> For the complete documentation index, see [llms.txt](https://contracts.synapseprotocol.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://contracts.synapseprotocol.com/messaging/interfaces/imessagebus.md).

# IMessageBus

## Methods

### estimateFee

```solidity
function estimateFee(uint256 _dstChainId, bytes _options) external nonpayable returns (uint256)
```

Returns srcGasToken fee to charge in wei for the cross-chain message based on the gas limit

#### Parameters

| Name         | Type    | Description                                                                                                                |
| ------------ | ------- | -------------------------------------------------------------------------------------------------------------------------- |
| \_dstChainId | uint256 | undefined                                                                                                                  |
| \_options    | bytes   | Versioned struct used to instruct relayer on how to proceed with gas limits. Contains data on gas limit to submit tx with. |

#### Returns

| Name | Type    | Description |
| ---- | ------- | ----------- |
| \_0  | uint256 | undefined   |

### executeMessage

```solidity
function executeMessage(uint256 _srcChainId, bytes _srcAddress, address _dstAddress, uint256 _gasLimit, uint256 _nonce, bytes _message, bytes32 _messageId) external nonpayable
```

Relayer executes messages through an authenticated method to the destination receiver based on the originating transaction on source chain

#### Parameters

| Name         | Type    | Description                                                                                                             |
| ------------ | ------- | ----------------------------------------------------------------------------------------------------------------------- |
| \_srcChainId | uint256 | Originating chain ID - typically a standard EVM chain ID, but may refer to a Synapse-specific chain ID on nonEVM chains |
| \_srcAddress | bytes   | Originating bytes address of the message sender on the srcChain                                                         |
| \_dstAddress | address | Destination address that the arbitrary message will be passed to                                                        |
| \_gasLimit   | uint256 | Gas limit to be passed alongside the message, depending on the fee paid on srcChain                                     |
| \_nonce      | uint256 | Nonce from origin chain                                                                                                 |
| \_message    | bytes   | Arbitrary message payload to pass to the destination chain receiver                                                     |
| \_messageId  | bytes32 | MessageId for uniqueness of messages (alongisde nonce)                                                                  |

### sendMessage

```solidity
function sendMessage(bytes32 _receiver, uint256 _dstChainId, bytes _message, bytes _options) external payable
```

Sends a message to a receiving contract address on another chain. Sender must make sure that the message is unique and not a duplicate message.

#### Parameters

| Name         | Type    | Description                                                                               |
| ------------ | ------- | ----------------------------------------------------------------------------------------- |
| \_receiver   | bytes32 | The bytes32 address of the destination contract to be called                              |
| \_dstChainId | uint256 | The destination chain ID - typically, standard EVM chain ID, but differs on nonEVM chains |
| \_message    | bytes   | The arbitrary payload to pass to the destination chain receiver                           |
| \_options    | bytes   | Versioned struct used to instruct relayer on how to proceed with gas limits               |

### withdrawFee

```solidity
function withdrawFee(address _account) external nonpayable
```

Withdraws message fee in the form of native gas token.

#### Parameters

| Name      | Type    | Description                    |
| --------- | ------- | ------------------------------ |
| \_account | address | The address receiving the fee. |