Interacting with contracts of the same type (specifically ER721)

[cryptobys-rami]

Hi

First of all - thank you very much for the library (its the only 'proper' flutter one).

I have a question regarding interaction with a contract ABI.

Suppose I would like to create functionality to interact with any contract that implements a certain standard (ER721) without having to get the ABI for each specific implementation of ER721 we may encounter. Would I be able to compile a 'standard' ABI of ER721 and be able to use it for any implementation? The use case here is very compelling. It is the ability for users of my flutter app to submit their own NFTs (by submitting their contract address) and for the app to interact with their NFT (provided of course that it is an ER721 but lets not worry about the validation part for the purpose of this question).

Thank you very much.

[simolus3]

Hi! In most cases, the EIP or ERC defines the solidity ABI to be used, so you don't need to look at a specific contract to invoke it.

For instance, to support the ERC20 contract in this library, we just define its interface. We then invoke solidity to generate the matching ABI for that. Finally, we can generate a Dart class based on the ABI. I don't see why that shouldn't be possible for ERC-721 either.

[cryptobys-rami]

Thank you. I shall give it a shot and let you know how it goes!

[cryptobys-rami]

So I'm having a go at using the openzeppelin ERC721URIStorage implementation, which is implementing ER721 and the associated extensions https://docs.openzeppelin.com/contracts/4.x/api/token/erc721#ERC721URIStorage

After building it successfully (using 'flutter pub run build_runner build'), i get two problems with the generated .g.dart file:

• safeTransferFrom is duplicated (almost identical but with to/from positional arguments swapped around)
• More importantly, safeTransferFrom now requires credentials argument, where the ABI defined above does not require that. After deleting safeTransferFrom (in order to fix the error in bullet 1), I tried calling safeTransferfrom on the deployed contract and unsurprisingly i had an error saying 'Too many elements' as the deployed contract does not have a credentials argument in safeTransferFrom.

Am I missing something blatantly obvious here? Or is it a bug? Thank you in advance.

For reference, here is the generated .g.dart file, and the said ABI:

{
  "_format": "hh-sol-artifact-1",
  "contractName": "ERC721URIStorage",
  "sourceName": "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol",
  "abi": [
    {
      "anonymous": false,
      "inputs": [
        {
          "indexed": true,
          "internalType": "address",
          "name": "owner",
          "type": "address"
        },
        {
          "indexed": true,
          "internalType": "address",
          "name": "approved",
          "type": "address"
        },
        {
          "indexed": true,
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "Approval",
      "type": "event"
    },
    {
      "anonymous": false,
      "inputs": [
        {
          "indexed": true,
          "internalType": "address",
          "name": "owner",
          "type": "address"
        },
        {
          "indexed": true,
          "internalType": "address",
          "name": "operator",
          "type": "address"
        },
        {
          "indexed": false,
          "internalType": "bool",
          "name": "approved",
          "type": "bool"
        }
      ],
      "name": "ApprovalForAll",
      "type": "event"
    },
    {
      "anonymous": false,
      "inputs": [
        {
          "indexed": true,
          "internalType": "address",
          "name": "from",
          "type": "address"
        },
        {
          "indexed": true,
          "internalType": "address",
          "name": "to",
          "type": "address"
        },
        {
          "indexed": true,
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "Transfer",
      "type": "event"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "to",
          "type": "address"
        },
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "approve",
      "outputs": [],
      "stateMutability": "nonpayable",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "owner",
          "type": "address"
        }
      ],
      "name": "balanceOf",
      "outputs": [
        {
          "internalType": "uint256",
          "name": "",
          "type": "uint256"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "getApproved",
      "outputs": [
        {
          "internalType": "address",
          "name": "",
          "type": "address"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "owner",
          "type": "address"
        },
        {
          "internalType": "address",
          "name": "operator",
          "type": "address"
        }
      ],
      "name": "isApprovedForAll",
      "outputs": [
        {
          "internalType": "bool",
          "name": "",
          "type": "bool"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [],
      "name": "name",
      "outputs": [
        {
          "internalType": "string",
          "name": "",
          "type": "string"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "ownerOf",
      "outputs": [
        {
          "internalType": "address",
          "name": "",
          "type": "address"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "from",
          "type": "address"
        },
        {
          "internalType": "address",
          "name": "to",
          "type": "address"
        },
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "safeTransferFrom",
      "outputs": [],
      "stateMutability": "nonpayable",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "from",
          "type": "address"
        },
        {
          "internalType": "address",
          "name": "to",
          "type": "address"
        },
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        },
        {
          "internalType": "bytes",
          "name": "_data",
          "type": "bytes"
        }
      ],
      "name": "safeTransferFrom",
      "outputs": [],
      "stateMutability": "nonpayable",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "operator",
          "type": "address"
        },
        {
          "internalType": "bool",
          "name": "approved",
          "type": "bool"
        }
      ],
      "name": "setApprovalForAll",
      "outputs": [],
      "stateMutability": "nonpayable",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "bytes4",
          "name": "interfaceId",
          "type": "bytes4"
        }
      ],
      "name": "supportsInterface",
      "outputs": [
        {
          "internalType": "bool",
          "name": "",
          "type": "bool"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [],
      "name": "symbol",
      "outputs": [
        {
          "internalType": "string",
          "name": "",
          "type": "string"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "tokenURI",
      "outputs": [
        {
          "internalType": "string",
          "name": "",
          "type": "string"
        }
      ],
      "stateMutability": "view",
      "type": "function"
    },
    {
      "inputs": [
        {
          "internalType": "address",
          "name": "from",
          "type": "address"
        },
        {
          "internalType": "address",
          "name": "to",
          "type": "address"
        },
        {
          "internalType": "uint256",
          "name": "tokenId",
          "type": "uint256"
        }
      ],
      "name": "transferFrom",
      "outputs": [],
      "stateMutability": "nonpayable",
      "type": "function"
    }
  ],
  "bytecode": "0x",
  "deployedBytecode": "0x",
  "linkReferences": {},
  "deployedLinkReferences": {}
}

