Dynamic metadata NFTs using Token Extensions

With the Token Extension program, you can create NFTs and digital assets using the metadata extensions. Together, these extensions (metadata pointer and token metadata) allow you to put any desired metadata natively on-chain. All within a customizable key-value data store directly on the token's mint account, reducing costs and complexity.

These can be especially great for web3 games since we can now have these "additional metadata fields" within an on-chain key-value store, allowing games to save/access unique state within the NFT itself (like for a game character's stats or inventory).

Building the on-chain program

In this developer guide, we will demonstrate how to build these Token Extension based NFTs and custom metadata using an Anchor program. This program will save the level and the collected resources of a game player within an NFT.

This NFT will be created by the Anchor program so it is very easy to mint from the JavaScript client. Each NFT will have some basic structure provided via the Token Metadata interface:

default on-chain fields - name, symbol and uri
- the uri is a link to an offchain json file which contains the off chain metadata of the NFT
we will also have custom "additional fields" that we define

All of these fields are saved using the metadata extension which is pointed to the NFT's mint account, making them accessible to anyone or any program.

Video and Source Code

You can find a video walkthrough of this example on the Solana Foundation Youtube channel:

Other use case within games

These types of NFTs with customizable on-chain metadata open up many interesting possibilities for game developers. Especially since this metadata can be directly interacted with or managed by an on-chain program.

Some of these gaming related use cases include:

save the level and XP of the player
the current weapon and armor
the current quest
the list goes on!

Minting the NFT

In order to create the NFT we need to perform a following steps:

Create a mint account
Initialize the mint account
Create a metadata pointer account
Initialize the metadata pointer account
Create the metadata account
Initialize the metadata account
Create the associated token account
Mint the token to the associated token account
Freeze the mint authority

Rust program code

Here is the rust code used to mint the NFT using the Token extension program:

// calculate the space need for the mint account with the desired extensions
let space = ExtensionType::try_calculate_account_len::<Mint>(
    &[ExtensionType::MetadataPointer])
    .unwrap();
 
// This is the space required for the metadata account.
// We put the metadata into the mint account at the end so we
// don't need to create and additional account.
// Then the metadata pointer points back to the mint account.
// Using this technique, only one account is needed for both the mint
// information and the metadata.
 
let meta_data_space = 250;
 
let lamports_required = (Rent::get()?).minimum_balance(space + meta_data_space);
 
msg!(
    "Create Mint and metadata account size and cost: {} lamports: {}",
    space as u64,
    lamports_required
);
 
system_program::create_account(
    CpiContext::new(
        ctx.accounts.token_program.to_account_info(),
        system_program::CreateAccount {
            from: ctx.accounts.signer.to_account_info(),
            to: ctx.accounts.mint.to_account_info(),
        },
    ),
    lamports_required,
    space as u64,
    &ctx.accounts.token_program.key(),
)?;
 
// Assign the mint to the token program
system_program::assign(
    CpiContext::new(
        ctx.accounts.token_program.to_account_info(),
        system_program::Assign {
            account_to_assign: ctx.accounts.mint.to_account_info(),
        },
    ),
    &token_2022::ID,
)?;
 
// Initialize the metadata pointer (Need to do this before initializing the mint)
let init_meta_data_pointer_ix =
spl_token_2022::extension::metadata_pointer::instruction::initialize(
    &Token2022::id(),
    &ctx.accounts.mint.key(),
    Some(ctx.accounts.nft_authority.key()),
    Some(ctx.accounts.mint.key()),
)
.unwrap();
 
invoke(
    &init_meta_data_pointer_ix,
    &[
        ctx.accounts.mint.to_account_info(),
        ctx.accounts.nft_authority.to_account_info()
    ],
)?;
 
