fa2-interfaces

Content

This document describes how to use the TypeScript/JavaScript FA2 API built on top of Taquito. It simplifies operations required to work with Non-Fungible Tokens (NFT), Fungible Tokens and when TypeScript is used, provide a type-safe API to contracts.

Table of Contents

• Creating a Collection (Originating a Contract)
• Creating Token Metadata
• Type-Safe Contract Abstraction
• Minting
• Transferring Token Ownership
• Update Operators
• Beyond NFT Contracts
• Custom Contracts
  • Custom Contract API Example
• Executing Multiple Operations in One Batch

Creating a Collection (Originating a Contract)

Your collection of tokens (non-fungible or fungible) is represented on the Tezos Blockchain by a smart contract. To create a collection, we need to originate (create) a contract on the blockchain. Each contract has a code representing its actions and storage. This package does not help you to create the code for the contract but it can simplify storage initialization. To create the contract code you can use the @oxheadalpha/fa2-contract package. Here we will show how to initialize a storage using storage combinators and originate a contract using Taquito.

The storage initialization combinators can be thought of as a (params: I) => S function, which takes an object representing input parameters I and returns an object representing an initial storage S. Storage S is a plain old JavaScript objects that can be used by the Taquito originate method. Functions are wrapped into the StorageBuilder type that allows functions to be composed together and receive new, more complicated functions. Here is an example of a very simple builder:

const simpleAdmin = storageBuilder(({ ownerAddress }: { owner: address }) => ({
  admin: ownerAddress,
  pending_admin: undefined
}));

The above creates a storage builder that requires one parameter, ownerAddress, and returns an initial storage with two fields: admin and pending_admin. To create a storage using this builder, you can invoke the build method:

  const storage = simpleAdmin.build({ownerAddress: 'tzAddress'})

TypeScript will infer the type correctly and will not allow to invoke the build with inappropriate parameters. After invoking the build method, TypeScript will also correctly infer the type of storage.

The storage builder has the .with method that allows two builders to be combined:

const newBuilder = storageA.with(storageB)

The above code will create a builder that requires both input parameters for storageA and storageB and will return an initial storage that will have fields of storageA and storageB.

In practice, you will only need to write builders if you use your own custom contracts that require a custom initial storage. For the predefined contracts, located in fa2-contracts, you can create an initial storage just by composing existing storage builders together. We usually start by using the contractStorage predefined builder, which requires just one parameter metadata and uses the .with method multiple times.

Here is an example:

const storageBuilder = contractStorage
  .with(pausableSimpleAdminStorage)
  .with(nftStorage) 
  .with(mintFreezeStorage) 

In the above example we create a contract initial storage by composing 3 builders. This is for a contract that can pause, store NFT tokens, and freeze the storage.

You can find out what kind of contract APIs you can create and how to initialize a storage for them here.

Now we can build the storage:

const storage = storageBuilder.build({
  owner: 'tzAddress',
  metadata: 'meta...'
});

We can also use tzGen, a tool from @oxheadalpha/fa2-contracts, to automatically generate storage builders composition from the contract specification.

To originate the contract with this initial storage you can use Taquito like this:

import { TezosToolkit } from '@taquito/taquito';
const tz = new TezosToolkit('https://...');

const op = await tz.contract.originate({ code: 'code...', storage })

Creating Token Metadata

In order to create a token, we first need to create token metadata. Token metadata has to conform to TZIP-21.

There are two ways to create metadata for a token: on-chain and off-chain. The artifact itself is always kept off-chain, usually in IPFS. However, the token attributes can be kept either on-chain or off-chian.

The simplest way to create on-chain metadata is by using the createSimpleNftMetadata function:

createSimpleNftMetadata(
  1, // Token ID
  'My Picture', // Token Name
  'ipfs://QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco' // IPFS URI
);

The metadata can have more attributes and can look like this:

{
  "decimals": 0,
  "isBooleanAmount": true,
  "name": "My Picture",
  "description": "",
  "tags": [
    "awesome",
    "nft"
  ],
  "minter": "tz1YPSCGWXwBdTncK2aCctSZAXWvGsGwVJqU",
  "artifactUri": "ipfs://QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco",
  "displayUri": "ipfs://QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco",
  "thumbnailUri": "ipfs://QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco",
  "creators": [],
  "rights": "",
  "attributes": [
    {
      "name": "location",
      "value": "New York"
    }
  ]
}

There can be separate URIs for display and thumbnail images. To make sure that the format of metadata confirms to TZIP-21 standard, it is a good idea to validate it before creation. This can be done with the validateTzip21 function as shown below:

import { validateTzip16 } from '@oxheadalpha/fa2-interfaces';

const meta = JSON.parse(metaJson);
const validationResults = validateTzip21(meta);
const errorsOnly = validationResults.filter(r => r.startsWith('Error:'));

Before creating off-chain metadata, we should first create it in the JSON format and upload to IPFS. Then, off-chain metadata can be created using a helper function:

const tokenMetadata = createOffChainTokenMetadata(
  1, // Token ID
  'ipfs://QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco' // IPFS URI
)

We are now ready to interact with our contract.

