l2_bridge.md

L2 Bridge

Events

TokenBridgeFinalizedEvent

The event is emitted when a executor finalized the token transfer from the L1 to L2.

// Emitted when a token bridge is finalized on l2 chain.
struct TokenBridgeFinalizedEvent has drop, store {
    from: address, // l1 address
    to: address, // l2 address
    l2_token: vector<u8>,
    amount: u64,
    l1_sequence: u64, // the sequence number which is assigned from the l1 bridge
}

TokenBridgeInitiatedEvent

The event is emitted when a user executes withdraw_token function to move token from L2 to L1.

• The bridge module maintain sequence number to give unique identifier to each relay operation.
• In v1, l2_sequence is the unique identifier.

// Emitted when a token bridge is initiated to the l1 chain.
struct TokenBridgeInitiatedEvent has drop, store {
    from: address, // l2 address
    to: address, // l1 address
    l2_token: vector<u8>,
    amount: u64,
    l2_sequence: u64, // the operation sequence number
}

Operations

Register Token

This function allows the block executor to initialize a new token type with registration on the bridge module. The name of the newly deployed module should follow the L1 bridge contract’s event message l2_token, such as 01::l2_${l2_token}::Coin.

Finalize Token Bridge

This function finalizes the token transfer from L1 to L2. Only the block executor is allowed to execute this operation.

Initiate Token Bridge

This function initiates the token bridge from L2 to L1. Users can execute withdraw_token to send tokens from L2 to L1. This operation emits the TokenBridgeInitiatedEvent with an l2_sequence number to prevent duplicate execution on L1.

The block executor should monitor this event to build withdraw storage for withdrawal proofs.