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lighthouse/consensus/proto_array/src/proto_array.rs
realbigsean cae40731a2 Strict count unrealized (#3522) 
## Issue Addressed

Add a flag that can increase count unrealized strictness, defaults to false

## Proposed Changes

Please list or describe the changes introduced by this PR.

## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.


Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: sean <seananderson33@gmail.com>
2022-09-05 04:50:47 +00:00

1057 lines
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Rust
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use crate::error::InvalidBestNodeInfo;
use crate::{error::Error, Block, ExecutionStatus};
use serde_derive::{Deserialize, Serialize};
use ssz::four_byte_option_impl;
use ssz::Encode;
use ssz_derive::{Decode, Encode};
use std::collections::{HashMap, HashSet};
use types::{
AttestationShufflingId, ChainSpec, Checkpoint, Epoch, EthSpec, ExecutionBlockHash, Hash256,
Slot,
};
// Define a "legacy" implementation of `Option<usize>` which uses four bytes for encoding the union
// selector.
four_byte_option_impl!(four_byte_option_usize, usize);
four_byte_option_impl!(four_byte_option_checkpoint, Checkpoint);
/// Defines an operation which may invalidate the `execution_status` of some nodes.
#[derive(Clone, Debug)]
pub enum InvalidationOperation {
/// Invalidate only `block_root` and it's descendants. Don't invalidate any ancestors.
InvalidateOne { block_root: Hash256 },
/// Invalidate blocks between `head_block_root` and `latest_valid_ancestor`.
///
/// If the `latest_valid_ancestor` is known to fork choice, invalidate all blocks between
/// `head_block_root` and `latest_valid_ancestor`. The `head_block_root` will be invalidated,
/// whilst the `latest_valid_ancestor` will not.
///
/// If `latest_valid_ancestor` is *not* known to fork choice, only invalidate the
/// `head_block_root` if `always_invalidate_head == true`.
InvalidateMany {
head_block_root: Hash256,
always_invalidate_head: bool,
latest_valid_ancestor: ExecutionBlockHash,
},
}
impl InvalidationOperation {
pub fn block_root(&self) -> Hash256 {
match self {
InvalidationOperation::InvalidateOne { block_root } => *block_root,
InvalidationOperation::InvalidateMany {
head_block_root, ..
} => *head_block_root,
}
}
pub fn latest_valid_ancestor(&self) -> Option<ExecutionBlockHash> {
match self {
InvalidationOperation::InvalidateOne { .. } => None,
InvalidationOperation::InvalidateMany {
latest_valid_ancestor,
..
} => Some(*latest_valid_ancestor),
}
}
pub fn invalidate_block_root(&self) -> bool {
match self {
InvalidationOperation::InvalidateOne { .. } => true,
InvalidationOperation::InvalidateMany {
always_invalidate_head,
..
} => *always_invalidate_head,
}
}
}
#[derive(Clone, PartialEq, Debug, Encode, Decode, Serialize, Deserialize)]
pub struct ProtoNode {
/// The `slot` is not necessary for `ProtoArray`, it just exists so external components can
/// easily query the block slot. This is useful for upstream fork choice logic.
pub slot: Slot,
/// The `state_root` is not necessary for `ProtoArray` either, it also just exists for upstream
/// components (namely attestation verification).
pub state_root: Hash256,
/// The root that would be used for the `attestation.data.target.root` if a LMD vote was cast
/// for this block.
///
/// The `target_root` is not necessary for `ProtoArray` either, it also just exists for upstream
/// components (namely fork choice attestation verification).
pub target_root: Hash256,
pub current_epoch_shuffling_id: AttestationShufflingId,
pub next_epoch_shuffling_id: AttestationShufflingId,
pub root: Hash256,
#[ssz(with = "four_byte_option_usize")]
pub parent: Option<usize>,
#[ssz(with = "four_byte_option_checkpoint")]
pub justified_checkpoint: Option<Checkpoint>,
#[ssz(with = "four_byte_option_checkpoint")]
pub finalized_checkpoint: Option<Checkpoint>,
pub weight: u64,
#[ssz(with = "four_byte_option_usize")]
pub best_child: Option<usize>,
#[ssz(with = "four_byte_option_usize")]
pub best_descendant: Option<usize>,
/// Indicates if an execution node has marked this block as valid. Also contains the execution
/// block hash.
pub execution_status: ExecutionStatus,
#[ssz(with = "four_byte_option_checkpoint")]
pub unrealized_justified_checkpoint: Option<Checkpoint>,
#[ssz(with = "four_byte_option_checkpoint")]
pub unrealized_finalized_checkpoint: Option<Checkpoint>,
}
#[derive(PartialEq, Debug, Encode, Decode, Serialize, Deserialize, Copy, Clone)]
pub struct ProposerBoost {
pub root: Hash256,
pub score: u64,
}
impl Default for ProposerBoost {
fn default() -> Self {
Self {
root: Hash256::zero(),
score: 0,
}
}
}
/// Indicate whether we should strictly count unrealized justification/finalization votes.
