#
cargo/util/network/
retry.rs

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    //! Utilities for retrying a network operation.
    //!
    //! Some network errors are considered "spurious", meaning it is not a real
    //! error (such as a 404 not found) and is likely a transient error (like a
    //! bad network connection) that we can hope will resolve itself shortly. The
    //! [`Retry`] type offers a way to repeatedly perform some kind of network
    //! operation with a delay if it detects one of these possibly transient
    //! errors.
    //!
    //! This supports errors from [`git2`], [`gix`], [`curl`], and
    //! [`HttpNotSuccessful`] 5xx HTTP errors.
    //!
    //! The number of retries can be configured by the user via the `net.retry`
    //! config option. This indicates the number of times to retry the operation
    //! (default 3 times for a total of 4 attempts).
    //!
    //! There are hard-coded constants that indicate how long to sleep between
    //! retries. The constants are tuned to balance a few factors, such as the
    //! responsiveness to the user (we don't want cargo to hang for too long
    //! retrying things), and accommodating things like Cloudfront's default
    //! negative TTL of 10 seconds (if Cloudfront gets a 5xx error for whatever
    //! reason it won't try to fetch again for 10 seconds).
    //!
    //! The timeout also implements a primitive form of random jitter. This is so
    //! that if multiple requests fail at the same time that they don't all flood
    //! the server at the same time when they are retried. This jitter still has
    //! some clumping behavior, but should be good enough.
    //!
    //! [`Retry`] is the core type for implementing retry logic. The
    //! [`Retry::try`] method can be called with a callback, and it will
    //! indicate if it needs to be called again sometime in the future if there
    //! was a possibly transient error. The caller is responsible for sleeping the
    //! appropriate amount of time and then calling [`Retry::try`] again.
    //!
    //! [`with_retry`] is a convenience function that will create a [`Retry`] and
    //! handle repeatedly running a callback until it succeeds, or it runs out of
    //! retries.
    //!
    //! Some interesting resources about retries:
    //! - <https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/>
    //! - <https://en.wikipedia.org/wiki/Exponential_backoff>
    //! - <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After>

    use crate::util::errors::HttpNotSuccessful;
    use crate::{CargoResult, GlobalContext};
    use anyhow::Error;
    use rand::Rng;
    use std::cmp::min;
    use std::time::Duration;

    /// State for managing retrying a network operation.
    pub struct Retry<'a> {
        gctx: &'a GlobalContext,
        /// The number of failed attempts that have been done so far.
        ///
        /// Starts at 0, and increases by one each time an attempt fails.
        retries: u64,
        /// The maximum number of times the operation should be retried.
        ///
        /// 0 means it should never retry.
        max_retries: u64,
    }

    /// The result of attempting some operation via [`Retry::try`].
    pub enum RetryResult<T> {
        /// The operation was successful.
        ///
        /// The wrapped value is the return value of the callback function.
        Success(T),
        /// The operation was an error, and it should not be tried again.
        Err(anyhow::Error),
        /// The operation failed, and should be tried again in the future.
        ///
        /// The wrapped value is the number of milliseconds to wait before trying
        /// again. The caller is responsible for waiting this long and then
        /// calling [`Retry::try`] again.
        Retry(u64),
    }

    /// Maximum amount of time a single retry can be delayed (milliseconds).
    const MAX_RETRY_SLEEP_MS: u64 = 10 * 1000;
    /// The minimum initial amount of time a retry will be delayed (milliseconds).
    ///
    /// The actual amount of time will be a random value above this.
    const INITIAL_RETRY_SLEEP_BASE_MS: u64 = 500;
    /// The maximum amount of additional time the initial retry will take (milliseconds).
    ///
    /// The initial delay will be [`INITIAL_RETRY_SLEEP_BASE_MS`] plus a random range
    /// from 0 to this value.
    const INITIAL_RETRY_JITTER_MS: u64 = 1000;

    impl<'a> Retry<'a> {
        pub fn new(gctx: &'a GlobalContext) -> CargoResult<Retry<'a>> {
            Ok(Retry {
                gctx,
                retries: 0,
                max_retries: gctx.net_config()?.retry.unwrap_or(3) as u64,
            })
        }

