batcher.md

Batch Submitter

The batch submitter, also referred to as the batcher, is the entity submitting the L2 sequencer data to L1, to make it available for verifiers.

The format of the data transactions is defined in the derivation spec: the data is constructed from L2 blocks in the reverse order as it is derived from data into L2 blocks.

The timing, operation and transaction signing is implementation-specific: any data can be submitted at any time, but only the data that matches the derivation spec rules will be valid from the verifier perspective.

The most minimal batcher implementation can be defined as a loop of the following operations:

1. See if the unsafe L2 block number is past the safe block number: unsafe data needs to be submitted.
2. Iterate over all unsafe L2 blocks, skip any that were previously submitted.
3. Open a channel, buffer all the L2 block data to be submitted, while applying the encoding and compression as defined in the derivation spec.
4. Pull frames from the channel to fill data transactions with, until the channel is empty.
5. Submit the data transactions to L1

The L2 view of safe/unsafe does not instantly update after data is submitted, nor when it gets confirmed on L1, so special care may have to be taken to not duplicate data submissions.