use-custom-contract-calls.md

Use custom contract calls

In this section we show how to use implement support for custom contract calls in ContractCondition.

Let's start with the following example:

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

const myFunctionAbi: conditions.base.contract.FunctionAbiProps =  {
  name: 'myFunction',
  type: 'function',
  stateMutability: 'view',
  inputs: [
    {
      internalType: 'address',
      name: 'account',
      type: 'address',
    },
    {
      internalType: 'uint256',
      name: 'myCustomParam',
      type: 'uint256',
    },
  ],
  outputs: [
    {
      internalType: 'uint256',
      name: 'someValue',
      type: 'uint256',
    },
  ],
};

const myContractCallCondition = new conditions.base.contract.ContractCondition({
  method: 'myFunction', // `myMethodAbi.name`
  parameters: [':userAddress', ':myCustomParam'], // `myMethodAbi.inputs`
  functionAbi: myFunctionAbi, // Our custom function ABI
  contractAddress: '0x0...1',
  chain: 5,
  returnValueTest: {
    comparator: '>',
    value: 0,
  },
});

First, let's take a look at myFunctionAbi:

• We define a complete function ABI with name, type, stateMutability, inputs, and outputs
• With those fields in place, our function shapes up to be defined as myFunction(address, uint256): uint256
• Note that type field required to be function and stateMutability to pure and view to avoid accidentally mutating the contract state

Now, looking at myContractCallCondition we can see that:

• We need to pass myFunction as method and myFunctionAbi as functionAbi for our contract call to be recognized correctly
• We've mapped our function parameters to parameters, so that address is represented as ':userAddress' and uint256 is represented as ':myCustomParam'. See Condition Context and Context Variables for more details.
• Lastly, the myFunctionAbi.outputs will be used by returnValueTest to compare with the selected threshold value, resulting in a test myFunctionAbi.outputs[0] > 0

Learn more

• See how to implement access control revocation using custom contract calls here.