From 06f5d486f552e2ead543024168035bcdbb29c027 Mon Sep 17 00:00:00 2001
From: Sebastian Kunert <skunert49@gmail.com>
Date: Mon, 20 Jan 2025 09:25:43 +0100
Subject: [PATCH] Collator: Fix `can_build_upon` by always allowing to build on
included block (#7205)
Follow-up to #6825, which introduced this bug.
We use the `can_build_upon` method to ask the runtime if it is fine to
build another block. The runtime checks this based on the
[`ConsensusHook`](https://github.com/paritytech/polkadot-sdk/blob/c1b7c3025aa4423d4cf3e57309b60fb7602c2db6/cumulus/pallets/aura-ext/src/consensus_hook.rs#L110-L110)
implementation, the most popular one being the `FixedConsensusHook`.
In #6825 I removed a check that would always allow us to build when we
are building on an included block. Turns out this check is still
required when:
1. The [`UnincludedSegment`
](https://github.com/paritytech/polkadot-sdk/blob/c1b7c3025aa4423d4cf3e57309b60fb7602c2db6/cumulus/pallets/parachain-system/src/lib.rs#L758-L758)
storage item in pallet-parachain-system is equal or larger than the
unincluded segment.
2. We are calling the `can_build_upon` runtime API where the included
block has progressed offchain to the current parent block (so last entry
in the `UnincludedSegment` storage item).
In this scenario the last entry in `UnincludedSegment` does not have a
hash assigned yet (because it was not available in `on_finalize` of the
previous block). So the unincluded segment will be reported at its
maximum length which will forbid building another block.
Ideally we would have a more elegant solution than to rely on the
node-side here. But for now the check is reintroduced and a test is
added to not break it again by accident.
---------
Co-authored-by: command-bot <>
Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>
---
Cargo.lock | 3 +
cumulus/client/consensus/aura/Cargo.toml | 5 +
.../consensus/aura/src/collators/mod.rs | 132 +++++++++++++++++-
prdoc/pr_7205.prdoc | 10 ++
4 files changed, 144 insertions(+), 6 deletions(-)
create mode 100644 prdoc/pr_7205.prdoc
diff --git a/Cargo.lock b/Cargo.lock
index da4e8551191..c9a139f3074 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4640,6 +4640,8 @@ dependencies = [
"cumulus-primitives-aura 0.7.0",
"cumulus-primitives-core 0.7.0",
"cumulus-relay-chain-interface",
+ "cumulus-test-client",
+ "cumulus-test-relay-sproof-builder 0.7.0",
"futures",
"parity-scale-codec",
"parking_lot 0.12.3",
@@ -4664,6 +4666,7 @@ dependencies = [
"sp-consensus-aura 0.32.0",
"sp-core 28.0.0",
"sp-inherents 26.0.0",
+ "sp-keyring 31.0.0",
"sp-keystore 0.34.0",
"sp-runtime 31.0.1",
"sp-state-machine 0.35.0",
diff --git a/cumulus/client/consensus/aura/Cargo.toml b/cumulus/client/consensus/aura/Cargo.toml
index 70223093864..8637133a5f5 100644
--- a/cumulus/client/consensus/aura/Cargo.toml
+++ b/cumulus/client/consensus/aura/Cargo.toml
@@ -59,6 +59,11 @@ polkadot-node-subsystem-util = { workspace = true, default-features = true }
polkadot-overseer = { workspace = true, default-features = true }
polkadot-primitives = { workspace = true, default-features = true }
+[dev-dependencies]
+cumulus-test-client = { workspace = true }
+cumulus-test-relay-sproof-builder = { workspace = true }
+sp-keyring = { workspace = true }
+
[features]
# Allows collator to use full PoV size for block building
full-pov-size = []
diff --git a/cumulus/client/consensus/aura/src/collators/mod.rs b/cumulus/client/consensus/aura/src/collators/mod.rs
index 031fa963ba6..66c6086eaf9 100644
--- a/cumulus/client/consensus/aura/src/collators/mod.rs
+++ b/cumulus/client/consensus/aura/src/collators/mod.rs
@@ -179,12 +179,19 @@ where
let authorities = runtime_api.authorities(parent_hash).ok()?;
let author_pub = aura_internal::claim_slot::<P>(para_slot, &authorities, keystore).await?;
- let Ok(Some(api_version)) =
- runtime_api.api_version::<dyn AuraUnincludedSegmentApi<Block>>(parent_hash)
- else {
- return (parent_hash == included_block)
- .then(|| SlotClaim::unchecked::<P>(author_pub, para_slot, timestamp));
- };
+ // This function is typically called when we want to build block N. At that point, the
+ // unincluded segment in the runtime is unaware of the hash of block N-1. If the unincluded
+ // segment in the runtime is full, but block N-1 is the included block, the unincluded segment
+ // should have length 0 and we can build. Since the hash is not available to the runtime
+ // however, we need this extra check here.
