Add some magic to signed statements and approval votes (#2585)

* add a magic number to backing statements encoded

* fix fallout in statement table

* fix some fallout in backing

* add magic to approval votes

* remove last references to Candidate variant

* update size-hint

polkadot/node/core/approval-voting/src/lib.rs

@@ -697,7 +697,9 @@ fn approval_signing_payload(
 	approval_vote: ApprovalVote,
 	session_index: SessionIndex,
 ) -> Vec<u8> {
-	(approval_vote, session_index).encode()
+	const MAGIC: [u8; 4] = *b"APPR";
+
+	(MAGIC, approval_vote, session_index).encode()
 }
 
 // `Option::cmp` treats `None` as less than `Some`.

polkadot/node/core/backing/src/lib.rs

@@ -195,7 +195,7 @@ struct InvalidErasureRoot;
 // the code. So this does the necessary conversion.
 fn primitive_statement_to_table(s: &SignedFullStatement) -> TableSignedStatement {
 	let statement = match s.payload() {
-		Statement::Seconded(c) => TableStatement::Candidate(c.clone()),
+		Statement::Seconded(c) => TableStatement::Seconded(c.clone()),
 		Statement::Valid(h) => TableStatement::Valid(h.clone()),
 		Statement::Invalid(h) => TableStatement::Invalid(h.clone()),
 	};
@@ -1239,7 +1239,7 @@ mod tests {
 		statement: TableStatement,
 	) -> Statement {
 		match statement {
-			TableStatement::Candidate(committed_candidate_receipt) => Statement::Seconded(committed_candidate_receipt),
+			TableStatement::Seconded(committed_candidate_receipt) => Statement::Seconded(committed_candidate_receipt),
 			TableStatement::Valid(candidate_hash) => Statement::Valid(candidate_hash),
 			TableStatement::Invalid(candidate_hash) => Statement::Invalid(candidate_hash),
 		}

polkadot/node/network/statement-distribution/src/lib.rs

@@ -172,7 +172,7 @@ impl PeerRelayParentKnowledge {
 		}
 
 		let new_known = match fingerprint.0 {
-			CompactStatement::Candidate(ref h) => {
+			CompactStatement::Seconded(ref h) => {
 				self.seconded_counts.entry(fingerprint.1)
 					.or_default()
 					.note_local(h.clone());
@@ -224,7 +224,7 @@ impl PeerRelayParentKnowledge {
 		}
 
 		let candidate_hash = match fingerprint.0 {
-			CompactStatement::Candidate(ref h) => {
+			CompactStatement::Seconded(ref h) => {
 				let allowed_remote = self.seconded_counts.entry(fingerprint.1)
 					.or_insert_with(Default::default)
 					.note_remote(h.clone());
@@ -437,7 +437,7 @@ impl ActiveHeadData {
 		};
 
 		match comparator.compact {
-			CompactStatement::Candidate(h) => {
+			CompactStatement::Seconded(h) => {
 				let seconded_so_far = self.seconded_counts.entry(validator_index).or_insert(0);
 				if *seconded_so_far >= VC_THRESHOLD {
 					return NotedStatement::NotUseful;
@@ -1241,8 +1241,8 @@ mod tests {
 		assert!(knowledge.received_message_count.is_empty());
 
 		// Make the peer aware of the candidate.
-		assert_eq!(knowledge.send(&(CompactStatement::Candidate(hash_a), ValidatorIndex(0))), Some(true));
-		assert_eq!(knowledge.send(&(CompactStatement::Candidate(hash_a), ValidatorIndex(1))), Some(false));
+		assert_eq!(knowledge.send(&(CompactStatement::Seconded(hash_a), ValidatorIndex(0))), Some(true));
+		assert_eq!(knowledge.send(&(CompactStatement::Seconded(hash_a), ValidatorIndex(1))), Some(false));
 		assert!(knowledge.known_candidates.contains(&hash_a));
 		assert_eq!(knowledge.sent_statements.len(), 2);
 		assert!(knowledge.received_statements.is_empty());
@@ -1263,8 +1263,8 @@ mod tests {
 		let mut knowledge = PeerRelayParentKnowledge::default();
 
 		let hash_a = CandidateHash([1; 32].into());
-		assert!(knowledge.receive(&(CompactStatement::Candidate(hash_a), ValidatorIndex(0)), 3).unwrap());
-		assert!(knowledge.send(&(CompactStatement::Candidate(hash_a), ValidatorIndex(0))).is_none());
+		assert!(knowledge.receive(&(CompactStatement::Seconded(hash_a), ValidatorIndex(0)), 3).unwrap());
+		assert!(knowledge.send(&(CompactStatement::Seconded(hash_a), ValidatorIndex(0))).is_none());
 	}
 
