pezkuwi-subxt/polkadot/runtime/src/parachains.rs

// Copyright 2017 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/>.

//! Main parachains logic. For now this is just the determination of which validators do what.

use rstd::prelude::*;
use codec::Decode;

use bitvec::BigEndian;
use sr_primitives::CheckInherentError;
use sr_primitives::traits::{
	Extrinsic, Block as BlockT, Hash as HashT, BlakeTwo256, ProvideInherent,
};
use primitives::parachain::{Id as ParaId, Chain, DutyRoster, AttestedCandidate, Statement};
use {system, session};

use srml_support::{StorageValue, StorageMap};
use srml_support::dispatch::Result;

#[cfg(any(feature = "std", test))]
use sr_primitives::{self, ChildrenStorageMap};

#[cfg(any(feature = "std", test))]
use rstd::marker::PhantomData;

use system::ensure_inherent;

pub trait Trait: session::Trait {
	/// The position of the set_heads call in the block.
	const SET_POSITION: u32;
}

decl_storage! {
	trait Store for Module<T: Trait> as Parachains {
		// Vector of all parachain IDs.
		pub Parachains get(active_parachains): Vec<ParaId>;
		// The parachains registered at present.
		pub Code get(parachain_code): map ParaId => Option<Vec<u8>>;
		// The heads of the parachains registered at present. these are kept sorted.
		pub Heads get(parachain_head): map ParaId => Option<Vec<u8>>;

		// Did the parachain heads get updated in this block?
		DidUpdate: bool;
	}
	add_extra_genesis {
		config(parachains): Vec<(ParaId, Vec<u8>, Vec<u8>)>;
		config(_phdata): PhantomData<T>;
		build(|storage: &mut sr_primitives::StorageMap, _: &mut ChildrenStorageMap, config: &GenesisConfig<T>| {
			use codec::Encode;

			let mut p = config.parachains.clone();
			p.sort_unstable_by_key(|&(ref id, _, _)| id.clone());
			p.dedup_by_key(|&mut (ref id, _, _)| id.clone());

			let only_ids: Vec<_> = p.iter().map(|&(ref id, _, _)| id).cloned().collect();

			storage.insert(Self::hash(<Parachains<T>>::key()).to_vec(), only_ids.encode());

			for (id, code, genesis) in p {
				let code_key = Self::hash(&<Code<T>>::key_for(&id)).to_vec();
				let head_key = Self::hash(&<Heads<T>>::key_for(&id)).to_vec();

				storage.insert(code_key, code.encode());
				storage.insert(head_key, genesis.encode());
			}
		});
	}
}

decl_module! {
	/// Parachains module.
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		/// Provide candidate receipts for parachains, in ascending order by id.
		fn set_heads(origin, heads: Vec<AttestedCandidate>) -> Result {
			ensure_inherent(origin)?;
			ensure!(!<DidUpdate<T>>::exists(), "Parachain heads must be updated only once in the block");
			ensure!(
				<system::Module<T>>::extrinsic_index() == Some(T::SET_POSITION),
				"Parachain heads update extrinsic must be at position {} in the block"
	//			, T::SET_POSITION
			);

			let active_parachains = Self::active_parachains();

			// perform integrity checks before writing to storage.
			{
				let n_parachains = active_parachains.len();
				ensure!(heads.len() <= n_parachains, "Too many parachain candidates");

				let mut last_id = None;
				let mut iter = active_parachains.iter();
				for head in &heads {
					// proposed heads must be ascending order by parachain ID without duplicate.
					ensure!(
						last_id.as_ref().map_or(true, |x| x < &head.parachain_index()),
						"Parachain candidates out of order by ID"
					);

					// must be unknown since active parachains are always sorted.
					ensure!(
						iter.find(|x| x == &&head.parachain_index()).is_some(),
						"Submitted candidate for unregistered or out-of-order parachain {}"
					);

					last_id = Some(head.parachain_index());
				}
			}

			Self::check_attestations(&heads)?;


			for head in heads {
				let id = head.parachain_index();
				<Heads<T>>::insert(id, head.candidate.head_data.0);
			}

			<DidUpdate<T>>::put(true);

			Ok(())
		}

		/// Register a parachain with given code.
		/// Fails if given ID is already used.
		pub fn register_parachain(id: ParaId, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result {
			let mut parachains = Self::active_parachains();
			match parachains.binary_search(&id) {
				Ok(_) => fail!("Parachain already exists"),
				Err(idx) => parachains.insert(idx, id),
			}