#[derive(Default, PartialEq, Eq, Debug, Serialize, Deserialize, Copy, Clone)]
pub enum CountUnrealizedFull {
True,
#[default]
False,
}
impl From<bool> for CountUnrealizedFull {
fn from(b: bool) -> Self {
if b {
CountUnrealizedFull::True
} else {
CountUnrealizedFull::False
}
}
}
#[derive(PartialEq, Debug, Serialize, Deserialize, Clone)]
pub struct ProtoArray {
/// Do not attempt to prune the tree unless it has at least this many nodes. Small prunes
/// simply waste time.
pub prune_threshold: usize,
pub justified_checkpoint: Checkpoint,
pub finalized_checkpoint: Checkpoint,
pub nodes: Vec<ProtoNode>,
pub indices: HashMap<Hash256, usize>,
pub previous_proposer_boost: ProposerBoost,
pub count_unrealized_full: CountUnrealizedFull,
}
impl ProtoArray {
/// Iterate backwards through the array, touching all nodes and their parents and potentially
/// the best-child of each parent.
///
/// The structure of the `self.nodes` array ensures that the child of each node is always
/// touched before its parent.
///
/// For each node, the following is done:
///
/// - Update the node's weight with the corresponding delta.
/// - Back-propagate each node's delta to its parents delta.
/// - Compare the current node with the parents best-child, updating it if the current node
/// should become the best child.
/// - If required, update the parents best-descendant with the current node or its best-descendant.
#[allow(clippy::too_many_arguments)]
pub fn apply_score_changes<E: EthSpec>(
&mut self,
mut deltas: Vec<i64>,
justified_checkpoint: Checkpoint,
finalized_checkpoint: Checkpoint,
new_balances: &[u64],
proposer_boost_root: Hash256,
current_slot: Slot,
spec: &ChainSpec,
) -> Result<(), Error> {
if deltas.len() != self.indices.len() {
return Err(Error::InvalidDeltaLen {
deltas: deltas.len(),
indices: self.indices.len(),
});
}
if justified_checkpoint != self.justified_checkpoint
|| finalized_checkpoint != self.finalized_checkpoint
{
self.justified_checkpoint = justified_checkpoint;
self.finalized_checkpoint = finalized_checkpoint;
}
// Default the proposer boost score to zero.
let mut proposer_score = 0;
// Iterate backwards through all indices in `self.nodes`.
for node_index in (0..self.nodes.len()).rev() {
let node = self
.nodes
.get_mut(node_index)
.ok_or(Error::InvalidNodeIndex(node_index))?;
// There is no need to adjust the balances or manage parent of the zero hash since it
// is an alias to the genesis block. The weight applied to the genesis block is
// irrelevant as we _always_ choose it and it's impossible for it to have a parent.
if node.root == Hash256::zero() {
continue;
}
let execution_status_is_invalid = node.execution_status.is_invalid();
let mut node_delta = if execution_status_is_invalid {
// If the node has an invalid execution payload, reduce its weight to zero.
0_i64
.checked_sub(node.weight as i64)
.ok_or(Error::InvalidExecutionDeltaOverflow(node_index))?
} else {
deltas
.get(node_index)
.copied()
.ok_or(Error::InvalidNodeDelta(node_index))?
};
// If we find the node for which the proposer boost was previously applied, decrease
// the delta by the previous score amount.
if self.previous_proposer_boost.root != Hash256::zero()
&& self.previous_proposer_boost.root == node.root
// Invalid nodes will always have a weight of zero so there's no need to subtract
// the proposer boost delta.
&& !execution_status_is_invalid
{
node_delta = node_delta
.checked_sub(self.previous_proposer_boost.score as i64)
.ok_or(Error::DeltaOverflow(node_index))?;
}
// If we find the node matching the current proposer boost root, increase
// the delta by the new score amount (unless the block has an invalid execution status).
