Required Memo

Summary

The required memo extension allows developers to mandate that all incoming transfers to a token account include a memo, facilitating enhanced transaction tracking and user identification.
When a transfer is initiated without a memo, the transaction will fail.
The required memo extension can be disabled by calling disableRequiredMemoTransfers.

For certain applications, such as exchanges or financial services, tracking the purpose or origin of a transaction is crucial. The required memo extension specifies that a memo is necessary for every incoming transfer to a token account. This requirement ensures that each transaction is accompanied by additional information, which can be used for compliance, auditing, or user-specific purposes. If the need for strict tracking diminishes, the requirement can be adjusted to make memos optional, offering flexibility in how transactions are handled and recorded.

It is important to note that this is a token account extension, not a mint extension. This means individual token accounts need to enable this feature. And like all extensions, this will only work with Token Extensions Program tokens.

Creating token with required memo

Initializing a token account with required memo involves three instructions:

SystemProgram.createAccount
initializeAccountInstruction
createEnableRequiredMemoTransfersInstruction

The first instruction SystemProgram.createAccount allocates space on the blockchain for the token account. This instruction accomplishes three things:

Allocates space
Transfers lamports for rent
Assigns to it's owning program

const accountLen = getAccountLen([ExtensionType.MemoTransfer]);
const lamports = await connection.getMinimumBalanceForRentExemption(accountLen);
 
const createAccountInstruction = SystemProgram.createAccount({
  fromPubkey: payer.publicKey,
  newAccountPubkey: tokenAccountKeypair.publicKey,
  space: accountLen,
  lamports,
  programId: TOKEN_2022_PROGRAM_ID,
});

The second instruction createInitializeAccountInstruction initializes the account instruction.

const initializeAccountInstruction = createInitializeAccountInstruction(
  tokenAccountKeypair.publicKey,
  mint,
  payer.publicKey,
  TOKEN_2022_PROGRAM_ID,
);

The third instruction createEnableRequiredMemoTransfersInstruction initializes the token account with required memo.

const enableRequiredMemoTransfersInstruction =
  createEnableRequiredMemoTransfersInstruction(
    tokenAccountKeypair.publicKey,
    payer.publicKey,
    undefined,
    TOKEN_2022_PROGRAM_ID,
  );

When the transaction with these three instructions is sent, a new token account is created with the required memo extension.

const transaction = new Transaction().add(
  createAccountInstruction,
  initializeAccountInstruction,
  enableRequiredMemoTransfersInstruction,
);
 
const transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer, tokenAccountKeypair], // Signers
);

Transferring with required memo

When transferring to a token account with the required memo instruction enabled, you need to send a memo first within the same transaction. We do this by creating a memo instruction to call the Memo program. Then, we add in our transfer instruction.

const message = "Hello, Solana";
 
const transaction = new Transaction().add(
  new TransactionInstruction({
    keys: [{ pubkey: payer.publicKey, isSigner: true, isWritable: true }],
    data: Buffer.from(message, "utf-8"), // Memo message. In this case it is "Hello, Solana"
    programId: new PublicKey("MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr"), // Memo program that validates keys and memo message
  }),
  createTransferInstruction(
    ourTokenAccount,
    otherTokenAccount, // Has required memo
    payer.publicKey,
    amountToTransfer,
    undefined,
    TOKEN_2022_PROGRAM_ID,
  ),
);
await sendAndConfirmTransaction(connection, transaction, [payer]);

Disabling required memo

The required memo extension can be disabled given you have the authority to modify the token account. To do this, simply call the disableRequiredMemoTransfers function and pass in the required arguments.

/**
 * Disable memo transfers on the given account
 *
 * @param connection     Connection to use
 * @param payer          Payer of the transaction fees
 * @param account        Account to modify
 * @param owner          Owner of the account
 * @param multiSigners   Signing accounts if `owner` is a multisig
 * @param confirmOptions Options for confirming the transaction
 * @param programId      SPL Token program account
 *
 * @return Signature of the confirmed transaction
 */
await disableRequiredMemoTransfers(
  connection,
  payer,
  otherTokenAccount,
  payer,
  undefined,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);

Lab

In this lab, we'll create a token account with the required memo extension. We'll then write tests to check if the extension is working as intended by attempting to transfer funds with and without a memo.

1. Setup Environment

To get started, create an empty directory named required-memo and navigate to it. We'll be initializing a brand new project. Run npm init and follow through the prompts.

