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core: grandpa limits votes to 3/4 of the unfinalized chain (#1554)

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* core: grandpa limits votes to 3/4 of the unfinalized chain

* core: test grandpa limited votes
This commit is contained in:
André Silva
2019-01-25 10:37:56 +00:00
committed by Gav Wood
parent a1586df41b
commit 375e01e6b1
2 changed files with 91 additions and 12 deletions
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substrate/core/finality-grandpa/src/lib.rs
+49 -8
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@@ -95,7 +95,7 @@ use consensus_common::{BlockImport, JustificationImport, Error as ConsensusError
use runtime_primitives::Justification;
use runtime_primitives::traits::{
NumberFor, Block as BlockT, Header as HeaderT, DigestFor, ProvideRuntimeApi, Hash as HashT,
DigestItemFor, DigestItem, As, Zero,
DigestItemFor, DigestItem, As, One, Zero,
};
use fg_primitives::GrandpaApi;
use runtime_primitives::generic::BlockId;
@@ -422,16 +422,57 @@ impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash, NumberFo
let limit = self.authority_set.current_limit();
debug!(target: "afg", "Finding best chain containing block {:?} with number limit {:?}", block, limit);
match self.inner.best_containing(block, limit) {
Ok(Some(hash)) => {
let header = self.inner.header(&BlockId::Hash(hash)).ok()?
match self.inner.best_containing(block, None) {
Ok(Some(mut best_hash)) => {
let base_header = self.inner.header(&BlockId::Hash(block)).ok()?
.expect("Header known to exist after `best_containing` call; qed");
Some((hash, header.number().clone()))
if let Some(limit) = limit {
// this is a rare case which might cause issues,
// might be better to return the header itself.
if *base_header.number() > limit {
debug!(target: "afg", "Encountered error finding best chain containing {:?} with limit {:?}: target block is after limit",
block,
limit,
);
return None;
}
}
let mut best_header = self.inner.header(&BlockId::Hash(best_hash)).ok()?
.expect("Header known to exist after `best_containing` call; qed");
// we target a vote towards 3/4 of the unfinalized chain (rounding up)
let target = {
let two = NumberFor::<Block>::one() + One::one();
let three = two + One::one();
let four = three + One::one();
let diff = *best_header.number() - *base_header.number();
let diff = ((diff * three) + two) / four;
*base_header.number() + diff
};
// unless our vote is currently being limited due to a pending change
let target = limit.map(|limit| limit.min(target)).unwrap_or(target);
// walk backwards until we find the target block
loop {
if *best_header.number() < target { unreachable!(); }
if *best_header.number() == target {
return Some((best_hash, *best_header.number()));
}
best_hash = *best_header.parent_hash();
best_header = self.inner.header(&BlockId::Hash(best_hash)).ok()?
.expect("Header known to exist after `best_containing` call; qed");
}
},
Ok(None) => {
debug!(target: "afg", "Encountered error finding best chain containing {:?}: couldn't find target block", block);
None
}
// Ok(None) can be returned when `block` is after `limit`. That might cause issues.
// might be better to return the header itself in this (rare) case.
Ok(None) => None,
Err(e) => {
debug!(target: "afg", "Encountered error finding best chain containing {:?}: {:?}", block, e);
None