add CheckBalance contract for querying token balances via Chainlink for other chain token balances

Author: cqlyj

src/CheckBalance.sol

@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.26;
+
+import {FunctionsClient} from "@chainlink/contracts/src/v0.8/functions/v1_0_0/FunctionsClient.sol";
+import {ConfirmedOwner} from "@chainlink/contracts/src/v0.8/shared/access/ConfirmedOwner.sol";
+import {FunctionsRequest} from "@chainlink/contracts/src/v0.8/functions/v1_0_0/libraries/FunctionsRequest.sol";
+
+contract CheckBalance is FunctionsClient, ConfirmedOwner {
+    using FunctionsRequest for FunctionsRequest.Request;
+
+    bytes32 private s_lastRequestId;
+    uint256 private s_lastResponse;
+    bytes private s_lastError;
+    uint32 private s_gasLimit = 300000;
+    bytes32 private s_donID;
+    string private s_chainBaseUrl;
+    address private s_tokenAddress;
+    address private s_subscriber;
+    string private s_source =
+        "const chainBaseUrl = args[0];"
+        "const tokenAddress = args[1];"
+        "const subscriber = args[2];"
+        "const apiResponse = await Functions.makeHttpRequest({"
+        " url: `https://${chainBaseUrl}//api?module=account&action=tokenbalance&contractaddress=${tokenAddress}&address=${subscriber}`"
+        "});"
+        "if (apiResponse.error) {"
+        "throw Error('Request failed');"
+        "}"
+        "const { data } = apiResponse;"
+        "return Functions.encodeString(data.result);";
+
+    error UnexpectedRequestID(bytes32 requestId);
+
+    event Response(bytes32 indexed requestId, uint256 response, bytes err);
+
+    constructor(
+        string memory _chainBaseUrl,
+        address _tokenAddress,
+        address _subscriber,
+        address router,
+        bytes32 donID
+    ) FunctionsClient(router) ConfirmedOwner(msg.sender) {
+        s_chainBaseUrl = _chainBaseUrl;
+        s_tokenAddress = _tokenAddress;
+        s_subscriber = _subscriber;
+        s_donID = donID;
+    }
+
+    /*//////////////////////////////////////////////////////////////
+                           OVERRIDE FUNCTIONS
+    //////////////////////////////////////////////////////////////*/
+
+    function sendRequest(
+        uint64 subscriptionId,
+        string[] calldata args
+    ) external onlyOwner returns (bytes32 requestId) {
+        FunctionsRequest.Request memory req;
+        req.initializeRequestForInlineJavaScript(s_source); // Initialize the request with JS code
+        if (args.length > 0) req.setArgs(args); // Set the arguments for the request
+
+        // Send the request and store the request ID
+        s_lastRequestId = _sendRequest(
+            req.encodeCBOR(),
+            subscriptionId,
+            s_gasLimit,
+            s_donID
+        );
+
+        return s_lastRequestId;
+    }
+
+    function fulfillRequest(
+        bytes32 requestId,
+        bytes memory response,
+        bytes memory err
+    ) internal override {
+        if (s_lastRequestId != requestId) {
+            revert UnexpectedRequestID(requestId); // Check if request IDs match
+        }
+        // Update the contract's state variables with the response and any errors
+        s_lastResponse = abi.decode(response, (uint256));
+        s_lastError = err;
+
+        // Emit an event to log the response
+        emit Response(requestId, s_lastResponse, s_lastError);
+    }
+
+    function getResponse() external view returns (uint256) {
+        return s_lastResponse;
+    }
+
+    function getLastError() external view returns (bytes memory) {
+        return s_lastError;
+    }
+}