265 lines
11 KiB
Markdown
265 lines
11 KiB
Markdown
# EIP-4844 -- Networking
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This document contains the consensus-layer networking specification for EIP-4844.
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The specification of these changes continues in the same format as the network specifications of previous upgrades, and assumes them as pre-requisite.
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## Table of contents
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<!-- TOC -->
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Preset](#preset)
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- [Configuration](#configuration)
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- [Containers](#containers)
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- [`BlobsSidecar`](#blobssidecar)
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- [`SignedBlobsSidecar`](#signedblobssidecar)
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- [The gossip domain: gossipsub](#the-gossip-domain-gossipsub)
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- [Topics and messages](#topics-and-messages)
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- [Global topics](#global-topics)
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- [`beacon_block`](#beacon_block)
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- [`blobs_sidecar`](#blobs_sidecar)
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- [Transitioning the gossip](#transitioning-the-gossip)
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- [The Req/Resp domain](#the-reqresp-domain)
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- [Messages](#messages)
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- [BeaconBlocksByRange v2](#beaconblocksbyrange-v2)
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- [BeaconBlocksByRoot v2](#beaconblocksbyroot-v2)
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- [BlobsSidecarsByRange v1](#blobssidecarsbyrange-v1)
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- [Design decision rationale](#design-decision-rationale)
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- [Why are blobs relayed as a sidecar, separate from beacon blocks?](#why-are-blobs-relayed-as-a-sidecar-separate-from-beacon-blocks)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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<!-- /TOC -->
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## Preset
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| Name | Value |
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| - | - |
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| `LIMIT_BLOBS_PER_SIDECAR` | `uint64(2**4)` (= 16) |
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## Configuration
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| Name | Value | Description |
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|------------------------------------------|-------------------------------|---------------------------------------------------------------------|
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| `MAX_REQUEST_BLOBS_SIDECARS` | `2**10` (= 1024) | Maximum number of blobs sidecars in a single request |
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| `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS` | `2**13` (= 8192, ~1.2 months) | The minimum epoch range over which a node must serve blobs sidecars |
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## Containers
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### `BlobsSidecar`
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```python
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class BlobsSidecar(Container):
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beacon_block_root: Root
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beacon_block_slot: Slot
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shard: uint64 # [ Forward compatibility ]
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blobs: List[Blob, LIMIT_BLOBS_PER_SIDECAR]
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```
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### `SignedBlobsSidecar`
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```python
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class SignedBlobsSidecar(Container):
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message: BlobsSidecar
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signature: BLSSignature
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```
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## The gossip domain: gossipsub
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Some gossip meshes are upgraded in the fork of EIP4844 to support upgraded types.
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### Topics and messages
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Topics follow the same specification as in prior upgrades.
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All topics remain stable except the beacon block topic which is updated with the modified type.
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The specification around the creation, validation, and dissemination of messages has not changed from the Bellatrix document unless explicitly noted here.
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The derivation of the `message-id` remains stable.
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The new topics along with the type of the `data` field of a gossipsub message are given in this table:
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| Name | Message Type |
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| - | - |
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| `beacon_block` | `SignedBeaconBlock` (modified) |
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| `blobs_sidecar` | `SignedBlobsSidecar` (new) |
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Note that the `ForkDigestValue` path segment of the topic separates the old and the new `beacon_block` topics.
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#### Global topics
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EIP4844 changes the type of the global beacon block topic and introduces a new global topic for blobs-sidecars.
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##### `beacon_block`
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The *type* of the payload of this topic changes to the (modified) `SignedBeaconBlock` found in EIP4844.
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In addition to the gossip validations for this topic from prior specifications,
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the following validations MUST pass before forwarding the `signed_beacon_block` on the network.
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Alias `block = signed_beacon_block.message`, `execution_payload = block.body.execution_payload`.
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- _[REJECT]_ The KZG commitments of the blobs are all correctly encoded compressed BLS G1 Points.
