#
cargo/util/network/
retry.rs

    1//! Utilities for retrying a network operation.
    2//!
    3//! Some network errors are considered "spurious", meaning it is not a real
    4//! error (such as a 404 not found) and is likely a transient error (like a
    5//! bad network connection) that we can hope will resolve itself shortly. The
    6//! [`Retry`] type offers a way to repeatedly perform some kind of network
    7//! operation with a delay if it detects one of these possibly transient
    8//! errors.
    9//!
    10//! This supports errors from [`git2`], [`gix`], [`curl`], and
    11//! [`HttpNotSuccessful`] 5xx HTTP errors.
    12//!
    13//! The number of retries can be configured by the user via the `net.retry`
    14//! config option. This indicates the number of times to retry the operation
    15//! (default 3 times for a total of 4 attempts).
    16//!
    17//! There are hard-coded constants that indicate how long to sleep between
    18//! retries. The constants are tuned to balance a few factors, such as the
    19//! responsiveness to the user (we don't want cargo to hang for too long
    20//! retrying things), and accommodating things like Cloudfront's default
    21//! negative TTL of 10 seconds (if Cloudfront gets a 5xx error for whatever
    22//! reason it won't try to fetch again for 10 seconds).
    23//!
    24//! The timeout also implements a primitive form of random jitter. This is so
    25//! that if multiple requests fail at the same time that they don't all flood
    26//! the server at the same time when they are retried. This jitter still has
    27//! some clumping behavior, but should be good enough.
    28//!
    29//! [`Retry`] is the core type for implementing retry logic. The
    30//! [`Retry::try`] method can be called with a callback, and it will
    31//! indicate if it needs to be called again sometime in the future if there
    32//! was a possibly transient error. The caller is responsible for sleeping the
    33//! appropriate amount of time and then calling [`Retry::try`] again.
    34//!
    35//! [`with_retry`] is a convenience function that will create a [`Retry`] and
    36//! handle repeatedly running a callback until it succeeds, or it runs out of
    37//! retries.
    38//!
    39//! Some interesting resources about retries:
    40//! - <https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/>
    41//! - <https://en.wikipedia.org/wiki/Exponential_backoff>
    42//! - <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After>
    43
    44use crate::util::errors::HttpNotSuccessful;
    45use crate::{CargoResult, GlobalContext};
    46use anyhow::Error;
    47use rand::Rng;
    48use std::cmp::min;
    49use std::time::Duration;
    50
    51/// State for managing retrying a network operation.
    52pub struct Retry<'a> {
    53    gctx: &'a GlobalContext,
    54    /// The number of failed attempts that have been done so far.
    55    ///
    56    /// Starts at 0, and increases by one each time an attempt fails.
    57    retries: u64,
    58    /// The maximum number of times the operation should be retried.
    59    ///
    60    /// 0 means it should never retry.
    61    max_retries: u64,
    62}
    63
    64/// The result of attempting some operation via [`Retry::try`].
    65pub enum RetryResult<T> {
    66    /// The operation was successful.
    67    ///
    68    /// The wrapped value is the return value of the callback function.
    69    Success(T),
    70    /// The operation was an error, and it should not be tried again.
    71    Err(anyhow::Error),
    72    /// The operation failed, and should be tried again in the future.
    73    ///
    74    /// The wrapped value is the number of milliseconds to wait before trying
    75    /// again. The caller is responsible for waiting this long and then
    76    /// calling [`Retry::try`] again.
    77    Retry(u64),
    78}
    79
    80/// Maximum amount of time a single retry can be delayed (milliseconds).
    81const MAX_RETRY_SLEEP_MS: u64 = 10 * 1000;
    82/// The minimum initial amount of time a retry will be delayed (milliseconds).
    83///
    84/// The actual amount of time will be a random value above this.
    85const INITIAL_RETRY_SLEEP_BASE_MS: u64 = 500;
    86/// The maximum amount of additional time the initial retry will take (milliseconds).
    87///
    88/// The initial delay will be [`INITIAL_RETRY_SLEEP_BASE_MS`] plus a random range
    89/// from 0 to this value.
    90const INITIAL_RETRY_JITTER_MS: u64 = 1000;
    91
    92impl<'a> Retry<'a> {
    93    pub fn new(gctx: &'a GlobalContext) -> CargoResult<Retry<'a>> {
    94        Ok(Retry {
    95            gctx,
    96            retries: 0,
    97            max_retries: gctx.net_config()?.retry.unwrap_or(3) as u64,
    98        })
    99    }
    100
    101    /// Calls the given callback, and returns a [`RetryResult`] which
    102    /// indicates whether or not this needs to be called again at some point
    103    /// in the future to retry the operation if it failed.
