Subcomponent: Celestia Reader

The Celestia Reader component fetches blobs containing sequencer block headers and rollup transactions from Celestia via JSON-RPC, validates them, and forwards them as firm blocks to the Executor.

The Celestia Reader's FetchConvertVerifyAndReconstruct task does the following:

• Fetches the block-header blobs and rollup blobs from Celestia, with exponential backoff on retries

• Attempts to decode the blobs to their expected types, dropping blobs that fail to decompress or decode

• Verifies, while decoding SubmittedMetadata, a Merkle proof that the rollup transaction root is included in the block

• Discards headers for blocks that are older than the current firm height

• Checks that each block header's chain ID and block hash agree with the sequencer's block for that height (fetched and cached from sequencer) and that the block was signed by a two-thirds majority of the sequencer's validators

• Reconstructs blocks from the headers and rollups blobs, dropping rollup blobs that do not have a valid inclusion proof for their associated header, which ensures that all and only the transactions associated with this sequencer block are included in the reconstructed block

• Yields the reconstructed blocks to the Celestia Reader's main loop, which inserts them into its block cache

The Celestia Reader's main loop acts as a scheduler:

• It schedules FetchConvertVerifyAndReconstruct tasks when Celestia's height is ahead of what has been processed and there are not too many reconstruction tasks pending.

• It handles shutdown requests from elsewhere in the conductor.

• It tracks which Celestia height the executor has last accepted.

• If it has reconstructed the block for the current firm height, it submits it as a firm block to the executor.

• It inserts reconstructed blocks into its block cache.

• It polls Celestia for its latest height.