// Initialize the mint cpi
let mint_cpi_ix = CpiContext::new(
    ctx.accounts.token_program.to_account_info(),
    token_2022::InitializeMint2 {
        mint: ctx.accounts.mint.to_account_info(),
    },
);
 
token_2022::initialize_mint2(
    mint_cpi_ix,
    0,
    &ctx.accounts.nft_authority.key(),
    None).unwrap();
 
// We use a PDA as a mint authority for the metadata account because
// we want to be able to update the NFT from the program.
let seeds = b"nft_authority";
let bump = ctx.bumps.nft_authority;
let signer: &[&[&[u8]]] = &[&[seeds, &[bump]]];
 
msg!("Init metadata {0}", ctx.accounts.nft_authority.to_account_info().key);
 
// Init the metadata account
let init_token_meta_data_ix =
&spl_token_metadata_interface::instruction::initialize(
    &spl_token_2022::id(),
    ctx.accounts.mint.key,
    ctx.accounts.nft_authority.to_account_info().key,
    ctx.accounts.mint.key,
    ctx.accounts.nft_authority.to_account_info().key,
    "Beaver".to_string(),
    "BVA".to_string(),
    "https://arweave.net/MHK3Iopy0GgvDoM7LkkiAdg7pQqExuuWvedApCnzfj0".to_string(),
);
 
invoke_signed(
    init_token_meta_data_ix,
    &[ctx.accounts.mint.to_account_info().clone(), ctx.accounts.nft_authority.to_account_info().clone()],
    signer,
)?;
 
// Update the metadata account with an additional metadata field in this case the player level
invoke_signed(
    &spl_token_metadata_interface::instruction::update_field(
        &spl_token_2022::id(),
        ctx.accounts.mint.key,
        ctx.accounts.nft_authority.to_account_info().key,
        spl_token_metadata_interface::state::Field::Key("level".to_string()),
        "1".to_string(),
    ),
    &[
        ctx.accounts.mint.to_account_info().clone(),
        ctx.accounts.nft_authority.to_account_info().clone(),
    ],
    signer
)?;
 
// Create the associated token account
associated_token::create(
    CpiContext::new(
    ctx.accounts.associated_token_program.to_account_info(),
    associated_token::Create {
        payer: ctx.accounts.signer.to_account_info(),
        associated_token: ctx.accounts.token_account.to_account_info(),
        authority: ctx.accounts.signer.to_account_info(),
        mint: ctx.accounts.mint.to_account_info(),
        system_program: ctx.accounts.system_program.to_account_info(),
        token_program: ctx.accounts.token_program.to_account_info(),
    },
))?;
 
// Mint one token to the associated token account of the player
token_2022::mint_to(
    CpiContext::new_with_signer(
        ctx.accounts.token_program.to_account_info(),
        token_2022::MintTo {
            mint: ctx.accounts.mint.to_account_info(),
            to: ctx.accounts.token_account.to_account_info(),
            authority: ctx.accounts.nft_authority.to_account_info(),
        },
        signer
    ),
    1,
)?;
 
// Freeze the mint authority so no more tokens can be minted to make it an NFT
token_2022::set_authority(
    CpiContext::new_with_signer(
        ctx.accounts.token_program.to_account_info(),
        token_2022::SetAuthority {
            current_authority: ctx.accounts.nft_authority.to_account_info(),
            account_or_mint: ctx.accounts.mint.to_account_info(),
        },
        signer
    ),
    AuthorityType::MintTokens,
    None,
)?;

