Cannot estimate gas on flash loan

I have the following script to request a USD flash loan on Polygon blockchain:

import * as api from "@protocolink/api";
import * as common from "@protocolink/common";
import ethers from "ethers";
import dotenv from "dotenv";

// Config
dotenv.config();
let chainId = common.ChainId.polygon;
let loanToken = "USDC";
let amount = 1;
let network = "matic";
let account = process.env.ACCOUNT;
let mnemonic = process.env.MNEMONIC;

try {
  // Setup wallet

  let wallet = ethers.Wallet.fromMnemonic(mnemonic);
  let provider = new ethers.providers.InfuraProvider(network, process.env.INFURA_KEY);
  let signer = wallet.connect(provider);

  console.log("Start bot");

  // Get token list for loan
  const tokenList = await api.protocols.aavev3.getFlashLoanTokenList(chainId);
  let underlyingToken;
  for (let token of tokenList) {
    if (token.symbol == loanToken) {
      underlyingToken = token;
    }
  }

  const loans = [
    {
      token: underlyingToken,
      amount: amount.toString(),
    },
  ];

  // Create loan
  const flashLoanQuotation = await api.protocols.aavev3.getFlashLoanQuotation(chainId, {
    loans,
  });

  let i = underlyingToken.address;
  console.log(
    "Amount to repay: ",
    flashLoanQuotation.repays.tokenAmountMap[i].amount + " " + flashLoanQuotation.repays.tokenAmountMap[i].token.symbol
  );

  const [flashLoanLoanLogic, flashLoanRepayLogic] = api.protocols.aavev3.newFlashLoanLogicPair(loans);
  const logics = [flashLoanLoanLogic, flashLoanRepayLogic];

  // Build router data
  const routerData: api.RouterData = {
    chainId,
    account: account,
    logics: logics,
  };
  let estimateResult = await api.estimateRouterData(routerData, { permit2Type: "permit" });

  console.log(
    "FUNDS: ",
    estimateResult.funds.tokenAmountMap[i].amount + " " + estimateResult.funds.tokenAmountMap[i].token.symbol
  );
  console.log("FEE 1: ", estimateResult.fees[0].feeAmount.amount + " " + estimateResult.fees[0].feeAmount.token.symbol);
  console.log("FEE 2: ", estimateResult.fees[1].feeAmount.amount + " " + estimateResult.fees[0].feeAmount.token.symbol);

  // Increase fee
  estimateResult.fees[0].feeAmount.amount = (Number(estimateResult.fees[0].feeAmount.amount) * 20).toString();
  estimateResult.fees[1].feeAmount.amount = (Number(estimateResult.fees[1].feeAmount.amount) * 20).toString();

  // Approve
  for (const approval of estimateResult.approvals) {
    console.log("Approve ...");
    const txApprove = await signer.sendTransaction(approval);
    txApprove.wait();
    console.log("Gas limit: ", Number(txApprove.gasLimit));
  }

  // Permit
  if (estimateResult.permitData) {
    console.log("Sign ...");
    const permitSig = await signer._signTypedData(
      estimateResult.permitData.domain,
      estimateResult.permitData.types,
      estimateResult.permitData.values
    );
    // console.log("PermitSig", permitSig);
    routerData.permitData = estimateResult.permitData;
    routerData.permitSig = permitSig;
  } else {
    console.log("NOTHING TO SIGN");
  }

  // Execute
  console.log("Execute ...");
  const transactionRequest = await api.buildRouterTransactionRequest(routerData);

  console.log("Send ...");
  const tx = await signer.sendTransaction(transactionRequest);
  console.log(tx);
} catch (e) {
  console.error("ERROR: ", e.reason || e);
}

This is the output log:

Start bot
Amount to repay:  1.0005 USDC
FUNDS:  0.0005 USDC
FEE 1:  0.000667898340426478 MATIC
FEE 2:  0.000001335796680852 MATIC
Approve ...
Gas limit:  56107
Sign ...
Set fees
Execute ...
Send ...
ERROR:  cannot estimate gas; transaction may fail or may require manual gas limit

Why is it trowing this error on gas fees?

Hey @lucarducci, thank you for your question.

To understand why the transaction failed, you can use tools like Tenderly to simulate the to, data, value in the transactionRequest for clarification.
I suggest starting with a balancer flash loan for clarification, as it has a 0% flash loan fee, thus eliminating the need for the Approve & Permit process.

Also with the balancer flash loan I get the 2 objects in approval and the permitData in the estimateResult. Is it normal? I keep getting the same error.

How can I set a manual gas limit in protocolink?

