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Add ExecutionPayloadHeader to LC data
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While the light client sync protocol currently provides access to the
latest `BeaconBlockHeader`, obtaining the matching execution data needs
workarounds such as downloading the full block.

Having ready access to the EL state root simplifies use cases that need
a way to cross-check `eth_getProof` responses against LC data.

Access to `block_hash` unlocks scenarios where a CL light client drives
an EL without `engine_newPayload`. As of Altair, only the CL beacon
block root is available, but the EL block hash is needed for engine API.

Other fields in the `ExecutionPayloadHeader` such as `logs_bloom` may
allow light client applications to monitor blocks for local interest,
e.g. for transfers affecting a certain wallet. This enables to download
only the few relevant blocks instead of every single one.

A new `LightClientStore` is proposed into the Capella spec that may be
used to sync LC data that includes execution data. Existing pre-Capella
LC data will remain as is, but can be locally upgraded before feeding it
into the new `LightClientStore` so that light clients do not need to run
a potentially expensive fork transition at a specific time. This enables
the `LightClientStore` to be upgraded at a use case dependent timing at
any time before Capella hits. Smart contract and embedded deployments
benefit from reduced code size and do not need synchronization with the
beacon chain clock to perform the Capella fork.
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etan-status committed Dec 11, 2022
1 parent 9ab22b3 commit e6e08e8
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2 changes: 1 addition & 1 deletion Makefile
Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ GENERATOR_VENVS = $(patsubst $(GENERATOR_DIR)/%, $(GENERATOR_DIR)/%venv, $(GENER
MARKDOWN_FILES = $(wildcard $(SPEC_DIR)/phase0/*.md) \
$(wildcard $(SPEC_DIR)/altair/*.md) $(wildcard $(SPEC_DIR)/altair/**/*.md) \
$(wildcard $(SPEC_DIR)/bellatrix/*.md) \
$(wildcard $(SPEC_DIR)/capella/*.md) \
$(wildcard $(SPEC_DIR)/capella/*.md) $(wildcard $(SPEC_DIR)/capella/**/*.md) \
$(wildcard $(SPEC_DIR)/custody/*.md) \
$(wildcard $(SPEC_DIR)/das/*.md) \
$(wildcard $(SPEC_DIR)/sharding/*.md) \
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2 changes: 1 addition & 1 deletion README.md
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Expand Up @@ -24,7 +24,7 @@ Features are researched and developed in parallel, and then consolidated into se
### In-development Specifications
| Code Name or Topic | Specs | Notes |
| - | - | - |
| Capella (tentative) | <ul><li>Core</li><ul><li>[Beacon chain changes](specs/capella/beacon-chain.md)</li><li>[Capella fork](specs/capella/fork.md)</li></ul><li>Additions</li><ul><li>[Validator additions](specs/capella/validator.md)</li><li>[P2P networking](specs/capella/p2p-interface.md)</li></ul></ul> |
| Capella (tentative) | <ul><li>Core</li><ul><li>[Beacon chain changes](specs/capella/beacon-chain.md)</li><li>[Capella fork](specs/capella/fork.md)</li></ul><li>Additions</li><ul><li>[Light client sync protocol changes](specs/capella/sync-protocol.md) ([fork](specs/capella/light-client/fork.md), [full node](specs/capella/light-client/full-node.md), [networking](specs/altair/light-client/p2p-interface.md))</li><li>[Validator additions](specs/capella/validator.md)</li></ul></ul><ul><li>[Validator additions](specs/capella/validator.md)</li><li>[P2P networking](specs/capella/p2p-interface.md)</li></ul></ul> |
| EIP4844 (tentative) | <ul><li>Core</li><ul><li>[Beacon Chain changes](specs/eip4844/beacon-chain.md)</li><li>[EIP-4844 fork](specs/eip4844/fork.md)</li><li>[Polynomial commitments](specs/eip4844/polynomial-commitments.md)</li></ul><li>Additions</li><ul><li>[Honest validator guide changes](specs/eip4844/validator.md)</li><li>[P2P networking](specs/eip4844/p2p-interface.md)</li></ul></ul> |
| Sharding (outdated) | <ul><li>Core</li><ul><li>[Beacon Chain changes](specs/sharding/beacon-chain.md)</li></ul><li>Additions</li><ul><li>[P2P networking](specs/sharding/p2p-interface.md)</li></ul></ul> |
| Custody Game (outdated) | <ul><li>Core</li><ul><li>[Beacon Chain changes](specs/custody_game/beacon-chain.md)</li></ul><li>Additions</li><ul><li>[Honest validator guide changes](specs/custody_game/validator.md)</li></ul></ul> | Dependent on sharding |
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20 changes: 20 additions & 0 deletions setup.py
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Expand Up @@ -616,6 +616,21 @@ def imports(cls, preset_name: str):
'''