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-- i.e. `all(bls.KeyValidate(commitment) for commitment in block.body.blob_kzgs)`
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- _[REJECT]_ The KZG commitments correspond to the versioned hashes in the transactions list.
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-- i.e. `verify_kzgs_against_transactions(block.body.execution_payload.transactions, block.body.blob_kzgs)`
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##### `blobs_sidecar`
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This topic is used to propagate data blobs included in any given beacon block.
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The following validations MUST pass before forwarding the `signed_blobs_sidecar` on the network;
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Alias `sidecar = signed_blobs_sidecar.message`.
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- _[IGNORE]_ the `sidecar.beacon_block_slot` is for the current slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) -- i.e. `blobs_sidecar.beacon_block_slot == current_slot`.
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- _[REJECT]_ the `sidecar.blobs` are all well formatted, i.e. the `BLSFieldElement` in valid range (`x < BLS_MODULUS`).
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- _[REJECT]_ the beacon proposer signature, `signed_blobs_sidecar.signature`, is valid -- i.e.
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```python
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domain = get_domain(state, DOMAIN_BLOBS_SIDECAR, blobs_sidecar.beacon_block_slot / SLOTS_PER_EPOCH)
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signing_root = compute_signing_root(blobs_sidecar, domain)
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assert bls.Verify(proposer_pubkey, signing_root, signed_blob_header.signature)
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```
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where `proposer_pubkey` is the pubkey of the beacon block proposer of `blobs_sidecar.beacon_block_slot`
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- _[IGNORE]_ The sidecar is the first sidecar with valid signature received for the `(proposer_index, sidecar.beacon_block_root)` combination,
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where `proposer_index` is the validator index of the beacon block proposer of `blobs_sidecar.beacon_block_slot`
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Note that a sidecar may be propagated before or after the corresponding beacon block.
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Once both sidecar and beacon block are received, `verify_blobs_sidecar` can unlock the data-availability fork-choice dependency.
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### Transitioning the gossip
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See gossip transition details found in the [Altair document](../altair/p2p-interface.md#transitioning-the-gossip) for
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details on how to handle transitioning gossip topics for Bellatrix.
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## The Req/Resp domain
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### Messages
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#### BeaconBlocksByRange v2
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**Protocol ID:** `/eth2/beacon_chain/req/beacon_blocks_by_range/2/`
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The EIP-4844 fork-digest is introduced to the `context` enum to specify EIP-4844 beacon block type.
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Per `context = compute_fork_digest(fork_version, genesis_validators_root)`:
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[0]: # (eth2spec: skip)
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| `fork_version` | Chunk SSZ type |
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|--------------------------|-------------------------------|
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| `GENESIS_FORK_VERSION` | `phase0.SignedBeaconBlock` |
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| `ALTAIR_FORK_VERSION` | `altair.SignedBeaconBlock` |
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| `BELLATRIX_FORK_VERSION` | `bellatrix.SignedBeaconBlock` |
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| `EIP4844_FORK_VERSION` | `eip4844.SignedBeaconBlock` |
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#### BeaconBlocksByRoot v2
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**Protocol ID:** `/eth2/beacon_chain/req/beacon_blocks_by_root/2/`
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The EIP-4844 fork-digest is introduced to the `context` enum to specify EIP-4844 beacon block type.
