> ## Documentation Index > Fetch the complete documentation index at: https://starkware-9575960b-starkzapv4.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Messaging functions and events For information on the messaging mechanism, see [Messaging mechanism](/learn/protocol/messaging/). ## L1 function reference ### `cancelL1ToL2Message` #### Description Cancels an L1 to L2 message. Call this function after calling the [`startL1ToL2MessageCancellation`](#startL1ToL2MessageCancellation) function. The time between the calls to these two functions must be at least the number of seconds defined by the [`messageCancellationDelay`](#messageCancellationDelay) function. Only a sender can cancel a message. If the message is missing, the call reverts. Be aware that the message fee is not refunded. #### State Mutability None. #### Parameters | | | | - | - | | `uint256 toAddress` | The address of the L2 contract. | | `uint256 selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] calldata payload` | The payload of the message. | | `uint256 nonce` | The nonce of the message. | #### Returns | | | | - | - | | `bytes32 msgHash` | The hash of the canceled message. | #### Emitted event [`MessageToL2Canceled`](#MessageToL2Canceled) #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`cancelL1ToL2Message`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L161) ### `consumeMessageFromL2` #### Description Consumes a message that was sent from an L2 contract. Returns the hash of the message. #### State Mutability None. #### Parameters | | | | - | - | | `uint256 fromAddress` | The address of the L2 contract sending the message. | | `uint256[] calldata payload` | The payload of the message. | #### Returns | | | | - | - | | `bytes32 msgHash` | The hash of the consumed message. | #### Emitted event [`ConsumedMessageToL1`](#ConsumedMessageToL1) #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`consumeMessageFromL2`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L132) *** ### `getMaxL1MsgFee` #### Description Returns the maximum fee, in Wei, that Starknet accepts for a single message. If the fee passed is higher than this value, the transaction is not accepted. #### State Mutability `pure` #### Parameters None. #### Returns | | | | - | - | | `uint256 MAX_L1_MSG_FEE` | The maximum fee, in Wei, that Starknet accepts for a single message. | #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`getMaxL1MsgFee`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L31) *** ### `l1ToL2MessageCancellations` #### Description Returns the timestamp of the cancellation request. #### State Mutability `view` #### Parameters | | | | - | - | | `bytes32 msgHash` | The message hash. | #### Returns | | | | - | - | | `uint256 result` | The Ethereum block timestamp. | Returns `0` if `cancelL1ToL2Message` was not called with the message hash `msgHash`. #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`l1ToL2MessageCancellations`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L73) *** ### `l1ToL2MessageNonce` #### Description Returns the nonce of the next message sent to the L2 contract. So if If `n` messages have been sent to Starknet, this function returns `n + 1`. #### State Mutability `view` #### Parameters None. #### Returns | | | | - | - | | `uint256 nonce` | The nonce of the next message sending to L2 contract. | #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`l1ToL2MessageNonce`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L55) *** ### `l1ToL2Messages` #### Description Indicates if a pending message is associated with a given message hash. #### State Mutability `view` #### Parameters | | | | - | - | | `bytes32 msgHash` | The message hash. | #### Returns Returns `uint256 result`, where `result` is one of the following: | | | | - | - | | `message_fee + 1` | A pending message is associated with the `msgHash` parameter. | | `0` | No pending message is associated with the `msgHash` parameter. | #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`l1ToL2Messages`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L39) *** ### `l2ToL1Messages` #### Description Indicates the number of pending messages associated with a given message hash. #### State Mutability `view` #### Parameters | | | | - | - | | `bytes32 msgHash` | The message hash. | #### Returns Returns `uint256 result`, where `result` is the number of pending messages associated with the `msgHash` parameter. #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`l2ToL1Messages`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L43) *** ### `messageCancellationDelay` #### Description Returns the time interval, in seconds, after which you can cancel a message starting from the moment of calling the [`startL1ToL2MessageCancellation`](#startL1ToL2MessageCancellation) function. You can get the real value by calling the [`messageCancellationDelay`](https://etherscan.io/address/0xc662c410c0ecf747543f5ba90660f6abebd9c8c4#readProxyContract#F11) function on a block explorer, such as Etherscan. #### State Mutability `view` #### Parameters None. #### Returns | | | | - | - | | `uint256 result` | The