Demo : Native meta-transaction via Biconomy

contracts/SapienChildERC20.sol

@@ -18,6 +18,27 @@ contract SapienChildERC20 is ChildERC20 {
     return transferWithPurpose(to, value, hex"");
   }
 
+  function transferWithPurposeAndSig(address to, uint256 value, bytes memory purpose, 
+    bytes memory sig, bytes32 data, uint256 expiration) public returns (bool) {
+
+    require(expiration == 0 || block.number <= expiration, "Signature is expired");
+
+    bytes32 dataHash = getTokenTransferOrderHash(
+      to,
+      value,
+      data,
+      expiration
+    );
+    require(disabledHashes[dataHash] == false, "Sig deactivated");
+    disabledHashes[dataHash] = true;
+
+    address from = ecrecovery(dataHash, sig);
+    if (parent != address(0x0) && !ISapienParentToken(parent).beforeTransfer(from, to, value, purpose)) {
+      return false;
+    }
+    return _transferFrom(from, to, value);
+  }
+
   /// @dev Function that is called when a user or another contract wants to transfer funds, including a purpose.
   /// @param to Address of token receiver.
   /// @param value Number of tokens to transfer.

demo-script/index.js

@@ -0,0 +1,128 @@
+var sigUtil = require('eth-sig-util');
+const Biconomy = require("@biconomy/mexa");
+const Web3 = require("web3");
+const {abi} = require("./abi");
+
+let tokenAddress = "SapienChildERC20_contract_address";
+
+//Initialize Biconomy
+// register on biconomy dashboard to create dapp_id & api_key
+const biconomy = new Biconomy(new Web3.providers.HttpProvider("https://betav2.matic.network"),
+{dappId: "dapp_id", apiKey: "api_key",debug:true});
+
+//initialise web3 with Biconomy
+web3 = new Web3(biconomy);
+
+let contract =  new web3.eth.Contract(abi , tokenAddress);
+let data = "4" //dynamic data
+let toAddress = "receiver_address";
+let fromAddress = "spender_address";
+let privateKey = "spender_private_key";
+
+biconomy.onEvent(biconomy.READY, () => {
+  // Initialize your dapp here like getting user accounts etc
+  sendSignedTransactionToSapien();
+}).onEvent(biconomy.ERROR, (error, message) => {
+  // Handle error while initializing mexa
+  console.log("error while initialising biconomy")
+  console.log(error);
+});
+
+async function sendSignedTransactionToSapien(){
+  //Sign Data
+  let transferSigResult =  getTransferSig(
+      privateKey,
+      toAddress,
+      data,
+      tokenAddress,
+      "1", //Transferring 1 sapien token
+      0
+  );   
+
+  let result = contract.methods.transferWithPurposeAndSig(
+          toAddress,
+          "1",
+          web3.utils.hexToBytes(web3.utils.stringToHex("0")),
+          transferSigResult.sig,
+          web3.utils.hexToBytes(web3.utils.stringToHex(data)),
+          0
+  ).encodeABI();
+
+  let txParams = {
+      "from": fromAddress,
+      "gasLimit": web3.utils.toHex(210000),
+      "to": tokenAddress,
+      "value": "0x0",
+      "data": result
+  };
+
+  // Sign Transaction
+  const signedTx = await web3.eth.accounts.signTransaction(txParams, `0x${privateKey}`);
+  let receipt = await web3.eth.sendSignedTransaction(signedTx.rawTransaction, (error, txHash)=>{
+      if(error) {
+          return console.error(error);
+      }
+      console.log(txHash);
+  });
+
+}
+
+function getTransferSig(
+  privateKey,
+  spender,
+  data,
+  tokenAddress,
+  tokenIdOrAmount,
+  expiration
+) {
+    const typedData = getTransferTypedData({
+        tokenAddress,
+        tokenIdOrAmount,
+        spender,
+        data,
+        expiration
+    });
+
+    const sig = sigUtil.signTypedMessage(new Buffer.from(privateKey,'hex'), {
+        data: typedData
+    },'V3')
+    return { sig };
+}
+
+function getTransferTypedData({
+  tokenAddress,
+  spender,
+  tokenIdOrAmount,
+  data,
+  expiration
+}) {
+  return {
+    types: {
+      EIP712Domain: [
+        { name: "name", type: "string" },
+        { name: "version", type: "string" },
+        { name: "chainId", type: "uint256" },
+        { name: "contract", type: "address" }
+      ],
+      TokenTransferOrder: [
+        { name: "spender", type: "address" },
+        { name: "tokenIdOrAmount", type: "uint256" },
+        { name: "data", type: "bytes32" },
+        { name: "expiration", type: "uint256" }
+      ]
+    },
+    domain: {
+      name: "Matic Network",
+      version: "1",
+      chainId: 16110,
+      contract: tokenAddress
+    },
+    primaryType: "TokenTransferOrder",
+    message: {
+      spender,
+      tokenIdOrAmount,
+      data,
+      expiration
+    }
+  }
+}

demo-script/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "script",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "@biconomy/mexa": "^1.5.1",
+    "eth-sig-util": "^2.5.3",
+    "ethereumjs-util": "^6.2.0",
+    "web3": "^1.2.6"
+  }
+}