Como Usar getFeeForMessage

# First, you need a base64 encoded message. 
# This typically involves creating a transaction, compiling its message, 
# and then base64 encoding the serialized message.
# The example message below is illustrative.
# Replace "MESSAGE_BASE64_ENCODED" with your actual encoded message.
curl https://mainnet.helius-rpc.com/?api-key=<api-key> -X POST -H "Content-Type: application/json" -d \
  '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getFeeForMessage",
    "params": [
      "MESSAGE_BASE64_ENCODED", // Replace with your actual base64 encoded message
      { "commitment": "processed" }
    ]
  }'

const { Connection, Keypair, SystemProgram, Transaction, LAMPORTS_PER_SOL } = require('@solana/web3.js');

async function estimateTransactionFee() {
  const connection = new Connection('https://devnet.helius-rpc.com/?api-key=<api-key>');

  try {
    const fromPublicKey = Keypair.generate().publicKey;
    const toPublicKey = Keypair.generate().publicKey;

    let transaction = new Transaction().add(
      SystemProgram.transfer({
        fromPubkey: fromPublicKey,
        toPubkey: toPublicKey,
        lamports: 1000,
      })
    );

    transaction.feePayer = fromPublicKey;
    const { blockhash } = await connection.getLatestBlockhash('confirmed');
    transaction.recentBlockhash = blockhash;

    const message = transaction.compileMessage();
    const messageBase64 = message.serialize().toString('base64');

    console.log(`Compiled Message (Base64): ${messageBase64}`);

    const feeResult = await connection.getFeeForMessage(message, 'confirmed');

    if (feeResult && feeResult.value !== null) {
      console.log(`Estimated Fee: ${feeResult.value} lamports`);
    } else {
      console.log('Could not estimate fee. The value was null.');
      console.log('This might happen if the blockhash is too old or the message is invalid.');
    }

  } catch (error) {
    console.error('Error estimating transaction fee:', error);
    if (error.message.includes('failed to get recent blockhash')) {
        console.error('Ensure your RPC endpoint is responsive or try a different commitment level for getLatestBlockhash.');
    }
  }
}

estimateTransactionFee();