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Gloas Partial Columns -- Networking

Note: This document is a work-in-progress for researchers and implementers.

Introduction

This document specifies the Gloas modifications to partial column dissemination via gossipsub's Partial Message Extension.

The specification of these changes continues in the same format as the network specifications of previous upgrades, and assumes them as pre-requisite. In particular, this document builds on the Fulu partial columns networking specification and the Gloas networking specification.

Preset

Type-specific SSZ bounds

[New in Gloas:EIP7688]

Name Value
MAX_PARTIAL_DATA_COLUMN_SIDECAR_SIZE Uint64(8585741) (= ~8 MiB)

Types

Modified CellsBitList

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# [Modified in Gloas:EIP7688]
class CellsBitList(ProgressiveBitList):
    """
    A bitfield over the cells of a column, one bit per blob.
    """

Containers

Modified PartialDataColumnSidecar

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class PartialDataColumnSidecar(Container):
    cells_present_bitmap: CellsBitList
    partial_column: DataColumn
    kzg_proofs: KZGProofs
    # [Modified in Gloas:EIP7732]
    # Removed `header`

Modified PartialDataColumnPartsMetadata

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class PartialDataColumnPartsMetadata(Container):
    # [Modified in Gloas:EIP7688]
    available: CellsBitList
    # [Modified in Gloas:EIP7688]
    requests: CellsBitList

Modified PartialDataColumnGroupID

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class PartialDataColumnGroupID(Container):
    beacon_block_root: Root
    # [New in Gloas:EIP7732]
    slot: Slot

The gossip domain: gossipsub

Blob subnets

Modified data_column_sidecar_{subnet_id} (partial messages)

Note: The KZG commitments needed to verify a partial sidecar are now carried by the bid at block.body.signed_execution_payload_bid.message.blob_kzg_commitments, where block is the BeaconBlock with root group_id.beacon_block_root. All header-related validations from Fulu are removed; their role is taken over by the bid commitments and the corresponding block validation.

Note: The optional check "for cells the receiver already has, the sidecar's cell and proof data are equal to the local copy" is not encoded below. The sender MUST always send valid cell and proof data; receivers MAY perform this equality check against their local copy as an additional safeguard.

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def validate_partial_data_column_sidecar_gossip(
    # [Modified in Gloas:EIP7732]
    # Removed `seen`
    store: Store,
    # [Modified in Gloas:EIP7732]
    # Removed `state`
    sidecar: PartialDataColumnSidecar,
    # [Modified in Gloas:EIP7732]
    # Removed `current_time_ms`
    group_id: PartialDataColumnGroupID,
    column_index: ColumnIndex,
) -> None:
    """
    Validate a PartialDataColumnSidecar for gossip propagation on a subnet.
    Raises GossipIgnore or GossipReject on validation failure.
    """
    num_cells_present = get_set_bit_count(sidecar.cells_present_bitmap)

    # [Modified in Gloas:EIP7732]
    # [REJECT] The message contains at least one cell
    if num_cells_present == 0:
        raise GossipReject("partial message is semantically empty")

    # [REJECT] The cell count equals the number of set bits in the bitmap
    if len(sidecar.partial_column) != num_cells_present:
        raise GossipReject("number of cells does not match number of set bits")

    # [REJECT] The proof count equals the number of set bits in the bitmap
    if len(sidecar.kzg_proofs) != num_cells_present:
        raise GossipReject("number of proofs does not match number of set bits")

    # [New in Gloas:EIP7732]
    # [IGNORE] The group ID's block has been seen (via gossip or non-gossip sources)
    # (MAY be queued until block is retrieved)
    # (SHOULD queue at least one sidecar per peer per subnet)
    if group_id.beacon_block_root not in store.blocks:
        raise GossipIgnore("group id's block has not been seen")

    # [New in Gloas:EIP7732]
    # [REJECT] The group ID's block passes validation
    if group_id.beacon_block_root not in store.block_states:
        raise GossipReject("group id's block failed validation")

    block = store.blocks[group_id.beacon_block_root]

    # [New in Gloas:EIP7732]
    # [REJECT] The group ID's slot matches the slot of the block
    if group_id.slot != block.slot:
        raise GossipReject("group id's slot does not match the block's slot")

    bid = block.body.signed_execution_payload_bid.message

    # [Modified in Gloas:EIP7732]
    # [REJECT] The cells present bitmap length equals the number of bid commitments
    if len(sidecar.cells_present_bitmap) != len(bid.blob_kzg_commitments):
        raise GossipReject("bitmap length does not match commitments length")

    # [Modified in Gloas:EIP7732]
    # [REJECT] The sidecar's cell and proof data passes KZG verification
    if not verify_partial_data_column_sidecar_kzg_proofs(
        sidecar, bid.blob_kzg_commitments, column_index
    ):
        raise GossipReject("invalid sidecar kzg proofs")