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Per `context = compute_fork_digest(fork_version, genesis_validators_root)`:
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[1]: # (eth2spec: skip)
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| `fork_version` | Chunk SSZ type |
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| ------------------------ | -------------------------- |
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| `GENESIS_FORK_VERSION` | `phase0.SignedBeaconBlock` |
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| `ALTAIR_FORK_VERSION` | `altair.SignedBeaconBlock` |
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| `BELLATRIX_FORK_VERSION` | `bellatrix.SignedBeaconBlock` |
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| `EIP4844_FORK_VERSION` | `eip4844.SignedBeaconBlock` |
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#### BlobsSidecarsByRange v1
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**Protocol ID:** `/eth2/beacon_chain/req/blobs_sidecars_by_range/1/`
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Request Content:
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```
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(
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start_slot: Slot
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count: uint64
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shard: uint64
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)
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```
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Response Content:
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```
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(
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List[BlobsSidecar, MAX_REQUEST_BLOBS_SIDECARS]
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)
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```
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Requests blobs sidecars in the slot range `[start_slot, start_slot + count)`,
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leading up to the current head block as selected by fork choice.
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The request and response format is forward-compatible with sharded sidecar sync, but MUST enforce `shard == 0` for now.
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The response is unsigned, i.e. `BlobsSidecarsByRange`, as the signature of the beacon block proposer
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may not be available beyond the initial distribution via gossip.
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Before consuming the next response chunk, the response reader SHOULD verify the blobs sidecar is well-formatted and
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correct w.r.t. the expected KZG commitments through `verify_blobs_sidecar`.
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`BlobsSidecarsByRange` is primarily used to sync blobs that may have been missed on gossip.
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The request MUST be encoded as an SSZ-container.
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The response MUST consist of zero or more `response_chunk`.
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Each _successful_ `response_chunk` MUST contain a single `SignedBlobsSidecar` payload.
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Clients MUST keep a record of signed blobs sidecars seen on the epoch range
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`[max(GENESIS_EPOCH, current_epoch - MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS), current_epoch]`
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where `current_epoch` is defined by the current wall-clock time,
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and clients MUST support serving requests of blocks on this range.
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Peers that are unable to reply to block requests within the `MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS`
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epoch range SHOULD respond with error code `3: ResourceUnavailable`.
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Such peers that are unable to successfully reply to this range of requests MAY get descored
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or disconnected at any time.
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*Note*: The above requirement implies that nodes that start from a recent weak subjectivity checkpoint
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MUST backfill the local blobs database to at least epoch `current_epoch - MIN_EPOCHS_FOR_BLOBS_SIDECARS_REQUESTS`
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to be fully compliant with `BlobsSidecarsByRange` requests. To safely perform such a
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backfill of blocks to the recent state, the node MUST validate both (1) the
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proposer signatures and (2) that the blocks form a valid chain up to the most
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recent block referenced in the weak subjectivity state.
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*Note*: Although clients that bootstrap from a weak subjectivity checkpoint can begin
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participating in the networking immediately, other peers MAY
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disconnect and/or temporarily ban such an un-synced or semi-synced client.
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Clients MUST respond with at least the first blobs sidecar that exists in the range, if they have it,
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and no more than `MAX_REQUEST_BLOBS_SIDECARS` blocks.
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The following blobs sidecars, where they exist, MUST be sent in consecutive order.
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Clients MAY limit the number of blobs sidecars in the response.
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The response MUST contain no more than `count` blobs sidecars.
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Clients MUST respond with blobs sidecars from their view of the current fork choice
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-- that is, blobs sidecars as included by blocks from the single chain defined by the current head.
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Of note, blocks from slots before the finalization MUST lead to the finalized block reported in the `Status` handshake.
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Clients MUST respond with blobs sidecars that are consistent from a single chain within the context of the request.
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After the initial blobs sidecar, clients MAY stop in the process of responding
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if their fork choice changes the view of the chain in the context of the request.
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# Design decision rationale
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## Why are blobs relayed as a sidecar, separate from beacon blocks?
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This "sidecar" design provides forward compatibility for further data increases by black-boxing `is_data_available()`:
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with full sharding `is_data_available()` can be replaced by data-availability-sampling (DAS)
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thus avoiding all blobs being downloaded by all beacon nodes on the network.
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Such sharding design may introduce an updated `BlobsSidecar` to identify the shard,
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but does not affect the `BeaconBlock` structure.
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