//
// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/fork-choice.md#get_latest_attesting_balance
if let Some(proposer_score_boost) = spec.proposer_score_boost {
if proposer_boost_root != Hash256::zero()
&& proposer_boost_root == node.root
// Invalid nodes (or their ancestors) should not receive a proposer boost.
&& !execution_status_is_invalid
{
proposer_score =
calculate_proposer_boost::<E>(new_balances, proposer_score_boost)
.ok_or(Error::ProposerBoostOverflow(node_index))?;
node_delta = node_delta
.checked_add(proposer_score as i64)
.ok_or(Error::DeltaOverflow(node_index))?;
}
}
// Apply the delta to the node.
if execution_status_is_invalid {
// Invalid nodes always have a weight of 0.
node.weight = 0
} else if node_delta < 0 {
// Note: I am conflicted about whether to use `saturating_sub` or `checked_sub`
// here.
//
// I can't think of any valid reason why `node_delta.abs()` should be greater than
// `node.weight`, so I have chosen `checked_sub` to try and fail-fast if there is
// some error.
//
// However, I am not fully convinced that some valid case for `saturating_sub` does
// not exist.
node.weight = node
.weight
.checked_sub(node_delta.unsigned_abs())
.ok_or(Error::DeltaOverflow(node_index))?;
} else {
node.weight = node
.weight
.checked_add(node_delta as u64)
.ok_or(Error::DeltaOverflow(node_index))?;
}
// Update the parent delta (if any).
if let Some(parent_index) = node.parent {
let parent_delta = deltas
.get_mut(parent_index)
.ok_or(Error::InvalidParentDelta(parent_index))?;
// Back-propagate the nodes delta to its parent.
*parent_delta += node_delta;
}
}
// After applying all deltas, update the `previous_proposer_boost`.
self.previous_proposer_boost = ProposerBoost {
root: proposer_boost_root,
score: proposer_score,
};
// A second time, iterate backwards through all indices in `self.nodes`.
//
// We _must_ perform these functions separate from the weight-updating loop above to ensure
// that we have a fully coherent set of weights before updating parent
// best-child/descendant.
for node_index in (0..self.nodes.len()).rev() {
let node = self
.nodes
.get_mut(node_index)
.ok_or(Error::InvalidNodeIndex(node_index))?;
// If the node has a parent, try to update its best-child and best-descendant.
if let Some(parent_index) = node.parent {
self.maybe_update_best_child_and_descendant::<E>(
parent_index,
node_index,
current_slot,
)?;
}
}
Ok(())
}
/// Register a block with the fork choice.
///
/// It is only sane to supply a `None` parent for the genesis block.
pub fn on_block<E: EthSpec>(&mut self, block: Block, current_slot: Slot) -> Result<(), Error> {
// If the block is already known, simply ignore it.
if self.indices.contains_key(&block.root) {
return Ok(());
}
let node_index = self.nodes.len();
let node = ProtoNode {
slot: block.slot,
root: block.root,
target_root: block.target_root,
current_epoch_shuffling_id: block.current_epoch_shuffling_id,
next_epoch_shuffling_id: block.next_epoch_shuffling_id,
state_root: block.state_root,
parent: block
.parent_root
.and_then(|parent| self.indices.get(&parent).copied()),
justified_checkpoint: Some(block.justified_checkpoint),
finalized_checkpoint: Some(block.finalized_checkpoint),
weight: 0,
best_child: None,
best_descendant: None,
execution_status: block.execution_status,
unrealized_justified_checkpoint: block.unrealized_justified_checkpoint,
unrealized_finalized_checkpoint: block.unrealized_finalized_checkpoint,
};
// If the parent has an invalid execution status, return an error before adding the block to
// `self`.
if let Some(parent_index) = node.parent {
let parent = self
.nodes
.get(parent_index)
.ok_or(Error::InvalidNodeIndex(parent_index))?;
if parent.execution_status.is_invalid() {
return Err(Error::ParentExecutionStatusIsInvalid {
block_root: block.root,
parent_root: parent.root,
});
}
}
self.indices.insert(node.root, node_index);
self.nodes.push(node.clone());
if let Some(parent_index) = node.parent {
self.maybe_update_best_child_and_descendant::<E>(
parent_index,
node_index,
current_slot,
)?;
if matches!(block.execution_status, ExecutionStatus::Valid(_)) {
self.propagate_execution_payload_validation_by_index(parent_index)?;
}
}
Ok(())
}
/// Updates the `block_root` and all ancestors to have validated execution payloads.