Type-Safe Contract Abstraction

To interact with a contract on the blockchain we need to create an API object that represents your contract (collection). As it is a wrapper around Taquito, first we will need to create Taquito TezosToolkit.

const tzt = new TezosToolkit(...);
const myContract = await tezosApi(tz).at(contractAddress)

At this point we can specify what kind of tokens and what methods we have in our contract. It is done like this:

const nftContract = myContract.asNft().withMint()

Depending on the type of token, contract methods can have different implementations and require different parameters. You have to specify the type of token by using asNft() (as we are going to mint NFTs), and then the required methods by using withMint(), withBurn(), withFreeze(), or a combination of methods. TypeScript will infer the right type of nftContract and validate the method with their parameters at compile time. Now we are ready to interact with our contract.

Minting

Minting (creating new tokens) can be done by calling the mint method:

const op: TransactionOperation = await fa2.runMethod(
  nftContract.mint([
    { 
      owner: 'tz1PSCGWXwBdTncK2aCctSZAXWvGsGwVJqU', 
      tokens: [tokenMetadata1, tokenMetadata2] }
  ])
);

In order to save gas, mint accepts a batch of mint requests in order to be able to bundle multiple tokens creation into one request. Methods that call/invoke contract entry points return the Taquito type <ContractMethod<ContractProvider>>.These methods can be sent and confirmed individually, or in a batch, directly using the Taquito API. However, as they are frequently used operations, we have two helpers: runMethod & runBatch

At this point it would be nice to inspect the created tokens. According to TZIP-12, standard contracts that handle tokens, weather they be non-fungible or fungible tokens have these methods: balance_of, transfer, update_operator. For NFTs we have the hasNftTokens wrapper that returns boolean values. However, to use it we have to extend our contract abstraction with the .withFa2 method:

const fa2Contract = nftContract.withFa2()

Now, we can use the hasNftTopkens method to inspect the created tokens:

const results = fa2Contract.hasNftTokens([
  { owner: 'tz1YPSCGWXwBdTncK2aCctSZAXWvGsGwVJqU', token_id: 1 },
  { owner: 'tz1YPSCGWXwBdTncK2aCctSZAXWvGsGwVJqU', token_id: 2 }
]);

const allGood = results.every(r => r === true)

For fungible tokens you would use the method, queryBalances, instead of hasNftTokens that will return a list of balances. For more information look here

Transferring Token Ownership

Token ownership can be transferred using the method, transferTokens. This method takes a list of transfers and executes them. Transfers can be constructed manually but it is easier to use "Transfers Batch API" to do that. It will automatically merge subsequent transactions from the same source in order to optimise gas usage. Here is how it can be done:

const transfers = transferBatch()
  .withTransfer('tzFromAccount1', 'tzToAccount1', 1 /* tokenId */, 1 /* amount */)
  .withTransfer('tzFromAccount1', 'tzToAccount2', 2 /* tokenId */, 1 /* amount */)
  .transfers;

const op = await fa2.runMethod(fa2Contract.transferTokens(transfers));

For NFT tokens the amount should always be 1.

Update Operators

Multiple operators can transfer tokens on behalf of the owner. The token owner can use the updateOperators method to add or remove other addresses that can transfer the owner's tokens. Updates can be built manually or, like transfers, can be built using the batch API:

const batch = operatorUpdateBatch().
   .addOperator('tzOwner1', 'tzOperator1', 1)
   .removeOperator('tzOwner2, 'tzOperator2', 2)
   .addOperators([
     { owner: 'tzOwner3', operator: 'tzOperator3', token_id: 3 },
     { owner: 'tzOwner4', operator: 'tzOperator4', token_id: 4 }
   ])
   .updates;
 
 await runMethod(contract.updateOperators(batch));

Beyond NFT Contracts

Besides interacting with contracts representing NFTs, it is possible to interact with any FA2 contract representing fungible tokens or multi-fungible tokens. It is also possible for a contract to have the ability to freeze created tokens, give rights to other addresses to administer contracts, etc. Many combinations of those contract traits can be expressed by using composable combinators on the contract abstraction.

Contract Abstraction Combinators and Storage Combinators are different and can be used independently. Contract Abstraction Combinators are used to describe the API to the contract, while Storage Combinators are used to describe the shape of the storage and its initial values. A storage is mostly used for contract origination and is rarely required for the interaction with the contract as Lambda Views are used to "read" the state of the contract. However, storage and contract actions (API methods) are related - certain actions require a contract to have certain data. For example, the freeze method requires a contract to have a flag in the storage that is described by .with(mintFreezeStorage). We give the description of those combinators together.

The combinators can be divided into groups. Only one combinator from each group can be used at a time on one contract.

