The minimal CCIP architecture
To recap, with Chainlink CCIP, one can:
Transfer (supported) tokens
Send both tokens and data
CCIP receiver can be:
Any smart contract that implements CCIPReceiver.sol
Note: If you send a message and token(s) to EOA, only tokens will arrive.
For now, you can consider CCIP as a "black-box" component and be aware of the Router contract only. We will explain the Chainlink CCIP architecture in the following chapters.
Getting started
You can use Chainlink CCIP with any blockchain development framework. For this Masterclass, we prepared the steps for Hardhat, Foundry, and Remix IDE.
Let's create a new project
Make sure you have and installed. To check, run the following command:
Create a new folder and name it ccip-masterclass
Navigate to it
Create a hew Hardhat project by running:
And then select either "Create a JavaScript project" or "Create a TypeScript project".
Make sure you have installed. To check, run the following command:
Alternatively, you can clone:
The @chainlink/contracts-ccip NPM package
To use Chainlink CCIP, you need to interact with Chainlink CCIP-specific contracts from the NPM package.
To install it, follow steps specific to the development environment you will use for this Masterclass.
Option 1)
We cannot use git submodules to install @chainlink/contracts-ccip because the content of this package is not available as a separate GitHub repo. This essentially means that we cannot run a forge install command.
Here's the workaround:
Add the following line to the .gitignore file
Then run the following command in your Terminal:
Finally, add the following lines to the foundry.toml
Basic interface
Although, as being said, CCIP sender and receiver can be EOA and smart contract, and all combinations are possible, we are going to cover the most complex use-case where both CCIP sender and receiver are smart contracts on different blockchains.
Source blockchain
To send CCIP Messages, the smart contract on the source blockchain must call the ccipSend() function, which is defined the IRouterClient.sol interface.
The CCIP Message which is being sent is a type of EVM2AnyMessage Solidity struct from the Client library.
Let's now understand what each property of the EVM2AnyMessage struct we are sending represents and how to use it.
receiver
Receiver address. It can be a smart contract or an EOA. Use abi.encode(receiver) to encode the address to the bytes Solidity data-type.
data
Payload sent within the CCIP message. This is that "any type of data" one can send as a CCIP Message we are referring to from the start. It can be anything from simple text like "Hello, world!" to Solidity structs or function selectors.
tokenAmounts
Tokens and their amounts in the source chain representation. Here we are specifying which tokens (out of supported ones) we are sending and how much of it. This is the array of a EVMTokenAmount struct, which consists of two properties only:
token - Address of a token we are sending on the local (source) blockchain
amount The amount of tokens we are sending. The sender must approve the CCIP router to spend this amount on behalf of the sender, otherwise the call to the ccipSend function will revert.
Currently, the maximum number of tokens one can send in a single CCIP send transaction is five.
feeToken
Address of feeToken. CCIP supports fee payments in LINK and in alternative assets, which currently include native blockchain gas coins and their ERC20 wrapped versions. For developers, this means you can simply pay on the source chain, and CCIP will take care of execution on the destination chain. Set address(0) to pay in native gas coins such as ETH on Ethereum or MATIC on Polygon. Keep in mind that even if you are paying for fees in the native asset, nodes in the Chainlink DON will be rewarded in LINK only.
extraArgs
Users fill in the EVMExtraArgsV1 struct and then encode it to bytes using the _argsToBytes function. The struct consists of two properties:
gasLimit - The maximum amount of gas CCIP can consume to execute ccipReceive() on the contract located on the destination blockchain. Unspent gas is not refunded. This means that if you are sending tokens to EOA, for example, you should put 0 as a gasLimit value because EOAs can't implement the ccipReceive() (or any other) function. To estimate the accurate gas limit for your destination contract, consider Leveraging Ethereum client RPC by applying eth_estimateGas on receiver.ccipReceive() function, or use the , or conduct .
If extraArgs are left empty, a.k.a extraArgs: "", a default of 200_000 gasLimit will be set with no strict sequencing. For production deployments, make sure that extraArgs is mutable. This allows you to build it off-chain and pass it in a call to a function or store it in a variable that you can update on demand. This makes extraArgs compatible with future CCIP upgrades.
Destination blockchain
To receive CCIP Messages, the smart contract on the destination blockchain must implement the IAny2EVMMessageReceiver interface. The NPM package comes up with the contract which implements it in the right way, called CCIPReceiver.sol, but we are going to talk more about it in the next chapter. For now, let's understand which functions from the IAny2EVMMessageReceiver interface must be implemented in the general-case scenario.
As you can see, the ccipReceive() function from the IAny2EVMMessageReceiver interface accepts object of the Any2EVMMessage struct from the Client library. This struct is the Solidity representation of the received CCIP Message. Please note that this struct, Any2EVMMessage is different than the one we used to send on the source blockchain - EVM2AnyMessage. They are not the same.
Let's now understand what each property of the Any2EVMMessage struct we are receiving represents and how to use it.
messageId - CCIP Message Id, generated on the source chain.
sourceChainSelector - Source chain selector.
sender - Sender address. abi.decode(sender, (address))
To recap, here's the diagram with the minimal architecture needed to send & receive the Chainlink CCIP Message:
