Outbox

The Outbox is a contract deployed on L1 that handles message passing from the rollup and to L1.

Links: Interface (GitHub link), Implementation (GitHub link).

insert()

Inserts the root of a merkle tree containing all of the L2 to L1 messages in a block specified by _l2BlockNumber.

outbox_insert

/**
 * @notice Inserts the root of a merkle tree containing all of the L2 to L1 messages in
 * a block specified by _l2BlockNumber.
 * @dev Only callable by the rollup contract
 * @dev Emits `RootAdded` upon inserting the root successfully
 * @param _l2BlockNumber - The L2 Block Number in which the L2 to L1 messages reside
 * @param _root - The merkle root of the tree where all the L2 to L1 messages are leaves
 * @param _minHeight - The min height of the merkle tree that the root corresponds to
 */
function insert(uint256 _l2BlockNumber, bytes32 _root, uint256 _minHeight) external;

^{_{Source code: l1-contracts/src/core/interfaces/messagebridge/IOutbox.sol#L22-L33}}

Name	Type	Description
_l2BlockNumber	uint256	The L2 Block Number in which the L2 to L1 messages reside
_root	bytes32	The merkle root of the tree where all the L2 to L1 messages are leaves
_minHeight	uint256	The minimum height of the merkle tree that the root corresponds to

Edge cases

• Will revert with Outbox__Unauthorized() if msg.sender != ROLLUP_CONTRACT.
• Will revert with Errors.Outbox__RootAlreadySetAtBlock(uint256 l2BlockNumber) if the root for the specific block has already been set.
• Will revert with Errors.Outbox__InsertingInvalidRoot() if the rollup is trying to insert bytes32(0) as the root.

consume()

Allows a recipient to consume a message from the Outbox.

outbox_consume

/**
 * @notice Consumes an entry from the Outbox
 * @dev Only useable by portals / recipients of messages
 * @dev Emits `MessageConsumed` when consuming messages
 * @param _message - The L2 to L1 message
 * @param _l2BlockNumber - The block number specifying the block that contains the message we want to consume
 * @param _leafIndex - The index inside the merkle tree where the message is located
 * @param _path - The sibling path used to prove inclusion of the message, the _path length directly depends
 * on the total amount of L2 to L1 messages in the block. i.e. the length of _path is equal to the depth of the
 * L1 to L2 message tree.
 */
function consume(
  DataStructures.L2ToL1Msg calldata _message,
  uint256 _l2BlockNumber,
  uint256 _leafIndex,
  bytes32[] calldata _path
) external;

^{_{Source code: l1-contracts/src/core/interfaces/messagebridge/IOutbox.sol#L35-L53}}

Name	Type	Description
_message	L2ToL1Msg	The L2 to L1 message we want to consume
_l2BlockNumber	uint256	The block number specifying the block that contains the message we want to consume
_leafIndex	uint256	The index inside the merkle tree where the message is located
_path	bytes32[]	The sibling path used to prove inclusion of the message, the _path length directly depends

Edge cases

• Will revert with Outbox__InvalidRecipient(address expected, address actual); if msg.sender != _message.recipient.actor.
• Will revert with Outbox__InvalidChainId() if block.chainid != _message.recipient.chainId.
• Will revert with Outbox__NothingToConsumeAtBlock(uint256 l2BlockNumber) if the root for the block has not been set yet.
• Will revert with Outbox__AlreadyNullified(uint256 l2BlockNumber, uint256 leafIndex) if the message at leafIndex for the block has already been consumed.
• Will revert with Outbox__InvalidPathLength(uint256 expected, uint256 actual) if the supplied height is less than the existing minimum height of the L2 to L1 message tree, or the supplied height is greater than the maximum (minimum height + log2(maximum messages)).
• Will revert with MerkleLib__InvalidRoot(bytes32 expected, bytes32 actual, bytes32 leaf, uint256 leafIndex) if unable to verify the message existence in the tree. It returns the message as a leaf, as well as the index of the leaf to expose more info about the error.

hasMessageBeenConsumedAtBlockAndIndex()

Checks to see if an index of the L2 to L1 message tree for a specific block has been consumed.

outbox_has_message_been_consumed_at_block_and_index

/**
 * @notice Checks to see if an index of the L2 to L1 message tree for a specific block has been consumed
 * @dev - This function does not throw. Out-of-bounds access is considered valid, but will always return false
 * @param _l2BlockNumber - The block number specifying the block that contains the index of the message we want to check
 * @param _leafIndex - The index of the message inside the merkle tree
 */
function hasMessageBeenConsumedAtBlockAndIndex(uint256 _l2BlockNumber, uint256 _leafIndex)
  external
  view
  returns (bool);

^{_{Source code: l1-contracts/src/core/interfaces/messagebridge/IOutbox.sol#L55-L66}}

Name	Type	Description
_l2BlockNumber	uint256	The block number specifying the block that contains the index of the message we want to check
_leafIndex	uint256	The index of the message inside the merkle tree

Edge cases

• This function does not throw. Out-of-bounds access is considered valid, but will always return false.