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Fungible Tokens (FT)

Besides the native NEAR token, NEAR accounts have access to a multitude of tokens to use throughout the ecosystem. Moreover, it is even possible for users to create their own fungible tokens.

In contrast with the NEAR native token, fungible token (FT) are not stored in the user's account. In fact, each FT lives in their own contract which is in charge of doing bookkeeping. This is, the contract keeps track of how many tokens each user has, and handles transfers internally.

FT

In order for a contract to be considered a FT-contract it has to follow the NEP-141 and NEP-148 standards. The NEP-141 & NEP-148 standards explain the minimum interface required to be implemented, as well as the expected functionality.

Creating a New Token​

The simplest way to create a new Fungible Token is by using a factory contract, to which you only need to provide the token metadata, and they will automatically deploy and initialize a canonical FT contract.

1. Using the Token Factory Tool

We have created a simple UI to interact with the existing tkn.primitives.testnet factory contract

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2. Interacting with a pre-deployed Token Factory smart contract

Here is how to directly interact with the factory contract through your application:

import { Wallet } from './near-wallet';

const wallet = new Wallet({});

const args = {
  args: {
    owner_id: 'bob.near',
    total_supply: '1000000000',
    metadata: {
      spec: 'ft-1.0.0',
      name: 'Test Token',
      symbol: 'test',
      icon: 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7',
      decimals: 18,
    },
  },
  account_id: 'bob.near',
};

await wallet.callMethod({
  method: 'create_token',
  args,
  contractId: 'tkn.primitives.near',
  gas: 300000000000000,
  deposit: '2234830000000000000000000',
});

The Wallet object comes from our quickstart template

The FT you create will live in the account <your_token_symbol>.tkn.primitives.near (e.g. test.tkn.primitives.near).

Deploying Your Own Contract​

You can also create a fungible token by deploying and initializing a canonical FT contract.

On initialization, you will define the token's metadata such as its name (e.g. Ethereum), symbol (e.g. ETH) and total supply (e.g. 10M). You will also define an owner, which will own the tokens total supply.

To initialize a FT contract you will need to deploy it and then call the new method defining the token's metadata.

cargo near deploy build-non-reproducible-wasm <account-id> \
  with-init-call new \
  json-args '{
    "owner_id": "<owner-account>",
    "total_supply": "1000000000000000",
    "metadata": {
      "spec": "ft-1.0.0",
      "name": "Example Token Name",
      "symbol": "EXLT",
      "decimals": 8
    }
  }' \
  prepaid-gas '100.0 Tgas' \
  attached-deposit '0 NEAR' \
  network-config testnet \
  sign-with-keychain send

Global Contracts​

You can deploy a new Fungible Token using our global FT contract - a pre-deployed standard FT contract that you can reuse. Global contracts are deployed once and can be reused by any account without incurring high storage costs.

near contract deploy <account-id> use-global-account-id ft.globals.primitives.testnet \
  with-init-call \
  new_default_meta \
  json-args '{"owner_id": "<account-id>", "total_supply": "100000000000000000000000000000"}' \
  prepaid-gas '100.0 Tgas' \
  attached-deposit '0 NEAR' \
  network-config testnet \
  sign-with-keychain send
note

Deploying by hash creates an immutable contract that never changes. Deploying by account ID creates an updatable contract that changes when the referenced account's contract is updated. Choose based on whether you want your FT contract to be updatable or permanent.

Querying Metadata​

You can query the FT's metadata by calling the ft_metadata.

import { Wallet } from './near-wallet';

const TOKEN_CONTRACT_ADDRESS = 'token.v2.ref-finance.near';
const wallet = new Wallet({ createAccessKeyFor: TOKEN_CONTRACT_ADDRESS });

await wallet.viewMethod({
  method: 'ft_metadata',
  args: {},
  contractId: TOKEN_CONTRACT_ADDRESS,
});
Example response

{
  "spec": "ft-1.0.0",
  "name": "Ref Finance Token",
  "symbol": "REF",
  "icon": "data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='16 24 248 248' style='background: %23000'%3E%3Cpath d='M164,164v52h52Zm-45-45,20.4,20.4,20.6-20.6V81H119Zm0,18.39V216h41V137.19l-20.6,20.6ZM166.5,81H164v33.81l26.16-26.17A40.29,40.29,0,0,0,166.5,81ZM72,153.19V216h43V133.4l-11.6-11.61Zm0-18.38,31.4-31.4L115,115V81H72ZM207,121.5h0a40.29,40.29,0,0,0-7.64-23.66L164,133.19V162h2.5A40.5,40.5,0,0,0,207,121.5Z' fill='%23fff'/%3E%3Cpath d='M189 72l27 27V72h-27z' fill='%2300c08b'/%3E%3C/svg%3E%0A",
  "reference": null,
  "reference_hash": null,
  "decimals": 18
}

The Wallet object comes from our quickstart template

Checking Balance​

To know how many coins a user has you will need to query the method ft_balance_of.

info

Remember about fungible token precision. You may need this value to show a response of balance requests in an understandable-to-user way in your app. How to get precision value (decimals) you may find here.

import { Wallet } from './near-wallet';

const TOKEN_CONTRACT_ADDRESS = 'token.v2.ref-finance.near';
const wallet = new Wallet({ createAccessKeyFor: TOKEN_CONTRACT_ADDRESS });

await wallet.viewMethod({
  method: 'ft_balance_of',
  args: {
    account_id: 'bob.near',
  },
  contractId: TOKEN_CONTRACT_ADDRESS,
});
Example response

"3479615037675962643842"

The Wallet object comes from our quickstart template

Registering a User​

In order for an user to own and transfer tokens they need to first register in the contract. This is done by calling storage_deposit and attaching 0.00125Ⓝ.