			<Code<T>>::insert(id, code);
			<Parachains<T>>::put(parachains);
			<Heads<T>>::insert(id, initial_head_data);

			Ok(())
		}

		/// Deregister a parachain with given id
		pub fn deregister_parachain(id: ParaId) -> Result {
			let mut parachains = Self::active_parachains();
			match parachains.binary_search(&id) {
				Ok(idx) => { parachains.remove(idx); }
				Err(_) => {}
			}

			<Code<T>>::remove(id);
			<Heads<T>>::remove(id);
			<Parachains<T>>::put(parachains);
			Ok(())
		}

		fn on_finalise(_n: T::BlockNumber) {
			assert!(<Self as Store>::DidUpdate::take(), "Parachain heads must be updated once in the block");
		}
	}
}

fn majority_of(list_len: usize) -> usize {
	list_len / 2 + list_len % 2
}

fn localized_payload(statement: Statement, parent_hash: ::primitives::Hash) -> Vec<u8> {
	use codec::Encode;

	let mut encoded = statement.encode();
	encoded.extend(parent_hash.as_ref());
	encoded
}

impl<T: Trait> Module<T> {
	/// Calculate the current block's duty roster using system's random seed.
	pub fn calculate_duty_roster() -> DutyRoster {
		let parachains = Self::active_parachains();
		let parachain_count = parachains.len();
		let validator_count = <session::Module<T>>::validator_count() as usize;
		let validators_per_parachain = if parachain_count != 0 { (validator_count - 1) / parachain_count } else { 0 };

		let mut roles_val = (0..validator_count).map(|i| match i {
			i if i < parachain_count * validators_per_parachain => {
				let idx = i / validators_per_parachain;
				Chain::Parachain(parachains[idx].clone())
			}
			_ => Chain::Relay,
		}).collect::<Vec<_>>();

		let mut roles_gua = roles_val.clone();

		let mut random_seed = system::Module::<T>::random_seed().as_ref().to_vec();
		random_seed.extend(b"validator_role_pairs");
		let mut seed = BlakeTwo256::hash(&random_seed);

		// shuffle
		for i in 0..(validator_count - 1) {
			// 8 bytes of entropy used per cycle, 32 bytes entropy per hash
			let offset = (i * 8 % 32) as usize;

			// number of roles remaining to select from.
			let remaining = (validator_count - i) as usize;

			// 4 * 2 32-bit ints per 256-bit seed.
			let val_index = u32::decode(&mut &seed[offset..offset + 4]).expect("using 4 bytes for a 32-bit quantity") as usize % remaining;
			let gua_index = u32::decode(&mut &seed[offset + 4..offset + 8]).expect("using 4 bytes for a 32-bit quantity") as usize % remaining;

			if offset == 24 {
				// into the last 8 bytes - rehash to gather new entropy
				seed = BlakeTwo256::hash(seed.as_ref());
			}

			// exchange last item with randomly chosen first.
			roles_val.swap(remaining - 1, val_index);
			roles_gua.swap(remaining - 1, gua_index);
		}

		DutyRoster {
			validator_duty: roles_val,
			guarantor_duty: roles_gua,
		}
	}

	// check the attestations on these candidates. The candidates should have been checked
	// that each candidates' chain ID is valid.
	fn check_attestations(attested_candidates: &[AttestedCandidate]) -> Result {
		use primitives::parachain::ValidityAttestation;
		use sr_primitives::traits::Verify;

		// returns groups of slices that have the same chain ID.
		// assumes the inner slice is sorted by id.
		struct GroupedDutyIter<'a> {
			next_idx: usize,
			inner: &'a [(usize, ParaId)],
		}

		impl<'a> GroupedDutyIter<'a> {
			fn new(inner: &'a [(usize, ParaId)]) -> Self {
				GroupedDutyIter { next_idx: 0, inner }
			}

			fn group_for(&mut self, wanted_id: ParaId) -> Option<&'a [(usize, ParaId)]> {
				while let Some((id, keys)) = self.next() {
					if wanted_id == id {
						return Some(keys)
					}
				}

