feat: add getFeeCalculatorForBlockhash method

web3.js/module.d.ts

@@ -271,6 +271,10 @@ declare module '@solana/web3.js' {
     getRecentBlockhashAndContext(
       commitment?: Commitment,
     ): Promise<RpcResponseAndContext<BlockhashAndFeeCalculator>>;
+    getFeeCalculatorForBlockhash(
+      blockhash: Blockhash,
+      commitment?: Commitment,
+    ): Promise<RpcResponseAndContext<FeeCalculator | null>>;
     getRecentBlockhash(
       commitment?: Commitment,
     ): Promise<BlockhashAndFeeCalculator>;

web3.js/module.flow.js

@@ -284,6 +284,10 @@ declare module '@solana/web3.js' {
     getRecentBlockhashAndContext(
       commitment: ?Commitment,
     ): Promise<RpcResponseAndContext<BlockhashAndFeeCalculator>>;
+    getFeeCalculatorForBlockhash(
+      blockhash: Blockhash,
+      commitment: ?Commitment,
+    ): Promise<RpcResponseAndContext<FeeCalculator | null>>;
     getRecentBlockhash(
       commitment: ?Commitment,
     ): Promise<BlockhashAndFeeCalculator>;

web3.js/src/connection.js

@@ -783,6 +783,20 @@ const GetRecentBlockhashAndContextRpcResult = jsonRpcResultAndContext(
   }),
 );
 
+/**
+ * Expected JSON RPC response for the "getFeeCalculatorForBlockhash" message
+ */
+const GetFeeCalculatorRpcResult = jsonRpcResultAndContext(
+  struct.union([
+    'null',
+    struct({
+      feeCalculator: struct({
+        lamportsPerSignature: 'number',
+      }),
+    }),
+  ]),
+);
+
 /**
  * Expected JSON RPC response for the "requestAirdrop" message
  */
@@ -1506,6 +1520,31 @@ export class Connection {
     return res.result;
   }
 
+  /**
+   * Fetch the fee calculator for a recent blockhash from the cluster, return with context
+   */
+  async getFeeCalculatorForBlockhash(
+    blockhash: Blockhash,
+    commitment: ?Commitment,
+  ): Promise<RpcResponseAndContext<FeeCalculator | null>> {
+    const args = this._argsWithCommitment([blockhash], commitment);
+    const unsafeRes = await this._rpcRequest(
+      'getFeeCalculatorForBlockhash',
+      args,
+    );
+
+    const res = GetFeeCalculatorRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error('failed to get fee calculator: ' + res.error.message);
+    }
+    assert(typeof res.result !== 'undefined');
+    const {context, value} = res.result;
+    return {
+      context,
+      value: value && value.feeCalculator,
+    };
+  }
+
   /**
    * Fetch a recent blockhash from the cluster
    * @return {Promise<{blockhash: Blockhash, feeCalculator: FeeCalculator}>}

web3.js/test/connection.test.js

@@ -203,6 +203,7 @@ test('get program accounts', async () => {
       },
     },
   ]);
+
   transaction = SystemProgram.assign({
     accountPubkey: account1.publicKey,
     programId: programId.publicKey,
@@ -213,8 +214,40 @@ test('get program accounts', async () => {
     skipPreflight: true,
   });
 
-  mockGetRecentBlockhash('recent');
+  mockRpc.push([
-  const {feeCalculator} = await connection.getRecentBlockhash();
+    url,
+    {
+      method: 'getFeeCalculatorForBlockhash',
+      params: [transaction.recentBlockhash, {commitment: 'recent'}],
+    },
+    {
+      error: null,
+      result: {
+        context: {
+          slot: 11,
+        },
+        value: {
+          feeCalculator: {
+            lamportsPerSignature: 42,
+          },
+        },
+      },
+    },
+  ]);
+
+  if (transaction.recentBlockhash === null) {
+    expect(transaction.recentBlockhash).not.toBeNull();
+    return;
+  }
+
+  const feeCalculator = (
+    await connection.getFeeCalculatorForBlockhash(transaction.recentBlockhash)
+  ).value;
+
+  if (feeCalculator === null) {
+    expect(feeCalculator).not.toBeNull();
+    return;
+  }
 
   mockRpc.push([
     url,
@@ -1077,6 +1110,43 @@ test('get recent blockhash', async () => {
   }
 });
 
+test('get fee calculator', async () => {
+  const connection = new Connection(url);
+
+  mockGetRecentBlockhash('recent');
+  const {blockhash} = await connection.getRecentBlockhash('recent');
+
+  mockRpc.push([
+    url,
+    {
+      method: 'getFeeCalculatorForBlockhash',
+      params: [blockhash, {commitment: 'recent'}],
+    },
+    {
+      error: null,
+      result: {
+        context: {
+          slot: 11,
+        },
+        value: {
+          feeCalculator: {
+            lamportsPerSignature: 5000,
+          },
+        },
+      },
+    },
+  ]);
+
+  const feeCalculator = (
+    await connection.getFeeCalculatorForBlockhash(blockhash, 'recent')
+  ).value;
+  if (feeCalculator === null) {
+    expect(feeCalculator).not.toBeNull();
+    return;
+  }
+  expect(feeCalculator.lamportsPerSignature).toEqual(5000);
+});
+
 test('get block time', async () => {
   const connection = new Connection(url);