Below is the list of contract administration methods:

• .withSimpleAdmin - adds the ability to set just one address to be the administrator of a contract. It allows you to call just 2 additional methods, setAdmin and confirmAdmin. For more information look here. To initialize the storage, use .with(simpleAdminStorage)

• .withPausableSimpleAdmin - adds the ability to pause and unpause the contract. For more information look here To initialize the storage use .with(pausableSimpleAdminStorage)

• .withMultiAdmin - adds the ability to have multiple admins for the same contract, as well as to add and remove admin. For more information look here. To initialize the storage use .with(multiAdminStorage)

Below is the list of combinators that specify what kind of tokens the contract holds. They do not add methods that can be used by a client, but they influence how subsequent methods like withMint or withBurn will work and what parameters they can take.

• .asNft - specifies that the contract represents NFTs. To initialize the storage use with(nftStorage)

• .asFungible - specify that the contract represents a single type of fungible token. To initialize the storage use with(fungibleTokenStorage)

• asMultiFungible - specifies that the contract represents multiple fungible tokens and it can have more that one type of token, which is specified by the token ID. To initialize the storage use with(multiFungibleTokenStorage)

Below is the group of combinators that should be used on top of any one of the combinators from the previous group. You can find more details about each method that the combinators can add here

• withMint - specifies that the contract can mint new tokens.

• withBurn - specifies that the contract can burn (remove) previously created tokens.

• withFreeze - specifies that the contract can freeze the collection, after a certain number of tokens are created. To initialize the storage use with(mintFreezeStorage).

There is also withMultiMinterAdmin, which allows us to add and remove addresses that can mint and burn token. Here are the details. To initialize the storage for this type of contract use with(multiMinterAdminStorage).

withFa2 adds the methods specified by TZIP-12 standard that every FA2 contract is required to have. You can find the details here

Here is a complete example:

const tzt = new TezosToolkit(...);
const myContract = await tezosApi(tz).at(contractAddress)

const nftContract = myContract
    .withPausableSimpleAdmin()
    .withFa2()
    .asNft()
    .withMint()
    .withBurn()
    .withFreeze()

In the above example we create an NFT contract that can mint, burn, and freeze. It is pausable, and can use methods specified by FA2. If you need to initialize the storage for it you can do this:

  const storage = contractStorage
    .with(pausableSimpleAdminStorage)
    .with(nftStorage)
    .with(mintFreezeStorage)
    .build({
      owner: 'tzAddress',
      metadata: 'meta...'
    })

Custom Contracts

Interaction with a custom contract in a type-safe way can be achieved with very little boilerplate code. A new API can be implemented by providing just one constructor function with the following signature:

<TProvider extends ContractProvider | Wallet, TInterface<TProvider>>(
    contract: Tzip12Contract<TProvider>) => TInterface<TProvider>

Introducing TProvider type parameter lets you define one contract interface implementation to use with both regular and wallet Tezos toolkits. The TInterface type here is just an object(a record of functions) and can be implemented anyway possible, including using a TypeScript class. If it is a TypeScript class, it has to be wrapped in a function like this:

export const MyContractApi = <
  TProvider extends ContractProvider | Wallet, TInterface<TProvider>>(
    contract: Tzip12Contract<TProvider>): TInterface<TProvider> =>
  new MyClass<TProvider>(contract);

Now, we can extend our contract abstraction with the generic .with combinator:

const contract = await tezosApi(toolkit).at(contractAddress);
const myContractApi = contract.with(MyContractApi);

The myContractApi object will have all the API methods defined by MyClass.

Custom Contract API Example

Let's assume that the contract has two custom entry points: set_counter that accepts a nat parameter and CPS-style view get_counter.

First, we define a TypeScript interface for those contract entry points:

export interface MyContract<TProvider extends ContractProvider | Wallet> {
  setCounter(counter: nat): ContractMethod<TProvider>;
  getCounter(): Promise<nat>;
}

Second, we define a constructor function with the contract calls implementation:

export const MyContractApi = <
  TProvider extends ContractProvider | Wallet>(
    contract: Tzip12Contract<TProvider>): MyContract<TProvider> => ({
  setCounter: (counter: nat) => contract.methods.set_counter(counter),
  getCounter: async () => contract.views.get_counter().read()
});

Executing Multiple Operations in One Batch

As described above, you can bundle multiple tokens in one mint request or batch requests to transferTokens & updateOperators. Sometimes, however, it is still not enough. You might want to send multiple requests that deal with different contracts or use unrelated methods in one batch. This can be done using the Taquito batch. We have a helper method, runBatch, that simplifies sending batches and waiting for their confirmations.

Here is an example:

const batch = toolkit.contract.batch();

batch.withContractCall(fa2Contract1.transferTokens(txs1));
batch.withContractCall(fa2Contract1.transferTokens(txs2));
const op: BatchOperation = await fa2.runBatch(batch);

For more information, please look here