 	#[test]
@@ -1279,7 +1279,7 @@ mod tests {
 		);
 
 		assert_eq!(
-			knowledge.receive(&(CompactStatement::Candidate(hash_a), ValidatorIndex(0)), 3),
+			knowledge.receive(&(CompactStatement::Seconded(hash_a), ValidatorIndex(0)), 3),
 			Ok(true),
 		);
 
@@ -1312,12 +1312,12 @@ mod tests {
 		let hash_c = CandidateHash([3; 32].into());
 
 		assert_eq!(
-			knowledge.receive(&(CompactStatement::Candidate(hash_b), ValidatorIndex(0)), 3),
+			knowledge.receive(&(CompactStatement::Seconded(hash_b), ValidatorIndex(0)), 3),
 			Ok(true),
 		);
 
 		assert_eq!(
-			knowledge.receive(&(CompactStatement::Candidate(hash_c), ValidatorIndex(0)), 3),
+			knowledge.receive(&(CompactStatement::Seconded(hash_c), ValidatorIndex(0)), 3),
 			Err(COST_UNEXPECTED_STATEMENT),
 		);
 
@@ -1328,7 +1328,7 @@ mod tests {
 		);
 
 		assert_eq!(
-			knowledge.receive(&(CompactStatement::Candidate(hash_b), ValidatorIndex(0)), 3),
+			knowledge.receive(&(CompactStatement::Seconded(hash_b), ValidatorIndex(0)), 3),
 			Err(COST_DUPLICATE_STATEMENT),
 		);
 	}
@@ -1451,7 +1451,7 @@ mod tests {
 
 			assert!(c_knowledge.known_candidates.contains(&candidate_hash));
 			assert!(c_knowledge.sent_statements.contains(
-				&(CompactStatement::Candidate(candidate_hash), ValidatorIndex(0))
+				&(CompactStatement::Seconded(candidate_hash), ValidatorIndex(0))
 			));
 			assert!(c_knowledge.sent_statements.contains(
 				&(CompactStatement::Valid(candidate_hash), ValidatorIndex(1))

polkadot/node/primitives/src/lib.rs

@@ -71,7 +71,7 @@ impl Statement {
 	/// of the candidate.
 	pub fn to_compact(&self) -> CompactStatement {
 		match *self {
-			Statement::Seconded(ref c) => CompactStatement::Candidate(c.hash()),
+			Statement::Seconded(ref c) => CompactStatement::Seconded(c.hash()),
 			Statement::Valid(hash) => CompactStatement::Valid(hash),
 			Statement::Invalid(hash) => CompactStatement::Invalid(hash),
 		}

polkadot/primitives/src/v0.rs

@@ -677,27 +677,74 @@ pub struct ErasureChunk {
 	pub proof: Vec<Vec<u8>>,
 }
 
+const BACKING_STATEMENT_MAGIC: [u8; 4] = *b"BKNG";
+
 /// Statements that can be made about parachain candidates. These are the
 /// actual values that are signed.
-#[derive(Clone, PartialEq, Eq, Encode, Decode)]
+#[derive(Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "std", derive(Debug, Hash))]
 pub enum CompactStatement {
 	/// Proposal of a parachain candidate.
-	#[codec(index = 1)]
-	Candidate(CandidateHash),
+	Seconded(CandidateHash),
 	/// State that a parachain candidate is valid.
-	#[codec(index = 2)]
 	Valid(CandidateHash),
 	/// State that a parachain candidate is invalid.
+	Invalid(CandidateHash),
+}
+
+// Inner helper for codec on `CompactStatement`.
+#[derive(Encode, Decode)]
+enum CompactStatementInner {
+	#[codec(index = 1)]
+	Seconded(CandidateHash),
+	#[codec(index = 2)]
+	Valid(CandidateHash),
 	#[codec(index = 3)]
 	Invalid(CandidateHash),
 }
 