time interval. | #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`messageCancellationDelay`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L59) *** ### `sendMessageToL2` #### Description Sends a message to an L2 contract. The message fee is the cost of executing this function. #### State Mutability `payable` #### Parameters | | | | - | - | | `uint256 toAddress` | The address of the L2 contract. | | `uint256 selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] calldata payload` | The payload of the message. | #### Returns | | | | - | - | | `bytes32 msgHash` | The hash of the message. | | `uint256 nonce` | The nonce of the message. | #### Emitted event [`LogMessageToL2`](#LogMessageToL2) #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`sendMessageToL2`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L110) *** ### `startL1ToL2MessageCancellation` #### Description Starts the cancellation of a message from L1 to L2. You can cancel a message after a predefined about of time from the moment this function is called. The amount of time is set by the [`messageCancellationDelay`](#messageCancellationDelay) function. You can only call this function for a message that is currently pending, and the caller must be the sender of that message. #### State Mutability None. #### Parameters | | | | - | - | | `uint256 toAddress` | The address of the L2 contract. | | `uint256 selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] calldata payload` | The payload of the message. | | `uint256 nonce` | The nonce of the message. | #### Returns | | | | - | - | | `bytes32 msgHash` | The hash of the cancellation message. | #### Emitted event [`MessageToL2CancellationStarted`](#MessageToL2CancellationStarted) #### Function definition Contract: [`StarknetMessaging.sol`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol) * Function: [`startL1ToL2MessageCancellation`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/StarknetMessaging.sol#L147) ## L1 event reference Events are listed in alphabetical order. *** ### `ConsumedMessageToL1` #### Description This event is emitted when a message from L2 to L1 is consumed by the [`consumeMessageFromL2`](#consumeMessageFromL2) function. #### Event attributes | | | | - | - | | `uint256 indexed fromAddress` | The address of the sender on L2. | | `address indexed toAddress` | The address of the receiver on L1. | | `uint256[] payload` | The payload of the consumed message. | #### Event definition * Contract: [`IStarknetMessagingEvents`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol) * Event: [`ConsumedMessageToL1`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol#L19) *** ### `LogMessageToL2` #### Description This event is emitted when a message is sent from L1 to L2 by the [`sendMessageToL2`](#sendMessageToL2) function. #### Event attributes | | | | - | - | | `address indexed fromAddress` | The address of the sender on L1. | | `uint256 indexed toAddress` | The address of the receiver on L2. | | `uint256 indexed selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] payload` | The payload of the message. | | `uint256 nonce` | The nonce of the message. | | `uint256 fee` | The fee associated with the message. | #### Event definition * Contract: [`IStarknetMessagingEvents`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol) * Event: [`LogMessageToL2`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol#L9) *** ### `MessageToL2Canceled` #### Description This event is emitted when an L1 to L2 message is canceled by the [`cancelL1ToL2Message`](#cancelL1ToL2Message) function. #### Event attributes | | | | - | - | | `address indexed fromAddress` | The address of the sender on L1. | | `uint256 indexed toAddress` | The address of the receiver on L2. | | `uint256 indexed selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] payload` | The payload of the canceled message. | | `uint256 nonce` | The nonce of the canceled message. | #### Event definition * Contract: [`IStarknetMessagingEvents`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol) * Event: [`MessageToL2Canceled`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol#L44) *** ### `MessageToL2CancellationStarted` #### Description This event is emitted when the cancellation of an L1 to L2 message is started by the [`startL1ToL2MessageCancellation`](#startL1ToL2MessageCancellation) function. #### Event attributes | | | | - | - | | `address indexed fromAddress` | The address of the sender on L1. | | `uint256 indexed toAddress` | The address of the receiver on L2. | | `uint256 indexed selector` | The function, in the recipient L2 contract, that the message called. | | `uint256[] payload` | The payload of the message to be canceled. | | `uint256 nonce` | The nonce of the message to be canceled. | #### Event definition * Contract: [`IStarknetMessagingEvents`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol) * Event: [`MessageToL2CancellationStarted`](https://github.com/starkware-libs/cairo-lang/blob/master/src/starkware/starknet/solidity/IStarknetMessagingEvents.sol#L35) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.