azure_core/policies/retry_policies/retry_policy.rs
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use crate::{
date,
error::{Error, ErrorKind, HttpError, ResultExt},
headers::{Headers, RETRY_AFTER, RETRY_AFTER_MS, X_MS_RETRY_AFTER_MS},
policies::{Policy, PolicyResult, Request},
sleep::sleep,
Context, StatusCode,
};
use async_trait::async_trait;
use std::{sync::Arc, time::Duration};
use time::OffsetDateTime;
use tracing::{debug, trace};
/// Attempts to parse the supplied string as an HTTP date, of the form defined by RFC 1123 (e.g. `Fri, 01 Jan 2021 00:00:00 GMT`).
/// Returns `None` if the string is not a valid HTTP date.
fn try_parse_retry_after_http_date(http_date: &str) -> Option<OffsetDateTime> {
crate::date::parse_rfc1123(http_date).ok()
}
/// A function that returns an `OffsetDateTime`.
type DateTimeFn = fn() -> OffsetDateTime;
/// Get the duration to delay between retry attempts, provided by the headers from the response.
///
/// This function checks for retry-after headers in the following order, following the
/// JS Azure SDK implementation: <https://github.com/Azure/azure-sdk-for-js/blob/17de1a2b7f3ad61f34ff62876eced7d077c10d4b/sdk/core/core-rest-pipeline/src/retryStrategies/throttlingRetryStrategy.ts#L35>
/// * `retry-after-ms`
/// * `x-ms-retry-after-ms`
/// * `Retry-After`
///
/// If no header is provided, None is returned.
pub(crate) fn get_retry_after(headers: &Headers, datetime_now: DateTimeFn) -> Option<Duration> {
[RETRY_AFTER_MS, X_MS_RETRY_AFTER_MS, RETRY_AFTER]
.iter()
.find_map(|header| {
headers.get_str(header).ok().and_then(|v| {
if header == &RETRY_AFTER {
// RETRY_AFTER values are either in seconds or a HTTP date
v.parse::<u64>().ok().map(Duration::from_secs).or_else(|| {
try_parse_retry_after_http_date(v).map(|retry_after_datetime| {
let now = datetime_now();
if retry_after_datetime < now {
Duration::from_secs(0)
} else {
date::diff(retry_after_datetime, now)
}
})
})
} else {
// RETRY_AFTER_MS or X_MS_RETRY_AFTER_MS values are in milliseconds
v.parse::<u64>().ok().map(Duration::from_millis)
}
})
})
}
/// A retry policy.
///
/// In the simple form, the policies need only differ in how
/// they determine if the retry has expired and for how long they should
/// sleep between retries.
///
/// `wait` can be implemented in more complex cases where a simple test of time
/// is not enough.
#[async_trait]
pub trait RetryPolicy: std::fmt::Debug + Send + Sync {
/// Determine if no more retries should be performed.
///
/// Must return true if no more retries should be attempted.
fn is_expired(&self, duration_since_start: Duration, retry_count: u32) -> bool;
/// Determine how long before the next retry should be attempted.
fn sleep_duration(&self, retry_count: u32) -> Duration;
/// A Future that will wait until the request can be retried.
/// `error` is the [`Error`] value the led to a retry attempt.
/// `retry_after` is the duration to wait before retrying, if provided by the server response.
async fn wait(&self, _error: &Error, retry_count: u32, retry_after: Option<Duration>) {
let policy_sleep_duration = self.sleep_duration(retry_count);
// If the server provided a retry-after header, use the max of that and the policy sleep duration
let sleep_duration = retry_after.map_or(policy_sleep_duration, |retry_after| {
std::cmp::max(retry_after, policy_sleep_duration)
});
sleep(sleep_duration).await;
}
}
/// The status codes where a retry should be attempted.
///
/// On all other 4xx and 5xx status codes no retry is attempted.
const RETRY_STATUSES: &[StatusCode] = &[
StatusCode::RequestTimeout,
StatusCode::TooManyRequests,
StatusCode::InternalServerError,
StatusCode::BadGateway,
StatusCode::ServiceUnavailable,
StatusCode::GatewayTimeout,
];
#[cfg_attr(target_arch = "wasm32", async_trait::async_trait(?Send))]
#[cfg_attr(not(target_arch = "wasm32"), async_trait::async_trait)]
impl<T> Policy for T
where
T: RetryPolicy,
{
async fn send(
&self,
ctx: &Context,
request: &mut Request,
next: &[Arc<dyn Policy>],
) -> PolicyResult {
let mut retry_count = 0;
let mut start = None;
loop {
if retry_count > 0 {
request.body.reset().await.context(
ErrorKind::Other,
"failed to reset body stream before retrying request",
)?;
}
let result = next[0].send(ctx, request, &next[1..]).await;
// only start keeping track of time after the first request is made
let start = start.get_or_insert_with(OffsetDateTime::now_utc);
let (last_error, retry_after) = match result {
Ok(response) if response.status().is_success() => {
trace!(
"Successful response. Request={:?} response={:?}",
request,
response
);
return Ok(response);
}
Ok(response) => {
// Error status code
let status = response.status();
// For a 429 response (TooManyRequests) or 503 (ServiceUnavailable),
// use any "retry-after" headers returned by the server to determine how long to wait before retrying.