///
/// Returns an error if:
///
/// - The `block-root` is unknown.
/// - Any of the to-be-validated payloads are already invalid.
pub fn propagate_execution_payload_validation(
&mut self,
block_root: Hash256,
) -> Result<(), Error> {
let index = *self
.indices
.get(&block_root)
.ok_or(Error::NodeUnknown(block_root))?;
self.propagate_execution_payload_validation_by_index(index)
}
/// Updates the `verified_node_index` and all ancestors to have validated execution payloads.
///
/// Returns an error if:
///
/// - The `verified_node_index` is unknown.
/// - Any of the to-be-validated payloads are already invalid.
fn propagate_execution_payload_validation_by_index(
&mut self,
verified_node_index: usize,
) -> Result<(), Error> {
let mut index = verified_node_index;
loop {
let node = self
.nodes
.get_mut(index)
.ok_or(Error::InvalidNodeIndex(index))?;
let parent_index = match node.execution_status {
// We have reached a node that we already know is valid. No need to iterate further
// since we assume an ancestors have already been set to valid.
ExecutionStatus::Valid(_) => return Ok(()),
// We have reached an irrelevant node, this node is prior to a terminal execution
// block. There's no need to iterate further, it's impossible for this block to have
// any relevant ancestors.
ExecutionStatus::Irrelevant(_) => return Ok(()),
// The block has an unknown status, set it to valid since any ancestor of a valid
// payload can be considered valid.
ExecutionStatus::Optimistic(payload_block_hash) => {
node.execution_status = ExecutionStatus::Valid(payload_block_hash);
if let Some(parent_index) = node.parent {
parent_index
} else {
// We have reached the root block, iteration complete.
return Ok(());
}
}
// An ancestor of the valid payload was invalid. This is a serious error which
// indicates a consensus failure in the execution node. This is unrecoverable.
ExecutionStatus::Invalid(ancestor_payload_block_hash) => {
return Err(Error::InvalidAncestorOfValidPayload {
ancestor_block_root: node.root,
ancestor_payload_block_hash,
})
}
};
index = parent_index;
}
}
/// Invalidate zero or more blocks, as specified by the `InvalidationOperation`.
///
/// See the documentation of `InvalidationOperation` for usage.
pub fn propagate_execution_payload_invalidation(
&mut self,
op: &InvalidationOperation,
) -> Result<(), Error> {
let mut invalidated_indices: HashSet<usize> = <_>::default();
let head_block_root = op.block_root();
/*
* Step 1:
*
* Find the `head_block_root` and maybe iterate backwards and invalidate ancestors. Record
* all invalidated block indices in `invalidated_indices`.
*/
let mut index = *self
.indices
.get(&head_block_root)
.ok_or(Error::NodeUnknown(head_block_root))?;
// Try to map the ancestor payload *hash* to an ancestor beacon block *root*.
let latest_valid_ancestor_root = op
.latest_valid_ancestor()
.and_then(|hash| self.execution_block_hash_to_beacon_block_root(&hash));
// Set to `true` if both conditions are satisfied:
//
// 1. The `head_block_root` is a descendant of `latest_valid_ancestor_hash`
// 2. The `latest_valid_ancestor_hash` is equal to or a descendant of the finalized block.
let latest_valid_ancestor_is_descendant =
latest_valid_ancestor_root.map_or(false, |ancestor_root| {
self.is_descendant(ancestor_root, head_block_root)
&& self.is_descendant(self.finalized_checkpoint.root, ancestor_root)
});
// Collect all *ancestors* which were declared invalid since they reside between the
// `head_block_root` and the `latest_valid_ancestor_root`.
loop {
let node = self
.nodes
.get_mut(index)
.ok_or(Error::InvalidNodeIndex(index))?;
match node.execution_status {
ExecutionStatus::Valid(hash)
| ExecutionStatus::Invalid(hash)
| ExecutionStatus::Optimistic(hash) => {
// If we're no longer processing the `head_block_root` and the last valid
// ancestor is unknown, exit this loop and proceed to invalidate and
// descendants of `head_block_root`/`latest_valid_ancestor_root`.
//
// In effect, this means that if an unknown hash (junk or pre-finalization) is
// supplied, don't validate any ancestors. The alternative is to invalidate
// *all* ancestors, which would likely involve shutting down the client due to
// an invalid justified checkpoint.
if !latest_valid_ancestor_is_descendant && node.root != head_block_root {
break;
} else if op.latest_valid_ancestor() == Some(hash) {
// If the `best_child` or `best_descendant` of the latest valid hash was
// invalidated, set those fields to `None`.