				None
			}
		}

		impl<'a> Iterator for GroupedDutyIter<'a> {
			type Item = (ParaId, &'a [(usize, ParaId)]);

			fn next(&mut self) -> Option<Self::Item> {
				if self.next_idx == self.inner.len() { return None }
				let start_idx = self.next_idx;
				self.next_idx += 1;
				let start_id = self.inner[start_idx].1;

				while self.inner.get(self.next_idx).map_or(false, |&(_, ref id)| id == &start_id) {
					self.next_idx += 1;
				}

				Some((start_id, &self.inner[start_idx..self.next_idx]))
			}
		}

		let authorities = super::Consensus::authorities();
		let duty_roster = Self::calculate_duty_roster();

		// convert a duty roster, which is originally a Vec<Chain>, where each
		// item corresponds to the same position in the session keys, into
		// a list containing (index, parachain duty) where indices are into the session keys.
		// this list is sorted ascending by parachain duty, just like the
		// parachain candidates are.
		let make_sorted_duties = |duty: &[Chain]| {
			let mut sorted_duties = Vec::with_capacity(duty.len());
			for (val_idx, duty) in duty.iter().enumerate() {
				let id = match duty {
					Chain::Relay => continue,
					Chain::Parachain(id) => id,
				};

				let idx = sorted_duties.binary_search_by_key(&id, |&(_, ref id)| id)
					.unwrap_or_else(|idx| idx);

				sorted_duties.insert(idx, (val_idx, *id));
			}

			sorted_duties
		};

		let sorted_validators = make_sorted_duties(&duty_roster.validator_duty);
		let sorted_guarantors = make_sorted_duties(&duty_roster.guarantor_duty);

		let parent_hash = super::System::parent_hash();
		let localized_payload = |statement: Statement| localized_payload(statement, parent_hash);

		let mut validator_groups = GroupedDutyIter::new(&sorted_validators[..]);
		let mut guarantor_groups = GroupedDutyIter::new(&sorted_guarantors[..]);

		for candidate in attested_candidates {
			let validator_group = validator_groups.group_for(candidate.parachain_index())
				.ok_or("no validator group for parachain")?;

			let availability_group = guarantor_groups.group_for(candidate.parachain_index())
				.ok_or("no availability group for parachain")?;

			ensure!(
				candidate.validity_votes.len() >= majority_of(validator_group.len()),
				"Not enough validity attestations"
			);

			ensure!(
				candidate.availability_votes.len() >= majority_of(availability_group.len()),
				"Not enough availability attestations"
			);

			let mut candidate_hash = None;
			let mut encoded_implicit = None;
			let mut encoded_explicit = None;

			// track which voters have voted already. the first `authorities.len()`
			// bits is for validity, the next are for availability.
			let mut track_voters = bitvec![0; authorities.len() * 2];
			for (auth_id, validity_attestation) in &candidate.validity_votes {
				// protect against double-votes.
				match validator_group.iter().find(|&(idx, _)| &authorities[*idx] == auth_id) {
					None => return Err("Attesting validator not on this chain's validation duty."),
					Some(&(idx, _)) => {
						if track_voters.get(idx) {
							return Err("Voter already attested validity once")
						}
						track_voters.set(idx, true)
					}
				}

				let (payload, sig) = match validity_attestation {
					ValidityAttestation::Implicit(sig) => {
						let payload = encoded_implicit.get_or_insert_with(|| localized_payload(
							Statement::Candidate(candidate.candidate.clone()),
						));

						(payload, sig)
					}
					ValidityAttestation::Explicit(sig) => {
						let hash = candidate_hash
							.get_or_insert_with(|| candidate.candidate.hash())
							.clone();

						let payload = encoded_explicit.get_or_insert_with(|| localized_payload(
							Statement::Valid(hash),
						));

						(payload, sig)
					}
				};

				ensure!(
					sig.verify(&payload[..], &auth_id.0.into()),
					"Candidate validity attestation signature is bad."
				);
			}

			let mut encoded_available = None;
			for (auth_id, sig) in &candidate.availability_votes {
				match availability_group.iter().find(|&(idx, _)| &authorities[*idx] == auth_id) {
					None => return Err("Attesting validator not on this chain's availability duty."),
					Some(&(idx, _)) => {
						if track_voters.get(authorities.len() + idx) {
							return Err("Voter already attested availability once")
						}
						track_voters.set(authorities.len() + idx, true)
					}
				}

				let hash = candidate_hash
					.get_or_insert_with(|| candidate.candidate.hash())
					.clone();

				let payload = encoded_available.get_or_insert_with(|| localized_payload(
					Statement::Available(hash),
				));

				ensure!(
					sig.verify(&payload[..], &auth_id.0.into()),
					"Candidate availability attestation signature is bad."
				)
			}
		}

