 5 minutes, with a maximum interval of 30 seconds and some
16/// randomized jitter.
17#[allow(clippy::module_name_repetitions)]
18#[must_use]
19pub fn default_backoff() -> ExponentialBackoff {
20    ExponentialBackoffBuilder::new()
21        .with_max_elapsed_time(Some(Duration::from_secs(300)))
22        .with_max_interval(Duration::from_secs(30))
23        .build()
24}
25
26/// Return `true` if the status code is one that could be retried.
27#[must_use]
28pub const fn status_code_is_retry(code: StatusCode) -> bool {
29    matches!(
30        code,
31        StatusCode::SERVICE_UNAVAILABLE | StatusCode::TOO_MANY_REQUESTS
32    )
33}
34
35/// Return `Some` if the response specifies a `Retry-After` header or the provided `backoff` has
36/// another backoff to try. If `None` is returned, the request should not be retried.
37#[must_use]
38pub fn duration_from_response(
39    status: StatusCode,
40    headers: &http::HeaderMap,
41    backoff: &mut ExponentialBackoff,
42) -> Option<Duration> {
43    use time::{format_description::well_known::Rfc2822, OffsetDateTime};
44
45    if status_code_is_retry(status) {
46        if let Some(value) = headers.get(http::header::RETRY_AFTER) {
47            if let Ok(value) = value.to_str() {
48                if let Ok(value) = value.parse::<u64>() {
49                    return Some(Duration::from_secs(value));
50                } else if let Ok(date) = OffsetDateTime::parse(value, &Rfc2822) {
51                    let duration = date - OffsetDateTime::now_utc();
52                    // This will fail if the number is too large or negative
53                    let millis = duration.whole_milliseconds().try_into().ok()?;
54                    return Some(Duration::from_millis(millis));
55                }
56            }
57        }
58
59        backoff.next_backoff()
60    } else {
61        None
62    }
63}
64
65fn can_retry_method(method: &http::Method) -> bool {
66    // Safe means the method is essentially read-only (see https://datatracker.ietf.org/doc/html/rfc7231#section-4.2.1)
67    // Idempotent means multiple identical requests have the same side-effects as a single one (see https://datatracker.ietf.org/doc/html/rfc7231#section-4.2.2)
68
69    // Idempotent methods are defined as safe methods + PUT and DELETE.
70    // Since we have some API endpoints using PUT and DELETE that are not idempotent, this function
71    // currently returns just safe methods.
72
73    method.is_safe()
74}
75
76/// Return `Some` if the error is one that makes sense to retry and `method` is one that indicates
77/// it is safe to retry.
78#[must_use]
79pub fn duration_from_reqwest_error(
80    method: &http::Method,
81    error: &reqwest::Error,
82    backoff: &mut ExponentialBackoff,
83) -> Option<Duration> {
84    if can_retry_method(method) {
85        // There is no exposed method to inspect the inner hyper error in the reqwest error, only
86        // `is_*` methods. There is no reqwest method corresponding to the hyper `is_closed`, so we
87        // inspect the debug string instead.
88        if error.is_timeout()
89            || error.is_connect()
90            || error.is_request()
91            || format!("{error:?}").contains("source: hyper::Error(ChannelClosed)")
92        {
93            backoff.next_backoff()
94        } else {
95            None
96        }
97    } else {
98        None
99    }
100}
101
102/// Return `Some` if the error is one that makes sense to retry and `method` is one that indicates
103/// it is safe to retry.
104#[must_use]
105pub fn duration_from_io_error(
106    method: &http::Method,
107    error: &std::io::Error,
108    backoff: &mut ExponentialBackoff,
109) -> Option<Duration> {
110    use std::io::ErrorKind;
111    if can_retry_method(method) {
112        if matches!(
113            error.kind(),
114            ErrorKind::ConnectionReset | ErrorKind::ConnectionAborted
115        ) {
116            backoff.next_backoff()
117        } else {
118            None
119        }
120    } else {
121        None
122    }
123}
qcs_api_client_common/backoff.rs

qcs_api_client_common/
backoff.rs
