# EIP-7594 -- Networking

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

## Table of contents

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- [Modifications in EIP-7594](#modifications-in-eip-7594)
  - [Preset](#preset)
  - [Configuration](#configuration)
  - [Containers](#containers)
    - [`DataColumnIdentifier`](#datacolumnidentifier)
  - [Helpers](#helpers)
      - [`verify_data_column_sidecar_kzg_proofs`](#verify_data_column_sidecar_kzg_proofs)
      - [`verify_data_column_sidecar_inclusion_proof`](#verify_data_column_sidecar_inclusion_proof)
      - [`compute_subnet_for_data_column_sidecar`](#compute_subnet_for_data_column_sidecar)
  - [MetaData](#metadata)
  - [The gossip domain: gossipsub](#the-gossip-domain-gossipsub)
    - [Topics and messages](#topics-and-messages)
      - [Blob subnets](#blob-subnets)
        - [Deprecated `blob_sidecar_{subnet_id}`](#deprecated-blob_sidecar_subnet_id)
        - [`data_column_sidecar_{subnet_id}`](#data_column_sidecar_subnet_id)
  - [The Req/Resp domain](#the-reqresp-domain)
    - [Messages](#messages)
      - [DataColumnSidecarsByRoot v1](#datacolumnsidecarsbyroot-v1)
      - [DataColumnSidecarsByRange v1](#datacolumnsidecarsbyrange-v1)
      - [GetMetaData v3](#getmetadata-v3)
  - [The discovery domain: discv5](#the-discovery-domain-discv5)
    - [ENR structure](#enr-structure)
      - [Custody subnet count](#custody-subnet-count)

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## Modifications in EIP-7594

### Preset

| Name                                    | Value                                                                                     | Description                                                       |
|-----------------------------------------|-------------------------------------------------------------------------------------------|-------------------------------------------------------------------|
| `KZG_COMMITMENTS_INCLUSION_PROOF_DEPTH` | `uint64(floorlog2(get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments')))` (= 4) | <!-- predefined --> Merkle proof index for `blob_kzg_commitments` |

### Configuration

*[New in EIP7594]*

| Name                                           | Value                                          | Description                                                               |
|------------------------------------------------|------------------------------------------------|---------------------------------------------------------------------------|
| `MAX_REQUEST_DATA_COLUMN_SIDECARS`             | `MAX_REQUEST_BLOCKS_DENEB * NUMBER_OF_COLUMNS` | Maximum number of data column sidecars in a single request                |
| `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 |

### Containers

#### `DataColumnIdentifier`

```python
class DataColumnIdentifier(Container):
    block_root: Root
    index: ColumnIndex
```

### Helpers

##### `verify_data_column_sidecar_kzg_proofs`

```python
def verify_data_column_sidecar_kzg_proofs(sidecar: DataColumnSidecar) -> bool:
    """
    Verify if the proofs are correct.
    """
    assert sidecar.index < NUMBER_OF_COLUMNS
    assert len(sidecar.column) == len(sidecar.kzg_commitments) == len(sidecar.kzg_proofs)

    # The column index also represents the cell index
    cell_indices = [CellIndex(sidecar.index)] * len(sidecar.column)

    # Batch verify that the cells match the corresponding commitments and proofs
    return verify_cell_kzg_proof_batch(
        commitments_bytes=sidecar.kzg_commitments,
        cell_indices=cell_indices,
        cells=sidecar.column,
        proofs_bytes=sidecar.kzg_proofs,
    )
```

##### `verify_data_column_sidecar_inclusion_proof`

```python
def verify_data_column_sidecar_inclusion_proof(sidecar: DataColumnSidecar) -> bool:
    """
    Verify if the given KZG commitments included in the given beacon block.
    """
    gindex = get_subtree_index(get_generalized_index(BeaconBlockBody, 'blob_kzg_commitments'))
    return is_valid_merkle_branch(
        leaf=hash_tree_root(sidecar.kzg_commitments),
        branch=sidecar.kzg_commitments_inclusion_proof,
        depth=KZG_COMMITMENTS_INCLUSION_PROOF_DEPTH,
        index=gindex,
        root=sidecar.signed_block_header.message.body_root,
    )
```

