feat: detect requested backoff

ethers-providers/src/transports/retry.rs

@@ -18,6 +18,9 @@ use tracing::trace;
 pub trait RetryPolicy<E>: Send + Sync + Debug {
     /// Whether to retry the request based on the given `error`
     fn should_retry(&self, error: &E) -> bool;
+
+    /// Providers may include the `backoff` in the error response directly
+    fn backoff_hint(&self, error: &E) -> Option<Duration>;
 }
 
 /// [RetryClient] presents as a wrapper around [JsonRpcClient] that will retry
@@ -282,13 +285,18 @@ where
                 }
 
                 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 = Duration::from_millis(
-                    self.initial_backoff.as_millis().pow(rate_limit_retry_number) as u64,
-                );
+
+                // try to extract the requested backoff from the error or compute the next backoff
+                // based on retry count
+                let mut next_backoff = self.policy.backoff_hint(&err).unwrap_or_else(|| {
+                    // 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
+                    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:
@@ -339,20 +347,41 @@ impl RetryPolicy<ClientError> for HttpRateLimitRetryPolicy {
             ClientError::ReqwestError(err) => {
                 err.status() == Some(http::StatusCode::TOO_MANY_REQUESTS)
             }
-            ClientError::JsonRpcError(JsonRpcError { code, message, data: _ }) => {
+            ClientError::JsonRpcError(JsonRpcError { code, message, .. }) => {
                 // alchemy throws it this way
                 if *code == 429 {
                     return true
                 }
-                // this is commonly thrown by infura and is apparently a load balancer issue, see also <https://github.com/MetaMask/metamask-extension/issues/7234>
-                if message == "header not found" {
-                    return true
+                match message.as_str() {
+                    // this is commonly thrown by infura and is apparently a load balancer issue, see also <https://github.com/MetaMask/metamask-extension/issues/7234>
+                    "header not found" => true,
+                    // also thrown by infura if out of budget for the day and ratelimited
+                    "daily request count exceeded, request rate limited" => true,
+                    _ => false,
                 }
-                false
             }
             _ => false,
         }
     }
+
+    fn backoff_hint(&self, error: &ClientError) -> Option<Duration> {
+        if let ClientError::JsonRpcError(JsonRpcError { data, .. }) = error {
+            let data = data.as_ref()?;
+
+            // if daily rate limit exceeded, infura returns the requested backoff in the error
+            // response
+            let backoff_seconds = &data["rate"]["backoff_seconds"];
+            // infura rate limit error
+            if let Some(seconds) = backoff_seconds.as_u64() {
+                return Some(Duration::from_secs(seconds))
+            }
+            if let Some(seconds) = backoff_seconds.as_f64() {
+                return Some(Duration::from_secs(seconds as u64 + 1))
+            }
+        }
+
+        None
+    }
 }
 
 /// Calculates an offset in seconds by taking into account the number of currently queued requests,
@@ -450,4 +479,25 @@ mod tests {
         // need to wait 1 second
         assert_eq!(to_wait, 1);
     }
+
+    #[test]
+    fn can_extract_backoff() {
+        let resp = r#"{"rate": {"allowed_rps": 1, "backoff_seconds": 30, "current_rps": 1.1}, "see": "https://infura.io/dashboard"}"#;
+
+        let err = ClientError::JsonRpcError(JsonRpcError {
+            code: 0,
+            message: "daily request count exceeded, request rate limited".to_string(),
+            data: Some(serde_json::from_str(resp).unwrap()),
+        });
+        let backoff = HttpRateLimitRetryPolicy.backoff_hint(&err).unwrap();
+        assert_eq!(backoff, Duration::from_secs(30));
+
+        let err = ClientError::JsonRpcError(JsonRpcError {
+            code: 0,
+            message: "daily request count exceeded, request rate limited".to_string(),
+            data: Some(serde_json::Value::String("blocked".to_string())),
+        });
+        let backoff = HttpRateLimitRetryPolicy.backoff_hint(&err);
+        assert!(backoff.is_none());
+    }
 }