How to integrate anyCall V6?

You can also test anyCall V6 on testnets freely now. Follow the link below for more information.

anyCall V6 Testnet Environments

anyCall V6 Workflow

anyCall V6 added an important middleware called AnyCallExecutor. This sandbox contract will make the final execution of your destination contract. Hence any caller verification modifier should authorize AnyCallExecutor.

The anyCall protocol is made up of three main functions anyCall , anyExec . These two methods exist in our deployed anyCall contracts.

DAPPS need to develop and deploy a sender contract on chain A and a receiver contract on chain B. On the receiver contract, a function named anyExecute needs to be present and it will be called.

DAPPS sender contract(Chain A) -> anyCall(Chain A) -> SMPC Network -> anyExec(Chain B) ->AnyCallExecutor -> anyExecute by DAPP receiver contract(Chain B)

DAPPS sender contract call anyCall on the Chain A. Then SMPC network will relay anyCall event which will call AnyCallExecutor to make the final execution of the anyExecute function on the DAPP receiver contract. Hence a function named anyExecute needs to be present in the DAPP receiver contract.

If the anyExec contract execution failed on Chain B, it can call _fallback function to send messages back to Chain A.

anyExecute DAPP receiver contract(Chain B failed) -> anyCall(Chain B) -> SMPC Network -> anyExec(Chain A) -> anyFallback DAPP sender contract(Chain A)

More docs on fallback can be found below:

anyFallback

AnyCallExecutor

As stated above, AnyCallExecutor will make the final execution to your destination contract as a sandbox.

The address of this executor contract is stored in the main anycall contract. It can be accessed with an interface function like below.

interface CallProxy{
 
    function executor() external view returns (address executor);
}

The executor should then be saved in your contract constructor

constructor(){
        anycallExecutor=CallProxy(anycallcontract).executor();
    }

anyCall Interfaces

anyCall (Called by Dapps)

function anyCall( address _to, bytes calldata _data, address _fallback, uint256 _toChainID, uint256 _flags )

Parameters

Param
Type
Description

_to

address

The target contract to interact with on _toChainID

_data

bytes calldata

The calldata supplied for the interaction with _to

anyExecute will be run with this _data on the receiver contract you deployed.

_fallback

address

This is the fallback contract on the SOURCE CHAIN if the destination chain contract execution failed. If you put address(0), it means you don’t have a fallback contract. Note that this fallback mechanism is done by the destination chain issuing another anyCall with the following parameters. So you need to design your fallback function to be compatible with the following parameters. abi.encodeWithSelector(IApp.anyFallback.selector, _to, _data)

_toChainID

uint256

The target chain id to interact with

_flags

uint256

How dapps are paying gas fee of tx execution:

0: Gas fee paid on destination chain. A gas balance needs to be topped up by dapps on destination chain.

2: Gas fee paid on source chain. Allow users to pay the gas fee. (The fee details will be explained further)

anyExec (Only called by our MPC address)

function anyExec( address _to, bytes memory _data, address _fallback, string memory _appID, RequestContext memory _ctx )

Parameters

Param
Type
Description

_to

address

The target contract to interact with

_data

bytes calldata

The calldata supplied for the interaction with target

_fallback

address

The address to call on _fromChainID if the cross chain interaction fails

_fromChainID

uint256

The originating chain id

_ctx

struct

A struct containing information about the source chain anyCall request.

struct RequestContext { bytes32 txhash; address from; uint256 fromChainID; uint256 nonce; uint256 flags; } Data includes: 1. txhash: Original txhash

2. from: Original txhash

txhash: Original txhash

3. fromChainID: The source chain id

4. nonce: The nonce of anyCall, used to keep track of order of anyCall.

5. flags: The fee setting flag. Used to determine if fees need to be deducted on destination chain.

Requirements to be compatible with anyCall interfaces:

  1. Sender Contract: Your sender contract needs to call the method anyCall on the official anyCall contract.

  2. Receiver Contract: A method named anyExecute needs to exist on your _to contract address. This is needed because anyExec (Our deployed anyCall Contract) will call anyExecute on your receiver contract.

Code Example

Refer to this example for the correct interface to implement

This example will send a simple message from BNB chain to Polygon chain. This message is represented as a string event.