This is unusual. Did you implement newFlashLoanLogicPair similar to the example? If so, your routerData should look like this:"

{
  "chainId": 137,
  "account": "0xaAaAaAaaAaAaAaaAaAAAAAAAAaaaAaAaAaaAaaAa",
  "logics": [
    {
      "rid": "balancer-v2:flash-loan",
      "fields": {
        "id": "6f6cc4d7-001f-4be8-a444-3f98abb9ba24",
        "loans": [
          {
            "token": {
              "chainId": 137,
              "address": "0x0d500B1d8E8eF31E21C99d1Db9A6444d3ADf1270",
              "decimals": 18,
              "symbol": "WMATIC",
              "name": "Wrapped Matic"
            },
            "amount": "10000"
          }
        ],
        "isLoan": true
      }
    },
    {
      "rid": "balancer-v2:flash-loan",
      "fields": {
        "id": "6f6cc4d7-001f-4be8-a444-3f98abb9ba24",
        "loans": [
          {
            "token": {
              "chainId": 137,
              "address": "0x0d500B1d8E8eF31E21C99d1Db9A6444d3ADf1270",
              "decimals": 18,
              "symbol": "WMATIC",
              "name": "Wrapped Matic"
            },
            "amount": "10000"
          }
        ],
        "isLoan": false
      }
    }
  ]
}

Ethers.js’s signer.sendTransaction() allows to set both gasLimit and gasPrice.

It worked adding transactionRequest.gasLimit = txApprove.gasLimit

Now I get the transaction completed with no errors but I can't see the tx in the blockchain explorer, it should be here: https://polygonscan.com/tx/0xbb4fed62d09fa508b757a67ee1786f7be86214d233653996a98ba7f2800f338c

And also I don't see the few USDC that I should have paid from my wallet. Am I missing something?

Below the full log of the result of the sendTransaction function:

{
  type: 2,
  chainId: 137,
  nonce: 100,
  maxPriorityFeePerGas: BigNumber { _hex: '0x59682f00', _isBigNumber: true },
  maxFeePerGas: BigNumber { _hex: '0x59682f3e', _isBigNumber: true },
  gasPrice: null,
  gasLimit: BigNumber { _hex: '0x01b656', _isBigNumber: true },
  to: '0xDec80E988F4baF43be69c13711453013c212feA8',
  value: BigNumber { _hex: '0x18cf45cf0201d3', _isBigNumber: true },
  data: '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  accessList: [],
  hash: '0xbb4fed62d09fa508b757a67ee1786f7be86214d233653996a98ba7f2800f338c',
  v: 0,
  r: '0xbe9c5136bedc0f66a8263c22cb383d452368466a2398517013922722e3352484',
  s: '0x2be3ec6375fe2fc420da53c7ee97de4cf93fe60bb1143bef030c93c58cba66ed',
  from: '0x53e09Dd70E20a0b5CeaF2447484063dcCbE3f219',
  confirmations: 0,
  wait: [Function (anonymous)]
}

The txApprove.gasLimit is typically insufficient for a flash loan. Consider using Ethers.js’s estimateGas for a more accurate gas estimate.
Additionally, simulate the transaction using tools like Tenderly to ensure it is ready for execution. You can then share the simulation results with us for more effective debugging.
Also, note that the nonce is set to 100, but it appears that the nonce for 0x53e09Dd70E20a0b5CeaF2447484063dcCbE3f219 on Polygon is not as high.

Could you clarify hot to get the gasLimit with Ethers.js's estimateGas?

I see I can get it with provider.getGasPrice() or provider.getFeeData() but both don't works. Then I tried with the contract.estimateGas but I miss some info, here what I tried:

  // Is this correct? I took it from the transactionRequest
  let protolinkContractAddress="0xDec80E988F4baF43be69c13711453013c212feA8"; 
  let contract = new ethers.Contract(protolinkContractAddress, ABIprotolink, provider);
  // here I miss the parameters to execute this function
  let estimategas = await contract.estimateGas.executeWithSignerFee();

If this is a standard procedure to get the gas limit it would be helpful to add this to the docs.

How do I set the nonce? It seems retrieved from api.buildRouterTransactionRequest
Here is the simulation results of Tenderly: https://www.tdly.co/shared/simulation/c4814ec9-3a6e-4f7f-aa61-e86d9bd14835

This Tenderly simulation indicates that 0x53e09dd70e20a0b5ceaf2447484063dccbe3f219 has not yet approved USDC for its agent 0x6E544A364fb3412E25809aA882EfD5b5d5ea36D1 (calcAgent).

If you are unfamiliar with how the Uniswap off-chain permit2 sign works, I recommend using permit2Type: approve initially (see documentation). First, execute the two approvals obtained from await api.estimateRouterData(routerData, { permit2Type: 'approve'}) on-chain. Afterwards, use Ethers.js’s estimateGas to estimate the gas limit and verify whether the transaction reverts.

@lucarducci Is there anything else we can help you with? And feel free to join our Discord we're here and happy to help!

So are flash loans working? Using furucombo I noticed it just fails the transactions.

Anyone know of alternative that works or have code that can be forked?

dinngo / protocolink-js-sdk

Cannot estimate gas on flash loan #51