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Version: SDK V4 (latest)

Paymaster sponsored

This tutorial represents the API integration flow where paymaster is used to sponsor the transactions.

Pre-requisites:​

  • Biconomy bundler url (refer to the docs to get the same)
  • Partial user operation, where
    • sender is the smart account Address
    • nonce can be calculated using the smart account contract methods
    • initCode will be 0x, if the account is already deployed or can be fetched using contract methods
    • paymasterAndData will be 0x initially.
    • callData is the abi encoded form of transaction
    • It also requires putting a semi-valid/ dummy signature (e.g. a signature in the right length).
type UserOperation = {
  sender: string;
  nonce: string;
  initCode: string;
  callData: string;
  callGasLimit: string;
  verificationGasLimit: string;
  preVerificationGas: string;
  maxFeePerGas: string;
  maxPriorityFeePerGas: string;
  paymasterAndData: string;
  signature: string;
}

let partialUserOp : Partial<UserOperation>  = {
  sender: '0x4dF23B78543F5c2F9CBCDF09956288B3e97bb9a4',
  nonce: '0x08',
  initCode: "0x",
  paymasterAndData: "0x",
  callData: "0x0000189a000000000000000000000000322af0da66d00be980c7aa006377fcaaeee3bdfd000000000000000000000000000000000000000000000000002386f26fc1000000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000000",
  signature: "0x00000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000001c5b32F37F5beA87BDD5374eB2aC54eA8e000000000000000000000000000000000000000000000000000000000000004181d4b4981670cb18f99f0b4a66446df1bf5b204d24cfcb659bf38ba27a4359b5711649ec2423c5e1247245eba2964679b6a1dbb85c992ae40b9b00c6935b02ff1b00000000000000000000000000000000000000000000000000000000000000",
}

1. Calculate Gas Fee Values:​

Based on the response, update the max gas fee values and add mock gas limits, which will be updated during the paymaster call.

async function getGasFeeValues (userOp: Partial<UserOperation>) : Promise<UserOperation>  {
    const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
    
    const { data } = await axios.post(url, {
      jsonrpc: "2.0",
      method: "biconomy_getGasFeeValues",
      params: [],
      id: Date.now()
    });
    const { maxPriorityFeePerGas, maxFeePerGas } = data.result;
    return { ...userOp, maxPriorityFeePerGas, maxFeePerGas, callGasLimit: "5000000", verificationGasLimit: "5000000", preVerificationGas: "5000000" } as UserOperation;
}

2. Get paymaster data:​

Get the paymaster url from the dashboard.

async function getPaymasterAndData (userOp: UserOperation) {
    const PAYMASTER_URL="paymaster url"
    const requestData = {
      jsonrpc: '2.0',
      method: 'pm_sponsorUserOperation',
      id: Date.now(),
      params: [
        { ...userOp, preVerificationGas: userOp.preVerificationGas.toString(), verificationGasLimit: userOp.verificationGasLimit.toString(), callGasLimit: userOp.callGasLimit.toString(), maxFeePerGas: userOp.maxFeePerGas.toString(), maxPriorityFeePerGas: userOp.maxPriorityFeePerGas.toString(), paymasterAndData: "0x" },
        {
          mode: 'SPONSORED',
          sponsorshipInfo: {
            webhookData: {},
            smartAccountInfo: {
              name: 'BICONOMY',
              version: '2.0.0',
            },
          },
          expiryDuration: 300,
          calculateGasLimits: true,
        },
      ],
  };
  
  const { data } = await axios.post(PAYMASTER_URL, requestData);
  const { paymasterAndData, preVerificationGas, verificationGasLimit, callGasLimit } = data.result;
  return { ...userOp, paymasterAndData, preVerificationGas: preVerificationGas.toString(), verificationGasLimit: verificationGasLimit.toString(), callGasLimit: callGasLimit.toString() };
}

3. Sign userOperation​

To sign the userOp, calculate the userOpHash and then sign it using the same signer, account was created. Follow this tutorial to learn about signing the userOp. Below is an example with ECDSA module.


async function signUserOp (userOp: UserOperation) {
    const userOpHash = getUserOpHash(userOp);

    const moduleSig = await signer.signMessage(ethers.utils.arrayify(userOpHash));
    const signatureWithModuleAddress = ethers.utils.defaultAbiCoder.encode(
        ["bytes", "address"],
        [moduleSig, "0x0000001c5b32F37F5beA87BDD5374eB2aC54eA8e"],
      );
    return { ...userOp, signature: signatureWithModuleAddress };
}

4. Send UserOperation:​

eth_sendUserOperation sends a user operation to the given network.

async function sendUserOp(userOp: UserOperation) {
    const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
    
    const requestData = {
        jsonrpc: '2.0',
        method: 'eth_sendUserOperation',
        id: Date.now(),
        params: [
          userOp,
          "0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789"
        ],
    };
    
    const { data }  =  await axios.post(url, requestData)
    return data.result;
}

5. Fetch user operation receipt​

This API returns null until the transaction is mined, you will either need to poll or set a timeout. For reference checkout the sdk code. You can also get transaction hash from the response

async function getUserOpReceipt(userOpHash: string) {
  const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
  const requestData = {
    jsonrpc: '2.0',
    method: 'eth_getUserOperationReceipt',
    id: Date.now(),
    params: [userOpHash],
  };

  const { data } = await axios.post(url, requestData);
  return data.result;
}

If you are facing errors while integration, do checkout the common errors.

