(fix): callback gasUsed should not count gasForCallExactCheck (#10104)

* (fix): callback gasUsed should not count gasForCallExactCheck

* (test): Add FaultyClient test

* rename testhelper to FunctionsClientWithEmptyCallback

contracts/src/v0.8/functions/dev/1_0_0/FunctionsRouter.sol

@@ -427,8 +427,9 @@ contract FunctionsRouter is IFunctionsRouter, FunctionsSubscriptions, Pausable,
       }
       // call and report whether we succeeded
       // call(gas,addr,value,argsOffset,argsLength,retOffset,retLength)
+      let gasBeforeCall := gas()
       success := call(callbackGasLimit, client, 0, add(encodedCallback, 0x20), mload(encodedCallback), 0, 0)
-      gasUsed := sub(g, gas())
+      gasUsed := sub(gasBeforeCall, gas())
 
       // limit our copy to MAX_CALLBACK_RETURN_BYTES bytes
       let toCopy := returndatasize()

contracts/src/v0.8/functions/tests/1_0_0/testhelpers/FunctionsClientWithEmptyCallback.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.6;
+
+import {ITermsOfServiceAllowList} from "../../../dev/1_0_0/accessControl/interfaces/ITermsOfServiceAllowList.sol";
+import {IFunctionsSubscriptions} from "../../../dev/1_0_0/interfaces/IFunctionsSubscriptions.sol";
+
+import {FunctionsRequest} from "../../../dev/1_0_0/libraries/FunctionsRequest.sol";
+import {FunctionsClient} from "../../../dev/1_0_0/FunctionsClient.sol";
+
+contract FunctionsClientWithEmptyCallback is FunctionsClient {
+  using FunctionsRequest for FunctionsRequest.Request;
+
+  event SendRequestInvoked(bytes32 requestId, string sourceCode, uint64 subscriptionId);
+  event FulfillRequestInvoked(bytes32 requestId, bytes response, bytes err);
+
+  constructor(address router) FunctionsClient(router) {}
+
+  function sendSimpleRequestWithJavaScript(
+    string memory sourceCode,
+    uint64 subscriptionId,
+    bytes32 donId,
+    uint32 callbackGasLimit
+  ) public returns (bytes32 requestId) {
+    FunctionsRequest.Request memory request;
+    request.initializeRequestForInlineJavaScript(sourceCode);
+    bytes memory requestData = FunctionsRequest.encodeCBOR(request);
+    requestId = _sendRequest(requestData, subscriptionId, callbackGasLimit, donId);
+    emit SendRequestInvoked(requestId, sourceCode, subscriptionId);
+  }
+
+  function fulfillRequest(bytes32 requestId, bytes memory response, bytes memory err) internal override {}
+}

contracts/test/v0.8/functions/v1/FunctionsClient.test.ts

@@ -173,3 +173,55 @@ describe('Functions Client', () => {
     })
   })
 })
+
+describe('Faulty Functions Client', () => {
+  it('can complete requests with an empty callback', async () => {
+    const clientWithEmptyCallbackTestHelperFactory =
+      await ethers.getContractFactory(
+        'src/v0.8/functions/tests/1_0_0/testhelpers/FunctionsClientWithEmptyCallback.sol:FunctionsClientWithEmptyCallback',
+        roles.consumer,
+      )
+
+    const clientWithEmptyCallback =
+      await clientWithEmptyCallbackTestHelperFactory
+        .connect(roles.consumer)
+        .deploy(contracts.router.address)
+
+    const subscriptionId = await createSubscription(
+      roles.subOwner,
+      [clientWithEmptyCallback.address],
+      contracts.router,
+      contracts.accessControl,
+      contracts.linkToken,
+    )
+    const tx = await clientWithEmptyCallback.sendSimpleRequestWithJavaScript(
+      'function run(){return response}',
+      subscriptionId,
+      ids.donId,
+      20_000,
+    )
+    const { events } = await tx.wait()
+    const requestId = getEventArg(events, 'RequestSent', 0)
+    await expect(tx)
+      .to.emit(clientWithEmptyCallback, 'RequestSent')
+      .withArgs(requestId)
+
+    const response = stringToBytes('response')
+    const error = stringToBytes('')
+    const oracleRequestEvent = await contracts.coordinator.queryFilter(
+      contracts.coordinator.filters.OracleRequest(),
+    )
+    const onchainMetadata = oracleRequestEvent[0].args?.['commitment']
+    const report = await encodeReport(
+      ethers.utils.hexZeroPad(requestId, 32),
+      response,
+      error,
+      onchainMetadata,
+      stringToBytes(''),
+    )
+    await expect(contracts.coordinator.callReport(report))
+      .to.emit(contracts.coordinator, 'OracleResponse')
+      .withArgs(requestId, await roles.defaultAccount.getAddress())
+      .to.emit(contracts.router, 'RequestProcessed')
+  })
+})