# Troubleshooting

# My contract is using OpenZeppelin. How do I add GSN support?

Here is a sample on how to use GSN with OpenZeppelin contracts. The _msgData and _msgSender methods methods of OpenZeppelin's Context base-contract are used by all other contracts, and thus the hooks below are enough to support tokens, Ownable, roles, etc.

(Note that OpenZeppelin's GSNRecipient is for GSN v1.0, and should not be used anymore)

pragma solidity ^0.8;

import "@opengsn/contracts/src/BaseRelayRecipient.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyContract is BaseRelayRecipient, ERC20 {

  constructor(string memory name_, string memory symbol_, address forwarder_) 
    ERC20(name_, symbol_) {
    _setTrustedForwarder(forwarder_);
  }

  string public override versionRecipient = "2.2.0";

  function _msgSender() internal view override(Context, BaseRelayRecipient)
      returns (address sender) {
      sender = BaseRelayRecipient._msgSender();
  }

  function _msgData() internal view override(Context, BaseRelayRecipient)
      returns (bytes calldata) {
      return BaseRelayRecipient._msgData();
  }
}

You can use instead OpenZeppelin's ERC2771Context, which is an equivalent implementation of BaseRelayRecipient.

# "signature mismatch" when using Metamask with local ganache

This is an old bug (opens new window) in Ganache. It was fixed in v6.11, but requires an extra command-line argument:

ganache-cli --chainId 1337

Next major release should work without it.

(if you're curious: ganache's RPC call reports that the chain-id is 1337, but the OPCODE chainid returns 1 - unless we explicitly add the above command-line argument)

# Error: Provided Hub version(2.0) is not supported by the current interactor(2.2.2)

The Paymaster version is wrong: The client checks that it is compatible with all the contracts. This happens when you create a custom paymaster with a version string that is less than 2.2.0

# I get an error: paymaster rejected in local view call to 'relayCall()' : Forwarder is not trusted

The paymaster doesn't support the forwarder that is used by your target contract. make sure to set the trustedForwarder on both the paymaster an recipient contract, and use the same forwarder.

# I have multiple tests, each run ok, but running them together, I get "Unacceptable relayMaxNonce"

There is an issue with the way a relayer currently work and Truffle's contract() test construct. Please use describe() or context instead (and avoid to snapshot/revert while a relayer is running)

An alternative is to start relayer in the begin() block of the contact. Just note that you need to recreate the provider, and update the forwarder for your contracts. e.g:

contract('mytest', ()=> {
  before(async()=> {
    await GsnTestEnvironment.startGsn('localhost')
    const { forwaderAddress, paymasterAddress } = GsnTestEnvironment.loadDeployment()
    provider = RelayProvider.newProvider({provider: web3.currentProvider, config: { paymasterAddress}})
  })

  after(async()=> {
    await GsnTestEnvironment.stopGsn()
  })
}

}

# My client fails with an error: Can't resolve 'fs'

Depending on your UI framework, you need to configure your webpack:

# Gatsby

Add this configuration file gatsby-node.js in the root of your project:

exports.onCreateWebpackConfig = ({
  stage,
  rules,
  loaders,
  plugins,
  actions,
}) => {
  actions.setWebpackConfig({
        node: {
          fs: 'empty'
        }
  })
}

# Next.JS

Add the following configuration to next.config.js at the root directory of the project:

module.exports = {
  future: { webpack5: true }, //needed only by earlier next.js versions (<= 10)
  webpack: (config, { isServer }) => {
    if (!isServer) {
      config.resolve.fallback.fs = false
    }
    return config
  },
}