Adding GSN support

contracts/CaptureTheFlag.sol

@@ -3,16 +3,24 @@
  */
 pragma solidity ^0.7.6;
 
-contract CaptureTheFlag {
+import "@opengsn/contracts/src/BaseRelayRecipient.sol";
+
+contract CaptureTheFlag is BaseRelayRecipient {
 
     event FlagCaptured(address previousHolder, address currentHolder);
 
     address public currentHolder = address(0);
 
+    constructor(address forwarder) {
+      trustedForwarder = forwarder;
+    }
+
+    string public override versionRecipient = "2.2.0";
+
     function captureTheFlag() external {
         address previousHolder = currentHolder;
 
-        currentHolder = msg.sender;
+        currentHolder = _msgSender();
 
         emit FlagCaptured(previousHolder, currentHolder);
     }

migrations/2_deploy_contracts.js

@@ -1,5 +1,9 @@
 const CaptureTheFlag = artifacts.require('CaptureTheFlag')
 
+
 module.exports = async function (deployer) {
-  await deployer.deploy(CaptureTheFlag)
+  const forwarder = require( '../build/gsn/Forwarder' ).address
+  await deployer.deploy(CaptureTheFlag, forwarder)
+
+  console.log( `Deployed CTF at ${CaptureTheFlag.address} with forwarder ${forwarder}`)
 }

package.json

@@ -16,6 +16,7 @@
   },
   "scripts": {
     "ganache": "yarn run ganache-cli -d --chainId 1337",
+    "gsn-with-ganache": "run-with-testrpc -d --chainId 1337 'gsn start'",
     "test": "run-with-testrpc 'truffle test'",
     "compile": "truffle compile",
     "start": "truffle deploy && ./ui/compile.sh && yarn serve ./html"

ui/index.js

@@ -1,5 +1,7 @@
 const ethers = require('ethers')
+const { RelayProvider } = require( '@opengsn/provider')
 
+const paymasterAddress = require( '../build/gsn/Paymaster').address
 const contractArtifact = require('../build/contracts/CaptureTheFlag.json')
 const contractAbi = contractArtifact.abi
 
@@ -21,7 +23,15 @@ async function initContract() {
   })
   const networkId = await window.ethereum.request({method: 'net_version'})
 
-  provider = new ethers.providers.Web3Provider(window.ethereum)
+  const gsnProvider = await RelayProvider.newProvider( {
+    provider: window.ethereum,
+    config: {
+        //loggerConfiguration: { logLevel: 'error' },
+        paymasterAddress
+    }
+  }).init()
+
+  provider = new ethers.providers.Web3Provider(gsnProvider)
 
   const network = await provider.getNetwork()
   const artifactNetwork = contractArtifact.networks[networkId]