//
// In theory, an invalid `best_child` necessarily infers an invalid
// `best_descendant`. However, we check each variable independently to
// defend against errors which might result in an invalid block being set as
// head.
if node
.best_child
.map_or(false, |i| invalidated_indices.contains(&i))
{
node.best_child = None
}
if node
.best_descendant
.map_or(false, |i| invalidated_indices.contains(&i))
{
node.best_descendant = None
}
break;
}
}
ExecutionStatus::Irrelevant(_) => break,
}
// Only invalidate the head block if either:
//
// - The head block was specifically indicated to be invalidated.
// - The latest valid hash is a known ancestor.
if node.root != head_block_root
|| op.invalidate_block_root()
|| latest_valid_ancestor_is_descendant
{
match &node.execution_status {
// It's illegal for an execution client to declare that some previously-valid block
// is now invalid. This is a consensus failure on their behalf.
ExecutionStatus::Valid(hash) => {
return Err(Error::ValidExecutionStatusBecameInvalid {
block_root: node.root,
payload_block_hash: *hash,
})
}
ExecutionStatus::Optimistic(hash) => {
invalidated_indices.insert(index);
node.execution_status = ExecutionStatus::Invalid(*hash);
// It's impossible for an invalid block to lead to a "best" block, so set these
// fields to `None`.
//
// Failing to set these values will result in `Self::node_leads_to_viable_head`
// returning `false` for *valid* ancestors of invalid blocks.
node.best_child = None;
node.best_descendant = None;
}
// The block is already invalid, but keep going backwards to ensure all ancestors
// are updated.
ExecutionStatus::Invalid(_) => (),
// This block is pre-merge, therefore it has no execution status. Nor do its
// ancestors.
ExecutionStatus::Irrelevant(_) => break,
}
}
if let Some(parent_index) = node.parent {
index = parent_index
} else {
// The root of the block tree has been reached (aka the finalized block), without
// matching `latest_valid_ancestor_hash`. It's not possible or useful to go any
// further back: the finalized checkpoint is invalid so all is lost!
break;
}
}
/*
* Step 2:
*
* Start at either the `latest_valid_ancestor` or the `head_block_root` and iterate
* *forwards* to invalidate all descendants of all blocks in `invalidated_indices`.
*/
let starting_block_root = latest_valid_ancestor_root
.filter(|_| latest_valid_ancestor_is_descendant)
.unwrap_or(head_block_root);
let latest_valid_ancestor_index = *self
.indices
.get(&starting_block_root)
.ok_or(Error::NodeUnknown(starting_block_root))?;
let first_potential_descendant = latest_valid_ancestor_index + 1;
// Collect all *descendants* which have been declared invalid since they're the descendant of a block
// with an invalid execution payload.
for index in first_potential_descendant..self.nodes.len() {
let node = self
.nodes
.get_mut(index)
.ok_or(Error::InvalidNodeIndex(index))?;
if let Some(parent_index) = node.parent {
if invalidated_indices.contains(&parent_index) {
match &node.execution_status {
ExecutionStatus::Valid(hash) => {
return Err(Error::ValidExecutionStatusBecameInvalid {
block_root: node.root,
payload_block_hash: *hash,
})
}
ExecutionStatus::Optimistic(hash) | ExecutionStatus::Invalid(hash) => {
node.execution_status = ExecutionStatus::Invalid(*hash)
}
ExecutionStatus::Irrelevant(_) => {
return Err(Error::IrrelevantDescendant {
block_root: node.root,
})
}
}
invalidated_indices.insert(index);
}
}
}
Ok(())
}
/// Follows the best-descendant links to find the best-block (i.e., head-block).
///
/// ## Notes
///
/// The result of this function is not guaranteed to be accurate if `Self::on_new_block` has
/// been called without a subsequent `Self::apply_score_changes` call. This is because
/// `on_new_block` does not attempt to walk backwards through the tree and update the
/// best-child/best-descendant links.
pub fn find_head<E: EthSpec>(
&self,
justified_root: &Hash256,
current_slot: Slot,
) -> Result<Hash256, Error> {
let justified_index = self
.indices
.get(justified_root)
.copied()
.ok_or(Error::JustifiedNodeUnknown(*justified_root))?;
let justified_node = self
.nodes
.get(justified_index)
.ok_or(Error::InvalidJustifiedIndex(justified_index))?;
// Since there are no valid descendants of a justified block with an invalid execution
// payload, there would be no head to choose from.
