Add some message types from subsystem definitions (#1265)

* introduce polkadot-node-primitives

* guide: change statement distribution message types

* guide: remove variant from `CandidateSelectionMessage`

* add a few more message types

* add TODOs

* Almost all messages

* NewBackedCandidate notification

* Formatting

* Use AttestedCandidate as BackedCandidate

* Update node/primitives/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* Fix the tests

* Bring in types from #1242

* Adds network bridge messages

* More message types from doc

* use fn pointer type

* Fixes from the review

* Add missing Runtime subsystem message

* rename to CandidateValidationMessage and fix tests

Co-authored-by: Fedor Sakharov <fedor.sakharov@gmail.com>
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

polkadot/node/primitives/src/lib.rs

@@ -0,0 +1,109 @@
+// Copyright 2017-2020 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/>.
+
+//! Primitive types used on the node-side.
+//!
+//! Unlike the `polkadot-primitives` crate, these primitives are only used on the node-side,
+//! not shared between the node and the runtime. This crate builds on top of the primitives defined
+//! there.
+
+use runtime_primitives::traits::AppVerify;
+use polkadot_primitives::Hash;
+use polkadot_primitives::parachain::{
+	AbridgedCandidateReceipt, CandidateReceipt, SigningContext, ValidatorSignature,
+	ValidatorIndex, ValidatorId,
+};
+use parity_scale_codec::{Encode, Decode};
+
+/// A statement, where the candidate receipt is included in the `Seconded` variant.
+#[derive(Debug, Clone, PartialEq, Encode, Decode)]
+pub enum Statement {
+	/// A statement that a validator seconds a candidate.
+	#[codec(index = "1")]
+	Seconded(AbridgedCandidateReceipt),
+	/// A statement that a validator has deemed a candidate valid.
+	#[codec(index = "2")]
+	Valid(Hash),
+	/// A statement that a validator has deemed a candidate invalid.
+	#[codec(index = "3")]
+	Invalid(Hash),
+}
+
+impl Statement {
+	/// Get the signing payload of the statement.
+	pub fn signing_payload(&self, context: &SigningContext) -> Vec<u8> {
+		// convert to fully hash-based payload.
+		let statement = match *self {
+			Statement::Seconded(ref c) => polkadot_primitives::parachain::Statement::Candidate(c.hash()),
+			Statement::Valid(hash) => polkadot_primitives::parachain::Statement::Valid(hash),
+			Statement::Invalid(hash) => polkadot_primitives::parachain::Statement::Invalid(hash),
+		};
+
+		statement.signing_payload(context)
+	}
+}
+
+/// A statement, the corresponding signature, and the index of the sender.
+///
+/// Signing context and validator set should be apparent from context.
+#[derive(Debug, Clone, PartialEq, Encode, Decode)]
+pub struct SignedStatement {
+	/// The statement signed.
+	pub statement: Statement,
+	/// The signature of the validator.
+	pub signature: ValidatorSignature,
+	/// The index in the validator set of the signing validator. Which validator set should
+	/// be apparent from context.
+	pub sender: ValidatorIndex,
+}
+
+impl SignedStatement {
+	/// Check the signature on a statement. Provide a list of validators to index into
+	/// and the context in which the statement is presumably signed.
+	///
+	/// Returns an error if out of bounds or the signature is invalid. Otherwise, returns Ok.
+	pub fn check_signature(
+		&self,
+		validators: &[ValidatorId],
+		signing_context: &SigningContext,
+	) -> Result<(), ()> {
+		let validator = validators.get(self.sender as usize).ok_or(())?;
+		let payload = self.statement.signing_payload(signing_context);
+
+		if self.signature.verify(&payload[..], validator) {
+			Ok(())
+		} else {
+			Err(())
+		}
+	}
+}
+
+/// A misbehaviour report.
+pub enum MisbehaviorReport {
+	/// These validator nodes disagree on this candidate's validity, please figure it out
+	///
+	/// Most likely, the list of statments all agree except for the final one. That's not
+	/// guaranteed, though; if somehow we become aware of lots of
+	/// statements disagreeing about the validity of a candidate before taking action,
+	/// this message should be dispatched with all of them, in arbitrary order.
+	///
+	/// This variant is also used when our own validity checks disagree with others'.
+	CandidateValidityDisagreement(CandidateReceipt, Vec<SignedStatement>),
+	/// I've noticed a peer contradicting itself about a particular candidate
+	SelfContradiction(CandidateReceipt, SignedStatement, SignedStatement),
+	/// This peer has seconded more than one parachain candidate for this relay parent head
+	DoubleVote(CandidateReceipt, SignedStatement, SignedStatement),
+}