// Generated code, do not modify. Run `build_runner build` to re-generate!
// @dart=2.12
import 'package:web3dart/web3dart.dart' as _i1;
import 'dart:typed_data' as _i2;

final _contractAbi = _i1.ContractAbi.fromJson(
    '[{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"operator","type":"address"}],"name":"isApprovedForAll","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"operator","type":"address"},{"internalType":"bool","name":"approved","type":"bool"}],"name":"setApprovalForAll","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes4","name":"interfaceId","type":"bytes4"}],"name":"supportsInterface","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"tokenURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"}]',
    'ERC721URIStorage');

class ERC721URIStorage extends _i1.GeneratedContract {
  ERC721URIStorage(
      {required _i1.EthereumAddress address,
      required _i1.Web3Client client,
      int? chainId})
      : super(_i1.DeployedContract(_contractAbi, address), client, chainId);

  /// The optional [transaction] parameter can be used to override parameters
  /// like the gas price, nonce and max gas. The `data` and `to` fields will be
  /// set by the contract.
  Future<String> approve(_i1.EthereumAddress to, BigInt tokenId,
      {required _i1.Credentials credentials,
      _i1.Transaction? transaction}) async {
    final function = self.function('approve');
    final params = [to, tokenId];
    return write(credentials, transaction, function, params);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<BigInt> balanceOf(_i1.EthereumAddress owner,
      {_i1.BlockNum? atBlock}) async {
    final function = self.function('balanceOf');
    final params = [owner];
    final response = await read(function, params, atBlock);
    return (response[0] as BigInt);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<_i1.EthereumAddress> getApproved(BigInt tokenId,
      {_i1.BlockNum? atBlock}) async {
    final function = self.function('getApproved');
    final params = [tokenId];
    final response = await read(function, params, atBlock);
    return (response[0] as _i1.EthereumAddress);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<bool> isApprovedForAll(
      _i1.EthereumAddress owner, _i1.EthereumAddress operator,
      {_i1.BlockNum? atBlock}) async {
    final function = self.function('isApprovedForAll');
    final params = [owner, operator];
    final response = await read(function, params, atBlock);
    return (response[0] as bool);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<String> name({_i1.BlockNum? atBlock}) async {
    final function = self.function('name');
    final params = [];
    final response = await read(function, params, atBlock);
    return (response[0] as String);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<_i1.EthereumAddress> ownerOf(BigInt tokenId,
      {_i1.BlockNum? atBlock}) async {
    final function = self.function('ownerOf');
    final params = [tokenId];
    final response = await read(function, params, atBlock);
    return (response[0] as _i1.EthereumAddress);
  }

  /// The optional [transaction] parameter can be used to override parameters
  /// like the gas price, nonce and max gas. The `data` and `to` fields will be
  /// set by the contract.
  Future<String> safeTransferFrom(
      _i1.EthereumAddress from, _i1.EthereumAddress to, BigInt tokenId,
      {required _i1.Credentials credentials,
      _i1.Transaction? transaction}) async {
    final function = self.function('safeTransferFrom');
    final params = [from, to, tokenId];
    return write(credentials, transaction, function, params);
  }

  /// The optional [transaction] parameter can be used to override parameters
  /// like the gas price, nonce and max gas. The `data` and `to` fields will be
  /// set by the contract.
  Future<String> safeTransferFrom(_i1.EthereumAddress from,
      _i1.EthereumAddress to, BigInt tokenId, _i2.Uint8List _data,
      {required _i1.Credentials credentials,
      _i1.Transaction? transaction}) async {
    final function = self.function('safeTransferFrom');
    final params = [from, to, tokenId, _data];
    return write(credentials, transaction, function, params);
  }