		Ok(())
	}

/*
	// TODO: Consider integrating if needed.
	/// Extract the parachain heads from the block.
	pub fn parachain_heads(&self) -> &[CandidateReceipt] {
		let x = self.inner.extrinsics.get(PARACHAINS_SET_POSITION as usize).and_then(|xt| match xt.function {
			Call::Parachains(ParachainsCall::set_heads(ref x)) => Some(&x[..]),
			_ => None
		});

		match x {
			Some(x) => x,
			None => panic!("Invalid polkadot block asserted at {:?}", self.file_line),
		}
	}
*/
}

impl<T: Trait> ProvideInherent for Module<T> {
	type Inherent = Vec<AttestedCandidate>;
	type Call = Call<T>;

	fn create_inherent_extrinsics(data: Self::Inherent) -> Vec<(u32, Self::Call)> {
		vec![(T::SET_POSITION, Call::set_heads(data))]
	}

	fn check_inherent<Block: BlockT, F: Fn(&Block::Extrinsic) -> Option<&Self::Call>>(
		block: &Block, _data: Self::Inherent, extract_function: &F
	) -> ::rstd::result::Result<(), CheckInherentError> {
		let has_heads = block
			.extrinsics()
			.get(T::SET_POSITION as usize)
			.map_or(false, |xt| {
				xt.is_signed() == Some(false) && match extract_function(&xt) {
					Some(Call::set_heads(_)) => true,
					_ => false,
				}
			});

		if !has_heads {
			return Err(CheckInherentError::Other(
				"No valid parachains inherent in block".into()
			));
		}

		Ok(())
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use sr_io::{TestExternalities, with_externalities};
	use substrate_primitives::{H256, Blake2Hasher};
	use sr_primitives::{generic, BuildStorage};
	use sr_primitives::traits::BlakeTwo256;
	use primitives::{parachain::{CandidateReceipt, HeadData, ValidityAttestation}, SessionKey};
	use keyring::Keyring;
	use {consensus, timestamp};

	impl_outer_origin! {
		pub enum Origin for Test {}
	}

	#[derive(Clone, Eq, PartialEq)]
	pub struct Test;
	impl consensus::Trait for Test {
		const NOTE_OFFLINE_POSITION: u32 = 1;
		type SessionKey = SessionKey;
		type InherentOfflineReport = ();
		type Log = ::Log;
	}
	impl system::Trait for Test {
		type Origin = Origin;
		type Index = ::Nonce;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type Digest = generic::Digest<::Log>;
		type AccountId = ::AccountId;
		type Header = ::Header;
		type Event = ();
		type Log = ::Log;
	}
	impl session::Trait for Test {
		type ConvertAccountIdToSessionKey = ::SessionKeyConversion;
		type OnSessionChange = ();
		type Event = ();
	}
	impl timestamp::Trait for Test {
		const TIMESTAMP_SET_POSITION: u32 = 0;
		type Moment = u64;
		type OnTimestampSet = ();
	}
	impl Trait for Test {
		const SET_POSITION: u32 = 0;
	}

	type Parachains = Module<Test>;

	fn new_test_ext(parachains: Vec<(ParaId, Vec<u8>, Vec<u8>)>) -> TestExternalities<Blake2Hasher> {
		let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap().0;
		let authority_keys = [
			Keyring::Alice,
			Keyring::Bob,
			Keyring::Charlie,
			Keyring::Dave,
			Keyring::Eve,
			Keyring::Ferdie,
			Keyring::One,
			Keyring::Two,
		];

		t.extend(consensus::GenesisConfig::<Test>{
			code: vec![],
			authorities: authority_keys.iter().map(|k| k.to_raw_public().into()).collect(),
		}.build_storage().unwrap().0);
		t.extend(session::GenesisConfig::<Test>{
			session_length: 1000,
			validators: authority_keys.iter().map(|k| k.to_raw_public().into()).collect(),
		}.build_storage().unwrap().0);
		t.extend(GenesisConfig::<Test>{
			parachains: parachains,
			_phdata: Default::default(),
		}.build_storage().unwrap().0);
		t.into()
	}

