Serialize `eth_feeHistory` block count as `QUANTITY` (#668)

* Serialize eth_feeHistory block count as QUANTITY

* update changelog

CHANGELOG.md

@@ -12,6 +12,8 @@
   [597](https://github.com/gakonst/ethers-rs/pull/597)
 - Implement hex display format for `ethers::core::Bytes`
   [#624](https://github.com/gakonst/ethers-rs/pull/624).
+- Fix `fee_history` to first try with `block_count` encoded as a hex `QUANTITY`.
+  [#668](https://github.com/gakonst/ethers-rs/pull/668)
 
 ## ethers-solc
 

ethers-providers/src/provider.rs

@@ -848,7 +848,7 @@ impl<P: JsonRpcClient> Middleware for Provider<P> {
         self.subscribe([logs, filter]).await
     }
 
-    async fn fee_history<T: Into<U256> + serde::Serialize + Send + Sync>(
+    async fn fee_history<T: Into<U256> + Send + Sync>(
         &self,
         block_count: T,
         last_block: BlockNumber,
@@ -862,7 +862,7 @@ impl<P: JsonRpcClient> Middleware for Provider<P> {
         // decode the param from client side would fallback to the old API spec.
         self.request(
             "eth_feeHistory",
-            [utils::serialize(&block_count), last_block.clone(), reward_percentiles.clone()],
+            [utils::serialize(&block_count.into()), last_block.clone(), reward_percentiles.clone()],
         )
         .await
         .or(self