  /// The optional [transaction] parameter can be used to override parameters
  /// like the gas price, nonce and max gas. The `data` and `to` fields will be
  /// set by the contract.
  Future<String> setApprovalForAll(_i1.EthereumAddress operator, bool approved,
      {required _i1.Credentials credentials,
      _i1.Transaction? transaction}) async {
    final function = self.function('setApprovalForAll');
    final params = [operator, approved];
    return write(credentials, transaction, function, params);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<bool> supportsInterface(_i2.Uint8List interfaceId,
      {_i1.BlockNum? atBlock}) async {
    final function = self.function('supportsInterface');
    final params = [interfaceId];
    final response = await read(function, params, atBlock);
    return (response[0] as bool);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<String> symbol({_i1.BlockNum? atBlock}) async {
    final function = self.function('symbol');
    final params = [];
    final response = await read(function, params, atBlock);
    return (response[0] as String);
  }

  /// The optional [atBlock] parameter can be used to view historical data. When
  /// set, the function will be evaluated in the specified block. By default, the
  /// latest on-chain block will be used.
  Future<String> tokenURI(BigInt tokenId, {_i1.BlockNum? atBlock}) async {
    final function = self.function('tokenURI');
    final params = [tokenId];
    final response = await read(function, params, atBlock);
    return (response[0] as String);
  }

  /// The optional [transaction] parameter can be used to override parameters
  /// like the gas price, nonce and max gas. The `data` and `to` fields will be
  /// set by the contract.
  Future<String> transferFrom(
      _i1.EthereumAddress from, _i1.EthereumAddress to, BigInt tokenId,
      {required _i1.Credentials credentials,
      _i1.Transaction? transaction}) async {
    final function = self.function('transferFrom');
    final params = [from, to, tokenId];
    return write(credentials, transaction, function, params);
  }

  /// Returns a live stream of all Approval events emitted by this contract.
  Stream<Approval> approvalEvents(
      {_i1.BlockNum? fromBlock, _i1.BlockNum? toBlock}) {
    final event = self.event('Approval');
    final filter = _i1.FilterOptions.events(
        contract: self, event: event, fromBlock: fromBlock, toBlock: toBlock);
    return client.events(filter).map((_i1.FilterEvent result) {
      final decoded = event.decodeResults(result.topics!, result.data!);
      return Approval(decoded);
    });
  }

  /// Returns a live stream of all ApprovalForAll events emitted by this contract.
  Stream<ApprovalForAll> approvalForAllEvents(
      {_i1.BlockNum? fromBlock, _i1.BlockNum? toBlock}) {
    final event = self.event('ApprovalForAll');
    final filter = _i1.FilterOptions.events(
        contract: self, event: event, fromBlock: fromBlock, toBlock: toBlock);
    return client.events(filter).map((_i1.FilterEvent result) {
      final decoded = event.decodeResults(result.topics!, result.data!);
      return ApprovalForAll(decoded);
    });
  }

  /// Returns a live stream of all Transfer events emitted by this contract.
  Stream<Transfer> transferEvents(
      {_i1.BlockNum? fromBlock, _i1.BlockNum? toBlock}) {
    final event = self.event('Transfer');
    final filter = _i1.FilterOptions.events(
        contract: self, event: event, fromBlock: fromBlock, toBlock: toBlock);
    return client.events(filter).map((_i1.FilterEvent result) {
      final decoded = event.decodeResults(result.topics!, result.data!);
      return Transfer(decoded);
    });
  }
}

class Approval {
  Approval(List<dynamic> response)
      : owner = (response[0] as _i1.EthereumAddress),
        approved = (response[1] as _i1.EthereumAddress),
        tokenId = (response[2] as BigInt);

  final _i1.EthereumAddress owner;

  final _i1.EthereumAddress approved;

  final BigInt tokenId;
}

class ApprovalForAll {
  ApprovalForAll(List<dynamic> response)
      : owner = (response[0] as _i1.EthereumAddress),
        operator = (response[1] as _i1.EthereumAddress),
        approved = (response[2] as bool);

  final _i1.EthereumAddress owner;

  final _i1.EthereumAddress operator;

  final bool approved;
}

class Transfer {
  Transfer(List<dynamic> response)
      : from = (response[0] as _i1.EthereumAddress),
        to = (response[1] as _i1.EthereumAddress),
        tokenId = (response[2] as BigInt);

  final _i1.EthereumAddress from;

  final _i1.EthereumAddress to;

  final BigInt tokenId;
}

[cryptobys-rami]

I think i figured out what the first problem is.

When you run 'flutter pub run build_runner build' on an ABI which has an overloaded function (safeTransferFrom has two definitions in the ABI, one with 3 and one with 4 parameters), it tries to generate two function definitions in DART. But, overloading functions is not supported in DART. So, you end up with a .g.dart file (that is meant to implement your contract interface) which cannot be compiled.

Is there any work around for this?

P.s. please ignore the second problem for now.

[simolus3]

The generator does not currently support overloaded functions, but I'll take a look at that now.

[simolus3]

Starting from 973ca2efb0c90438dfd9492d6ec2397322345db4, we support overloading in the generator (which should actually fix the second problem as well).

Could you try setting up a dependency override and check if that fixes the problem?

# add this to your pubspec:
dependency_overrides:
  web3dart:
    git: https://github.com/simolus3/web3dart.git

[cryptobys-rami]

That works thank you very much!

[simolus3]

Thanks for trying it out, this is fixed in version 2.3.0 which I have just released.