Deployed sender contract on BNB chain and receiver contract on Polygon:

Sender contract on BNB chain

pragma solidity ^0.8.10;

interface CallProxy{
    function anyCall(
        address _to,
        bytes calldata _data,
        address _fallback,
        uint256 _toChainID,
        uint256 _flags

    ) external;
}
  

contract AnycallV6senderBNBMainnet{

    // The Multichain anycall contract on bnb mainnet
    address private anycallcontractbnb=0xC10Ef9F491C9B59f936957026020C321651ac078
;


    address private owneraddress=0xfa7e030d2ac001c2bA147c0b147D468E4609f7CC;

    // Destination contract on Polygon
    address private receivercontract=0x3E2347a6F93eaC793C56DC508206e397eA11e83D;
    
    event NewMsg(string msg);

    function step1_initiateAnyCallSimple(string calldata _msg) external {
        emit NewMsg(_msg);
        if (msg.sender == owneraddress){
        CallProxy(anycallcontractbnb).anyCall(
            receivercontract,

            // sending the encoded bytes of the string msg and decode on the destination chain
            abi.encode(_msg),

            // 0x as fallback address because we don't have a fallback function
            address(0),

            // chainid of polygon
            137,

            // Using 0 flag to pay fee on destination chain
            0
            );
            
        }

    }
}

1. Import the anyCall interface, so we can call the deployed anyCall contract.

2. Define the AnycallV6senderBNBMainnet contract.

anycallcontractbnb: define where the anyCall contract exists which will use the interface above to call the anyCall. This is the contract deployed by Multichain team.

owneraddress: Simple owner address protection.

receivercontract: The receiver contract deployed on Polygon.

An event is also defined to show what message is being sent on Polygon. This is not 100% necessary.

3. step1_initiateAnyCallSimple

This method takes a string input. Then it uses the interface and anyCall contract address defined above to call the anyCall function with the following parameters.

  • Address _to: This is the receiver contract address on Polygon.

  • Bytes calldata _data: This is the bytes data the destination anyExecute will take. This can be any data you want. In this case, we are using abi.encode to encode our message string. And the destination contract will process this byte data.

  • Address _fallback: We're putting address(0) because we don't have a fallback function.

  • Uint256 _toChainID: The destination chain id. Polygon is 137.

  • uint256 _flags: 0 in our case because we want gas fees to be paid on the destination chain.

Receiver contract on Polygon

The function anyExecute is executed with the _data passed in from anyCall above.

Compatibility Notes:

  1. It needs to be named anyExecute.

  2. returns (bool success, bytes memory result) has to be the return values to be compatible.

This function simply decodes the _data that was previously encoded by abi.encode back to a string and creates an event containing that message. 

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.10;

contract anycallV6receiverPolygon{
    event NewMsg(string msg);

    function anyExecute(bytes memory _data) external returns (bool success, bytes memory result){
        (string memory _msg) = abi.decode(_data, (string));  
        emit NewMsg(_msg);
        success=true;
        result='';

    }
    }

anyCall example workflow

Step 1 on BNB Chain:

The function step1_initiateAnyCallSimple(string calldata _msg) is called with the msg 'hi polygon 7 with correct returns'

Txhash: https://bscscan.com/tx/0x5f4f2486153aced0f3bca0d967836624cc71525417a0e32c9a81c266425c1cae

Step 2 on Polygon Chain:

SMPC networks relay the anyCall event, then invoke anyExecute function on our Polygon receiver contract.

Txhash: https://polygonscan.com/tx/0x41dadc279612965c142c1e37262d70652a30ea44482ea9aced1afab1f0e18b35

This function emits the message from BNB chain.

Deploy Requirements

  1. Fees: Before using the anyCall protocol, projects need to deposit some gas fee to the destination anyCall contract.

Note that the address argument of the deposit(address _account) function should be the sender contract address on the source chain. The fee depends on the calldata size. The totalCost of one transaction = (gasUsed - gasleft()) * (tx.gasprice + _feeData.premium)

You can also pay fees on the source chain, refer to this article

Fees Paid on Source Chain

Whitelisting is not required anymore for anyCall V6.

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