feat: support retrying connection errors (#1629)

ethers-providers/src/transports/retry.rs

@@ -6,6 +6,7 @@ use crate::{provider::ProviderError, JsonRpcClient};
 use async_trait::async_trait;
 use serde::{de::DeserializeOwned, Serialize};
 use std::{
+    error::Error,
     fmt::Debug,
     sync::atomic::{AtomicU32, Ordering},
     time::Duration,
@@ -22,6 +23,27 @@ pub trait RetryPolicy<E>: Send + Sync + Debug {
 
 /// [RetryClient] presents as a wrapper around [JsonRpcClient] that will retry
 /// requests based with an exponential backoff and filtering based on [RetryPolicy].
+///
+/// The `RetryPolicy`, mainly for rate-limiting errors, can be adjusted for specific applications,
+/// endpoints. In addition to the `RetryPolicy` errors due to connectivity issues, like timed out
+/// connections or responses in range `5xx` can be retried separately.
+///
+/// # Example
+///
+/// ```
+/// #  async fn demo() {
+/// use ethers_providers::{Http, RetryClient, RetryClientBuilder, HttpRateLimitRetryPolicy};
+/// use std::time::Duration;
+/// use url::Url;
+///
+/// let http = Http::new(Url::parse("http://localhost:8545").unwrap());
+/// let client = RetryClientBuilder::default()
+///     .rate_limit_retries(10)
+///     .timeout_retries(3)
+///     .initial_backoff(Duration::from_millis(500))
+///     .build(http, Box::new(HttpRateLimitRetryPolicy::default()));
+/// # }
+/// ```
 #[derive(Debug)]
 pub struct RetryClient<T>
 where
@@ -30,9 +52,14 @@ where
 {
     inner: T,
     requests_enqueued: AtomicU32,
+    /// The policy to use to determine whether to retry a request due to rate limiting
     policy: Box<dyn RetryPolicy<T::Error>>,
-    max_retry: u32,
+    /// How many connection `TimedOut` should be retried.
-    initial_backoff: u64,
+    timeout_retries: u32,
+    /// How many retries for rate limited responses
+    rate_limit_retries: u32,
+    /// How long to wait initially
+    initial_backoff: Duration,
     /// available CPU per second
     compute_units_per_second: u64,
 }
@@ -67,15 +94,10 @@ where
         // in milliseconds
         initial_backoff: u64,
     ) -> Self {
-        Self {
+        RetryClientBuilder::default()
-            inner,
+            .initial_backoff(Duration::from_millis(initial_backoff))
-            requests_enqueued: AtomicU32::new(0),
+            .rate_limit_retries(max_retry)
-            policy,
+            .build(inner, policy)
-            max_retry,
-            initial_backoff,
-            // alchemy max cpus <https://github.com/alchemyplatform/alchemy-docs/blob/master/documentation/compute-units.md#rate-limits-cups>
-            compute_units_per_second: 330,
-        }
     }
 
     /// Sets the free compute units per second limit.
@@ -90,6 +112,87 @@ where
     }
 }
 
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct RetryClientBuilder {
+    /// How many connection `TimedOut` should be retried.
+    timeout_retries: u32,
+    /// How many retries for rate limited responses
+    rate_limit_retries: u32,
+    /// How long to wait initially
+    initial_backoff: Duration,
+    /// available CPU per second
+    compute_units_per_second: u64,
+}
+
+// === impl RetryClientBuilder ===
+
+impl RetryClientBuilder {
+    /// Sets the number of retries after a connection times out
+    ///
+    /// **Note:** this will only be used for `request::Error::TimedOut`
+    pub fn timeout_retries(mut self, timeout_retries: u32) -> Self {
+        self.timeout_retries = timeout_retries;
+        self
+    }
+
+    /// How many retries for rate limited responses
+    pub fn rate_limit_retries(mut self, rate_limit_retries: u32) -> Self {
+        self.rate_limit_retries = rate_limit_retries;
+        self
+    }
+
+    /// Sets the number of assumed available compute units per second
+    ///
+    /// See also, <https://github.com/alchemyplatform/alchemy-docs/blob/master/documentation/compute-units.md#rate-limits-cups>
+    pub fn compute_units_per_second(mut self, compute_units_per_second: u64) -> Self {
+        self.compute_units_per_second = compute_units_per_second;
+        self
+    }
+
+    /// Sets the duration to wait initially before retrying
+    pub fn initial_backoff(mut self, initial_backoff: Duration) -> Self {
+        self.initial_backoff = initial_backoff;
+        self
+    }
+
+    /// Creates the `RetryClient` with the configured settings
+    pub fn build<T>(self, client: T, policy: Box<dyn RetryPolicy<T::Error>>) -> RetryClient<T>
+    where
+        T: JsonRpcClient,
+        T::Error: Sync + Send + 'static,
+    {
+        let RetryClientBuilder {
+            timeout_retries,
+            rate_limit_retries,
+            initial_backoff,
+            compute_units_per_second,
+        } = self;
+        RetryClient {
+            inner: client,
+            requests_enqueued: AtomicU32::new(0),
+            policy,
+            timeout_retries,
+            rate_limit_retries,
+            initial_backoff,
+            compute_units_per_second,
+        }
+    }
+}
+
+// Some sensible defaults
+impl Default for RetryClientBuilder {
+    fn default() -> Self {
+        Self {
+            timeout_retries: 3,
+            // this should be enough to even out heavy loads
+            rate_limit_retries: 10,
+            initial_backoff: Duration::from_millis(100),
+            // alchemy max cpus <https://github.com/alchemyplatform/alchemy-docs/blob/master/documentation/compute-units.md#rate-limits-cups>
+            compute_units_per_second: 330,
+        }
+    }
+}
+
 /// Error thrown when:
 /// 1. Internal client throws an error we do not wish to try to recover from.
 /// 2. Params serialization failed.
@@ -137,7 +240,7 @@ where
 