	fn make_attestations(candidate: &mut AttestedCandidate) {
		let mut vote_implicit = false;
		let parent_hash = ::System::parent_hash();

		let duty_roster = Parachains::calculate_duty_roster();
		let candidate_hash = candidate.candidate.hash();

		let authorities = ::Consensus::authorities();
		let extract_key = |public: SessionKey| {
			Keyring::from_raw_public(public.0).unwrap()
		};

		let validation_entries = duty_roster.validator_duty.iter()
			.enumerate()
			.map(|(i, d)| (i, d, true));

		let availability_entries = duty_roster.guarantor_duty.iter()
			.enumerate()
			.map(|(i, d)| (i, d, false));

		for (idx, &duty, is_validation) in validation_entries.chain(availability_entries) {
			if duty != Chain::Parachain(candidate.parachain_index()) { continue }
			if is_validation { vote_implicit = !vote_implicit };

			let key = extract_key(authorities[idx]);

			let statement = if is_validation && vote_implicit {
				Statement::Candidate(candidate.candidate.clone())
			} else if is_validation {
				Statement::Valid(candidate_hash.clone())
			} else {
				Statement::Available(candidate_hash.clone())
			};

			let payload = localized_payload(statement, parent_hash);
			let signature = key.sign(&payload[..]).into();

			if is_validation {
				candidate.validity_votes.push((authorities[idx], if vote_implicit {
					ValidityAttestation::Implicit(signature)
				} else {
					ValidityAttestation::Explicit(signature)
				}));
			} else {
				candidate.availability_votes.push((authorities[idx], signature));
			}
		}
	}

	#[test]
	fn active_parachains_should_work() {
		let parachains = vec![
			(5u32.into(), vec![1,2,3], vec![1]),
			(100u32.into(), vec![4,5,6], vec![2]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			assert_eq!(Parachains::active_parachains(), vec![5u32.into(), 100u32.into()]);
			assert_eq!(Parachains::parachain_code(&5u32.into()), Some(vec![1,2,3]));
			assert_eq!(Parachains::parachain_code(&100u32.into()), Some(vec![4,5,6]));
		});
	}

	#[test]
	fn register_deregister() {
		let parachains = vec![
			(5u32.into(), vec![1,2,3], vec![1]),
			(100u32.into(), vec![4,5,6], vec![2,]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			assert_eq!(Parachains::active_parachains(), vec![5u32.into(), 100u32.into()]);

			assert_eq!(Parachains::parachain_code(&5u32.into()), Some(vec![1,2,3]));
			assert_eq!(Parachains::parachain_code(&100u32.into()), Some(vec![4,5,6]));

			assert_ok!(Parachains::register_parachain(99u32.into(), vec![7,8,9], vec![1, 1, 1]));

			assert_eq!(Parachains::active_parachains(), vec![5u32.into(), 99u32.into(), 100u32.into()]);
			assert_eq!(Parachains::parachain_code(&99u32.into()), Some(vec![7,8,9]));

			assert_ok!(Parachains::deregister_parachain(5u32.into()));

			assert_eq!(Parachains::active_parachains(), vec![99u32.into(), 100u32.into()]);
			assert_eq!(Parachains::parachain_code(&5u32.into()), None);
		});
	}

	#[test]
	fn duty_roster_works() {
		let parachains = vec![
			(0u32.into(), vec![], vec![]),
			(1u32.into(), vec![], vec![]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			let check_roster = |duty_roster: &DutyRoster| {
				assert_eq!(duty_roster.validator_duty.len(), 8);
				assert_eq!(duty_roster.guarantor_duty.len(), 8);
				for i in (0..2).map(ParaId::from) {
					assert_eq!(duty_roster.validator_duty.iter().filter(|&&j| j == Chain::Parachain(i)).count(), 3);
					assert_eq!(duty_roster.guarantor_duty.iter().filter(|&&j| j == Chain::Parachain(i)).count(), 3);
				}
				assert_eq!(duty_roster.validator_duty.iter().filter(|&&j| j == Chain::Relay).count(), 2);
				assert_eq!(duty_roster.guarantor_duty.iter().filter(|&&j| j == Chain::Relay).count(), 2);
			};

			system::Module::<Test>::set_random_seed([0u8; 32].into());
			let duty_roster_0 = Parachains::calculate_duty_roster();
			check_roster(&duty_roster_0);

			system::Module::<Test>::set_random_seed([1u8; 32].into());
			let duty_roster_1 = Parachains::calculate_duty_roster();
			check_roster(&duty_roster_1);
			assert!(duty_roster_0 != duty_roster_1);


			system::Module::<Test>::set_random_seed([2u8; 32].into());
			let duty_roster_2 = Parachains::calculate_duty_roster();
			check_roster(&duty_roster_2);
			assert!(duty_roster_0 != duty_roster_2);
			assert!(duty_roster_1 != duty_roster_2);
		});
	}

