docs(token 2022): guide for mint close authority extension

content/guides/token-extensions/mint-close-authority.md

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+---
+date: Dec 05, 2023
+seoTitle: "Token Extensions: Mint Close Authority"
+title: How to use the Mint Close Authority extension
+description:
+  "With Token Extensions, it is possible to close token mint accounts by
+  initializing the MintCloseAuthority extension before initializing the mint."
+keywords:
+  - token 2022
+  - token extensions
+  - token program
+difficulty: beginner
+tags:
+  - token 2022
+  - token extensions
+---
+
+With the original SPL token program, there was no option to close Mint Accounts
+owned by the Token Program and reclaim the SOL allocated to these accounts.
+
+The `MintCloseAuthority` extension introduces a solution to this limitation by
+allowing a designated Close Authority to close a Mint Account if the supply of
+the mint is 0. This feature provides a mechanism to recover SOL allocated to
+Mint Accounts that are no longer in use.
+
+In this guide, we'll walk through an example of using Solana Playground. Here is
+the [final script](https://beta.solpg.io/65700c73fb53fa325bfd0c4a).
+
+## Getting Started
+
+Start by opening this Solana Playground
+[link](https://beta.solpg.io/656e19acfb53fa325bfd0c46) with the following
+starter code.
+
+```javascript
+// 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.
+
+To get devnet SOL, run the `solana airdrop` command in the Playground's
+terminal, or visit this [devnet faucet](https://faucet.solana.com/).
+
+```
+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` and
+`@solana/spl-token` libraries.
+
+Replace the starter code with the following:
+
+```javascript
+import {
+  Connection,
+  Keypair,
+  SystemProgram,
+  Transaction,
+  clusterApiUrl,
+  sendAndConfirmTransaction,
+} from "@solana/web3.js";
+import {
+  ExtensionType,
+  TOKEN_2022_PROGRAM_ID,
+  closeAccount,
+  createInitializeMintCloseAuthorityInstruction,
+  createInitializeMintInstruction,
+  getMintLen,
+} from "@solana/spl-token";
+
+// Playground wallet
+const payer = pg.wallet.keypair;
+
+// Connection to devnet cluster
+const connection = new Connection(clusterApiUrl("devnet"), "confirmed");
+
+// Transaction signature returned from sent transaction
+let transactionSignature: string;
+```
+
+## Mint Setup
+
+First, let's define the properties of the Mint Account we'll be creating in the
+following step.
+
+```javascript
+// Generate new keypair for Mint Account
+const mintKeypair = Keypair.generate();
+// Address for Mint Account
+const mint = mintKeypair.publicKey;
+// Decimals for Mint Account
+const decimals = 2;
+// Authority that can mint new tokens
+const mintAuthority = pg.wallet.publicKey;
+// Authority that can close the Mint Account
+const closeAuthority = pg.wallet.publicKey;
+```
+
+Next, let's determine the size of the new Mint Account and calculate the minimum
+lamports needed for rent exemption.
+
+```javascript
+// Size of Mint Account with extension
+const mintLen = getMintLen([ExtensionType.MintCloseAuthority]);
+// Minimum lamports required for Mint Account
+const lamports = await connection.getMinimumBalanceForRentExemption(mintLen);
+```
+
+With Token Extensions, the size of the Mint 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 `MintCloseAuthority` extension
+- Initialize the remaining Mint Account data
+
+First, build the instruction to invoke the System Program to create an account
+and assign ownership to the Token Extensions Program.
+
+```javascript
+// 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: mint, // Address of the account to create
+  space: mintLen, // 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 `MintCloseAuthority` extension for
+the Mint Account.
+
+```javascript
+// Instruction to initialize the MintCloseAuthority Extension
+const initializeMintCloseAuthorityInstruction =
+  createInitializeMintCloseAuthorityInstruction(
+    mint, // Mint Account address
+    closeAuthority, // Designated Close Authority
+    TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
+  );
+```
+
+Lastly, build the instruction to initialize the rest of the Mint Account data.
+This is the same as with the original Token Program.
+
+```javascript
+// Instruction to initialize Mint Account data
+const initializeMintInstruction = createInitializeMintInstruction(
+  mint, // Mint Account Address
+  decimals, // Decimals of Mint
+  mintAuthority, // Designated Mint Authority
+  null, // Optional Freeze Authority
+  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
+);
+```
+
+## Send Transaction
+
+Next, let's add the instructions to a new transaction and send it to the
+network. This will create a Mint Account with the `MintCloseAuthority` extension
+enabled.
+
+```javascript
+// Add instructions to new transaction
+const transaction = new Transaction().add(
+  createAccountInstruction,
+  initializeMintCloseAuthorityInstruction,
+  initializeMintInstruction,
+);
+
+// Send transaction
+transactionSignature = await sendAndConfirmTransaction(
+  connection,
+  transaction,
+  [payer, mintKeypair], // Signers
+);
+
+console.log(
+  "\nCreate Mint 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.
+
+## Close Mint Account
+
+With the `MintCloseAuthority` extension enabled, the Close Authority can close
+the Mint Account to reclaim the lamports from the account.
+
+```javascript
+// Send transaction to close Mint Account
+transactionSignature = await closeAccount(
+  connection,
+  payer, // Transaction fee payer
+  mint, // Mint Account address
+  payer.publicKey, // Account to receive lamports from closed account
+  closeAuthority, // Close Authority for Mint Account
+  undefined, // Additional signers
+  undefined, // Confirmation options
+  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
+);
+
+console.log(
+  "\nClose Mint 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 the SolanaFM.
+
+## Conclusion
+
+The `MintCloseAuthority` extension enables developers to reclaim SOL that
+otherwise would have been permanently locked in a Mint Account. This feature is
+particularly useful for applications or games involving single-use NFTs that are
+meant to be burned. It ensures that the SOL allocated to Mint Accounts which are
+no longer used can be reclaimed and reused.