# Contract reference (https://docs.axelar.dev/gmp/integrations/evm/gmp-contracts) Gateway and gas service addresses for every chain are on [Chains and contracts](https://docs.axelar.dev/llms.mdx/infrastructure/network/chains-and-contracts/content.md). For the gas service, see the [Gas](https://docs.axelar.dev/llms.mdx/gmp/gas/estimate-and-pay/content.md#payment-functions) chapter. ## Gateway [#gateway] Consensus chains run [`AxelarGateway`](https://github.com/axelarnetwork/axelar-cgp-solidity/blob/main/contracts/AxelarGateway.sol) from axelar-cgp-solidity. Amplifier chains run [`AxelarAmplifierGateway`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/gateway/AxelarAmplifierGateway.sol) from axelar-gmp-sdk-solidity. Both implement [`IAxelarGateway`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/interfaces/IAxelarGateway.sol), which is what `AxelarExecutable` uses. ### Send [#send] ```solidity 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`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/interfaces/IAxelarGatewayWithToken.sol)): ```solidity 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 [#receive] A message is identified on the destination gateway by its command ID. Executables validate it with: ```solidity // 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 [#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](https://docs.axelar.dev/llms.mdx/its/integrations/evm/transfers-with-data/content.md) | Amplifier gateways also identify messages by source chain and message ID ([`IBaseAmplifierGateway`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/interfaces/IBaseAmplifierGateway.sol)): ```solidity 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 `-`, as shown on Axelarscan. ### Pausing [#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 [#executables] | Contract | Use it to | You implement | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------- | ------------------------------------------------------ | | [`AxelarExecutable`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/executable/AxelarExecutable.sol) | [Receive messages](https://docs.axelar.dev/llms.mdx/gmp/integrations/evm/gmp-messages/content.md) | `_execute` | | [`AxelarExecutableWithToken`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/executable/AxelarExecutableWithToken.sol) | [Receive messages with gateway tokens](https://docs.axelar.dev/llms.mdx/gmp/integrations/evm/send-tokens-with-messages/content.md) | `_execute`, `_executeWithToken` | | [`AxelarExpressExecutableWithToken`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/express/AxelarExpressExecutableWithToken.sol) | Receive messages with [Express](https://docs.axelar.dev/llms.mdx/gmp/integrations/evm/express/content.md) | `_execute`, `_executeWithToken` | | [`AxelarValuedExpressExecutable`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/express/AxelarValuedExpressExecutable.sol) | Express for messages whose value is in the payload | `_execute`, `contractCallValue` | | [`AxelarValuedExpressExecutableWithToken`](https://github.com/axelarnetwork/axelar-gmp-sdk-solidity/blob/main/contracts/express/AxelarValuedExpressExecutableWithToken.sol) | The same, with gateway tokens | Also `_executeWithToken`, `contractCallWithTokenValue` | ```solidity // 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. --- All pages of these docs, as Markdown: https://docs.axelar.dev/llms.txt