Track received attestations from recent blocks (#337)

* record attestations in storage ringbuffer

* remove some reliance on Aura

* fix up test configuration

* extract attestations stuff out to its own module

* add dummy inherent

* use double_map

* fix a couple more compilation errors

polkadot/runtime/src/attestations.rs

@@ -0,0 +1,162 @@
+// Copyright 2019 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/>.
+
+//! A module for tracking all attestations that fell on a given candidate receipt.
+//!
+//! In the future, it is planned that this module will handle dispute resolution
+//! as well.
+
+use rstd::prelude::*;
+use parity_codec::{Encode, Decode};
+use srml_support::{decl_storage, decl_module, ensure};
+
+use primitives::{Hash, parachain::{AttestedCandidate, CandidateReceipt, Id as ParaId}};
+use {system, session::{self, SessionIndex}};
+use srml_support::{
+	StorageValue, StorageMap, StorageDoubleMap, dispatch::Result, traits::Get,
+};
+
+use inherents::{ProvideInherent, InherentData, RuntimeString, MakeFatalError, InherentIdentifier};
+use system::ensure_none;
+
+/// Parachain blocks included in a recent relay-chain block.
+#[derive(Encode, Decode)]
+pub struct IncludedBlocks<T: Trait> {
+	/// The actual relay chain block number where blocks were included.
+	pub actual_number: T::BlockNumber,
+	/// The session index at this block.
+	pub session: SessionIndex,
+	/// The randomness seed at this block.
+	pub random_seed: [u8; 32],
+	/// All parachain IDs active at this block.
+	pub active_parachains: Vec<ParaId>,
+	/// Hashes of the parachain candidates included at this block.
+	pub para_blocks: Vec<Hash>,
+}
+
+/// Attestations kept over time on a parachain block.
+#[derive(Encode, Decode)]
+pub struct BlockAttestations<T: Trait> {
+	receipt: CandidateReceipt,
+	valid: Vec<T::AccountId>, // stash account ID of voter.
+	invalid: Vec<T::AccountId>, // stash account ID of voter.
+}
+
+/// Additional attestations on a parachain block, after it was included.
+#[derive(Encode, Decode, Clone, PartialEq)]
+#[cfg_attr(feature = "std", derive(Debug))]
+pub struct MoreAttestations;
+
+pub trait Trait: session::Trait {
+	/// How many blocks ago we're willing to accept attestations for.
+	type AttestationPeriod: Get<Self::BlockNumber>;
+
+	/// Get a list of the validators' underlying identities.
+	type ValidatorIdentities: Get<Vec<Self::AccountId>>;
+}
+
+decl_storage! {
+	trait Store for Module<T: Trait> as Attestations {
+		/// A mapping from modular block number (n % AttestationPeriod)
+		/// to session index and the list of candidate hashes.
+		pub RecentParaBlocks: map T::BlockNumber => Option<IncludedBlocks<T>>;
+
+		/// Attestations on a recent parachain block.
+		pub ParaBlockAttestations: double_map T::BlockNumber, blake2_128(Hash) => Option<BlockAttestations<T>>;
+
+		// Did we already have more attestations included in this block?
+		DidUpdate: bool;
+	}
+}
+
+decl_module! {
+	/// Parachain-attestations module.
+	pub struct Module<T: Trait> for enum Call where origin: <T as system::Trait>::Origin {
+		/// Provide candidate receipts for parachains, in ascending order by id.
+		fn more_attestations(origin, _more: MoreAttestations) -> Result {
+			ensure_none(origin)?;
+			ensure!(!<DidUpdate>::exists(), "More attestations can be added only once in a block.");
+			<DidUpdate>::put(true);
+
+			Ok(())
+		}
+
+		fn on_finalize(_n: T::BlockNumber) {
+			<DidUpdate>::kill();
+		}
+	}
+}
+
+impl<T: Trait> Module<T> {
+	/// Update recent candidates to contain the already-checked parachain candidates.
+	pub(crate) fn note_included(heads: &[AttestedCandidate], para_blocks: IncludedBlocks<T>) {
+		let attestation_period = T::AttestationPeriod::get();
+		let mod_num = para_blocks.actual_number % attestation_period;
+
+		// clear old entry that was in this place.
+		if let Some(old_entry) = <RecentParaBlocks<T>>::take(&mod_num) {
+			<ParaBlockAttestations<T>>::remove_prefix(&old_entry.actual_number);
+		}
+
+		let validators = T::ValidatorIdentities::get();
+
+		// make new entry.
+		for (head, hash) in heads.iter().zip(&para_blocks.para_blocks) {
+			let mut valid = Vec::new();
+			let invalid = Vec::new();
+
+			for (auth_index, _) in head.validator_indices
+				.iter()
+				.enumerate()
+				.filter(|(_, bit)| *bit)
+			{
+				let stash_id = validators.get(auth_index)
+					.expect("auth_index checked to be within bounds in `check_candidates`; qed")
+					.clone();
+
+				valid.push(stash_id);
+			}
+
+			let summary = BlockAttestations {
+				receipt: head.candidate().clone(),
+				valid,
+				invalid,
+			};
+
+			<ParaBlockAttestations<T>>::insert(&para_blocks.actual_number, hash, &summary);
+		}
+
+		<RecentParaBlocks<T>>::insert(&mod_num, &para_blocks);
+	}
+}
+
+/// An identifier for inherent data that provides after-the-fact attestations
+/// on already included parachain blocks.
+pub const MORE_ATTESTATIONS_IDENTIFIER: InherentIdentifier = *b"par-atts";
+
+pub type InherentType = MoreAttestations;
+
+impl<T: Trait> ProvideInherent for Module<T> {
+	type Call = Call<T>;
+	type Error = MakeFatalError<RuntimeString>;
+	const INHERENT_IDENTIFIER: InherentIdentifier = MORE_ATTESTATIONS_IDENTIFIER;
+
+	fn create_inherent(data: &InherentData) -> Option<Self::Call> {
+		data.get_data::<InherentType>(&MORE_ATTESTATIONS_IDENTIFIER)
+			.ok()
+			.and_then(|x| x.map(Call::more_attestations))
+	}
+}