Add GSN provider support

minimal set of changes to add GSN support to the contract and the dApp
so that calling user no longer needs eth.

Actual payment is done by the default "accept everything" paymaster
contract.

README.md

@@ -1,24 +1,23 @@
 # GSN v3 integration workshop
 
-### (Base branch - before adding any GSN support)
+### (This branch already contains frontend and contract integration with GSN)
 
 This sample dapp emits an event with the last account that clicked on the "capture the flag" button. We will integrate
 this dapp to work gaslessly with GSN v3. This will allow an externally owned account without ETH to capture the flag by
 signing a meta transaction.
 
-
 ### To run the sample:
 
 1. first clone and `yarn install`
-2. run `yarn ganache`
+2. run `yarn gsn-with-ganache` to start a node, and also deploy GSN contracts and start a relayer service.
 3. Make sure you have Metamask installed, and pointing to "localhost"
 4. In a different window, run `yarn start`, to deploy the contract, and start the UI
 5. Start a browser pointing to "http://localhost:3000"
-6. Click the "Capture the Flag" button. Notice that you do need an account with eth for that..
+6. Click the "Capture the Flag" button. Notice that you don't need eth in your account: You only sign the transaction.
 
 You can see the integrations as GitHub pull requests:
 
-1. [Basic: Minimum viable GSN integration](https://github.com/opengsn/workshop/pull/1/files)
+1. (this branch) [Basic: Minimum viable GSN integration](https://github.com/opengsn/workshop/pull/1/files)
 2. [Advanced: Write your own custom Paymaster](https://github.com/opengsn/workshop/pull/2/files_)
 
 Note: on testnet we maintain a public service "pay for everything" paymaster so writing your own is not strictly

contracts/CaptureTheFlag.sol

@@ -3,16 +3,24 @@
  */
 pragma solidity ^0.8.7;
 
-contract CaptureTheFlag {
+import "@opengsn/contracts/src/ERC2771Recipient.sol";
+
+contract CaptureTheFlag is ERC2771Recipient {
 
     event FlagCaptured(address previousHolder, address currentHolder);
 
     address public currentHolder = address(0);
 
+    constructor(address forwarder) {
+        _setTrustedForwarder(forwarder);
+    }
+
+    string public override versionRecipient = "3.0.0";
+
     function captureTheFlag() external {
         address previousHolder = currentHolder;
 
-        currentHolder = msg.sender;
+        currentHolder = _msgSender();
 
         emit FlagCaptured(previousHolder, currentHolder);
     }

migrations/2_deploy_contracts.js

@@ -1,5 +1,8 @@
 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

@@ -4,15 +4,18 @@
   "description": "Simple example of how to use GSNv3",
   "private": true,
   "dependencies": {
+    "@opengsn/contracts": "^3.0.0-alpha.6",
+    "@opengsn/dev": "^3.0.0-alpha.6",
+    "@opengsn/provider": "^3.0.0-alpha.6",
     "browserify": "^17.0.0",
     "ethers": "^5.6.8",
     "ganache-cli": "^6.12.2",
     "run-with-testrpc": "^0.3.1",
     "serve": "^13.0.0"
   },
   "scripts": {
-    "ganache": "yarn run ganache-cli -d --chainId 1337",
-    "gsn-with-ganache": "run-with-testrpc -d --chainId 1337 'gsn start'",
+    "ganache": "yarn run ganache-cli -d --networkId 1337 --chainId 1337",
+    "gsn-with-ganache": "run-with-testrpc -d --networkId 1337 --chainId 1337 'gsn start'",
     "test": "truffle test",
     "compile": "truffle compile",
     "build": "./ui/build.sh",

test/testcontracts.js

@@ -1,3 +1,6 @@
+const {RelayProvider} = require('@opengsn/provider')
+const {GsnTestEnvironment} = require('@opengsn/dev')
+
 const CaptureTheFlag = artifacts.require('CaptureTheFlag')
 
 const ZERO_ADDRESS = '0x0000000000000000000000000000000000000000'
@@ -8,16 +11,34 @@ contract("CaptureTheFlag", async accounts => {
     let captureFlagContract
 
     before(async () => {
-        captureFlagContract = await CaptureTheFlag.new();
+        const {forwarderAddress, paymasterAddress} = GsnTestEnvironment.loadDeployment()
+
+        captureFlagContract = await CaptureTheFlag.new(forwarderAddress);
+
+        const gsnProvider = await RelayProvider.newProvider({
+            provider: web3.currentProvider,
+            config: {
+                loggerConfiguration: {logLevel: 'error'},
+                paymasterAddress,
+                //these 2 params are needed only for ganache:
+                methodSuffix: '',
+                jsonStringifyRequest: false,
+            }
+        }).init()
 
-        account = accounts[0]
+        //during test, "artifacts" initialize the the default web3
+        // we need to replace the provider.
+        CaptureTheFlag.web3.setProvider(gsnProvider)
+
+        // default ganache accounts all have eth.
+        // test from a different account, without any eth
+        account = gsnProvider.newAccount().address
     })
 
-    it('Runs without GSN', async () => {
+    it('Runs with GSN', async () => {
         const res = await captureFlagContract.captureTheFlag({from: account});
         assert.equal(res.logs[0].event, "FlagCaptured", "Wrong event");
         assert.equal(res.logs[0].args.previousHolder, ZERO_ADDRESS, "Wrong previous flag holder");
         assert.equal(res.logs[0].args.currentHolder, account, "Wrong current flag holder");
     });
-
 });

ui/index.js

@@ -1,10 +1,13 @@
 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
 
 let theContract
 let provider
+let gsnProvider
 
 async function initContract() {
 
@@ -21,7 +24,15 @@ async function initContract() {
     })
     const networkId = await window.ethereum.request({method: 'net_version'})
 
-    provider = new ethers.providers.Web3Provider(window.ethereum)
+    gsnProvider = await RelayProvider.newProvider({
+        provider: window.ethereum,
+        config: {
+            loggerConfiguration: {logLevel: 'debug'},
+            paymasterAddress
+        }
+    }).init()
+
+    provider = new ethers.providers.Web3Provider(gsnProvider)
 
     const network = await provider.getNetwork()
     const artifactNetwork = contractArtifact.networks[networkId]