        /// Calls the given callback, and returns a [`RetryResult`] which
        /// indicates whether or not this needs to be called again at some point
        /// in the future to retry the operation if it failed.
        pub fn r#try<T>(&mut self, f: impl FnOnce() -> CargoResult<T>) -> RetryResult<T> {
            match f() {
                Err(ref e) if maybe_spurious(e) && self.retries < self.max_retries => {
                    let err_msg = e
                        .downcast_ref::<HttpNotSuccessful>()
                        .map(|http_err| http_err.display_short())
                        .unwrap_or_else(|| e.root_cause().to_string());
                    let msg = format!(
                        "spurious network error ({} tries remaining): {err_msg}",
                        self.max_retries - self.retries,
                    );
                    if let Err(e) = self.gctx.shell().warn(msg) {
                        return RetryResult::Err(e);
                    }
                    self.retries += 1;
                    RetryResult::Retry(self.next_sleep_ms())
                }
                Err(e) => RetryResult::Err(e),
                Ok(r) => RetryResult::Success(r),
            }
        }

        /// Gets the next sleep duration in milliseconds.
        fn next_sleep_ms(&self) -> u64 {
            if let Ok(sleep) = self.gctx.get_env("__CARGO_TEST_FIXED_RETRY_SLEEP_MS") {
                return sleep.parse().expect("a u64");
            }

            if self.retries == 1 {
                let mut rng = rand::thread_rng();
                INITIAL_RETRY_SLEEP_BASE_MS + rng.gen_range(0..INITIAL_RETRY_JITTER_MS)
            } else {
                min(
                    ((self.retries - 1) * 3) * 1000 + INITIAL_RETRY_SLEEP_BASE_MS,
                    MAX_RETRY_SLEEP_MS,
                )
            }
        }
    }

    fn maybe_spurious(err: &Error) -> bool {
        if let Some(git_err) = err.downcast_ref::<git2::Error>() {
            match git_err.class() {
                git2::ErrorClass::Net
                | git2::ErrorClass::Os
                | git2::ErrorClass::Zlib
                | git2::ErrorClass::Http => return git_err.code() != git2::ErrorCode::Certificate,
                _ => (),
            }
        }
        if let Some(curl_err) = err.downcast_ref::<curl::Error>() {
            if curl_err.is_couldnt_connect()
                || curl_err.is_couldnt_resolve_proxy()
                || curl_err.is_couldnt_resolve_host()
                || curl_err.is_operation_timedout()
                || curl_err.is_recv_error()
                || curl_err.is_send_error()
                || curl_err.is_http2_error()
                || curl_err.is_http2_stream_error()
                || curl_err.is_ssl_connect_error()
                || curl_err.is_partial_file()
            {
                return true;
            }
        }
        if let Some(not_200) = err.downcast_ref::<HttpNotSuccessful>() {
            if 500 <= not_200.code && not_200.code < 600 {
                return true;
            }
        }

        use gix::protocol::transport::IsSpuriousError;

        if let Some(err) = err.downcast_ref::<crate::sources::git::fetch::Error>() {
            if err.is_spurious() {
                return true;
            }
        }

        false
    }

    /// Wrapper method for network call retry logic.
    ///
    /// Retry counts provided by Config object `net.retry`. Config shell outputs
    /// a warning on per retry.
    ///
    /// Closure must return a `CargoResult`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use crate::cargo::util::{CargoResult, GlobalContext};
    /// # let download_something = || return Ok(());
    /// # let gctx = GlobalContext::default().unwrap();
    /// use cargo::util::network;
    /// let cargo_result = network::retry::with_retry(&gctx, || download_something());
    /// ```
    pub fn with_retry<T, F>(gctx: &GlobalContext, mut callback: F) -> CargoResult<T>
    where
        F: FnMut() -> CargoResult<T>,
    {
        let mut retry = Retry::new(gctx)?;
        loop {
            match retry.r#try(&mut callback) {
                RetryResult::Success(r) => return Ok(r),
                RetryResult::Err(e) => return Err(e),
                RetryResult::Retry(sleep) => std::thread::sleep(Duration::from_millis(sleep)),
            }
        }
    }

