fix(providers): handle zst params in retry provider correctly (#1481)

ethers-providers/src/transports/retry.rs

@@ -5,7 +5,6 @@ use super::{common::JsonRpcError, http::ClientError};
 use crate::{provider::ProviderError, JsonRpcClient};
 
 use std::{
-    clone::Clone,
     fmt::Debug,
     sync::atomic::{AtomicU32, Ordering},
     time::Duration,
@@ -135,10 +134,23 @@ where
         A: std::fmt::Debug + Serialize + Send + Sync,
         R: DeserializeOwned,
     {
-        let ahead_in_queue = self.requests_enqueued.fetch_add(1, Ordering::SeqCst) as u64;
+        // Helper type that caches the `params` value across several retries
+        // This is necessary because the wrapper provider is supposed to skip he `params` if it's of
+        // size 0, see `crate::transports::common::Request`
+        enum RetryParams<Params> {
+            Value(Params),
+            Zst(()),
+        }
 
+        let params = if std::mem::size_of::<A>() == 0 {
+            RetryParams::Zst(())
+        } else {
             let params =
                 serde_json::to_value(params).map_err(|err| RetryClientError::SerdeJson(err))?;
+            RetryParams::Value(params)
+        };
+
+        let ahead_in_queue = self.requests_enqueued.fetch_add(1, Ordering::SeqCst) as u64;
 
         let mut retry_number: u32 = 0;
 
@@ -148,7 +160,11 @@ where
             // hack to not hold `R` across an await in the sleep future and prevent requiring
             // R: Send + Sync
             {
-                match self.inner.request(method, params.clone()).await {
+                let resp = match params {
+                    RetryParams::Value(ref params) => self.inner.request(method, params).await,
+                    RetryParams::Zst(unit) => self.inner.request(method, unit).await,
+                };
+                match resp {
                     Ok(ret) => {
                         self.requests_enqueued.fetch_sub(1, Ordering::SeqCst);
                         return Ok(ret)

ethers-providers/tests/provider.rs

@@ -91,6 +91,28 @@ mod eth_tests {
         let (_max_fee_per_gas, _max_priority_fee_per_gas) =
             provider.estimate_eip1559_fees(None).await.unwrap();
     }
+
+    #[tokio::test]
+    #[ignore]
+    async fn test_hardhat_compatibility() {
+        use ethers_providers::RetryClient;
+
+        async fn send_zst_requests<M: Middleware>(provider: M) {
+            let _ = provider.get_chainid().await.unwrap();
+            let _ = provider.get_block_number().await.unwrap();
+            let _ = provider.get_gas_price().await.unwrap();
+            let _ = provider.get_accounts().await.unwrap();
+            let _ = provider.get_net_version().await.unwrap();
+        }
+
+        let provider = Provider::<Http>::try_from("http://localhost:8545").unwrap();
+        send_zst_requests(provider).await;
+
+        let provider =
+            Provider::<RetryClient<Http>>::new_client("http://localhost:8545", 10, 200).unwrap();
+
+        send_zst_requests(provider).await;
+    }
 }
 
 #[cfg(feature = "celo")]