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L1 Bridge Module

Events

TokenRegisteredEvent

The event is emitted when a new token support is added to bridge contract.

  • In v1 spec, the bridge executor should add a new token support manually.
/// Emitted when deposit store is registered.
struct TokenRegisteredEvent has drop, store {
    l2_id: String,
    l1_token: String,
    l2_token: vector<u8>, // sha3_256(type_name(`L2ID`) || type_name(`l1_token`))
}

TokenBridgeInitiatedEvent

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

  • The bridge module maintain sequence number to give an unique identifier for each relaying operation.
  • In v1, l2_id + l1_sequence is the unique identifier.
/// Emitted when a token bridge is initiated to the l2 chain.
struct TokenBridgeInitiatedEvent has drop, store {
    from: address, // l1 address
    to: address, // l2 address
    l2_id: String,
    l1_token: String,
    l2_token: vector<u8>,
    amount: u64,
    l1_sequence: u64, 
}

TokenBridgeFinalizedEvent

The event is emitted when a withdrawal transaction is proved and finalized.

  • In v1, sha3(bcs(l2_sequence) + bcs(from) + bcs(to) + bcs(amount) + bytes(l1_token)) is the unique identifier for each withdrawal operation.
/// Emitted when a token bridge is finalized on l1 chain.
struct TokenBridgeFinalizedEvent has drop, store {
    from: address, // l2 address
    to: address, // l1 address
    l2_id: String,
    l1_token: String,
    l2_token: vector<u8>,
    amount: u64,
    l2_sequence: u64, // the sequence number which is assigned from the l2 bridge
}

Operations

Register Token

This function is for the bridge executor, who controls the bridge relaying operations. In version 1, only the bridge executor can add support for a new token type. After registration, the TokenRegisteredEvent event is emitted to deploy a new coin type module on L2.

The bridge executor should monitor the TokenRegisteredEvent and deploy a new coin type module on L2. They should also execute the L2 bridge's /minitia.rollup.v1.MsgCreateToken function for initialization.

Initiate Token Bridge

This function enables a user to transfer their asset from L1 to L2. The deposited token will be locked in the bridge's DepositStore and can only be released using the withdraw operation in L2. When executed, this operation emits a TokenBridgeInitiatedEvent. A bridge executor should subscribe to this event and transfer the token to L2 by executing the finalize_token_bridge function in the L2 bridge.

Finalize Token Bridge

This function is used to prove and finalize the withdrawal transaction from L2. The proving process is described here. Once the proving is complete, the deposited tokens are withdrawn to the recipient address, and the TokenBridgeFinalizedEvent event is emitted. To prevent duplicate withdrawal attempts, the bridge uses a unique identifier calculated as sha3(bcs(l2_sequence) + bcs(from) + bcs(to) + bcs(amount) + bytes(l1_token)).