// https://learn.microsoft.com/en-us/azure/architecture/best-practices/retry-service-specific#retry-usage-guidance
let retry_after = match status {
StatusCode::TooManyRequests | StatusCode::ServiceUnavailable => {
get_retry_after(response.headers(), OffsetDateTime::now_utc)
}
_ => None,
};
let http_error = HttpError::new(response).await;
let error_kind = ErrorKind::http_response(
status,
http_error.error_code().map(std::borrow::ToOwned::to_owned),
);
if !RETRY_STATUSES.contains(&status) {
debug!(
"server returned error status which will not be retried: {}",
status
);
// Server didn't return a status we retry on so return early
let error = Error::full(
error_kind,
http_error,
format!(
"server returned error status which will not be retried: {status}"
),
);
return Err(error);
}
debug!(
"server returned error status which requires retry: {}",
status
);
(Error::new(error_kind, http_error), retry_after)
}
Err(error) => {
if error.kind() == &ErrorKind::Io {
debug!(
"io error occurred when making request which will be retried: {}",
error
);
// IO error so no Retry-After headers - leave the retry period up to the policy
let retry_after = None;
(error, retry_after)
} else {
return Err(
error.context("non-io error occurred which will not be retried")
);
}
}
};
let time_since_start = (OffsetDateTime::now_utc() - *start)
.try_into()
.unwrap_or_default();
if self.is_expired(time_since_start, retry_count) {
return Err(last_error
.context("retry policy expired and the request will no longer be retried"));
}
retry_count += 1;
self.wait(&last_error, retry_count, retry_after).await;
}
}
}
// Unit tests
#[cfg(test)]
mod test {
use super::*;
use time::macros::datetime;
// A function that returns a fixed "now" value for testing.
fn datetime_now() -> OffsetDateTime {
datetime!(2021-01-01 0:00:00 UTC)
}
#[test]
fn test_try_parse_retry_after_http_date() {
// Test parsing a valid HTTP date
let retry_after = try_parse_retry_after_http_date("Fri, 01 Jan 2021 00:00:00 GMT");
assert_eq!(retry_after, Some(datetime!(2021-01-01 0:00:00 UTC)));
// Test parsing an invalid HTTP date (missing day of week)
let retry_after = try_parse_retry_after_http_date("01 Jan 2021 00:00:00 GMT");
assert_eq!(retry_after, None);
// Test parsing an invalid HTTP date (complete garbage)
let retry_after = try_parse_retry_after_http_date("invalid");
assert_eq!(retry_after, None);
// Test parsing an integer value fails
let retry_after = try_parse_retry_after_http_date("123");
assert_eq!(retry_after, None);
}
#[test]
fn test_get_retry_after() {
// Test parsing a valid HTTP date that is 10 secs in the future
let mut headers = Headers::new();
headers.insert(RETRY_AFTER, "Fri, 01 Jan 2021 00:00:10 GMT");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_secs(10)));
// Test parsing a valid HTTP date that is in the past returns 0
let mut headers = Headers::new();
headers.insert(RETRY_AFTER, "Thu, 31 Dec 2020 23:59:50 GMT");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_secs(0)));
// Test that when no retry headers are present, None is returned
let headers = Headers::new();
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, None);
// Test parsing an invalid HTTP date
let mut headers = Headers::new();
headers.insert(RETRY_AFTER, "invalid");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, None);
// Test `RETRY_AFTER` parsing an integer value
let mut headers = Headers::new();
headers.insert(RETRY_AFTER, "123");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_secs(123)));
// Test `RETRY_AFTER_MS` parsing an integer value
let mut headers = Headers::new();
headers.insert(RETRY_AFTER_MS, "123");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(123)));
// Test `RETRY_AFTER_MS` parsing an integer value
let mut headers = Headers::new();
headers.insert(RETRY_AFTER_MS, "123");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(123)));
// Test `X_MS_RETRY_AFTER_MS` parsing an integer value
let mut headers = Headers::new();
headers.insert(X_MS_RETRY_AFTER_MS, "123");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(123)));
// Test that when both `RETRY_AFTER_MS` and `RETRY_AFTER` are present, `RETRY_AFTER_MS` is used
let mut headers = Headers::new();
headers.insert(RETRY_AFTER_MS, "123");
headers.insert(RETRY_AFTER, "456");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(123)));
// Test that when both `X_MS_RETRY_AFTER_MS` and `RETRY_AFTER` are present, `X_MS_RETRY_AFTER_MS` is used
let mut headers = Headers::new();
headers.insert(X_MS_RETRY_AFTER_MS, "123");
headers.insert(RETRY_AFTER, "456");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(123)));
// Test that when both `X_MS_RETRY_AFTER_MS` and `RETRY_AFTER_MS` are present, `RETRY_AFTER_MS` is used
let mut headers = Headers::new();
headers.insert(X_MS_RETRY_AFTER_MS, "123");
headers.insert(RETRY_AFTER_MS, "456");
let retry_after = get_retry_after(&headers, datetime_now);
assert_eq!(retry_after, Some(Duration::from_millis(456)));
}
}