By calling this storage_deposit the user can register themselves or register other users.

await wallet.callMethod({
  method: 'storage_deposit',
  args: {
    account_id: 'alice.near',
  },
  contractId: TOKEN_CONTRACT_ADDRESS,
  deposit: 1250000000000000000000,
});

The Wallet object comes from our quickstart template

info

You can make sure a user is registered by calling storage_balance_of.

tip

After a user calls the storage_deposit the FT will appear in their Wallets.

Transferring Tokens​

To send FT to another account you will use the ft_transfer method, indicating the receiver and the amount of FT you want to send.

#[near]
impl Contract {
  #[payable]
  pub fn send_tokens(&mut self, receiver_id: AccountId, amount: U128) -> Promise {
    assert_eq!(env::attached_deposit(), 1, "Requires attached deposit of exactly 1 yoctoNEAR");

    let promise = ext(self.ft_contract.clone())
      .with_attached_deposit(YOCTO_NEAR)
      .ft_transfer(receiver_id, amount, None);

    return promise.then( // Create a promise to callback query_greeting_callback
      Self::ext(env::current_account_id())
      .with_static_gas(Gas(30*TGAS))
      .external_call_callback()
    )
  }

  #[private] // Public - but only callable by env::current_account_id()
  pub fn external_call_callback(&self, #[callback_result] call_result: Result<(), PromiseError>) {
    // Check if the promise succeeded
    if call_result.is_err() {
      log!("There was an error contacting external contract");
    }
  }
}

This snippet assumes that the contract is already holding some FTs and that you want to send them to another account.

Attaching FTs to a Call​

Natively, only NEAR tokens (Ⓝ) can be attached to a function calls. However, the FT standard enables to attach fungible tokens in a call by using the FT-contract as intermediary. This means that, instead of you attaching tokens directly to the call, you ask the FT-contract to do both a transfer and a function call in your name.

Let's assume that you need to deposit FTs on Ref Finance.

#[payable]
pub fn call_with_attached_tokens(&mut self, receiver_id: AccountId, amount: U128) -> Promise {
  assert_eq!(env::attached_deposit(), 1, "Requires attached deposit of exactly 1 yoctoNEAR");

  let promise = ext(self.ft_contract.clone())
    .with_static_gas(Gas(150*TGAS))
    .with_attached_deposit(YOCTO_NEAR)
    .ft_transfer_call(receiver_id, amount, None, "".to_string());

  return promise.then( // Create a promise to callback query_greeting_callback
    Self::ext(env::current_account_id())
    .with_static_gas(Gas(100*TGAS))
    .external_call_callback()
  )
}

How it works:

  1. You call ft_transfer_call in the FT contract passing: the receiver, a message, and the amount.
  2. The FT contract transfers the amount to the receiver.
  3. The FT contract calls receiver.ft_on_transfer(sender, msg, amount)
  4. The FT contract handles errors in the ft_resolve_transfer callback.
  5. The FT contract returns you how much of the attached amount was actually used.

Handling Deposits (Contract Only)​

If you want your contract to handle deposit in FTs you have to implement the ft_on_transfer method. When executed, such method will know:

  • Which FT was transferred, since it is the predecessor account.
  • Who is sending the FT, since it is a parameter
  • How many FT were transferred, since it is a parameter
  • If there are any parameters encoded as a message

The ft_on_transfer must return how many FT tokens have to be refunded, so the FT contract gives them back to the sender.

// Implement the contract structure
#[near(contract_state)]
impl Contract {}

#[near]
impl FungibleTokenReceiver for Contract {
  // Callback on receiving tokens by this contract.
  // `msg` format is either "" for deposit or `TokenReceiverMessage`.
  fn ft_on_transfer(
    &mut self,
    sender_id: AccountId,
    amount: U128,
    msg: String,
  ) -> PromiseOrValue<U128> {
    let token_in = env::predecessor_account_id();

    assert!(token_in == self.ft_contract, "{}", "The token is not supported");
    assert!(amount >= self.price, "{}", "The attached amount is not enough");

    env::log_str(format!("Sender id: {:?}", sender_id).as_str());

    if msg.is_empty() {
      // Your internal logic here
      PromiseOrValue::Value(U128(0))
    } else {
      let message =
        serde_json::from_str::<TokenReceiverMessage>(&msg).expect("WRONG_MSG_FORMAT");
      match message {
        TokenReceiverMessage::Action {
          buyer_id,
        } => {
          let buyer_id = buyer_id.map(|x| x.to_string());
          env::log_str(format!("Target buyer id: {:?}", buyer_id).as_str());
          // Your internal business logic
          PromiseOrValue::Value(U128(0))
        }
      }
    }
  }
}

Additional Resources​

  1. NEP-141 and NEP-148 standards
  2. FT Event Standards
  3. FT reference implementation
  4. Fungible Tokens 101 - a set of tutorials that cover how to create a FT contract using Rust.