Token Extensions: Required Memo

The MemoTransfer extension enforces that every incoming transfer to a Token Account is accompanied by a memo instruction. This memo instruction records a message in the transaction's program logs. This feature is particularly useful for adding context to transactions, making it easier to understand their purpose when reviewing the transaction logs later.

In this guide, we'll walk through an example of using Solana Playground. Here is the final script.

Getting Started

Start by opening this Solana Playground link with the following starter code.

// Client
console.log("My address:", pg.wallet.publicKey.toString());
const balance = await pg.connection.getBalance(pg.wallet.publicKey);
console.log(`My balance: ${balance / web3.LAMPORTS_PER_SOL} SOL`);

If it is your first time using Solana Playground, you'll first need to create a Playground Wallet and fund the wallet with devnet SOL.

If you do not have a Playground wallet, you may see a type error within the editor on all declarations of pg.wallet.publicKey. This type error will clear after you create a Playground wallet.

To get devnet SOL, run the solana airdrop command in the Playground's terminal, or visit this devnet faucet.

solana airdrop 5

Once you've created and funded the Playground wallet, click the "Run" button to run the starter code.

Add Dependencies

Let's start by setting up our script. We'll be using the @solana/web3.js, @solana/spl-token, and @solana/spl-memo libraries.

Replace the starter code with the following:

import {
  Connection,
  Keypair,
  SystemProgram,
  Transaction,
  clusterApiUrl,
  sendAndConfirmTransaction,
  TransactionInstruction,
  PublicKey,
} from "@solana/web3.js";
import {
  ExtensionType,
  TOKEN_2022_PROGRAM_ID,
  createEnableRequiredMemoTransfersInstruction,
  createInitializeAccountInstruction,
  createMint,
  disableRequiredMemoTransfers,
  enableRequiredMemoTransfers,
  getAccountLen,
  createAccount,
  mintTo,
  createTransferInstruction,
} from "@solana/spl-token";
import { createMemoInstruction } from "@solana/spl-memo";

// Playground wallet
const payer = pg.wallet.keypair;

// Connection to devnet cluster
const connection = new Connection(clusterApiUrl("devnet"), "confirmed");

// Transaction to send
let transaction: Transaction;
// Transaction signature returned from sent transaction
let transactionSignature: string;

Mint Setup

We'll first need to create a new Mint Account before we can create Token Accounts.

// Authority that can mint new tokens
const mintAuthority = pg.wallet.publicKey;
// Decimals for Mint Account
const decimals = 2;

// Create Mint Account
const mint = await createMint(
  connection,
  payer, // Payer of the transaction and initialization fees
  mintAuthority, // Mint Authority
  null, // Optional Freeze Authority
  decimals, // Decimals of Mint
  undefined, // Optional keypair
  undefined, // Options for confirming the transaction
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Memo Transfer Token Account

Next, let's build a transaction to enable the MemoTransfer extension for a new Token Account.

First, let's generate a new keypair to use as the address of the Token Account.

// Random keypair to use as owner of Token Account
const tokenAccountKeypair = Keypair.generate();
// Address for Token Account
const tokenAccount = tokenAccountKeypair.publicKey;

Next, let's determine the size of the new Token Account and calculate the minimum lamports needed for rent exemption.

// Size of Token Account with extension
const accountLen = getAccountLen([ExtensionType.MemoTransfer]);
// Minimum lamports required for Token Account
const lamports = await connection.getMinimumBalanceForRentExemption(accountLen);

With Token Extensions, the size of the Token Account will vary based on the extensions enabled.

Build Instructions

Next, let's build the set of instructions to:

Create a new account
Initialize the Token Account data
Enable the MemoTransfer extension

First, build the instruction to invoke the System Program to create an account and assign ownership to the Token Extensions Program.

// Instruction to invoke System Program to create new account
const createAccountInstruction = SystemProgram.createAccount({
  fromPubkey: payer.publicKey, // Account that will transfer lamports to created account
  newAccountPubkey: tokenAccount, // Address of the account to create
  space: accountLen, // Amount of bytes to allocate to the created account
  lamports, // Amount of lamports transferred to created account
  programId: TOKEN_2022_PROGRAM_ID, // Program assigned as owner of created account
});

Next, build the instruction to initialize the Token Account data.

// Instruction to initialize Token Account data
const initializeAccountInstruction = createInitializeAccountInstruction(
  tokenAccount, // Token Account Address
  mint, // Mint Account
  payer.publicKey, // Token Account Owner
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Lastly, build the instruction to enable the MemoTransfer extension for the Token Account.

// Instruction to initialize the MemoTransfer Extension
const enableRequiredMemoTransfersInstruction =
  createEnableRequiredMemoTransfersInstruction(
    tokenAccount, // Token Account address
    payer.publicKey, // Token Account Owner
    undefined, // Additional signers
    TOKEN_2022_PROGRAM_ID, // Token Program ID
  );

Send Transaction

Next, let's add the instructions to a new transaction and send it to the network. This will create a Token Account with the MemoTransfer extension enabled.

// Add instructions to new transaction
transaction = new Transaction().add(
  createAccountInstruction,
  initializeAccountInstruction,
  enableRequiredMemoTransfersInstruction,
);

// Send transaction
transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer, tokenAccountKeypair], // Signers
);

console.log(
  "\nCreate Token Account:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Run the script by clicking the Run button. You can then inspect the transaction details on SolanaFM.

