add borrow liquidity endpoint

api/api/borrow/liquidity.ts

@@ -0,0 +1,48 @@
+import { BigNumber } from "bignumber.js";
+import { ethers, providers } from "ethers";
+import { VercelRequest, VercelResponse } from "@vercel/node";
+
+const contractAddress = "0x3d9819210A31b4961b30EF54bE2aeD79B9c9Cd3B";
+const provider = new providers.JsonRpcProvider("http://localhost:8545");
+
+// Comptroller
+const abi = [
+  // Read-Only Functions
+  "function getAccountLiquidity(address account) view returns (uint, uint, uint)",
+  "function markets(address cTokenAddress) view returns (bool, uint, bool)"
+];
+
+export default async (req: VercelRequest, res: VercelResponse) => {
+  if (req.body === undefined || req.body.amount === undefined) {
+    res.status(400).json({ error: "No borrow amount provided." });
+    return;
+  }
+
+  const amount = req.body.amount;
+  const cTokenAddress = "0x39AA39c021dfbaE8faC545936693aC917d5E7563";
+  const contract = new ethers.Contract(contractAddress, abi, provider);
+
+  const market = await contract.markets(cTokenAddress);
+  const { 1: collateralFactorMantissa } = market;
+
+  let collateralFactor = new BigNumber(collateralFactorMantissa.toString());
+  collateralFactor = collateralFactor.shiftedBy(-18);
+  const collateralFactorSafetyAdjusted = collateralFactor
+    .minus(0.05)
+    .toNumber();
+  console.log(
+    amount,
+    collateralFactorMantissa,
+    collateralFactor.toNumber(),
+    collateralFactorSafetyAdjusted
+  );
+
+  // amount divided by collateral factor minus safety of 5%
+  // we would never want to get our user liquidated
+  // (probably there is a better way to calc this)
+  const collateral = amount / collateralFactorSafetyAdjusted;
+  res.json({
+    borrowAmount: amount,
+    collateralNeeded: Math.ceil(collateral)
+  });
+};

api/package.json

@@ -8,6 +8,7 @@
   },
   "dependencies": {
     "@compound-finance/compound-js": "^0.2.13",
+    "bignumber.js": "^9.0.1",
     "ethers": "^5.3.1",
     "web3": "^1.3.6"
   },