| `MIN_EPOCHS_FOR_DATA_COLUMN_SIDECARS_REQUESTS` | `2**12` (= 4096 epochs, ~18 days) | The minimum epoch range over which a node must serve data column sidecars |
This topic is used to propagate column sidecars, where each column maps to some `subnet_id`.
The *type* of the payload of this topic is `DataColumnSidecar`.
The following validations MUST pass before forwarding the `sidecar: DataColumnSidecar` on the network, assuming the alias `block_header = sidecar.signed_block_header.message`:
- _[REJECT]_ The sidecar's index is consistent with `NUMBER_OF_COLUMNS` -- i.e. `sidecar.index < NUMBER_OF_COLUMNS`.
- _[REJECT]_ The sidecar is for the correct subnet -- i.e. `compute_subnet_for_data_column_sidecar(sidecar.index) == subnet_id`.
- _[IGNORE]_ The sidecar is not from a future slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) -- i.e. validate that `block_header.slot <= current_slot` (a client MAY queue future sidecars for processing at the appropriate slot).
- _[IGNORE]_ The sidecar is from a slot greater than the latest finalized slot -- i.e. validate that `block_header.slot > compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)`
- _[REJECT]_ The proposer signature of `sidecar.signed_block_header`, is valid with respect to the `block_header.proposer_index` pubkey.
- _[IGNORE]_ The sidecar's block's parent (defined by `block_header.parent_root`) has been seen (via both gossip and non-gossip sources) (a client MAY queue sidecars for processing once the parent block is retrieved).
- _[REJECT]_ The sidecar's block's parent (defined by `block_header.parent_root`) passes validation.
- _[REJECT]_ The sidecar is from a higher slot than the sidecar's block's parent (defined by `block_header.parent_root`).
- _[REJECT]_ The current finalized_checkpoint is an ancestor of the sidecar's block -- i.e. `get_checkpoint_block(store, block_header.parent_root, store.finalized_checkpoint.epoch) == store.finalized_checkpoint.root`.
- _[REJECT]_ The sidecar's `kzg_commitments` field inclusion proof is valid as verified by `verify_data_column_sidecar_inclusion_proof(sidecar)`.
- _[IGNORE]_ The sidecar is the first sidecar for the tuple `(block_header.slot, block_header.proposer_index, sidecar.index)` with valid header signature, sidecar inclusion proof, and kzg proof.
- _[REJECT]_ The sidecar is proposed by the expected `proposer_index` for the block's slot in the context of the current shuffling (defined by `block_header.parent_root`/`block_header.slot`).
If the `proposer_index` cannot immediately be verified against the expected shuffling, the sidecar MAY be queued for later processing while proposers for the block's branch are calculated -- in such a case _do not_`REJECT`, instead `IGNORE` this message.
*Note:* In the `verify_data_column_sidecar_inclusion_proof(sidecar)` check, for all the sidecars of the same block, it verifies against the same set of `kzg_commitments` of the given beacon block. Client can choose to cache the result of the arguments tuple `(sidecar.kzg_commitments, sidecar.kzg_commitments_inclusion_proof, sidecar.signed_block_header)`.
The response is a list of `DataColumnIdentifier` whose length is less than or equal to the number of requests.
It may be less in the case that the responding peer is missing blocks or sidecars.
Before consuming the next response chunk, the response reader SHOULD verify the data column sidecar is well-formatted, has valid inclusion proof, and is correct w.r.t. the expected KZG commitments through `verify_data_column_sidecar_kzg_proofs`.
No more than `MAX_REQUEST_DATA_COLUMN_SIDECARS` may be requested at a time.
The response MUST consist of zero or more `response_chunk`.
Each _successful_`response_chunk` MUST contain a single `DataColumnSidecar` payload.
Clients MUST support requesting sidecars since `minimum_request_epoch`, where `minimum_request_epoch = max(finalized_epoch, current_epoch - MIN_EPOCHS_FOR_DATA_COLUMN_SIDECARS_REQUESTS, EIP7594_FORK_EPOCH)`. If any root in the request content references a block earlier than `minimum_request_epoch`, peers MAY respond with error code `3: ResourceUnavailable` or not include the data column sidecar in the response.
Clients MUST respond with at least one sidecar, if they have it.
Clients MAY limit the number of blocks and sidecars in the response.
Clients SHOULD include a sidecar in the response as soon as it passes the gossip validation rules.
Clients SHOULD NOT respond with sidecars related to blocks that fail gossip validation rules.
Clients SHOULD NOT respond with sidecars related to blocks that fail the beacon chain state transition
Requests data column sidecars in the slot range `[start_slot, start_slot + count)` of the given `columns`, leading up to the current head block as selected by fork choice.
Before consuming the next response chunk, the response reader SHOULD verify the data column sidecar is well-formatted, has valid inclusion proof, and is correct w.r.t. the expected KZG commitments through `verify_data_column_sidecar_kzg_proofs`.
`DataColumnSidecarsByRange` is primarily used to sync data columns that may have been missed on gossip and to sync within the `MIN_EPOCHS_FOR_DATA_COLUMN_SIDECARS_REQUESTS` window.
The request MUST be encoded as an SSZ-container.
The response MUST consist of zero or more `response_chunk`.
Each _successful_`response_chunk` MUST contain a single `DataColumnSidecar` payload.
Let `data_column_serve_range` be `[max(current_epoch - MIN_EPOCHS_FOR_DATA_COLUMN_SIDECARS_REQUESTS, EIP7594_FORK_EPOCH), current_epoch]`.
Clients MUST keep a record of data column sidecars seen on the epoch range `data_column_serve_range`
where `current_epoch` is defined by the current wall-clock time,
and clients MUST support serving requests of data columns on this range.
Peers that are unable to reply to data column sidecar requests within the
range `data_column_serve_range` SHOULD respond with error code `3: ResourceUnavailable`.
Such peers that are unable to successfully reply to this range of requests MAY get descored
or disconnected at any time.
*Note*: The above requirement implies that nodes that start from a recent weak subjectivity checkpoint
MUST backfill the local data columns database to at least the range `data_column_serve_range`
to be fully compliant with `DataColumnSidecarsByRange` requests.
*Note*: Although clients that bootstrap from a weak subjectivity checkpoint can begin
participating in the networking immediately, other peers MAY
disconnect and/or temporarily ban such an un-synced or semi-synced client.
Clients MUST respond with at least the data column sidecars of the first blob-carrying block that exists in the range, if they have it, and no more than `MAX_REQUEST_DATA_COLUMN_SIDECARS` sidecars.
Clients MUST include all data column sidecars of each block from which they include data column sidecars.
Slots that do not contain known data columns MUST be skipped, mimicking the behaviour
of the `BlocksByRange` request. Only response chunks with known data columns should
therefore be sent.
Clients MAY limit the number of data column sidecars in the response.
The response MUST contain no more than `count * NUMBER_OF_COLUMNS` data column sidecars.
Clients MUST respond with data columns sidecars from their view of the current fork choice
-- that is, data column sidecars as included by blocks from the single chain defined by the current head.
Of note, blocks from slots before the finalization MUST lead to the finalized block reported in the `Status` handshake.
Clients MUST respond with data column sidecars that are consistent from a single chain within the context of the request.
After the initial data column sidecar, clients MAY stop in the process of responding if their fork choice changes the view of the chain in the context of the request.