##### `compute_subnet_for_data_column_sidecar`

```python
def compute_subnet_for_data_column_sidecar(column_index: ColumnIndex) -> SubnetID:
    return SubnetID(column_index % DATA_COLUMN_SIDECAR_SUBNET_COUNT)
```

### MetaData

The `MetaData` stored locally by clients is updated with an additional field to communicate the custody subnet count.

```
(
  seq_number: uint64
  attnets: Bitvector[ATTESTATION_SUBNET_COUNT]
  syncnets: Bitvector[SYNC_COMMITTEE_SUBNET_COUNT]
  custody_subnet_count: uint8 # csc
)
```

Where

- `seq_number`, `attnets`, and `syncnets` have the same meaning defined in the Altair document.
- `csc` represents the node's custody subnet count. Clients MAY reject ENRs with a value less than `CUSTODY_REQUIREMENT`.

### The gossip domain: gossipsub

Some gossip meshes are upgraded in the EIP-7594 fork to support upgraded types.

#### Topics and messages

##### Blob subnets

###### Deprecated `blob_sidecar_{subnet_id}`

`blob_sidecar_{subnet_id}` is deprecated.

###### `data_column_sidecar_{subnet_id}`

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)`.
- _[REJECT]_ The sidecar's column data is valid as verified by `verify_data_column_sidecar_kzg_proofs(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 Req/Resp domain

#### Messages

##### DataColumnSidecarsByRoot v1

**Protocol ID:** `/eth2/beacon_chain/req/data_column_sidecars_by_root/1/`

*[New in EIP7594]*

The `<context-bytes>` field is calculated as `context = compute_fork_digest(fork_version, genesis_validators_root)`:

[1]: # (eth2spec: skip)

| `fork_version`         | Chunk SSZ type              |
|------------------------|-----------------------------|
| `EIP7594_FORK_VERSION` | `eip7594.DataColumnSidecar` |

Request Content:

```
(
  List[DataColumnIdentifier, MAX_REQUEST_DATA_COLUMN_SIDECARS]
)
```

Response Content:

```
(
    List[DataColumnSidecar, MAX_REQUEST_DATA_COLUMN_SIDECARS]
)
```

Requests sidecars by block root and index.
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

##### DataColumnSidecarsByRange v1

**Protocol ID:** `/eth2/beacon_chain/req/data_column_sidecars_by_range/1/`

The `<context-bytes>` field is calculated as `context = compute_fork_digest(fork_version, genesis_validators_root)`:

[1]: # (eth2spec: skip)

| `fork_version`         | Chunk SSZ type              |
|------------------------|-----------------------------|
| `EIP7594_FORK_VERSION` | `eip7594.DataColumnSidecar` |

Request Content:
```
(
  start_slot: Slot
  count: uint64
  columns: List[ColumnIndex, NUMBER_OF_COLUMNS]
)
```

Response Content:
```
(
  List[DataColumnSidecar, MAX_REQUEST_DATA_COLUMN_SIDECARS]
)
```

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.

The following data column sidecars, where they exist, MUST be sent in `(slot, column_index)` order.

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.

##### GetMetaData v3

**Protocol ID:** `/eth2/beacon_chain/req/metadata/3/`

No Request Content.

Response Content:

```
(
  MetaData
)
```

Requests the MetaData of a peer, using the new `MetaData` definition given above that is extended from Altair. Other conditions for the `GetMetaData` protocol are unchanged from the Altair p2p networking document.

### The discovery domain: discv5

#### ENR structure

##### Custody subnet count

A new field is added to the ENR under the key `csc` to facilitate custody data column discovery.

| Key    | Value                               |
|--------|-------------------------------------|
| `csc`  | Custody subnet count, uint8 integer |