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Fix longest chain finalization target lookup (#13289)

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* Finalization target should be chosed as some ancestor of SelectChain::best_chain

* More test assertions

* Improve docs

* Removed stale docs

* Rename 'target' to 'base' in lookup method

* Fix typo

* Apply suggestions from code review

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Rename 'target_hash' to 'base_hash' in 'SelectChain::finality_target()'

* Apply suggestions from code review

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Docs improvement

* Doc fix

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

* Apply more code suggestions

---------

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>
Co-authored-by: Anton <anton.kalyaev@gmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>
This commit is contained in:
Davide Galassi
2023-02-11 18:35:04 +01:00
committed by GitHub
parent 9a8bbbab03
commit d48fc58729
5 changed files with 242 additions and 149 deletions
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substrate/primitives/blockchain/src/backend.rs
+15 -69
View File
@@ -183,96 +183,43 @@ pub trait Backend<Block: BlockT>:
/// Return hashes of all blocks that are children of the block with `parent_hash`.
fn children(&self, parent_hash: Block::Hash) -> Result<Vec<Block::Hash>>;
/// Get the most recent block hash of the best (longest) chains
/// that contain block with the given `target_hash`.
/// Get the most recent block hash of the longest chain that contains
/// a block with the given `base_hash`.
///
/// The search space is always limited to blocks which are in the finalized
/// chain or descendents of it.
///
/// If `maybe_max_block_number` is `Some(max_block_number)`
/// the search is limited to block `numbers <= max_block_number`.
/// in other words as if there were no blocks greater `max_block_number`.
/// Returns `Ok(None)` if `target_hash` is not found in search space.
/// TODO: document time complexity of this, see [#1444](https://github.com/paritytech/substrate/issues/1444)
fn best_containing(
/// Returns `Ok(None)` if `base_hash` is not found in search space.
// TODO: document time complexity of this, see [#1444](https://github.com/paritytech/substrate/issues/1444)
fn longest_containing(
&self,
target_hash: Block::Hash,
maybe_max_number: Option<NumberFor<Block>>,
base_hash: Block::Hash,
import_lock: &RwLock<()>,
) -> Result<Option<Block::Hash>> {
let target_header = {
match self.header(target_hash)? {
Some(x) => x,
// target not in blockchain
None => return Ok(None),
}
let Some(base_header) = self.header(base_hash)? else {
return Ok(None)
};
if let Some(max_number) = maybe_max_number {
// target outside search range
if target_header.number() > &max_number {
return Ok(None)
}
}
let leaves = {
// ensure no blocks are imported during this code block.
// an import could trigger a reorg which could change the canonical chain.
// we depend on the canonical chain staying the same during this code block.
let _import_guard = import_lock.read();
let info = self.info();
// this can be `None` if the best chain is shorter than the target header.
let maybe_canon_hash = self.hash(*target_header.number())?;
if maybe_canon_hash.as_ref() == Some(&target_hash) {
// if a `max_number` is given we try to fetch the block at the
// given depth, if it doesn't exist or `max_number` is not
// provided, we continue to search from all leaves below.
if let Some(max_number) = maybe_max_number {
if let Some(header) = self.hash(max_number)? {
return Ok(Some(header))
}
}
} else if info.finalized_number >= *target_header.number() {
// header is on a dead fork.
if info.finalized_number > *base_header.number() {
// `base_header` is on a dead fork.
return Ok(None)
}
self.leaves()?
};
// for each chain. longest chain first. shortest last
for leaf_hash in leaves {
// start at the leaf
let mut current_hash = leaf_hash;
// if search is not restricted then the leaf is the best
let mut best_hash = leaf_hash;
// go backwards entering the search space
// waiting until we are <= max_number
if let Some(max_number) = maybe_max_number {
loop {
let current_header = self
.header(current_hash)?
.ok_or_else(|| Error::MissingHeader(current_hash.to_string()))?;
if current_header.number() <= &max_number {
best_hash = current_header.hash();
break
}
current_hash = *current_header.parent_hash();
}
}
// go backwards through the chain (via parent links)
loop {
// until we find target
if current_hash == target_hash {
return Ok(Some(best_hash))
if current_hash == base_hash {
return Ok(Some(leaf_hash))
}
let current_header = self
@@ -280,7 +227,7 @@ pub trait Backend<Block: BlockT>:
.ok_or_else(|| Error::MissingHeader(current_hash.to_string()))?;
// stop search in this chain once we go below the target's block number
if current_header.number() < target_header.number() {
if current_header.number() < base_header.number() {
break
}
@@ -293,9 +240,8 @@ pub trait Backend<Block: BlockT>:
//
// FIXME #1558 only issue this warning when not on a dead fork
warn!(
"Block {:?} exists in chain but not found when following all \
leaves backwards. Number limit = {:?}",
target_hash, maybe_max_number,
"Block {:?} exists in chain but not found when following all leaves backwards",
base_hash,
);
Ok(None)