nimbus-eth2/beacon_chain/spec/eip7594_helpers.nim

# beacon_chain
# Copyright (c) 2018-2024 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.

{.push raises: [].}

# Uncategorized helper functions from the spec
import
  std/algorithm,
  results,
  eth/p2p/discoveryv5/[node],
  ./[helpers, digest],
  ./datatypes/[eip7594]

func sortedColumnIndices*(columnsPerSubnet: ColumnIndex,
                          subnetIds: HashSet[uint64]):
                          seq[ColumnIndex] =
  var res: seq[ColumnIndex] = @[]
  for i in 0'u64 ..< columnsPerSubnet:
    for subnetId in subnetIds:
      let index = DATA_COLUMN_SIDECAR_SUBNET_COUNT * i + subnetId
      res.add(ColumnIndex(index))
  res.sort
  res

func sortedColumnIndexList*(columnsPerSubnet: ColumnIndex,
                            subnetIds: HashSet[uint64]):
                            List[ColumnIndex, NUMBER_OF_COLUMNS] =
  var
    res: seq[ColumnIndex]
  for i in 0'u64 ..< columnsPerSubnet:
    for subnetId in subnetIds:
      let index = DATA_COLUMN_SIDECAR_SUBNET_COUNT * i + subnetId
      res.add(ColumnIndex(index))
  res.sort()
  List[ColumnIndex, NUMBER_OF_COLUMNS].init(res)

func get_custody_column_subnets*(node_id: NodeId,
                                 custody_subnet_count: uint64):
                                 HashSet[uint64] =

  # Decouples the custody subnet computation part from
  # `get_custody_columns`, in order to later use this subnet list
  # in order to maintain subscription to specific column subnets.

  var
    subnet_ids: HashSet[uint64]
    current_id = node_id

  while subnet_ids.lenu64 < custody_subnet_count:
    var
      hashed_bytes: array[8, byte]

    let
      current_id_bytes = current_id.toBytesLE()
      hashed_current_id = eth2digest(current_id_bytes)

    hashed_bytes[0..7] = hashed_current_id.data.toOpenArray(0,7)
    let subnet_id = bytes_to_uint64(hashed_bytes) mod
      DATA_COLUMN_SIDECAR_SUBNET_COUNT

    subnet_ids.incl(subnet_id)

    if current_id == UInt256.high.NodeId:
      # Overflow prevention
      current_id = NodeId(StUint[256].zero)
    current_id += NodeId(StUint[256].one)

  subnet_ids

# https://github.com/ethereum/consensus-specs/blob/v1.5.0-alpha.5/specs/_features/eip7594/das-core.md#get_custody_columns
func get_custody_columns*(node_id: NodeId,
                          custody_subnet_count: uint64):
                          seq[ColumnIndex] =
  let
    subnet_ids =
      get_custody_column_subnets(node_id, custody_subnet_count)
  const
    columns_per_subnet =
      NUMBER_OF_COLUMNS div DATA_COLUMN_SIDECAR_SUBNET_COUNT

  sortedColumnIndices(ColumnIndex(columns_per_subnet), subnet_ids)

func get_custody_column_list*(node_id: NodeId,
                              custody_subnet_count: uint64):
                              List[ColumnIndex, NUMBER_OF_COLUMNS] =

  # Not in spec in the exact format, but it is useful in sorting custody columns
  # before sending, data_column_sidecars_by_range requests
  let
    subnet_ids =
      get_custody_column_subnets(node_id, custody_subnet_count)
  const
    columns_per_subnet =
      NUMBER_OF_COLUMNS div DATA_COLUMN_SIDECAR_SUBNET_COUNT

  sortedColumnIndexList(ColumnIndex(columns_per_subnet), subnet_ids)