feat: add max priority fee per gas from RPC

Before falling back to the default max priority fee (currently 1gwei) attempt
to call `eth_maxPriorityFeePerGas` as an RPC call and use that if available.

If the user has set a `maxPriorityFeePerGas` in config, that takes priority over
the RPC call.

Resolves #743

packages/core/src/internal/execution/jsonrpc-client.ts

@@ -12,6 +12,8 @@ import {
 } from "./types/jsonrpc";
 import { toChecksumFormat } from "./utils/address";
 
+const DEFAULT_MAX_FEE_PER_GAS = 1_000_000_000n;
+
 /**
  * The params to make an `eth_call`.
  */
@@ -638,9 +640,9 @@ export class EIP1193JsonRpcClient implements JsonRpcClient {
     // We prioritize EIP-1559 fees over legacy gasPrice fees, however,
     // polygon (chainId 137) requires legacy gasPrice fees so we skip EIP-1559 logic in that case
     if (latestBlock.baseFeePerGas !== undefined && chainId !== 137) {
+      const maxPriorityFeePerGas = await this._resolveMaxFeePerGas();
+
       // Logic copied from ethers v6
-      const maxPriorityFeePerGas =
-        this._config?.maxPriorityFeePerGas ?? 1_000_000_000n; // 1gwei
       const maxFeePerGas =
         latestBlock.baseFeePerGas * 2n + maxPriorityFeePerGas;
 
@@ -659,6 +661,44 @@ export class EIP1193JsonRpcClient implements JsonRpcClient {
 
     return { gasPrice: jsonRpcQuantityToBigInt(response) };
   }
+
+  /**
+   * The max fee per gas is needed in the max fee calculation.
+   *
+   * It is resolved from config if present, falling back to
+   * the  `eth_maxPriorityFeePerGas` RPC call if supported by the chain,
+   * and finally falling back to the default max fee per gas.
+   *
+   * @returns a max fee per gas based on the config, RPC call, or default value.
+   */
+  private async _resolveMaxFeePerGas(): Promise<bigint> {
+    if (this._config?.maxPriorityFeePerGas !== undefined) {
+      return this._config?.maxPriorityFeePerGas;
+    }
+
+    try {
+      return await this._getMaxPrioirtyFeePerGas();
+    } catch {
+      // the max prioirty fee RPC call is not supported by
+      // this chain
+    }
+
+    return DEFAULT_MAX_FEE_PER_GAS;
+  }
+
+  private async _getMaxPrioirtyFeePerGas(): Promise<bigint> {
+    const fee = await this._provider.request({
+      method: "eth_maxPriorityFeePerGas",
+    });
+
+    assertResponseType(
+      "eth_maxPriorityFeePerGas",
+      fee,
+      typeof fee === "string"
+    );
+
+    return jsonRpcQuantityToBigInt(fee);
+  }
 }
 
 /**

packages/core/test-integrations/new-api/internal/new-execution/jsonrpc-client.ts

@@ -153,6 +153,56 @@ describe("JSON-RPC client", function () {
 
           assert.equal(fees.gasPrice, 1n);
         });
+
+        it("Should use the `maxPriorityFeePerGas` from the node if `eth_maxPriorityFeePerGas` is present (and there is no config)", async function () {
+          // TODO: Hardhat does not support `eth_maxPriorityFeePerGas` yet, when it does, this
+          // can be removed.
+          const proxiedProvider = {
+            ...this.hre.network.provider,
+            request: async (req: { method: string }) => {
+              if (req.method === "eth_maxPriorityFeePerGas") {
+                return "2000000000";
+              }
+
+              return this.hre.network.provider.request(req);
+            },
+          };
+
+          const maxFeeClient = new EIP1193JsonRpcClient(proxiedProvider, {
+            maxPriorityFeePerGas: undefined, // no config set for maxPriorityFeePerGas
+          });
+
+          const fees = await maxFeeClient.getNetworkFees();
+
+          assert("maxPriorityFeePerGas" in fees);
+
+          assert.equal(fees.maxPriorityFeePerGas, 2_000_000_000n);
+        });
+
+        it("Should default to 1gwei for maxPriorityFeePerGas if `eth_maxPriorityFeePerGas` is not available and no config set", async function () {
+          const proxiedProvider = {
+            ...this.hre.network.provider,
+            request: async (req: { method: string }) => {
+              if (req.method === "eth_maxPriorityFeePerGas") {
+                throw new Error(
+                  "Method eth_maxPriorityFeePerGas is not supported"
+                );
+              }
+
+              return this.hre.network.provider.request(req);
+            },
+          };
+
+          const maxFeeClient = new EIP1193JsonRpcClient(proxiedProvider, {
+            maxPriorityFeePerGas: undefined, // no config set for maxPriorityFeePerGas
+          });
+
+          const fees = await maxFeeClient.getNetworkFees();
+
+          assert("maxPriorityFeePerGas" in fees);
+
+          assert.equal(fees.maxPriorityFeePerGas, 1_000_000_000n);
+        });
       });
     });