feat: add getEstimatedFee to Transaction (#23579)

web3.js/src/transaction.ts

@@ -2,6 +2,7 @@ import nacl from 'tweetnacl';
 import bs58 from 'bs58';
 import {Buffer} from 'buffer';
 
+import {Connection} from './connection';
 import {Message} from './message';
 import {PublicKey} from './publickey';
 import * as shortvec from './util/shortvec-encoding';
@@ -405,6 +406,13 @@ export class Transaction {
     return this._compile().serialize();
   }
 
+  /**
+   * Get the estimated fee associated with a transaction
+   */
+  async getEstimatedFee(connection: Connection): Promise<number> {
+    return (await connection.getFeeForMessage(this.compileMessage())).value;
+  }
+
   /**
    * Specify the public keys which will be used to sign the Transaction.
    * The first signer will be used as the transaction fee payer account.

web3.js/test/transaction.test.ts

@@ -3,6 +3,7 @@ import {Buffer} from 'buffer';
 import nacl from 'tweetnacl';
 import {expect} from 'chai';
 
+import {Connection} from '../src/connection';
 import {Keypair} from '../src/keypair';
 import {PublicKey} from '../src/publickey';
 import {Transaction, TransactionInstruction} from '../src/transaction';
@@ -11,6 +12,7 @@ import {SystemProgram} from '../src/system-program';
 import {Message} from '../src/message';
 import invariant from '../src/util/assert';
 import {toBuffer} from '../src/util/to-buffer';
+import {helpers} from './mocks/rpc-http';
 
 describe('Transaction', () => {
   describe('compileMessage', () => {
@@ -112,6 +114,28 @@ describe('Transaction', () => {
     });
   });
 
+  it('getEstimatedFee', async () => {
+    const connection = new Connection('https://api.testnet.solana.com');
+    const accountFrom = Keypair.generate();
+    const accountTo = Keypair.generate();
+
+    const {blockhash} = await helpers.latestBlockhash({connection});
+
+    const transaction = new Transaction({
+      feePayer: accountFrom.publicKey,
+      recentBlockhash: blockhash,
+    }).add(
+      SystemProgram.transfer({
+        fromPubkey: accountFrom.publicKey,
+        toPubkey: accountTo.publicKey,
+        lamports: 10,
+      }),
+    );
+
+    const fee = await transaction.getEstimatedFee(connection);
+    expect(fee).to.eq(5000);
+  });
+
   it('partialSign', () => {
     const account1 = Keypair.generate();
     const account2 = Keypair.generate();