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    //! Utilities for retrying a network operation.

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

    pub struct Retry<'a> {
        config: &'a Config,
        retries: u64,
        max_retries: u64,
    }

    pub enum RetryResult<T> {
        Success(T),
        Err(anyhow::Error),
        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(config: &'a Config) -> CargoResult<Retry<'a>> {
            Ok(Retry {
                config,
                retries: 0,
                max_retries: config.net_config()?.retry.unwrap_or(3) as u64,
            })
        }

        /// Returns `Ok(None)` for operations that should be re-tried.
        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.config.shell().warn(msg) {
                        return RetryResult::Err(e);
                    }
                    self.retries += 1;
                    let sleep = 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,
                        )
                    };
                    RetryResult::Retry(sleep)
                }
                Err(e) => RetryResult::Err(e),
                Ok(r) => RetryResult::Success(r),
            }
        }
    }

    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, Config};
    /// # let download_something = || return Ok(());
    /// # let config = Config::default().unwrap();
    /// use cargo::util::network;
    /// let cargo_result = network::retry::with_retry(&config, || download_something());
    /// ```
    pub fn with_retry<T, F>(config: &Config, mut callback: F) -> CargoResult<T>
    where
        F: FnMut() -> CargoResult<T>,
    {
        let mut retry = Retry::new(config)?;
        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 config = Config::default().unwrap();
        *config.shell() = Shell::from_write(Box::new(Vec::new()));
        let result = with_retry(&config, || 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 config = Config::default().unwrap();
        *config.shell() = Shell::from_write(Box::new(Vec::new()));
        let result = with_retry(&config, || 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 config = Config::default().unwrap();
        *config.shell() = Shell::from_write(Box::new(Vec::new()));
        let mut retry = Retry::new(&config).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()));
    }