+ if parent_hash == included_block {
+ return Some(SlotClaim::unchecked::<P>(author_pub, para_slot, timestamp));
+ }
+
+ let api_version = runtime_api
+ .api_version::<dyn AuraUnincludedSegmentApi<Block>>(parent_hash)
+ .ok()
+ .flatten()?;
let slot = if api_version > 1 { relay_slot } else { para_slot };
@@ -243,3 +250,116 @@ where
.max_by_key(|a| a.depth)
.map(|parent| (included_block, parent))
}
+
+#[cfg(test)]
+mod tests {
+ use crate::collators::can_build_upon;
+ use codec::Encode;
+ use cumulus_primitives_aura::Slot;
+ use cumulus_primitives_core::BlockT;
+ use cumulus_relay_chain_interface::PHash;
+ use cumulus_test_client::{
+ runtime::{Block, Hash},
+ Client, DefaultTestClientBuilderExt, InitBlockBuilder, TestClientBuilder,
+ TestClientBuilderExt,
+ };
+ use cumulus_test_relay_sproof_builder::RelayStateSproofBuilder;
+ use polkadot_primitives::HeadData;
+ use sc_consensus::{BlockImport, BlockImportParams, ForkChoiceStrategy};
+ use sp_consensus::BlockOrigin;
+ use sp_keystore::{Keystore, KeystorePtr};
+ use sp_timestamp::Timestamp;
+ use std::sync::Arc;
+
+ async fn import_block<I: BlockImport<Block>>(
+ importer: &I,
+ block: Block,
+ origin: BlockOrigin,
+ import_as_best: bool,
+ ) {
+ let (header, body) = block.deconstruct();
+
+ let mut block_import_params = BlockImportParams::new(origin, header);
+ block_import_params.fork_choice = Some(ForkChoiceStrategy::Custom(import_as_best));
+ block_import_params.body = Some(body);
+ importer.import_block(block_import_params).await.unwrap();
+ }
+
+ fn sproof_with_parent_by_hash(client: &Client, hash: PHash) -> RelayStateSproofBuilder {
+ let header = client.header(hash).ok().flatten().expect("No header for parent block");
+ let included = HeadData(header.encode());
+ let mut builder = RelayStateSproofBuilder::default();
+ builder.para_id = cumulus_test_client::runtime::PARACHAIN_ID.into();
+ builder.included_para_head = Some(included);
+
+ builder
+ }
+ async fn build_and_import_block(client: &Client, included: Hash) -> Block {
+ let sproof = sproof_with_parent_by_hash(client, included);
+
+ let block_builder = client.init_block_builder(None, sproof).block_builder;
+
+ let block = block_builder.build().unwrap().block;
+
+ let origin = BlockOrigin::NetworkInitialSync;
+ import_block(client, block.clone(), origin, true).await;
+ block
+ }
+
+ fn set_up_components() -> (Arc<Client>, KeystorePtr) {
+ let keystore = Arc::new(sp_keystore::testing::MemoryKeystore::new()) as Arc<_>;
+ for key in sp_keyring::Sr25519Keyring::iter() {
+ Keystore::sr25519_generate_new(
+ &*keystore,
+ sp_application_crypto::key_types::AURA,
+ Some(&key.to_seed()),
+ )
+ .expect("Can insert key into MemoryKeyStore");
+ }
+ (Arc::new(TestClientBuilder::new().build()), keystore)
+ }
+
+ /// This tests a special scenario where the unincluded segment in the runtime
+ /// is full. We are calling `can_build_upon`, passing the last built block as the
+ /// included one. In the runtime we will not find the hash of the included block in the
+ /// unincluded segment. The `can_build_upon` runtime API would therefore return `false`, but
+ /// we are ensuring on the node side that we are are always able to build on the included block.
+ #[tokio::test]
+ async fn test_can_build_upon() {
+ let (client, keystore) = set_up_components();
+
+ let genesis_hash = client.chain_info().genesis_hash;
+ let mut last_hash = genesis_hash;
+
+ // Fill up the unincluded segment tracker in the runtime.
+ while can_build_upon::<_, _, sp_consensus_aura::sr25519::AuthorityPair>(
+ Slot::from(u64::MAX),
+ Slot::from(u64::MAX),
+ Timestamp::default(),
+ last_hash,
+ genesis_hash,
+ &*client,
+ &keystore,
+ )
+ .await
+ .is_some()
+ {
+ let block = build_and_import_block(&client, genesis_hash).await;
+ last_hash = block.header().hash();
+ }
+
+ // Blocks were built with the genesis hash set as included block.
+ // We call `can_build_upon` with the last built block as the included block.
+ let result = can_build_upon::<_, _, sp_consensus_aura::sr25519::AuthorityPair>(
+ Slot::from(u64::MAX),
+ Slot::from(u64::MAX),
+ Timestamp::default(),
+ last_hash,
+ last_hash,
+ &*client,
+ &keystore,
+ )
+ .await;
+ assert!(result.is_some());
+ }
+}
diff --git a/prdoc/pr_7205.prdoc b/prdoc/pr_7205.prdoc
new file mode 100644
index 00000000000..758beb0b631
--- /dev/null
+++ b/prdoc/pr_7205.prdoc
@@ -0,0 +1,10 @@
+title: 'Collator: Fix `can_build_upon` by always allowing to build on included block'
+doc:
+- audience: Node Dev
+ description: |-
+ Fixes a bug introduced in #6825.
+ We should always allow building on the included block of parachains. In situations where the unincluded segment
+ is full, but the included block moved to the most recent block, building was wrongly disallowed.
+crates:
+- name: cumulus-client-consensus-aura
+ bump: minor
--
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