ContractCondition

ContractCondition is based on the evaluation of contract calls.

Below, we can see an example of using ContractConditon to gate access to our data behind an NFT ownership condition.

import { conditions } from '@nucypher/taco';

const ownsNFT = new conditions.base.contract.ContractCondition({
  method: 'balanceOf',
  parameters: [':userAddress'],
  standardContractType: 'ERC721',
  contractAddress: '0x1e988ba4692e52Bc50b375bcC8585b95c48AaD77',
  chain: 1,
  returnValueTest: {
    comparator: '>',
    value: 0,
  },
});

Now, let's break it down step by step.

With ContractCondition, we can either use one of the predefined contracts, such as ERC20 or ERC721 standards. Alternatively, we can also use any arbitrary contract calls provided we include functionAbi into our condition.

In the case of our condition, we use a standardContractType of ERC721.

standardContractType: 'ERC721',

This contract exposes a number of methods, including balanceOf. Knowing the signature of this method, we need to pass one parameter into parameters

 method: 'balanceOf',
 parameters: [':userAddress'],

':userAddress' is a reserved context parameter that denotes the address of the recipient that will attempt to decrypt our data. Before the attempt is made, the ':userAddress' value will be replaced with the actual wallet address.

Now that we've specified our contract call, we need to figure out what to do with the contract call results. Let's take a look at the returnValueTest field:

returnValueTest: {
  comparator: '>',
  value: 0,
},

returnValueTest is going to evaluate the contract call result according to the following logic:

• Since the contract call returns only one value, we don't need to specify the index field

• Compare it using the following comparator, comparator: '>'

• Compare it to the following value, value: 0

Combining these three, we can see that the returnValueTest will hold true if the value returned by the contract call is greater than zero.

In other words, our condition is only satisfied if ERC721.balanceOf(:userAddress) > 0 i.e. if the user's wallet has the relevant NFT balance greater than 0.

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