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Specify the number of sidecar subnets #3346

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May 18, 2023
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Specify the number of sidecar subnets #3346

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2f218f8
Specify the number of sidecar subnets
ppopth May 5, 2023
08a1326
Use SubnetID instead of uint64
ppopth May 9, 2023
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8 changes: 4 additions & 4 deletions specs/deneb/p2p-interface.md
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ The specification of these changes continues in the same format as the network s
- [Topics and messages](#topics-and-messages)
- [Global topics](#global-topics)
- [`beacon_block`](#beacon_block)
- [`blob_sidecar_{index}`](#blob_sidecar_index)
- [`blob_sidecar_{subnet_id}`](#blob_sidecar_subnet_id)
- [Transitioning the gossip](#transitioning-the-gossip)
- [The Req/Resp domain](#the-reqresp-domain)
- [Messages](#messages)
Expand Down Expand Up @@ -107,7 +107,7 @@ The new topics along with the type of the `data` field of a gossipsub message ar

| Name | Message Type |
| - | - |
| `blob_sidecar_{index}` | `SignedBlobSidecar` (new) |
| `blob_sidecar_{subnet_id}` | `SignedBlobSidecar` (new) |

##### Global topics

Expand All @@ -117,13 +117,13 @@ Deneb introduces new global topics for blob sidecars.

The *type* of the payload of this topic changes to the (modified) `SignedBeaconBlock` found in deneb.

###### `blob_sidecar_{index}`
###### `blob_sidecar_{subnet_id}`

This topic is used to propagate signed blob sidecars, one for each sidecar index. The number of indices is defined by `MAX_BLOBS_PER_BLOCK`.

The following validations MUST pass before forwarding the `signed_blob_sidecar` on the network, assuming the alias `sidecar = signed_blob_sidecar.message`:

- _[REJECT]_ The sidecar is for the correct topic -- i.e. `sidecar.index` matches the topic `{index}`.
- _[REJECT]_ The sidecar is for the correct subnet -- i.e. `compute_subnet_for_blob_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 `sidecar.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 `sidecar.slot > compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)`
- _[IGNORE]_ The sidecar's block's parent (defined by `sidecar.block_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).
Expand Down
21 changes: 20 additions & 1 deletion specs/deneb/validator.md
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Expand Up @@ -10,6 +10,8 @@

- [Introduction](#introduction)
- [Prerequisites](#prerequisites)
- [Constants](#constants)
- [Misc](#misc)
- [Helpers](#helpers)
- [`BlobsBundle`](#blobsbundle)
- [Modified `GetPayloadResponse`](#modified-getpayloadresponse)
Expand Down Expand Up @@ -38,6 +40,14 @@ All behaviors and definitions defined in this document, and documents it extends
All terminology, constants, functions, and protocol mechanics defined in the updated [Beacon Chain doc of Deneb](./beacon-chain.md) are requisite for this document and used throughout.
Please see related Beacon Chain doc before continuing and use them as a reference throughout.

## Constants

### Misc

| Name | Value | Unit |
| - | - | :-: |
| `BLOB_SIDECAR_SUBNET_COUNT` | `4` | The number of blob sidecar subnets used in the gossipsub protocol. |

## Helpers

### `BlobsBundle`
Expand Down Expand Up @@ -136,7 +146,7 @@ def get_blob_sidecars(block: BeaconBlock,

```

Then for each sidecar, `signed_sidecar = SignedBlobSidecar(message=sidecar, signature=signature)` is constructed and published to the `blob_sidecar_{index}` topics according to its index.
Then for each sidecar, `signed_sidecar = SignedBlobSidecar(message=sidecar, signature=signature)` is constructed and published to the associated sidecar topic, the `blob_sidecar_{subnet_id}` pubsub topic.

`signature` is obtained from:

Expand All @@ -149,6 +159,15 @@ def get_blob_sidecar_signature(state: BeaconState,
return bls.Sign(privkey, signing_root)
```

The `subnet_id` for the `signed_sidecar` is calculated with:
- Let `blob_index = signed_sidecar.message.index`.
- Let `subnet_id = compute_subnet_for_blob_sidecar(blob_index)`.

```python
def compute_subnet_for_blob_sidecar(blob_index: BlobIndex) -> SubnetID:
return SubnetID(blob_index % BLOB_SIDECAR_SUBNET_COUNT)
```

After publishing the peers on the network may request the sidecar through sync-requests, or a local user may be interested.

The validator MUST hold on to sidecars for `MIN_EPOCHS_FOR_BLOB_SIDECARS_REQUESTS` epochs and serve when capable,
Expand Down