pvf-precheck: PVF pre-checker subsystem

This commit implements the last major piece of #3211: the subsystem that
tracks PVFs that require voting, issues pre-check requests to
candidate-validation and makes sure that the votes are submitted to the
chain.

TODO:

- [ ] Run once more with polkadot-launch

Cargo.toml

@@ -61,6 +61,7 @@ members = [
 	"node/core/parachains-inherent",
 	"node/core/provisioner",
 	"node/core/pvf",
+	"node/core/pvf-checker",
 	"node/core/runtime-api",
 	"node/network/approval-distribution",
 	"node/network/bridge",

node/core/pvf-checker/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "polkadot-node-core-pvf-checker"
+version = "0.9.13"
+authors = ["Parity Technologies <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+futures = "0.3.17"
+thiserror = "1.0.30"
+tracing = "0.1.29"
+
+polkadot-node-primitives = { path = "../../primitives" }
+polkadot-node-subsystem = { path = "../../subsystem" }
+polkadot-primitives = { path = "../../../primitives" }
+polkadot-node-subsystem-util = { path = "../../subsystem-util" }
+polkadot-overseer = { path = "../../overseer" }
+
+sp-keystore = { git = "https://github.com/paritytech/substrate", branch = "master" }
+
+[dev-dependencies]
+sp-core = { git = "https://github.com/paritytech/substrate", branch = "master" }
+sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master" }
+sc-keystore = { git = "https://github.com/paritytech/substrate", branch = "master" }
+sp-keyring = { git = "https://github.com/paritytech/substrate", branch = "master" }
+polkadot-node-subsystem-test-helpers = { path = "../../subsystem-test-helpers"}
+test-helpers = { package = "polkadot-primitives-test-helpers", path = "../../../primitives/test-helpers" }
+sp-application-crypto = { git = "https://github.com/paritytech/substrate", branch = "master" }
+futures-timer = "3.0.2"

node/core/pvf-checker/src/interest_view.rs

@@ -0,0 +1,124 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use polkadot_primitives::v1::{Hash, ValidationCodeHash};
+use std::collections::{
+	btree_map::{self, BTreeMap},
+	HashSet,
+};
+
+/// Data about a particular validation code.
+#[derive(Default, Debug)]
+struct PvfData {
+	/// If `Some` then the PVF pre-checking was run for this PVF. If `None` we are either waiting
+	/// for the judgement to come in or the PVF pre-checking failed.
+	judgement: Option<bool>,
+
+	/// The set of block hashes where this PVF was seen.
+	seen_in: HashSet<Hash>,
+}
+
+impl PvfData {
+	/// Initialize a new `PvfData` which is awaiting for the initial judgement.
+	fn pending(origin: Hash) -> Self {
+		// Preallocate the hashset with 5 items. This is the anticipated maximum leafs we can
+		// deal at the same time. In the vast majority of the cases it will have length of 1.
+		let mut seen_in = HashSet::with_capacity(5);
+		seen_in.insert(origin);
+		Self { judgement: None, seen_in }
+	}
+
+	pub fn seen_in(&mut self, relay_hash: Hash) {
+		self.seen_in.insert(relay_hash);
+	}
+
+	/// Removes the given `relay_hash` from the set of seen in, and returns if the set is now empty.
+	pub fn remove_origin(&mut self, relay_hash: &Hash) -> bool {
+		self.seen_in.remove(relay_hash);
+		self.seen_in.is_empty()
+	}
+}
+
+/// A structure that keeps track of relevant PVFs and judgements about them. A relevant PVF is one
+/// that resides in at least a single active leaf.
+#[derive(Debug)]
+pub struct InterestView {
+	active_leaves: BTreeMap<Hash, HashSet<ValidationCodeHash>>,
+	pvfs: BTreeMap<ValidationCodeHash, PvfData>,
+}
+
+impl InterestView {
+	pub fn new() -> Self {
+		Self { active_leaves: BTreeMap::new(), pvfs: BTreeMap::new() }
+	}
+
+	pub fn on_leaves_update(
+		&mut self,
+		activated: Option<(Hash, Vec<ValidationCodeHash>)>,
+		deactivated: &[Hash],
+	) -> Vec<ValidationCodeHash> {
+		let mut newcomers = Vec::new();
+
+		if let Some((leaf, pending_pvfs)) = activated {
+			for pvf in &pending_pvfs {
+				match self.pvfs.entry(*pvf) {
+					btree_map::Entry::Vacant(v) => {
+						v.insert(PvfData::pending(leaf));
+						newcomers.push(*pvf);
+					},
+					btree_map::Entry::Occupied(mut o) => {
+						o.get_mut().seen_in(leaf);
+					},
+				}
+			}
+			self.active_leaves.entry(leaf).or_default().extend(pending_pvfs);
+		}
+
+		for leaf in deactivated {
+			let pvfs = self.active_leaves.remove(leaf);
+			for pvf in pvfs.into_iter().flatten() {
+				if let btree_map::Entry::Occupied(mut o) = self.pvfs.entry(pvf) {
+					let now_empty = o.get_mut().remove_origin(leaf);
+					if now_empty {
+						o.remove();
+					}
+				}
+			}
+		}
+
+		newcomers
+	}
+
+	/// Handles a new judgement for the given `pvf`.
+	///
+	/// Returns `Err` if the given PVF hash is not known.
+	pub fn on_judgement(&mut self, subject: ValidationCodeHash, accept: bool) -> Result<(), ()> {
+		match self.pvfs.get_mut(&subject) {
+			Some(data) => {
+				data.judgement = Some(accept);
+				Ok(())
+			},
+			None => Err(()),
+		}
+	}
+
+	/// Returns all PVFs that previously received a judgement.
+	pub fn judgements(&self) -> impl Iterator<Item = (ValidationCodeHash, bool)> + '_ {
+		self.pvfs
+			.iter()
+			.filter_map(|(code_hash, data)| data.judgement.map(|accept| (*code_hash, accept)))
+	}
+}