API overview

The token standard implementation is a Token Manager zkApp that is split in 2 parts: low-level and high-level one.

The low-level implementation is included in o1js library TokenContract abstract class. See the overview in the o1js Custom Tokens tutorial

[!WARNING] Please note that this is a beta release. The implementation will change soon. The API may also change in future.

The high-level part inherits from the TokenContract class and has following user-facing features:

On-chain State, decimals and deploy arguments

The on-chain state is defined as follows:

@state(PublicKey) public owner = State<PublicKey>();
@state(UInt64) public supply = State<UInt64>();
@state(UInt64) public circulating = State<UInt64>();

• owner is set on deployment, and some of token functionality requires an admin signature.

  If you want to implement admin-only method, just call this.ensureOwnerSignature() helper in the method you want to protect.

• supply defines a maximum amount of tokens to exist. It is set on deployment and can be modified with setSupply() function (can be called by admin only)

• circulating tracks the total amount in circulation. When new tokens are minted, the circulating increases by an amount minted.

• The decimals is a constant, that defines where to place the decimal comma in the token amounts.

• The deploy() function requires owner and supply to be passed as parameters.

• Along with state variables initial values, the deploy() function also takes symbol (to set account.tokenSymbol) and src (to set account.zkappUri)

Methods

Methods that can be called only by admin are:

mint(address: PublicKey, amount: UInt64)
setTotalSupply(amount: UInt64)
setOwner(owner: PublicKey)

Transfer and burn functionality is available by following methods:

transfer(from: PublicKey, to: PublicKey, amount: UInt64)
burn(from: PublicKey, amount: UInt64)

Helper methods for reading state variables and account balance

getBalanceOf(address: PublicKey)
getSupply()
getCirculating()
getDecimals()

Events

On each token operation, the event is emitted. The events are declared as follows:

events = {
  SetOwner: PublicKey,
  Mint: MintEvent,
  SetSupply: UInt64,
  Burn: BurnEvent,
  Transfer: TransferEvent,
}

class MintEvent extends Struct({
  recipient: PublicKey,
  amount: UInt64,
}) {}

class BurnEvent extends Struct({
  from: PublicKey,
  amount: UInt64,
}) {}

class TransferEvent extends Struct({
  from: PublicKey,
  to: PublicKey,
  amount: UInt64,
}) {}

That completes a review of a fungible token.