@classmethod
def sundry_functions(cls) -> str:
return super().sundry_functions() + '\n\n' + '''
def compute_merkle_proof_for_block_body(body: BeaconBlockBody,
index: GeneralizedIndex) -> Sequence[Bytes32]:
return build_proof(body.get_backing(), index)'''


@classmethod
def hardcoded_ssz_dep_constants(cls) -> Dict[str, str]:
constants = {
'EXECUTION_PAYLOAD_INDEX': 'GeneralizedIndex(25)',
}
return {**super().hardcoded_ssz_dep_constants(), **constants}

#
# EIP4844SpecBuilder
#
Expand Down Expand Up @@ -718,6 +733,7 @@ def format_protocol(protocol_name: str, protocol_def: ProtocolDefinition) -> str
if k in [
"ceillog2",
"floorlog2",
"compute_merkle_proof_for_block_body",
"compute_merkle_proof_for_state",
]:
del spec_object.functions[k]
Expand Down Expand Up @@ -1010,6 +1026,10 @@ def finalize_options(self):
"""
if self.spec_fork in (CAPELLA, EIP4844):
self.md_doc_paths += """
specs/capella/light-client/fork.md
specs/capella/light-client/full-node.md
specs/capella/light-client/p2p-interface.md
specs/capella/light-client/sync-protocol.md
specs/capella/beacon-chain.md
specs/capella/fork.md
specs/capella/fork-choice.md
Expand Down
93 changes: 93 additions & 0 deletions specs/capella/light-client/fork.md
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@@ -0,0 +1,93 @@
# Capella Light Client -- Fork Logic

## Table of contents

<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->

- [Introduction](#introduction)
- [Upgrading light client data](#upgrading-light-client-data)
- [Upgrading the store](#upgrading-the-store)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->

## Introduction

This document describes how to upgrade existing light client objects based on the [Altair specification](../../altair/light-client/sync-protocol.md) to Capella. This is necessary when processing pre-Capella data with a post-Capella `LightClientStore`. Note that the data being exchanged over the network protocols uses the original format.

### Upgrading light client data

A Capella `LightClientStore` can still process earlier light client data. In order to do so, that pre-Capella data needs to be locally upgraded to Capella before processing.

```python
def upgrade_lc_header_to_capella(pre: BeaconBlockHeader) -> LightClientHeader:
return LightClientHeader(
beacon=pre,
execution=ExecutionPayloadHeader(),
)
```

```python
def upgrade_lc_bootstrap_to_capella(pre: altair.LightClientBootstrap) -> LightClientBootstrap:
return LightClientBootstrap(
header=upgrade_lc_header_to_capella(pre.header),
current_sync_committee=pre.current_sync_committee,
current_sync_committee_branch=pre.current_sync_committee_branch,
)
```

```python
def upgrade_lc_update_to_capella(pre: altair.LightClientUpdate) -> LightClientUpdate:
return LightClientUpdate(
attested_header=upgrade_lc_header_to_capella(pre.attested_header),
next_sync_committee=pre.next_sync_committee,
next_sync_committee_branch=pre.next_sync_committee_branch,
finalized_header=upgrade_lc_header_to_capella(pre.finalized_header),
finality_branch=pre.finality_branch,
sync_aggregate=pre.sync_aggregate,
signature_slot=pre.signature_slot,
)
```

```python
def upgrade_lc_finality_update_to_capella(pre: altair.LightClientFinalityUpdate) -> LightClientFinalityUpdate:
return LightClientFinalityUpdate(
attested_header=upgrade_lc_header_to_capella(pre.attested_header),
finalized_header=upgrade_lc_header_to_capella(pre.finalized_header),
finality_branch=pre.finality_branch,
sync_aggregate=pre.sync_aggregate,
signature_slot=pre.signature_slot,
)
```

```python
def upgrade_lc_optimistic_update_to_capella(pre: altair.LightClientOptimisticUpdate) -> LightClientOptimisticUpdate:
return LightClientOptimisticUpdate(
attested_header=upgrade_lc_header_to_capella(pre.attested_header),
sync_aggregate=pre.sync_aggregate,
signature_slot=pre.signature_slot,
)
```

### Upgrading the store

Existing `LightClientStore` objects based on Altair MUST be upgraded to Capella before Capella based light client data can be processed. The `LightClientStore` upgrade MAY be performed before `CAPELLA_FORK_EPOCH`.

```python
def upgrade_lc_store_to_capella(pre: altair.LightClientStore) -> LightClientStore:
if pre.best_valid_update is None:
best_valid_update = None
else:
best_valid_update = upgrade_lc_update_to_capella(pre.best_valid_update)
return LightClientStore(
finalized_header=upgrade_lc_header_to_capella(pre.finalized_header),
current_sync_committee=pre.current_sync_committee,
next_sync_committee=pre.next_sync_committee,
best_valid_update=best_valid_update,
optimistic_header=upgrade_lc_header_to_capella(pre.optimistic_header),
previous_max_active_participants=pre.previous_max_active_participants,
current_max_active_participants=pre.current_max_active_participants,
)
```
72 changes: 72 additions & 0 deletions specs/capella/light-client/full-node.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,72 @@
# Capella Light Client -- Full Node

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

## Table of contents

<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->

- [Introduction](#introduction)
- [Helper functions](#helper-functions)
- [`compute_merkle_proof_for_block_body`](#compute_merkle_proof_for_block_body)
- [Modified `block_to_light_client_header`](#modified-block_to_light_client_header)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->

## Introduction

This upgrade adds information about the execution payload to light client data as part of the Capella upgrade.

