Nitro Forwarders
Basics about Nitro forwarders
Intro to Nitro Forwarders
In simple terms, the Nitro forwarder is a permissionless module that listens to the Nitro deposit event from
the source chain and settles the request for the user on the destination chain. It is
a Go service that handles cross-chain messages and token transactions across
blockchain networks. It starts with the run function, which listens to
blockchain events and relays data as needed. This modular system includes separate
listeners and relayers for each blockchain, managed by a central processor. It
features comprehensive logging, error management, and health monitoring for reliability.
Components of a Nitro Forwarder
Listener
Nitro Listener is a sub-module within the Nitro forwarder that captures events from blockchains, specifically from the "Asset Forwarder" contract. For every supported chain, there will be a listener instance of a forwarder that will listen to the events emitted from that chain.
It stores the processed block number, and it resumes from the last processed block
to avoid reprocessing. The ProcessInboundEvents method fetches and processes
new events, including fundDepositedEvents and fundDepositedWithMessageEvents,
and updates the database with the latest event information. If errors occur, the
listener stops.
Processor
The RequestProcessor works on queued database requests (msgTxqArray),
continuously pulling unprocessed transactions and marking
them as Picked to avoid duplication. It processes transactions
based on their type using specific methods and updates a registry to handle
transactions on the appropriate blockchain.
Chain Relayer
For every supported chain, the forwarder will run a relayer sub-module: the ChainRelayer module runs
continuously, waiting for messages on two channels to relay funds and messages. It validates
incoming messages and uses the IRelay method for processing. Errors are
logged, and successful messages are processed further.
Executor:
As part of the relayer, the Executor prepares transaction data, estimates gas
costs, and checks for profitability. It sends transactions through
assetForwarderWrapper, waits for confirmation, and
updates the database with transaction details.
The relayer sub-module within a Nitro forwarder is different from Router Chain relayers.