//
// Fork choice is effectively broken until a new justified root is set. It might not be
// practically possible to set a new justified root if we are unable to find a new head.
//
// This scenario is *unsupported*. It represents a serious consensus failure.
if justified_node.execution_status.is_invalid() {
return Err(Error::InvalidJustifiedCheckpointExecutionStatus {
justified_root: *justified_root,
});
}
let best_descendant_index = justified_node.best_descendant.unwrap_or(justified_index);
let best_node = self
.nodes
.get(best_descendant_index)
.ok_or(Error::InvalidBestDescendant(best_descendant_index))?;
// Perform a sanity check that the node is indeed valid to be the head.
if !self.node_is_viable_for_head::<E>(best_node, current_slot) {
return Err(Error::InvalidBestNode(Box::new(InvalidBestNodeInfo {
current_slot,
start_root: *justified_root,
justified_checkpoint: self.justified_checkpoint,
finalized_checkpoint: self.finalized_checkpoint,
head_root: justified_node.root,
head_justified_checkpoint: justified_node.justified_checkpoint,
head_finalized_checkpoint: justified_node.finalized_checkpoint,
})));
}
Ok(best_node.root)
}
/// Update the tree with new finalization information. The tree is only actually pruned if both
/// of the two following criteria are met:
///
/// - The supplied finalized epoch and root are different to the current values.
/// - The number of nodes in `self` is at least `self.prune_threshold`.
///
/// # Errors
///
/// Returns errors if:
///
/// - The finalized epoch is less than the current one.
/// - The finalized epoch is equal to the current one, but the finalized root is different.
/// - There is some internal error relating to invalid indices inside `self`.
pub fn maybe_prune(&mut self, finalized_root: Hash256) -> Result<(), Error> {
let finalized_index = *self
.indices
.get(&finalized_root)
.ok_or(Error::FinalizedNodeUnknown(finalized_root))?;
if finalized_index < self.prune_threshold {
// Pruning at small numbers incurs more cost than benefit.
return Ok(());
}
// Remove the `self.indices` key/values for all the to-be-deleted nodes.
for node_index in 0..finalized_index {
let root = &self
.nodes
.get(node_index)
.ok_or(Error::InvalidNodeIndex(node_index))?
.root;
self.indices.remove(root);
}
// Drop all the nodes prior to finalization.
self.nodes = self.nodes.split_off(finalized_index);
// Adjust the indices map.
for (_root, index) in self.indices.iter_mut() {
*index = index
.checked_sub(finalized_index)
.ok_or(Error::IndexOverflow("indices"))?;
}
// Iterate through all the existing nodes and adjust their indices to match the new layout
// of `self.nodes`.
for node in self.nodes.iter_mut() {
if let Some(parent) = node.parent {
// If `node.parent` is less than `finalized_index`, set it to `None`.
node.parent = parent.checked_sub(finalized_index);
}
if let Some(best_child) = node.best_child {
node.best_child = Some(
best_child
.checked_sub(finalized_index)
.ok_or(Error::IndexOverflow("best_child"))?,
);
}
if let Some(best_descendant) = node.best_descendant {
node.best_descendant = Some(
best_descendant
.checked_sub(finalized_index)
.ok_or(Error::IndexOverflow("best_descendant"))?,
);
}
}
Ok(())
}
/// Observe the parent at `parent_index` with respect to the child at `child_index` and
/// potentially modify the `parent.best_child` and `parent.best_descendant` values.
///
/// ## Detail
///
/// There are four outcomes:
///
/// - The child is already the best child but it's now invalid due to a FFG change and should be removed.
/// - The child is already the best child and the parent is updated with the new
/// best-descendant.
/// - The child is not the best child but becomes the best child.
/// - The child is not the best child and does not become the best child.
fn maybe_update_best_child_and_descendant<E: EthSpec>(
&mut self,
parent_index: usize,
child_index: usize,
current_slot: Slot,
) -> Result<(), Error> {
let child = self
.nodes
.get(child_index)
.ok_or(Error::InvalidNodeIndex(child_index))?;
let parent = self
.nodes
.get(parent_index)
.ok_or(Error::InvalidNodeIndex(parent_index))?;
let child_leads_to_viable_head =
self.node_leads_to_viable_head::<E>(child, current_slot)?;
// These three variables are aliases to the three options that we may set the
// `parent.best_child` and `parent.best_descendant` to.