	#[test]
	fn unattested_candidate_is_rejected() {
		let parachains = vec![
			(0u32.into(), vec![], vec![]),
			(1u32.into(), vec![], vec![]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			system::Module::<Test>::set_random_seed([0u8; 32].into());
			let candidate = AttestedCandidate {
				validity_votes: vec![],
				availability_votes: vec![],
				candidate: CandidateReceipt {
					parachain_index: 0.into(),
					collator: Default::default(),
					signature: Default::default(),
					head_data: HeadData(vec![1, 2, 3]),
					balance_uploads: vec![],
					egress_queue_roots: vec![],
					fees: 0,
					block_data_hash: Default::default(),
				}
			};

			assert!(Parachains::dispatch(Call::set_heads(vec![candidate]), Origin::INHERENT).is_err());
		})
	}

	#[test]
	fn attested_candidates_accepted_in_order() {
		let parachains = vec![
			(0u32.into(), vec![], vec![]),
			(1u32.into(), vec![], vec![]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			system::Module::<Test>::set_random_seed([0u8; 32].into());
			let mut candidate_a = AttestedCandidate {
				validity_votes: vec![],
				availability_votes: vec![],
				candidate: CandidateReceipt {
					parachain_index: 0.into(),
					collator: Default::default(),
					signature: Default::default(),
					head_data: HeadData(vec![1, 2, 3]),
					balance_uploads: vec![],
					egress_queue_roots: vec![],
					fees: 0,
					block_data_hash: Default::default(),
				}
			};

			let mut candidate_b = AttestedCandidate {
				validity_votes: vec![],
				availability_votes: vec![],
				candidate: CandidateReceipt {
					parachain_index: 1.into(),
					collator: Default::default(),
					signature: Default::default(),
					head_data: HeadData(vec![2, 3, 4]),
					balance_uploads: vec![],
					egress_queue_roots: vec![],
					fees: 0,
					block_data_hash: Default::default(),
				}
			};

			make_attestations(&mut candidate_a);
			make_attestations(&mut candidate_b);

			assert!(Parachains::dispatch(
				Call::set_heads(vec![candidate_b.clone(), candidate_a.clone()]),
				Origin::INHERENT,
			).is_err());

			assert!(Parachains::dispatch(
				Call::set_heads(vec![candidate_a.clone(), candidate_b.clone()]),
				Origin::INHERENT,
			).is_ok());
		});
	}

	#[test]
	fn duplicate_vote_is_rejected() {
		let parachains = vec![
			(0u32.into(), vec![], vec![]),
			(1u32.into(), vec![], vec![]),
		];

		with_externalities(&mut new_test_ext(parachains), || {
			system::Module::<Test>::set_random_seed([0u8; 32].into());
			let mut candidate = AttestedCandidate {
				validity_votes: vec![],
				availability_votes: vec![],
				candidate: CandidateReceipt {
					parachain_index: 0.into(),
					collator: Default::default(),
					signature: Default::default(),
					head_data: HeadData(vec![1, 2, 3]),
					balance_uploads: vec![],
					egress_queue_roots: vec![],
					fees: 0,
					block_data_hash: Default::default(),
				}
			};

			make_attestations(&mut candidate);

			let mut double_validity = candidate.clone();
			double_validity.validity_votes.push(candidate.validity_votes[0].clone());

			assert!(Parachains::dispatch(
				Call::set_heads(vec![double_validity]),
				Origin::INHERENT,
			).is_err());

			let mut double_availability = candidate.clone();
			double_availability.availability_votes.push(candidate.availability_votes[0].clone());

			assert!(Parachains::dispatch(
				Call::set_heads(vec![double_availability]),
				Origin::INHERENT,
			).is_err());
		});
	}
}