    104    pub fn r#try<T>(&mut self, f: impl FnOnce() -> CargoResult<T>) -> RetryResult<T> {
    105        match f() {
    106            Err(ref e) if maybe_spurious(e) && self.retries < self.max_retries => {
    107                let err_msg = e
    108                    .downcast_ref::<HttpNotSuccessful>()
    109                    .map(|http_err| http_err.display_short())
    110                    .unwrap_or_else(|| e.root_cause().to_string());
    111                let msg = format!(
    112                    "spurious network error ({} tries remaining): {err_msg}",
    113                    self.max_retries - self.retries,
    114                );
    115                if let Err(e) = self.gctx.shell().warn(msg) {
    116                    return RetryResult::Err(e);
    117                }
    118                self.retries += 1;
    119                RetryResult::Retry(self.next_sleep_ms())
    120            }
    121            Err(e) => RetryResult::Err(e),
    122            Ok(r) => RetryResult::Success(r),
    123        }
    124    }
    125
    126    /// Gets the next sleep duration in milliseconds.
    127    fn next_sleep_ms(&self) -> u64 {
    128        if let Ok(sleep) = self.gctx.get_env("__CARGO_TEST_FIXED_RETRY_SLEEP_MS") {
    129            return sleep.parse().expect("a u64");
    130        }
    131
    132        if self.retries == 1 {
    133            let mut rng = rand::rng();
    134            INITIAL_RETRY_SLEEP_BASE_MS + rng.random_range(0..INITIAL_RETRY_JITTER_MS)
    135        } else {
    136            min(
    137                ((self.retries - 1) * 3) * 1000 + INITIAL_RETRY_SLEEP_BASE_MS,
    138                MAX_RETRY_SLEEP_MS,
    139            )
    140        }
    141    }
    142}
    143
    144fn maybe_spurious(err: &Error) -> bool {
    145    if let Some(git_err) = err.downcast_ref::<git2::Error>() {
    146        match git_err.class() {
    147            git2::ErrorClass::Net
    148            | git2::ErrorClass::Os
    149            | git2::ErrorClass::Zlib
    150            | git2::ErrorClass::Http => return git_err.code() != git2::ErrorCode::Certificate,
    151            _ => (),
    152        }
    153    }
    154    if let Some(curl_err) = err.downcast_ref::<curl::Error>() {
    155        if curl_err.is_couldnt_connect()
    156            || curl_err.is_couldnt_resolve_proxy()
    157            || curl_err.is_couldnt_resolve_host()
    158            || curl_err.is_operation_timedout()
    159            || curl_err.is_recv_error()
    160            || curl_err.is_send_error()
    161            || curl_err.is_http2_error()
    162            || curl_err.is_http2_stream_error()
    163            || curl_err.is_ssl_connect_error()
    164            || curl_err.is_partial_file()
    165        {
    166            return true;
    167        }
    168    }
    169    if let Some(not_200) = err.downcast_ref::<HttpNotSuccessful>() {
    170        if 500 <= not_200.code && not_200.code < 600 {
    171            return true;
    172        }
    173    }
    174
    175    use gix::protocol::transport::IsSpuriousError;
    176
    177    if let Some(err) = err.downcast_ref::<crate::sources::git::fetch::Error>() {
    178        if err.is_spurious() {
    179            return true;
    180        }
    181    }
    182
    183    false
    184}
    185
    186/// Wrapper method for network call retry logic.
    187///
    188/// Retry counts provided by Config object `net.retry`. Config shell outputs
    189/// a warning on per retry.
    190///
    191/// Closure must return a `CargoResult`.
