rust_etcd_utils/

retry.rs

use {
    retry::delay::Exponential,
    std::{error::Error, future::Future, time::Duration},
    tracing::{error, warn},
};

///
/// Check if an etcd error is transient.
///
/// Transient error are error that are caused by "outside" forces that cannot be prevented such as a network partition.
///
/// If the error is for example gRPC status "Not found", the function will return false.
///
/// Transient errors are worth retrying -- See [`retry_etcd`] for an example.
///
pub fn is_transient(err: &etcd_client::Error) -> bool {
    match err {
        etcd_client::Error::GRpcStatus(status) => match status.code() {
            tonic::Code::Ok => false,
            tonic::Code::Cancelled => false,
            tonic::Code::Unknown => {
                match status.source() {
                    Some(e) => {
                        match e.downcast_ref::<tonic::transport::Error>() {
                            Some(_) => {
                                // Because if the error is a transport error, it's likely a transient error due to connection reset.
                                true
                            }
                            None => false,
                        }
                    }
                    None => true,
                }
            }
            tonic::Code::InvalidArgument => false,
            tonic::Code::DeadlineExceeded => true,
            tonic::Code::NotFound => false,
            tonic::Code::AlreadyExists => false,
            tonic::Code::PermissionDenied => false,
            tonic::Code::ResourceExhausted => true,
            tonic::Code::FailedPrecondition => false,
            tonic::Code::Aborted => false,
            tonic::Code::OutOfRange => false,
            tonic::Code::Unimplemented => false,
            tonic::Code::Internal => true,
            tonic::Code::Unavailable => true,
            tonic::Code::DataLoss => true,
            tonic::Code::Unauthenticated => false,
        },
        _ => false,
    }
}

///
/// Retry an etcd transaction if the error is transient.
///
pub async fn retry_etcd_txn(
    etcd: etcd_client::Client,
    txn: etcd_client::Txn,
) -> Result<etcd_client::TxnResponse, etcd_client::Error> {
    retry_etcd(etcd, (txn,), move |etcd, (txn,)| async move {
        etcd.kv_client().txn(txn).await
    })
    .await
}

///
/// Retry an etcd get if the error is transient.
///
pub async fn retry_etcd_get(
    etcd: etcd_client::Client,
    key: String,
    opts: Option<etcd_client::GetOptions>,
) -> Result<etcd_client::GetResponse, etcd_client::Error> {
    retry_etcd(etcd, (key, opts), move |etcd, (key, opts)| async move {
        etcd.kv_client().get(key, opts).await
    })
    .await
}

///
/// Retry an etcd operation by captures a reusable args and a closure that compute the future to try.
///
/// The future must return an etcd result type where the error could be any etcd error.
///
/// The `retry_etcd` function retry only on "transient" error, meaning error that happen because of "outside" forces
/// that cannot be prevented such as a network partition.
///
/// If the error is for example gRPC status "Not found", the function won't retry it.
///
/// Examples
///
/// ```
/// use rust_etcd_utils::{retry::retry_etcd};
/// use etcd_client::Client;
///
/// let etcd = Client::connect(["http://localhost:2379"], None).await.expect("failed to connect to etcd");
///
/// let result = retry_etcd(
///     etcd.clone(),
///     ("my_key",),
///     move |etcd, (my_key,)| {
///         async move {
///             etcd.kv_client().get(my_key, None).await
///         }
///     }   
/// ).await;
///
/// ```
///
pub async fn retry_etcd<A, T, F, Fut>(
    etcd: etcd_client::Client,
    reusable_args: A,
    f: F,
) -> Result<T, etcd_client::Error>
where
    A: Clone + Send + 'static,
    Fut: Future<Output = Result<T, etcd_client::Error>> + Send + 'static,
    F: FnMut(etcd_client::Client, A) -> Fut,
    T: Send + 'static,
{
    let retry_strategy = Exponential::from_millis_with_factor(10, 10.0).take(3);
    retry_etcd_with_strategy(etcd, reusable_args, retry_strategy, f).await
}

///
/// Similar to [`retry_etcd`] but with a custom retry strategy.
///
pub async fn retry_etcd_with_strategy<A, T, F, Fut>(
    etcd: etcd_client::Client,
    reusable_args: A,
    retry_strategy: impl IntoIterator<Item = Duration>,
    mut f: F,
) -> Result<T, etcd_client::Error>
where
    A: Clone + Send + 'static,
    Fut: Future<Output = Result<T, etcd_client::Error>> + Send + 'static,
    F: FnMut(etcd_client::Client, A) -> Fut,
    T: Send + 'static,
{
    let mut retry_strategy = retry_strategy.into_iter();
    loop {
        match f(etcd.clone(), reusable_args.clone()).await {
            Ok(o) => return Ok(o),
            Err(e) => {
                if is_transient(&e) {
                    warn!("failed due to transient state {:?}", e);
                    match retry_strategy.next() {
                        Some(duration) => {
                            tokio::time::sleep(duration).await;
                        }
                        None => return Err(e),
                    }
                } else {
                    error!("failed due to non-transient state: {:?}", e);
                    return Err(e);
                }
            }
        }
    }
}

pub(crate) async fn retry_etcd_legacy<T, F, Fut>(
    retry_strategy: impl IntoIterator<Item = Duration>,
    mut f: F,
) -> Result<T, etcd_client::Error>
where
    Fut: Future<Output = Result<T, etcd_client::Error>> + Send + 'static,
    F: FnMut() -> Fut,
    T: Send + 'static,
{
    let mut retry_strategy = retry_strategy.into_iter();
    loop {
        match f().await {
            Ok(o) => return Ok(o),
            Err(e) => {
                if is_transient(&e) {
                    warn!("failed due to transient state {:?}", e);
                    match retry_strategy.next() {
                        Some(duration) => {
                            tokio::time::sleep(duration).await;
                        }
                        None => return Err(e),
                    }
                } else {
                    error!("failed due to non-transient state: {:?}", e);
                    return Err(e);
                }
            }
        }
    }
}