+impl From<CompactStatement> for CompactStatementInner {
+	fn from(s: CompactStatement) -> Self {
+		match s {
+			CompactStatement::Seconded(h) => CompactStatementInner::Seconded(h),
+			CompactStatement::Valid(h) => CompactStatementInner::Valid(h),
+			CompactStatement::Invalid(h) => CompactStatementInner::Invalid(h),
+		}
+	}
+}
+
+impl parity_scale_codec::Encode for CompactStatement {
+	fn size_hint(&self) -> usize {
+		// magic + discriminant + payload
+		4 + 1 + 32
+	}
+
+	fn encode_to<T: parity_scale_codec::Output + ?Sized>(&self, dest: &mut T) {
+		dest.write(&BACKING_STATEMENT_MAGIC);
+		CompactStatementInner::from(self.clone()).encode_to(dest)
+	}
+}
+
+impl parity_scale_codec::Decode for CompactStatement {
+	fn decode<I: parity_scale_codec::Input>(input: &mut I) -> Result<Self, parity_scale_codec::Error> {
+		let maybe_magic = <[u8; 4]>::decode(input)?;
+		if maybe_magic != BACKING_STATEMENT_MAGIC {
+			return Err(parity_scale_codec::Error::from("invalid magic string"));
+		}
+
+		Ok(match CompactStatementInner::decode(input)? {
+			CompactStatementInner::Seconded(h) => CompactStatement::Seconded(h),
+			CompactStatementInner::Valid(h) => CompactStatement::Valid(h),
+			CompactStatementInner::Invalid(h) => CompactStatement::Invalid(h),
+		})
+	}
+}
+
 impl CompactStatement {
 	/// Get the underlying candidate hash this references.
 	pub fn candidate_hash(&self) -> &CandidateHash {
 		match *self {
-			CompactStatement::Candidate(ref h)
+			CompactStatement::Seconded(ref h)
 				| CompactStatement::Valid(ref h)
 				| CompactStatement::Invalid(ref h)
 				=> h
@@ -740,7 +787,7 @@ impl ValidityAttestation {
 	) -> Vec<u8> {
 		match *self {
 			ValidityAttestation::Implicit(_) => (
-				CompactStatement::Candidate(candidate_hash),
+				CompactStatement::Seconded(candidate_hash),
 				signing_context,
 			).encode(),
 			ValidityAttestation::Explicit(_) => (

polkadot/statement-table/src/generic.rs

@@ -66,7 +66,7 @@ pub enum Statement<Candidate, Digest> {
 	///
 	/// Broadcasting two different candidate messages per round is not allowed.
 	#[codec(index = 1)]
-	Candidate(Candidate),
+	Seconded(Candidate),
 	/// Broadcast by a authority to attest that the candidate with given digest is valid.
 	#[codec(index = 2)]
 	Valid(Digest),
@@ -115,10 +115,10 @@ impl<Candidate, Digest, Signature> ValidityDoubleVote<Candidate, Digest, Signatu
 	{
 		match self {
 			Self::IssuedAndValidity((c, s1), (d, s2)) => {
-				((Statement::Candidate(c), s1), (Statement::Valid(d), s2))
+				((Statement::Seconded(c), s1), (Statement::Valid(d), s2))
 			}
 			Self::IssuedAndInvalidity((c, s1), (d, s2)) => {
-				((Statement::Candidate(c), s1), (Statement::Invalid(d), s2))
+				((Statement::Seconded(c), s1), (Statement::Invalid(d), s2))
 			}
 			Self::ValidityAndInvalidity(c, s1, s2) => {
 				(
@@ -134,7 +134,7 @@ impl<Candidate, Digest, Signature> ValidityDoubleVote<Candidate, Digest, Signatu
 #[derive(PartialEq, Eq, Debug, Clone)]
 pub enum DoubleSign<Candidate, Digest, Signature> {
 	/// On candidate.
-	Candidate(Candidate, Signature, Signature),
+	Seconded(Candidate, Signature, Signature),
 	/// On validity.
 	Validity(Digest, Signature, Signature),
 	/// On invalidity.
@@ -146,7 +146,7 @@ impl<Candidate, Digest, Signature> DoubleSign<Candidate, Digest, Signature> {
 	/// precisely where in the process the issue was detected.
 	pub fn deconstruct(self) -> (Statement<Candidate, Digest>, Signature, Signature) {
 		match self {
-			Self::Candidate(candidate, a, b) => (Statement::Candidate(candidate), a, b),
+			Self::Seconded(candidate, a, b) => (Statement::Seconded(candidate), a, b),
 			Self::Validity(digest, a, b) => (Statement::Valid(digest), a, b),
 			Self::Invalidity(digest, a, b) => (Statement::Invalid(digest), a, b),
 		}
@@ -365,7 +365,7 @@ impl<Ctx: Context> Table<Ctx> {
 		let SignedStatement { statement, signature, sender: signer } = statement;
 
