Using CCIP local simulator in your Hardhat project

Setup

To transfer tokens using CCIP, we need the following:

• Destination chain selector
• Source CCIP router
• LINK token for paying CCIP fees
• A test token contract (such as CCIP-BnM)
• A sender account (Alice)
• A receiver account (Bob)

The deployFixture function is used to set up the initial state for the tests. This function deploys the CCIP local simulator contract and initializes the sender and receiver accounts.

1. Initialize the CCIP local simulator contract:

   

   const ccipLocalSimulatorFactory = await hre.ethers.getContractFactory("CCIPLocalSimulator")
   const ccipLocalSimulator: CCIPLocalSimulator = await ccipLocalSimulatorFactory.deploy()
   

2. Initialize the sender and receiver accounts:

   

   const [alice, bob] = await hre.ethers.getSigners()
   

Test case: Transfer with LINK fees

The it("Should transfer CCIP test tokens from EOA to EOA") function tests the transfer of tokens between two externally owned accounts (EOA) while paying fees in LINK. Here are the steps involved in this test case:

1. Invoke the deployFixture function to set up the necessary variables:

   

   const { ccipLocalSimulator, alice, bob } = await loadFixture(deployFixture)
   

2. Invoke the configuration function to retrieve the configuration details for the pre-deployed contracts and services needed for local CCIP simulations.

3. Connect to the source router and CCIP-BnM contracts.

4. Call ccipBnM.drip to request CCIP-BnM tokens for Alice (sender).

5. Create an array Client.EVMTokenAmount[] to specify the token transfer details:

   

   const tokenAmounts = [
     {
       token: config.ccipBnM_,
       amount: amountToSend,
     },
   ]
   

6. Construct the Client.EVM2AnyMessage structure with the receiver, token amounts, and other necessary details.

   • Use an empty string for the data parameter because you are not sending any arbitrary data (only tokens).
   • Set gasLimit to 0 because you are sending tokens to an EOA, which means you do not expect any execution of receiver logic (and therefore do not need gas for that).
   

   const gasLimit = 0
   const functionSelector = id("CCIP EVMExtraArgsV1").slice(0, 10)
   const defaultAbiCoder = AbiCoder.defaultAbiCoder()
   const extraArgs = defaultAbiCoder.encode(["uint256"], [gasLimit])
   const encodedExtraArgs = `${functionSelector}${extraArgs.slice(2)}`
   
   const message = {
     receiver: defaultAbiCoder.encode(["address"], [bob.address]),
     data: defaultAbiCoder.encode(["string"], [""]), // no data
     tokenAmounts: tokenAmounts,
     feeToken: config.linkToken_,
     extraArgs: encodedExtraArgs,
   }
   

7. Calculate the required fees for the transfer and approve the router to spend LINK tokens for these fees:

   

   const fee = await mockCcipRouter.getFee(config.chainSelector_, message)
   await linkToken.connect(alice).approve(mockCcipRouterAddress, fee)
   

8. Send the CCIP transfer request to the router:

   

   await mockCcipRouter.connect(alice).ccipSend(config.chainSelector_, message)
   

9. Verify that Alice's balance has decreased by the amount sent and Bob's balance has increased by the same amount:

   

   expect(await ccipBnM.balanceOf(alice.address)).to.deep.equal(ONE_ETHER - amountToSend)
   expect(await ccipBnM.balanceOf(bob.address)).to.deep.equal(amountToSend)