Peer das core

[nalepae]

Please read this PR commit by commit.

What type of PR is this?
Feature

What does this PR do? Why is it needed?
Implement https://github.com/ethereum/consensus-specs/blob/peer-das/specs/_features/eip7594/das-core.md

[nalepae]

Ideally, I think all subnets list should be converted at all levels into subnets maps.
As far as I know:

1. We want items in these lists not to have duplicates
2. We at some places look if an item is in the list (O(n))

==> These 2 conditions makes a set to be a good candidate to store those data. Moreover lookup will go from O(n) to O(1).

[nisdas]

Can you make i part of the for loop, separating out the way it is done is odd

[nalepae]

Fixed in 039f9eb.

[nisdas]

please remove computeSubscribedColumnSubnet if the function is unused

[nalepae]

Fixed in 676cc71.

[nisdas]

Suggested change

	func CustodyColumnSubnets(nodeId enode.ID, custodySubnetCount uint64) (map[uint64]bool, error) {
	func CustodyColumnSubnets(nodeId enode.ID) (map[uint64]bool, error) {

I do not think the custody count should be an argument, it is not dynamic but a value determined by the specification

[nalepae]

Actually the spec defines get_custody_columns with the custody count as an argument:

def get_custody_columns(node_id: NodeID, custody_subnet_count: uint64) -> Sequence[ColumnIndex]:
    assert custody_subnet_count <= DATA_COLUMN_SIDECAR_SUBNET_COUNT

    subnet_ids = []
    i = 0
    while len(subnet_ids) < custody_subnet_count:
        subnet_id = (
            bytes_to_uint64(hash(uint_to_bytes(uint64(node_id + i)))[0:8])
            % DATA_COLUMN_SIDECAR_SUBNET_COUNT
        )
        if subnet_id not in subnet_ids:
            subnet_ids.append(subnet_id)
        i += 1
    assert len(subnet_ids) == len(set(subnet_ids))

    columns_per_subnet = NUMBER_OF_COLUMNS // DATA_COLUMN_SIDECAR_SUBNET_COUNT
    return [
        ColumnIndex(DATA_COLUMN_SIDECAR_SUBNET_COUNT * i + subnet_id)
        for i in range(columns_per_subnet)
        for subnet_id in subnet_ids
    ]

The custody subnet count has an impact on the number of custody column subnet count.

it is not dynamic but a value determined by the specification

My understanding is the specification determines CUSTODY_REQUIREMENT (Minimum number of subnets an honest node custodies and serves samples from).

params.BeaconConfig().CustodyRequirement // in Prysm

CUSTODY_REQUIREMENT is a minimum custody subnet count, but it is possible for a node to custody more. (And in the extreme case, a "supernode" can custody all the subnets.)

In my opinion, both for spec compliance and possibility of custodying more than the minimum required, it's better to keep the custody count as an argument.