Next, we'll need to add our dependencies. Run the following to install the required packages:

npm i @solana-developers/helpers@2 @solana/spl-token @solana/web3.js@1 esrun dotenv typescript

Create a directory named src. In this directory, create a file named index.ts. This is where we will run checks against the rules of this extension. Paste the following code in index.ts:

import {
  TOKEN_2022_PROGRAM_ID,
  getAccount,
  mintTo,
  createTransferInstruction,
  createMint,
  disableRequiredMemoTransfers,
  enableRequiredMemoTransfers,
} from "@solana/spl-token";
import {
  sendAndConfirmTransaction,
  Connection,
  Transaction,
  PublicKey,
  TransactionInstruction,
} from "@solana/web3.js";
// import { createTokenWithMemoExtension } from "./token-helper"; // We'll uncomment this later
import { initializeKeypair, makeKeypairs } from "@solana-developers/helpers";
 
require("dotenv").config();
 
const connection = new Connection("http://127.0.0.1:8899", "confirmed");
const payer = await initializeKeypair(connection);
const mintDecimals = 9;
 
const [ourTokenAccountKeypair, otherTokenAccountKeypair] = makeKeypairs(2);
const ourTokenAccount = ourTokenAccountKeypair.publicKey;
const otherTokenAccount = otherTokenAccountKeypair.publicKey;
 
const amountToMint = 1000;
const amountToTransfer = 300;
 
// CREATE MINT
 
// CREATE TOKENS
 
// MINT TOKENS
 
// ATTEMPT TO TRANSFER WITHOUT MEMO
 
// ATTEMPT TO TRANSFER WITH MEMO
 
// DISABLE MEMO EXTENSION AND TRANSFER

2. Run validator node

For the sake of this guide, we'll be running our own validator node.

In a separate terminal, run the following command: solana-test-validator. This will run the node and also log out some keys and values. The value we need to retrieve and use in our connection is the JSON RPC URL, which in this case is http://127.0.0.1:8899. We then use that in the connection to specify to use the local RPC URL.

const connection = new Connection("http://127.0.0.1:8899", "confirmed");

Alternatively, if you'd like to use testnet or devnet, import the clusterApiUrl from @solana/web3.js and pass it to the connection as such:

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

3. Helpers

When we pasted the index.ts code from earlier, we added the following helpers provided by the @solana-developers/helpers package and some starting variables.

initializeKeypair: This function creates the keypair for the payer and also airdrops 1 testnet SOL to it
makeKeypairs: This function creates keypairs without airdropping any SOL

4. Create the mint

First things first, since the required memo extension is a token extension, we don't need to do anything fancy with the mint. It just needs to be a Token Extensions Program mint. That being said, we can just create one using the createMint function.

Let's do this in src/index.ts:

// CREATE MINT
const mint = await createMint(
  connection,
  payer,
  payer.publicKey,
  null,
  mintDecimals,
  undefined,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);

5. Create Token Account with required memo

Let's create a new file src/token-helper.ts and create a new function within it called createTokenWithMemoExtension. As the name implies, we'll use this to create our token accounts with the required memo extension enabled. The function will take the following arguments:

connection: The connection object
mint: Public key for the new mint
payer: Payer for the transaction
tokenAccountKeypair: The token account keypair associated with the token account

import {
  TOKEN_2022_PROGRAM_ID,
  getAccountLen,
  ExtensionType,
  createInitializeAccountInstruction,
  createEnableRequiredMemoTransfersInstruction,
} from "@solana/spl-token";
import {
  sendAndConfirmTransaction,
  Connection,
  Keypair,
  Transaction,
  PublicKey,
  SystemProgram,
} from "@solana/web3.js";
 
export async function createTokenWithMemoExtension(
  connection: Connection,
  payer: Keypair,
  tokenAccountKeypair: Keypair,
  mint: PublicKey,
): Promise<string> {
  // CREATE ACCOUNT INSTRUCTION
 
  // CREATE INITIALIZE ACCOUNT INSTRUCTION
 
  // CREATE ENABLE REQUIRED MEMO TRANSFER INSTRUCTION
 
  // SEND AND CONFIRM TRANSACTION
 
  return await "TODO FINISH FUNCTION";
}

Let's start adding our code.

The first step in creating the token account is reserving space on Solana with the SystemProgram.createAccount method:

// CREATE ACCOUNT INSTRUCTION
const accountLen = getAccountLen([ExtensionType.MemoTransfer]);
const lamports = await connection.getMinimumBalanceForRentExemption(accountLen);
 
const createAccountInstruction = SystemProgram.createAccount({
  fromPubkey: payer.publicKey,
  newAccountPubkey: tokenAccountKeypair.publicKey,
  space: accountLen,
  lamports,
  programId: TOKEN_2022_PROGRAM_ID,
});

Now we need to initialize the token account. To create this instruction we call createInitializeAccountInstruction and pass in the required arguments. This function is provided by the SPL Token package and it constructs a transaction instruction that initializes a new token account.

// CREATE INITIALIZE ACCOUNT INSTRUCTION
const initializeAccountInstruction = createInitializeAccountInstruction(
  tokenAccountKeypair.publicKey,
  mint,
  payer.publicKey,
  TOKEN_2022_PROGRAM_ID,
);

The last instruction we need is the one that enables the required memo. We get this by calling the createEnableRequiredMemoTransfersInstruction function. When the required memos are enabled, any transfer of tokens into the account must include a memo.

