Contract reference

Gateway functions and events on consensus and Amplifier EVM chains, and the executable base contracts.

Gateway and gas service addresses for every chain are on Chains and contracts. For the gas service, see the Gas chapter.

Gateway

Consensus chains run AxelarGateway from axelar-cgp-solidity. Amplifier chains run AxelarAmplifierGateway from axelar-gmp-sdk-solidity. Both implement IAxelarGateway, which is what AxelarExecutable uses.

Send

function callContract(
    string calldata destinationChain,
    string calldata destinationContractAddress,
    bytes calldata payload
) external;

event ContractCall(
    address indexed sender,
    string destinationChain,
    string destinationContractAddress,
    bytes32 indexed payloadHash,
    bytes payload
);

On consensus chains, callContractWithToken also sends gateway tokens, and emits ContractCallWithToken (IAxelarGatewayWithToken):

function callContractWithToken(
    string calldata destinationChain,
    string calldata contractAddress,
    bytes calldata payload,
    string calldata symbol,
    uint256 amount
) external;

function tokenAddresses(string memory symbol) external view returns (address);

Receive

A message is identified on the destination gateway by its command ID. Executables validate it with:

// Checks that the message was approved for msg.sender, and marks it executed.
// Returns false if it wasn't approved, or was already executed.
function validateContractCall(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    bytes32 payloadHash
) external returns (bool);

// View version, for a given contract; doesn't mark it executed
function isContractCallApproved(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    address contractAddress,
    bytes32 payloadHash
) external view returns (bool);

function isCommandExecuted(bytes32 commandId) external view returns (bool);

Despite its name, isCommandExecuted returns true as soon as the message is approved on the gateway, before your contract executes it. To check whether a message was executed, use isMessageExecuted on Amplifier gateways. On consensus gateways, an approved message is executed once isContractCallApproved returns false.

The token version on consensus chains, validateContractCallAndMint(commandId, sourceChain, sourceAddress, payloadHash, symbol, amount), also sends the tokens to the caller.

Differences between the gateways

	Consensus chains	Amplifier chains
Command ID	Assigned by Axelar	`keccak256(bytes(string.concat(sourceChain, "_", messageId)))`, from `messageToCommandId`
Approval event	`ContractCallApproved(commandId, sourceChain, sourceAddress, contractAddress, payloadHash, sourceTxHash, sourceEventIndex)`	`MessageApproved(commandId, sourceChain, messageId, sourceAddress, contractAddress, payloadHash)`
Execution event	`ContractCallExecuted(commandId)`	`MessageExecuted(commandId)`
Tokens	`callContractWithToken`, `validateContractCallAndMint`	Not supported; use ITS

Amplifier gateways also identify messages by source chain and message ID (IBaseAmplifierGateway):

function messageToCommandId(string calldata sourceChain, string calldata messageId) external pure returns (bytes32);

function isMessageApproved(
    string calldata sourceChain,
    string calldata messageId,
    string calldata sourceAddress,
    address contractAddress,
    bytes32 payloadHash
) external view returns (bool);

function isMessageExecuted(string calldata sourceChain, string calldata messageId) external view returns (bool);

The message ID of a message from an EVM chain is <transaction hash>-<log index>, as shown on Axelarscan.

Pausing

Recent gateway versions (axelar-gmp-sdk-solidity 6.2.0 and axelar-cgp-solidity 6.5.0) can be paused in an emergency. While a gateway is paused, callContract and callContractWithToken revert, and so does validation, so approved messages wait until it's unpaused and can then be executed.

Executables

Contract	Use it to	You implement
`AxelarExecutable`	Receive messages	`_execute`
`AxelarExecutableWithToken`	Receive messages with gateway tokens	`_execute`, `_executeWithToken`
`AxelarExpressExecutableWithToken`	Receive messages with Express	`_execute`, `_executeWithToken`
`AxelarValuedExpressExecutable`	Express for messages whose value is in the payload	`_execute`, `contractCallValue`
`AxelarValuedExpressExecutableWithToken`	The same, with gateway tokens	Also `_executeWithToken`, `contractCallWithTokenValue`

// AxelarExecutable
function execute(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    bytes calldata payload
) external;

function _execute(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    bytes calldata payload
) internal virtual;

function gateway() public view returns (IAxelarGateway);

// AxelarExecutableWithToken
function executeWithToken(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    bytes calldata payload,
    string calldata tokenSymbol,
    uint256 amount
) external;

function _executeWithToken(
    bytes32 commandId,
    string calldata sourceChain,
    string calldata sourceAddress,
    bytes calldata payload,
    string calldata tokenSymbol,
    uint256 amount
) internal virtual;

function gatewayWithToken() internal view returns (IAxelarGatewayWithToken);

execute and executeWithToken revert with NotApprovedByGateway if validation fails.