View Complete Code
import { ethers, utils } from "ethers";
import axios, { AxiosRequestConfig, AxiosResponse, AxiosError } from 'axios';
import { string, string } from "ethers";

let provider = new ethers.providers.JsonRpcProvider("https://rpc-amoy.polygon.technology/");
let signer = new ethers.Wallet("private key", provider);

type UserOperation = {
  sender: string;
  nonce: string;
  initCode: string;
  callData: string;
  callGasLimit: string;
  verificationGasLimit: string;
  preVerificationGas: string;
  maxFeePerGas: string;
  maxPriorityFeePerGas: string;
  paymasterAndData: string;
  signature: string;
}

async function getGasFeeValues (userOp: Partial<UserOperation>) : Promise<UserOperation>  {
    const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
    
    const { data } = await axios.post(url, {
      jsonrpc: "2.0",
      method: "biconomy_getGasFeeValues",
      params: [],
      id: Date.now()
    });
    const { maxPriorityFeePerGas, maxFeePerGas } = data.result;
    return { ...userOp, maxPriorityFeePerGas, maxFeePerGas, callGasLimit: 5000000, verificationGasLimit: 5000000, preVerificationGas: 5000000 } as UserOperation;
}


async function getPaymasterAndData (userOp: UserOperation) {
    const PAYMASTER_URL="paymaster url"
    const requestData = {
      jsonrpc: '2.0',
      method: 'pm_sponsorUserOperation',
      id: Date.now(),
      params: [
        userOp,
        {
          mode: 'SPONSORED',
          sponsorshipInfo: {
            webhookData: {},
            smartAccountInfo: {
              name: 'BICONOMY',
              version: '2.0.0',
            },
          },
          expiryDuration: 300,
          calculateGasLimits: true,
        },
      ],
  };

  const { data } = await axios.post(PAYMASTER_URL, requestData);
  const { paymasterAndData, preVerificationGas, verificationGasLimit, callGasLimit } = data.result;
  return { ...userOp, paymasterAndData, preVerificationGas, verificationGasLimit, callGasLimit };

}

function getUserOpHash(useOpMinusSignature: UserOperation) {
    const packedData = ethers.utils.defaultAbiCoder.encode(
        [
          "address","uint256","bytes32","bytes32","uint256","uint256","uint256","uint256","uint256","bytes32",
        ],
        [
          useOpMinusSignature.sender,
          useOpMinusSignature.nonce,
          ethers.utils.keccak256(useOpMinusSignature.initCode),
          ethers.utils.keccak256(useOpMinusSignature.callData),
          useOpMinusSignature.callGasLimit,
          useOpMinusSignature.verificationGasLimit,
          useOpMinusSignature.preVerificationGas,
          useOpMinusSignature.maxFeePerGas,
          useOpMinusSignature.maxPriorityFeePerGas,
          ethers.utils.keccak256(useOpMinusSignature.paymasterAndData),
        ]
      );
      
      const enc = ethers.utils.defaultAbiCoder.encode(
        ["bytes32", "address", "uint256"],
        [ethers.utils.keccak256(packedData), "0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789", 80002]
      );
      
      const userOpHash = ethers.utils.keccak256(enc);
      return userOpHash;
}

async function signUserOp (userOp: UserOperation) {
    const userOpHash = getUserOpHash(userOp);

    const moduleSig = await signer.signMessage(ethers.utils.arrayify(userOpHash));
    const signatureWithModuleAddress = ethers.utils.defaultAbiCoder.encode(
        ["bytes", "address"],
        [moduleSig, "0x0000001c5b32F37F5beA87BDD5374eB2aC54eA8e"],
      );
      return { ...userOp, signature: signatureWithModuleAddress };
}

async function sendUserOp(userOp: UserOperation) {
    const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
    
    const requestData = {
        jsonrpc: '2.0',
        method: 'eth_sendUserOperation',
        id: Date.now(),
        params: [
          userOp,
          "0x5ff137d4b0fdcd49dca30c7cf57e578a026d2789"
        ],
    };
    
    const { data }  =  await axios.post(url, requestData)
    return data.result;

}

async function getUserOpReceipt(userOpHash: string) {
  const url="https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44"
  const requestData = {
    jsonrpc: '2.0',
    method: 'eth_getUserOperationReceipt',
    id: Date.now(),
    params: [userOpHash],
  };

  const { data } = await axios.post(url, requestData);
  return data.result;
}

async function executePartialUserOp() {
    
 try {
    let partialUserOp: Partial<UserOperation> = {
        sender: '0x4dF23B78543F5c2F9CBCDF09956288B3e97bb9a4',
        nonce: '0x1D',
        initCode: "0x",
        paymasterAndData: "0x",
        callData: "0x0000189a000000000000000000000000322af0da66d00be980c7aa006377fcaaeee3bdfd000000000000000000000000000000000000000000000000002386f26fc1000000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000000",
        signature: "0x00000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000001c5b32F37F5beA87BDD5374eB2aC54eA8e000000000000000000000000000000000000000000000000000000000000004181d4b4981670cb18f99f0b4a66446df1bf5b204d24cfcb659bf38ba27a4359b5711649ec2423c5e1247245eba2964679b6a1dbb85c992ae40b9b00c6935b02ff1b00000000000000000000000000000000000000000000000000000000000000",
    }

    // Step 1 Gas estimation
    let userOp = await getGasFeeValues(partialUserOp)

    // Step 2 Get paymaster data
    userOp = await getPaymasterAndData(userOp)

    // Step 3 sign user op
    userOp = await signUserOp(userOp)

    // Step 4: send user operation
    const userOpHash = await sendUserOp(userOp);
    console.log("userOpHash", userOpHash)
    // Step 5: Get UserOpReceipt
    const receipt = await getUserOpReceipt(userOpHash);
    
  }
  catch (error) {
        console.error(error)
   }
}

executePartialUserOp();

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