## Helper functions

### `compute_merkle_proof_for_block_body`

```python
def compute_merkle_proof_for_block_body(body: BeaconBlockBody,
index: GeneralizedIndex) -> Sequence[Bytes32]:
...
```

### Modified `block_to_light_client_header`

```python
def block_to_light_client_header(block: SignedBeaconBlock) -> LightClientHeader:
if compute_epoch_at_slot(block.message.slot) >= CAPELLA_FORK_EPOCH:
payload = block.message.body.execution_payload
execution_header = ExecutionPayloadHeader(
parent_hash=payload.parent_hash,
fee_recipient=payload.fee_recipient,
state_root=payload.state_root,
receipts_root=payload.receipts_root,
logs_bloom=payload.logs_bloom,
prev_randao=payload.prev_randao,
block_number=payload.block_number,
gas_limit=payload.gas_limit,
gas_used=payload.gas_used,
timestamp=payload.timestamp,
extra_data=payload.extra_data,
base_fee_per_gas=payload.base_fee_per_gas,
block_hash=payload.block_hash,
transactions_root=hash_tree_root(payload.transactions),
withdrawals_root=hash_tree_root(payload.withdrawals),
)
execution_branch = compute_merkle_proof_for_block_body(block.message.body, EXECUTION_PAYLOAD_INDEX)
else:
execution_header = ExecutionPayloadHeader()
execution_branch = [Bytes32() for _ in range(floorlog2(EXECUTION_PAYLOAD_INDEX))]

return LightClientHeader(
beacon=BeaconBlockHeader(
slot=block.message.slot,
proposer_index=block.message.proposer_index,
parent_root=block.message.parent_root,
state_root=block.message.state_root,
body_root=hash_tree_root(block.message.body),
),
execution=execution_header,
execution_branch=execution_branch,
)
```
99 changes: 99 additions & 0 deletions specs/capella/light-client/p2p-interface.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,99 @@
# Capella Light Client -- Networking

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

## Table of contents

<!-- TOC -->
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->

- [Networking](#networking)
- [The gossip domain: gossipsub](#the-gossip-domain-gossipsub)
- [Topics and messages](#topics-and-messages)
- [Global topics](#global-topics)
- [`light_client_finality_update`](#light_client_finality_update)
- [`light_client_optimistic_update`](#light_client_optimistic_update)
- [The Req/Resp domain](#the-reqresp-domain)
- [Messages](#messages)
- [GetLightClientBootstrap](#getlightclientbootstrap)
- [LightClientUpdatesByRange](#lightclientupdatesbyrange)
- [GetLightClientFinalityUpdate](#getlightclientfinalityupdate)
- [GetLightClientOptimisticUpdate](#getlightclientoptimisticupdate)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->
<!-- /TOC -->

## Networking

The [Altair light client networking specification](../../altair/light-client/p2p-interface.md) is extended to exchange [Capella light client data](./sync-protocol.md).

### The gossip domain: gossipsub

#### Topics and messages

##### Global topics

###### `light_client_finality_update`

[0]: # (eth2spec: skip)

| `fork_version` | Message SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientFinalityUpdate` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientFinalityUpdate` |

###### `light_client_optimistic_update`

[0]: # (eth2spec: skip)

| `fork_version` | Message SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientOptimisticUpdate` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientOptimisticUpdate` |

### The Req/Resp domain

#### Messages

##### GetLightClientBootstrap

[0]: # (eth2spec: skip)

| `fork_version` | Response SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientBootstrap` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientBootstrap` |

##### LightClientUpdatesByRange

[0]: # (eth2spec: skip)

| `fork_version` | Response chunk SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientUpdate` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientUpdate` |

##### GetLightClientFinalityUpdate

[0]: # (eth2spec: skip)

| `fork_version` | Response SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientFinalityUpdate` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientFinalityUpdate` |

##### GetLightClientOptimisticUpdate

[0]: # (eth2spec: skip)

| `fork_version` | Response SSZ type |
| ------------------------------------------------------ | ------------------------------------- |
| `GENESIS_FORK_VERSION` | n/a |
| `ALTAIR_FORK_VERSION` through `BELLATRIX_FORK_VERSION` | `altair.LightClientOptimisticUpdate` |
| `CAPELLA_FORK_VERSION` and later | `capella.LightClientOptimisticUpdate` |
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