JavaScript client code

Calling mint NFT from the client is very easy:

const nftAuthority = PublicKey.findProgramAddressSync(
  [Buffer.from("nft_authority")],
  program.programId,
);
 
const mint = new Keypair();
 
const destinationTokenAccount = getAssociatedTokenAddressSync(
  mint.publicKey,
  publicKey,
  false,
  TOKEN_2022_PROGRAM_ID,
);
 
const transaction = await program.methods
  .mintNft()
  .accounts({
    signer: publicKey,
    systemProgram: SystemProgram.programId,
    tokenProgram: TOKEN_2022_PROGRAM_ID,
    tokenAccount: destinationTokenAccount,
    mint: mint.publicKey,
    rent: web3.SYSVAR_RENT_PUBKEY,
    associatedTokenProgram: ASSOCIATED_TOKEN_PROGRAM_ID,
    nftAuthority: nftAuthority[0],
  })
  .signers([mint])
  .transaction();
 
console.log("transaction", transaction);
 
const txSig = await sendTransaction(transaction, connection, {
  signers: [mint],
  skipPreflight: true,
});
 
console.log(`https://explorer.solana.com/tx/${txSig}?cluster=devnet`);

Quickstart example

The example above is based on the Solana Games Preset, which generates you a scaffold that includes a JavaScript and Unity client for this game, including the configuration for interacting with the Solana Anchor program.

You can run it yourself with the following command:

npx create-solana-game gameName

Setup your local environment

In order to run this example locally, you will need to make sure you have setup your local environment for Solana development, including installing and configuring the Anchor CLI. If you do not already, you can follow the previously linked setup guide to do so.

Project structure

The Anchor project is structured like this:

The entry point is in the lib.rs file. Here we define the program id and the instructions. The instructions are defined in the instructions folder. The state is defined in the state folder.

So the calls arrive in the lib.rs file and are then forwarded to the instructions. The instructions then call the state to get the data and update it.

You can find the mint NFT instruction in the instructions folder.

├── src
│   ├── instructions
│   │   ├── chop_tree.rs
│   │   ├── init_player.rs
│   │   ├── mint_nft.rs
│   │   └── update_energy.rs
│   ├── state
│   │   ├── game_data.rs
│   │   ├── mod.rs
│   │   └── player_data.rs
│   ├── lib.rs
│   └── constants.rs
│   └── errors.rs

Anchor program

To finish setting up the Anchor program generated from the create-solana-game tool:

cd program to end the program directory
Run anchor build to build the program
Run anchor deploy to deploy the program
Copy the program id from the terminal into the lib.rs, anchor.toml and within the Unity project in the AnchorService and if you use JavaScript in the anchor.ts file
Build and deploy again

NextJS client

To finish setting up the NextJS client generated from the create-solana-game tool:

Copy the programId into app/utils/anchor.ts
cd app to end the app directory
Run yarn install to install the Node dependencies
Run yarn dev to start the client
After doing changes to the Anchor program make sure to copy over the types from the program into the client so you can use them. You can find the TypeScript types in the target/idl folder.

Run this example locally

Using Anchor's test command with the --detach flag will start and configure your Solana local test validator to have the program deployed (and keep the validator running after the tests complete):

cd program
anchor test --detach

Then you can set the Solana Explorer to use your local test validator (which starts when running the anchor test command) so you can look at the transactions:

https://explorer.solana.com/?cluster=custom&customUrl=http%3A%2F%2Flocalhost%3A8899

The program is also already deployed to net so you can try it out on devnet. The JavaScript client also has a button to mint the NFT. Starting the JavaScript client:

cd app
yarn install
yarn dev

Open the Unity project

First open the Unity project with Unity Version 2021.3.32.f1 (or similar), then open the GameScene or LoginScene and hit play. Use the editor login button in the bottom left.

If you can't get devnet SOL you can copy your address from the console and follow the instructions on this guide on how to get devnet SOL

Connect to the Solana test validator in Unity

If you want to avoid having to worry about maintaining devnet SOL, you can connect to your running local test validator from within Unity. Simply add these links on the wallet holder game object:

http://localhost:8899
ws://localhost:8900

Run the JavaScript client

To start the JavaScript client and be able to interact with the game and program using your web browser:

open the app directory within the repo
install the Node dependencies
run the dev command to start the development server

cd app
yarn install
yarn dev

To start changing the program and connecting to your own program follow the steps below.

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