//
// I use the aliases to assist readability.
let change_to_none = (None, None);
let change_to_child = (
Some(child_index),
child.best_descendant.or(Some(child_index)),
);
let no_change = (parent.best_child, parent.best_descendant);
let (new_best_child, new_best_descendant) =
if let Some(best_child_index) = parent.best_child {
if best_child_index == child_index && !child_leads_to_viable_head {
// If the child is already the best-child of the parent but it's not viable for
// the head, remove it.
change_to_none
} else if best_child_index == child_index {
// If the child is the best-child already, set it again to ensure that the
// best-descendant of the parent is updated.
change_to_child
} else {
let best_child = self
.nodes
.get(best_child_index)
.ok_or(Error::InvalidBestDescendant(best_child_index))?;
let best_child_leads_to_viable_head =
self.node_leads_to_viable_head::<E>(best_child, current_slot)?;
if child_leads_to_viable_head && !best_child_leads_to_viable_head {
// The child leads to a viable head, but the current best-child doesn't.
change_to_child
} else if !child_leads_to_viable_head && best_child_leads_to_viable_head {
// The best child leads to a viable head, but the child doesn't.
no_change
} else if child.weight == best_child.weight {
// Tie-breaker of equal weights by root.
if child.root >= best_child.root {
change_to_child
} else {
no_change
}
} else {
// Choose the winner by weight.
if child.weight >= best_child.weight {
change_to_child
} else {
no_change
}
}
}
} else if child_leads_to_viable_head {
// There is no current best-child and the child is viable.
change_to_child
} else {
// There is no current best-child but the child is not viable.
no_change
};
let parent = self
.nodes
.get_mut(parent_index)
.ok_or(Error::InvalidNodeIndex(parent_index))?;
parent.best_child = new_best_child;
parent.best_descendant = new_best_descendant;
Ok(())
}
/// Indicates if the node itself is viable for the head, or if it's best descendant is viable
/// for the head.
fn node_leads_to_viable_head<E: EthSpec>(
&self,
node: &ProtoNode,
current_slot: Slot,
) -> Result<bool, Error> {
let best_descendant_is_viable_for_head =
if let Some(best_descendant_index) = node.best_descendant {
let best_descendant = self
.nodes
.get(best_descendant_index)
.ok_or(Error::InvalidBestDescendant(best_descendant_index))?;
self.node_is_viable_for_head::<E>(best_descendant, current_slot)
} else {
false
};
Ok(best_descendant_is_viable_for_head
|| self.node_is_viable_for_head::<E>(node, current_slot))
}
/// This is the equivalent to the `filter_block_tree` function in the eth2 spec:
///
/// https://github.com/ethereum/eth2.0-specs/blob/v0.10.0/specs/phase0/fork-choice.md#filter_block_tree
///
/// Any node that has a different finalized or justified epoch should not be viable for the
/// head.
fn node_is_viable_for_head<E: EthSpec>(&self, node: &ProtoNode, current_slot: Slot) -> bool {
if node.execution_status.is_invalid() {
return false;
}
let genesis_epoch = Epoch::new(0);
let checkpoint_match_predicate =
|node_justified_checkpoint: Checkpoint, node_finalized_checkpoint: Checkpoint| {
let correct_justified = node_justified_checkpoint == self.justified_checkpoint
|| self.justified_checkpoint.epoch == genesis_epoch;
let correct_finalized = node_finalized_checkpoint == self.finalized_checkpoint
|| self.finalized_checkpoint.epoch == genesis_epoch;
correct_justified && correct_finalized
};
if let (
Some(unrealized_justified_checkpoint),
Some(unrealized_finalized_checkpoint),
Some(justified_checkpoint),
Some(finalized_checkpoint),
) = (
node.unrealized_justified_checkpoint,
node.unrealized_finalized_checkpoint,
node.justified_checkpoint,
node.finalized_checkpoint,
) {
let current_epoch = current_slot.epoch(E::slots_per_epoch());
// If previous epoch is justified, pull up all tips to at least the previous epoch
if CountUnrealizedFull::True == self.count_unrealized_full
&& (current_epoch > genesis_epoch
&& self.justified_checkpoint.epoch + 1 == current_epoch)
{
unrealized_justified_checkpoint.epoch + 1 >= current_epoch
// If previous epoch is not justified, pull up only tips from past epochs up to the current epoch
} else {
// If block is from a previous epoch, filter using unrealized justification & finalization information
if node.slot.epoch(E::slots_per_epoch()) < current_epoch {
checkpoint_match_predicate(
unrealized_justified_checkpoint,
unrealized_finalized_checkpoint,
)
// If block is from the current epoch, filter using the head state's justification & finalization information
} else {
checkpoint_match_predicate(justified_checkpoint, finalized_checkpoint)
}
}
} else if let (Some(justified_checkpoint), Some(finalized_checkpoint)) =
(node.justified_checkpoint, node.finalized_checkpoint)
{
checkpoint_match_predicate(justified_checkpoint, finalized_checkpoint)
} else {
false
}
}
/// Return a reverse iterator over the nodes which comprise the chain ending at `block_root`.