Create and Fund Token Account

Next, let's set up another Token Account to demonstrate the functionality of the MemoTransfer extension.

First, create a sourceTokenAccount owned by the Playground wallet.

// Create Token Account for Playground wallet
const sourceTokenAccount = await createAccount(
  connection,
  payer, // Payer to create Token Account
  mint, // Mint Account address
  payer.publicKey, // Token Account owner
  undefined, // Optional keypair, default to Associated Token Account
  undefined, // Confirmation options
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Next, mint 2 tokens to the sourceTokenAccount to fund it.

// Mint tokens to sourceTokenAccount
transactionSignature = await mintTo(
  connection,
  payer, // Transaction fee payer
  mint, // Mint Account address
  sourceTokenAccount, // Mint to
  mintAuthority, // Mint Authority address
  200, // Amount
  undefined, // Additional signers
  undefined, // Confirmation options
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

console.log(
  "\nMint Tokens:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Transfer and Memo Instruction

Next, let's prepare the token transfer and memo instructions.

First, build the instruction to transfer tokens from the sourceTokenAccount to the tokenAccount which has the MemoTransfer extension enabled.

// Instruction to transfer tokens
const transferInstruction = createTransferInstruction(
  sourceTokenAccount, // Source Token Account
  tokenAccount, // Destination Token Account
  payer.publicKey, // Source Token Account owner
  100, // Amount
  undefined, // Additional signers
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Next, build the memo instruction. The message will be included in the program logs of the transaction the instruction is added to.

// Message for the memo
const message = "Hello, Solana";
// Instruction to add memo
const memoInstruction = new TransactionInstruction({
  keys: [{ pubkey: payer.publicKey, isSigner: true, isWritable: true }],
  data: Buffer.from(message, "utf-8"),
  programId: new PublicKey("MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr"),
});

Alternatively, you can create the instruction using the @solana/spl-memo library:

// Message for the memo
const message = "Hello, Solana";
// Instruction to add memo
const memoInstruction = createMemoInstruction(message, [payer.publicKey]);

Attempt Transfer without Memo

To demonstrate the functionality of the MemoTransfer extension, let's first attempt to send a token transfer without a memo.

try {
  // Attempt to transfer without memo
  transaction = new Transaction().add(transferInstruction);

  // Send transaction
  await sendAndConfirmTransaction(
    connection,
    transaction,
    [payer], // Signers
  );
} catch (error) {
  console.log("\nExpect Error:", error);
}

Run the script by clicking the Run button. You can then inspect the error in the Playground terminal. You should see a message similar to the following:

Expect Error: { [Error: failed to send transaction: Transaction simulation failed: Error processing Instruction 0: custom program error: 0x24]
  logs:
   [ 'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb invoke [1]',
     'Program log: Instruction: Transfer',
     'Program log: Error: No memo in previous instruction; required for recipient to receive a transfer',
     'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb consumed 6571 of 200000 compute units',
     'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb failed: custom program error: 0x24' ] }

Transfer with Memo

Next, send a token transfer with the memo instruction included on the transaction.

// Add instructions to new transaction
transaction = new Transaction().add(memoInstruction, transferInstruction);

// Send transaction
transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer], // Signers
);

console.log(
  "\nTransfer with Memo:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Run the script by clicking the Run button. You can then inspect the transaction details on SolanaFM.

Enable and Disable Memo Transfer

The MemoTransfer extension can also be freely enabled or disabled by the Token Account owner.

To enable the MemoTransfer extension, use the enableRequiredMemoTransfers instruction.

// Enable Required Memo Transfers
transactionSignature = await enableRequiredMemoTransfers(
  connection, // Connection to use
  payer, // Payer of the transaction fee
  tokenAccount, // Token Account to modify
  payer.publicKey, // Owner of Token Account
  undefined, // Additional signers
  undefined, // Confirmation options
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

console.log(
  "\nEnable Required Memo Transfers:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

To disable the MemoTransfer extension, use the disableRequiredMemoTransfers instruction.

// Disable Required Memo Transfers
transactionSignature = await disableRequiredMemoTransfers(
  connection, // Connection to use
  payer, // Payer of the transaction fee
  tokenAccount, // Token Account to modify
  payer.publicKey, // Owner of Token Account
  undefined, // Additional signers
  undefined, // Confirmation options
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

console.log(
  "\nDisable Required Memo Transfers:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Once the MemoTransfer extension is disabled, transactions to transfer tokens without a memo instruction will complete successfully.

// Add instructions to new transaction
transaction = new Transaction().add(transferInstruction);

// Send transaction
transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer], // Signers
);

console.log(
  "\nTransfer without Memo:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Run the script by clicking the Run button. You can then inspect the transaction details on SolanaFM.

Conclusion

The MemoTransfer extension ensures every incoming transfer to a Token Account includes a memo. By requiring a memo instruction with each transfer, a message is recorded in the transaction's program logs. This feature is especially useful for understanding the purpose of transactions when reviewing logs at a later time.

How to use the Required Memo token extension

Inhoudsopgave

Getting Started

Add Dependencies

Mint Setup

Memo Transfer Token Account

Build Instructions

Send Transaction

Create and Fund Token Account

Transfer and Memo Instruction

Attempt Transfer without Memo

Transfer with Memo

Enable and Disable Memo Transfer

Conclusion