     async fn request<A, R>(&self, method: &str, params: A) -> Result<R, Self::Error>
     where
-        A: std::fmt::Debug + Serialize + Send + Sync,
+        A: Debug + Serialize + Send + Sync,
         R: DeserializeOwned,
     {
         // Helper type that caches the `params` value across several retries
@@ -158,7 +261,8 @@ where
 
         let ahead_in_queue = self.requests_enqueued.fetch_add(1, Ordering::SeqCst) as u64;
 
-        let mut retry_number: u32 = 0;
+        let mut rate_limit_retry_number: u32 = 0;
+        let mut timeout_retries: u32 = 0;
 
         loop {
             let err;
@@ -179,20 +283,22 @@ where
                 }
             }
 
-            retry_number += 1;
-            if retry_number > self.max_retry {
-                trace!("request timed out after {} retries", self.max_retry);
-                return Err(RetryClientError::TimeoutError)
-            }
-
             let should_retry = self.policy.should_retry(&err);
             if should_retry {
+                rate_limit_retry_number += 1;
+                if rate_limit_retry_number > self.rate_limit_retries {
+                    trace!("request timed out after {} retries", self.rate_limit_retries);
+                    return Err(RetryClientError::TimeoutError)
+                }
+
                 let current_queued_requests = self.requests_enqueued.load(Ordering::SeqCst) as u64;
                 // using `retry_number` for creating back pressure because
                 // of already queued requests
                 // this increases exponentially with retries and adds a delay based on how many
                 // requests are currently queued
-                let mut next_backoff = self.initial_backoff * 2u64.pow(retry_number);
+                let mut next_backoff = Duration::from_millis(
+                    self.initial_backoff.as_millis().pow(rate_limit_retry_number) as u64,
+                );
 
                 // requests are usually weighted and can vary from 10 CU to several 100 CU, cheaper
                 // requests are more common some example alchemy weights:
@@ -209,12 +315,17 @@ where
                     current_queued_requests,
                     ahead_in_queue,
                 );
-                // backoff is measured in millis
+                next_backoff += Duration::from_secs(seconds_to_wait_for_compute_budge);
-                next_backoff += seconds_to_wait_for_compute_budge * 1000;
 
-                trace!("retrying and backing off for {}ms", next_backoff);
+                trace!("retrying and backing off for {:?}", next_backoff);
-                tokio::time::sleep(Duration::from_millis(next_backoff)).await;
+                tokio::time::sleep(next_backoff).await;
             } else {
+                if timeout_retries < self.timeout_retries && maybe_connectivity(&err) {
+                    timeout_retries += 1;
+                    trace!(err = ?err, "retrying due to spurious network");
+                    continue
+                }
+
                 trace!(err = ?err, "should not retry");
                 self.requests_enqueued.fetch_sub(1, Ordering::SeqCst);
                 return Err(RetryClientError::ProviderError(err))
@@ -266,6 +377,24 @@ fn compute_unit_offset_in_secs(
     }
 }
 
+/// Checks whether the `error` is the result of a connectivity issue, like
+/// `request::Error::TimedOut`
+fn maybe_connectivity(err: &(dyn Error + 'static)) -> bool {
+    if let Some(reqwest_err) = err.downcast_ref::<reqwest::Error>() {
+        if reqwest_err.is_timeout() || reqwest_err.is_connect() {
+            return true
+        }
+        // Error HTTP codes (5xx) are considered connectivity issues and will prompt retry
+        if let Some(status) = reqwest_err.status() {
+            let code = status.as_u16();
+            if (500..600).contains(&code) {
+                return true
+            }
+        }
+    }
+    false
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;