pub fn iter_nodes<'a>(&'a self, block_root: &Hash256) -> Iter<'a> {
let next_node_index = self.indices.get(block_root).copied();
Iter {
next_node_index,
proto_array: self,
}
}
/// Return a reverse iterator over the block roots of the chain ending at `block_root`.
///
/// Note that unlike many other iterators, this one WILL NOT yield anything at skipped slots.
pub fn iter_block_roots<'a>(
&'a self,
block_root: &Hash256,
) -> impl Iterator<Item = (Hash256, Slot)> + 'a {
self.iter_nodes(block_root)
.map(|node| (node.root, node.slot))
}
/// Returns `true` if the `descendant_root` has an ancestor with `ancestor_root`. Always
/// returns `false` if either input root is unknown.
///
/// ## Notes
///
/// Still returns `true` if `ancestor_root` is known and `ancestor_root == descendant_root`.
pub fn is_descendant(&self, ancestor_root: Hash256, descendant_root: Hash256) -> bool {
self.indices
.get(&ancestor_root)
.and_then(|ancestor_index| self.nodes.get(*ancestor_index))
.and_then(|ancestor| {
self.iter_block_roots(&descendant_root)
.take_while(|(_root, slot)| *slot >= ancestor.slot)
.find(|(_root, slot)| *slot == ancestor.slot)
.map(|(root, _slot)| root == ancestor_root)
})
.unwrap_or(false)
}
/// Returns the first *beacon block root* which contains an execution payload with the given
/// `block_hash`, if any.
pub fn execution_block_hash_to_beacon_block_root(
&self,
block_hash: &ExecutionBlockHash,
) -> Option<Hash256> {
self.nodes
.iter()
.rev()
.find(|node| {
node.execution_status
.block_hash()
.map_or(false, |node_block_hash| node_block_hash == *block_hash)
})
.map(|node| node.root)
}
}
/// A helper method to calculate the proposer boost based on the given `validator_balances`.
/// This does *not* do any verification about whether a boost should or should not be applied.
/// The `validator_balances` array used here is assumed to be structured like the one stored in
/// the `BalancesCache`, where *effective* balances are stored and inactive balances are defaulted
/// to zero.
///
/// Returns `None` if there is an overflow or underflow when calculating the score.
///
/// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/fork-choice.md#get_latest_attesting_balance
pub fn calculate_proposer_boost<E: EthSpec>(
validator_balances: &[u64],
proposer_score_boost: u64,
) -> Option<u64> {
let mut total_balance: u64 = 0;
let mut num_validators: u64 = 0;
for &balance in validator_balances {
// We need to filter zero balances here to get an accurate active validator count.
// This is because we default inactive validator balances to zero when creating
// this balances array.
if balance != 0 {
total_balance = total_balance.checked_add(balance)?;
num_validators = num_validators.checked_add(1)?;
}
}
let average_balance = total_balance.checked_div(num_validators)?;
let committee_size = num_validators.checked_div(E::slots_per_epoch())?;
let committee_weight = committee_size.checked_mul(average_balance)?;
committee_weight
.checked_mul(proposer_score_boost)?
.checked_div(100)
}
/// Reverse iterator over one path through a `ProtoArray`.
pub struct Iter<'a> {
next_node_index: Option<usize>,
proto_array: &'a ProtoArray,
}
impl<'a> Iterator for Iter<'a> {
type Item = &'a ProtoNode;
fn next(&mut self) -> Option<Self::Item> {
let next_node_index = self.next_node_index?;
let node = self.proto_array.nodes.get(next_node_index)?;
self.next_node_index = node.parent;
Some(node)
}
}
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