// CREATE ENABLE REQUIRED MEMO TRANSFERS INSTRUCTION
const enableRequiredMemoTransfersInstruction =
  createEnableRequiredMemoTransfersInstruction(
    tokenAccountKeypair.publicKey,
    payer.publicKey,
    undefined,
    TOKEN_2022_PROGRAM_ID,
  );

Lastly, let's add all of the instructions to a transaction, send it to the blockchain and return the signature

// SEND AND CONFIRM TRANSACTION
const transaction = new Transaction().add(
  createAccountInstruction,
  initializeAccountInstruction,
  enableRequiredMemoTransfersInstruction,
);
 
const transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer, tokenAccountKeypair], // Signers
);
 
return transactionSignature;

Let's go back to index.ts and create two new token accounts: ourTokenAccountKeypair and otherTokenAccountKeypair using our newly created function.

// CREATE TOKENS
await createTokenWithMemoExtension(
  connection,
  payer,
  ourTokenAccountKeypair,
  mint,
);
 
await createTokenWithMemoExtension(
  connection,
  payer,
  otherTokenAccountKeypair,
  mint,
);

Lastly, let's call mintTo to mint some initial tokens to ourTokenAccountKeypair:

// MINT TOKENS
await mintTo(
  connection,
  payer,
  mint,
  ourTokenAccount,
  payer,
  amountToMint,
  undefined,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);

Note: The required memo extension only requires a memo on transferring, not minting.

6. Tests

Now that we've created some accounts with the required memo instruction. Let's write some tests to see how they function.

We'll write 3 tests in total:

Transferring without a memo
Transferring with a memo
Disabling Required Memo extension and transferring without a memo

6.1 Transfer without Memo

This first test will attempt to transfer tokens from ourTokenAccount to otherTokenAccount. This test is expected to fail as there is no memo attached to the transaction.

// ATTEMPT TO TRANSFER WITHOUT MEMO
try {
  const transaction = new Transaction().add(
    createTransferInstruction(
      ourTokenAccount,
      otherTokenAccount,
      payer.publicKey,
      amountToTransfer,
      undefined,
      TOKEN_2022_PROGRAM_ID,
    ),
  );
 
  await sendAndConfirmTransaction(connection, transaction, [payer]);
 
  console.error("You should not be able to transfer without a memo.");
} catch (error) {
  console.log(
    `✅ - We expected this to fail because you need to send a memo with the transfer.`,
  );
}

Run this test, you should see the following error logged out in the terminal, meaning the extension is working as intended: ✅ - We expected this to fail because you need to send a memo with the transfer.

npx esrun src/index.ts

6.2 Test transfer with memo

This test will attempt to transfer tokens with a memo. This test is expected to pass. Pay extra attention to the first instruction - It is the part of the transaction that adds the memo instruction to it:

// ATTEMPT TO TRANSFER WITH MEMO
const message = "Hello, Solana";
 
const transaction = new Transaction().add(
  new TransactionInstruction({
    keys: [{ pubkey: payer.publicKey, isSigner: true, isWritable: true }],
    data: Buffer.from(message, "utf-8"), // Memo message. In this case it is "Hello, Solana"
    programId: new PublicKey("MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr"), // Memo program that validates keys and memo message
  }),
 
  createTransferInstruction(
    ourTokenAccount,
    otherTokenAccount,
    payer.publicKey,
    amountToTransfer,
    undefined,
    TOKEN_2022_PROGRAM_ID,
  ),
);
await sendAndConfirmTransaction(connection, transaction, [payer]);
 
const accountAfterMemoTransfer = await getAccount(
  connection,
  otherTokenAccount,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);
 
console.log(
  `✅ - We have transferred ${accountAfterMemoTransfer.amount} tokens to ${otherTokenAccount} with the memo: ${message}`,
);

Run the test and see that it passes:

npx esrun src/index.ts

6.3 Test transfer with disabled memo

In our last test, we'll disable the required memo extension on the otherTokenAccount and send it some tokens without a memo. We expect this to pass.

// DISABLE MEMO EXTENSION AND TRANSFER
await disableRequiredMemoTransfers(
  connection,
  payer,
  otherTokenAccount,
  payer,
  undefined,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);
 
// Transfer tokens to otherTokenAccount
const transfer = new Transaction().add(
  createTransferInstruction(
    ourTokenAccount,
    otherTokenAccount,
    payer.publicKey,
    amountToTransfer,
    undefined,
    TOKEN_2022_PROGRAM_ID,
  ),
);
 
await sendAndConfirmTransaction(connection, transfer, [payer]);
 
const accountAfterDisable = await getAccount(
  connection,
  otherTokenAccount,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);
 
// Re-enable memo transfers to show it exists
await enableRequiredMemoTransfers(
  connection,
  payer,
  otherTokenAccount,
  payer,
  undefined,
  undefined,
  TOKEN_2022_PROGRAM_ID,
);
 
console.log(
  `✅ - We have transferred ${accountAfterDisable.amount} tokens to ${otherTokenAccount} without a memo.`,
);

Run the tests. You will notice that otherTokenAccount now has 600 tokens, meaning it has successfully transferred without a memo after disabling the extension.

npx esrun src/index.ts

Congratulations! We've just tested the required memo extension!

Challenge

Go create your own token account with required memo.