 		let res = match statement {
-			Statement::Candidate(candidate) => self.import_candidate(
+			Statement::Seconded(candidate) => self.import_candidate(
 				context,
 				signer.clone(),
 				candidate,
@@ -429,7 +429,7 @@ impl<Ctx: Context> Table<Ctx> {
 			return Err(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
 				statement: SignedStatement {
 					signature,
-					statement: Statement::Candidate(candidate),
+					statement: Statement::Seconded(candidate),
 					sender: authority,
 				},
 			}));
@@ -554,7 +554,7 @@ impl<Ctx: Context> Table<Ctx> {
 
 						// two signatures on same candidate
 						(ValidityVote::Issued(a), ValidityVote::Issued(b)) =>
-							make_ds(DoubleSign::Candidate(votes.candidate.clone(), a, b)),
+							make_ds(DoubleSign::Seconded(votes.candidate.clone(), a, b)),
 
 						// two signatures on same validity vote
 						(ValidityVote::Valid(a), ValidityVote::Valid(b)) =>
@@ -717,13 +717,13 @@ mod tests {
 
 		let mut table = create();
 		let statement_a = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
 
 		let statement_b = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 999)),
+			statement: Statement::Seconded(Candidate(2, 999)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -753,7 +753,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -764,7 +764,7 @@ mod tests {
 			table.detected_misbehavior[&AuthorityId(1)][0],
 			Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
 				statement: SignedStatement {
-					statement: Statement::Candidate(Candidate(2, 100)),
+					statement: Statement::Seconded(Candidate(2, 100)),
 					signature: Signature(1),
 					sender: AuthorityId(1),
 				},
@@ -786,7 +786,7 @@ mod tests {
 		let mut table = create();
 
 		let candidate_a = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -829,7 +829,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -878,7 +878,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -887,7 +887,7 @@ mod tests {
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let invalid_statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(999),
 			sender: AuthorityId(1),
 		};
@@ -910,7 +910,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -973,7 +973,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -1041,7 +1041,7 @@ mod tests {
 		// have 2/3 validity guarantors note validity.
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -1086,7 +1086,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};
@@ -1112,7 +1112,7 @@ mod tests {
 
 		let mut table = create();
 		let statement = SignedStatement {
-			statement: Statement::Candidate(Candidate(2, 100)),
+			statement: Statement::Seconded(Candidate(2, 100)),
 			signature: Signature(1),
 			sender: AuthorityId(1),
 		};

polkadot/statement-table/src/lib.rs

@@ -53,7 +53,7 @@ pub mod v1 {
 			match *s {
 				generic::Statement::Valid(s) => PrimitiveStatement::Valid(s),
 				generic::Statement::Invalid(s) => PrimitiveStatement::Invalid(s),
-				generic::Statement::Candidate(ref s) => PrimitiveStatement::Candidate(s.hash()),
+				generic::Statement::Seconded(ref s) => PrimitiveStatement::Seconded(s.hash()),
 			}
 		}
 	}