    192///
    193/// # Examples
    194///
    195/// ```
    196/// # use crate::cargo::util::{CargoResult, GlobalContext};
    197/// # let download_something = || return Ok(());
    198/// # let gctx = GlobalContext::default().unwrap();
    199/// use cargo::util::network;
    200/// let cargo_result = network::retry::with_retry(&gctx, || download_something());
    201/// ```
    202pub fn with_retry<T, F>(gctx: &GlobalContext, mut callback: F) -> CargoResult<T>
    203where
    204    F: FnMut() -> CargoResult<T>,
    205{
    206    let mut retry = Retry::new(gctx)?;
    207    loop {
    208        match retry.r#try(&mut callback) {
    209            RetryResult::Success(r) => return Ok(r),
    210            RetryResult::Err(e) => return Err(e),
    211            RetryResult::Retry(sleep) => std::thread::sleep(Duration::from_millis(sleep)),
    212        }
    213    }
    214}
    215
    216#[test]
    217fn with_retry_repeats_the_call_then_works() {
    218    use crate::core::Shell;
    219
    220    //Error HTTP codes (5xx) are considered maybe_spurious and will prompt retry
    221    let error1 = HttpNotSuccessful {
    222        code: 501,
    223        url: "Uri".to_string(),
    224        ip: None,
    225        body: Vec::new(),
    226        headers: Vec::new(),
    227    }
    228    .into();
    229    let error2 = HttpNotSuccessful {
    230        code: 502,
    231        url: "Uri".to_string(),
    232        ip: None,
    233        body: Vec::new(),
    234        headers: Vec::new(),
    235    }
    236    .into();
    237    let mut results: Vec<CargoResult<()>> = vec![Ok(()), Err(error1), Err(error2)];
    238    let gctx = GlobalContext::default().unwrap();
    239    *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
    240    let result = with_retry(&gctx, || results.pop().unwrap());
    241    assert!(result.is_ok())
    242}
    243
    244#[test]
    245fn with_retry_finds_nested_spurious_errors() {
    246    use crate::core::Shell;
    247
    248    //Error HTTP codes (5xx) are considered maybe_spurious and will prompt retry
    249    //String error messages are not considered spurious
    250    let error1 = anyhow::Error::from(HttpNotSuccessful {
    251        code: 501,
    252        url: "Uri".to_string(),
    253        ip: None,
    254        body: Vec::new(),
    255        headers: Vec::new(),
    256    });
    257    let error1 = anyhow::Error::from(error1.context("A non-spurious wrapping err"));
    258    let error2 = anyhow::Error::from(HttpNotSuccessful {
    259        code: 502,
    260        url: "Uri".to_string(),
    261        ip: None,
    262        body: Vec::new(),
    263        headers: Vec::new(),
    264    });
    265    let error2 = anyhow::Error::from(error2.context("A second chained error"));
    266    let mut results: Vec<CargoResult<()>> = vec![Ok(()), Err(error1), Err(error2)];
    267    let gctx = GlobalContext::default().unwrap();
    268    *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
    269    let result = with_retry(&gctx, || results.pop().unwrap());
    270    assert!(result.is_ok())
    271}
    272
    273#[test]
    274fn default_retry_schedule() {
    275    use crate::core::Shell;
    276
    277    let spurious = || -> CargoResult<()> {
    278        Err(anyhow::Error::from(HttpNotSuccessful {
    279            code: 500,
    280            url: "Uri".to_string(),
    281            ip: None,
    282            body: Vec::new(),
    283            headers: Vec::new(),
    284        }))
    285    };
    286    let gctx = GlobalContext::default().unwrap();
    287    *gctx.shell() = Shell::from_write(Box::new(Vec::new()));
    288    let mut retry = Retry::new(&gctx).unwrap();
    289    match retry.r#try(|| spurious()) {
    290        RetryResult::Retry(sleep) => {
    291            assert!(
    292                sleep >= INITIAL_RETRY_SLEEP_BASE_MS
    293                    && sleep < INITIAL_RETRY_SLEEP_BASE_MS + INITIAL_RETRY_JITTER_MS
    294            );
    295        }
    296        _ => panic!("unexpected non-retry"),
    297    }
    298    match retry.r#try(|| spurious()) {
    299        RetryResult::Retry(sleep) => assert_eq!(sleep, 3500),
    300        _ => panic!("unexpected non-retry"),
    301    }
    302    match retry.r#try(|| spurious()) {
    303        RetryResult::Retry(sleep) => assert_eq!(sleep, 6500),
    304        _ => panic!("unexpected non-retry"),
    305    }
    306    match retry.r#try(|| spurious()) {
    307        RetryResult::Err(_) => {}
    308        _ => panic!("unexpected non-retry"),
    309    }
    310}
    311
    312#[test]
    313fn curle_http2_stream_is_spurious() {
    314    let code = curl_sys::CURLE_HTTP2_STREAM;
    315    let err = curl::Error::new(code);
    316    assert!(maybe_spurious(&err.into()));
    317}