    #[test]
    fn with_retry_repeats_the_call_then_works() {
        use crate::core::Shell;

        //Error HTTP codes (5xx) are considered maybe_spurious and will prompt retry
        let error1 = HttpNotSuccessful {
            code: 501,
            url: "Uri".to_string(),
            ip: None,
            body: Vec::new(),
            headers: Vec::new(),
        }
        .into();
        let error2 = HttpNotSuccessful {
            code: 502,
            url: "Uri".to_string(),
            ip: None,
            body: Vec::new(),
            headers: Vec::new(),
        }
        .into();
        let mut results: Vec<CargoResult<()>> = vec![Ok(()), Err(error1), Err(error2)];
        let gctx = GlobalContext::default().unwrap();
        *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
        let result = with_retry(&gctx, || results.pop().unwrap());
        assert!(result.is_ok())
    }

    #[test]
    fn with_retry_finds_nested_spurious_errors() {
        use crate::core::Shell;

        //Error HTTP codes (5xx) are considered maybe_spurious and will prompt retry
        //String error messages are not considered spurious
        let error1 = anyhow::Error::from(HttpNotSuccessful {
            code: 501,
            url: "Uri".to_string(),
            ip: None,
            body: Vec::new(),
            headers: Vec::new(),
        });
        let error1 = anyhow::Error::from(error1.context("A non-spurious wrapping err"));
        let error2 = anyhow::Error::from(HttpNotSuccessful {
            code: 502,
            url: "Uri".to_string(),
            ip: None,
            body: Vec::new(),
            headers: Vec::new(),
        });
        let error2 = anyhow::Error::from(error2.context("A second chained error"));
        let mut results: Vec<CargoResult<()>> = vec![Ok(()), Err(error1), Err(error2)];
        let gctx = GlobalContext::default().unwrap();
        *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
        let result = with_retry(&gctx, || results.pop().unwrap());
        assert!(result.is_ok())
    }

    #[test]
    fn default_retry_schedule() {
        use crate::core::Shell;

        let spurious = || -> CargoResult<()> {
            Err(anyhow::Error::from(HttpNotSuccessful {
                code: 500,
                url: "Uri".to_string(),
                ip: None,
                body: Vec::new(),
                headers: Vec::new(),
            }))
        };
        let gctx = GlobalContext::default().unwrap();
        *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
        let mut retry = Retry::new(&gctx).unwrap();
        match retry.r#try(|| spurious()) {
            RetryResult::Retry(sleep) => {
                assert!(
                    sleep >= INITIAL_RETRY_SLEEP_BASE_MS
                        && sleep < INITIAL_RETRY_SLEEP_BASE_MS + INITIAL_RETRY_JITTER_MS
                );
            }
            _ => panic!("unexpected non-retry"),
        }
        match retry.r#try(|| spurious()) {
            RetryResult::Retry(sleep) => assert_eq!(sleep, 3500),
            _ => panic!("unexpected non-retry"),
        }
        match retry.r#try(|| spurious()) {
            RetryResult::Retry(sleep) => assert_eq!(sleep, 6500),
            _ => panic!("unexpected non-retry"),
        }
        match retry.r#try(|| spurious()) {
            RetryResult::Err(_) => {}
            _ => panic!("unexpected non-retry"),
        }
    }

    #[test]
    fn curle_http2_stream_is_spurious() {
        let code = curl_sys::CURLE_HTTP2_STREAM;
        let err = curl::Error::new(code);
        assert!(maybe_spurious(&err.into()));
    }