47 lines
1.9 KiB
Markdown
47 lines
1.9 KiB
Markdown
# Data Availability Sampling -- Fork Choice
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**Notice**: This document is a work-in-progress for researchers and implementers.
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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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- [Introduction](#introduction)
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- [Dependency calculation](#dependency-calculation)
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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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## Introduction
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This document is the beacon chain fork choice spec for Data Availability Sampling. The only change that we add from phase 0 is that we add a concept of "data dependencies";
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a block is only eligible for consideration in the fork choice after a data availability test has been successfully completed for all dependencies.
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The "root" of a shard block for data dependency purposes is considered to be a `DataCommitment` object, which is a pair of a Kate commitment and a length.
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## Dependency calculation
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```python
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def get_new_dependencies(state: BeaconState) -> Set[DataCommitment]:
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return set(
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# Already confirmed during this epoch
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[c.commitment for c in state.current_epoch_pending_headers if c.confirmed] +
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# Already confirmed during previous epoch
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[c.commitment for c in state.previous_epoch_pending_headers if c.confirmed] +
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# Confirmed in the epoch before the previous
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[c for c in shard for shard in state.grandparent_epoch_confirmed_commitments if c != DataCommitment()]
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)
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```
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```python
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def get_all_dependencies(store: Store, block: BeaconBlock) -> Set[DataCommitment]:
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if compute_epoch_at_slot(block.slot) < SHARDING_FORK_EPOCH:
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return set()
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else:
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latest = get_new_dependencies(store.block_states[hash_tree_root(block)])
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older = get_all_dependencies(store, store.blocks[block.parent_root])
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return latest.union(older)
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```
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