merge duty roster changes

substrate/wasm-runtime/polkadot/src/runtime/parachains.rs

@@ -0,0 +1,141 @@
+// 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 runtime_std::mem;
+use codec::{Slicable, Joiner};
+use support::{Hashable, with_env, storage};
+use runtime::session;
+
+const PARACHAIN_COUNT: &[u8] = b"par:cou";
+
+/// Identifier for a chain, either one of a number of parachains or the relay chain.
+#[derive(Copy, Clone, PartialEq)]
+#[cfg_attr(test, derive(Debug))]
+pub enum Chain {
+	/// The relay chain.
+	Relay,
+	/// A parachain of the given index.
+	Parachain(u32),
+}
+
+/// The duty roster specifying what jobs each validator must do.
+#[derive(Clone, PartialEq)]
+#[cfg_attr(test, derive(Default, Debug))]
+pub struct DutyRoster {
+	/// Lookup from validator index to chain on which that validator has a duty to validate.
+	pub validator_duty: Vec<Chain>,
+	/// Lookup from validator index to chain on which that validator has a duty to guarantee
+	/// availability.
+	pub guarantor_duty: Vec<Chain>,
+}
+
+/// Get the number of parachains registered at present.
+pub fn parachain_count() -> u32 {
+	storage::get_or(PARACHAIN_COUNT, 0)
+}
+
+/// Calculate the current block's duty roster.
+pub fn calculate_duty_roster() -> DutyRoster {
+	let parachain_count = parachain_count();
+	let validator_count = session::validator_count() as u32;
+	let validators_per_parachain = (validator_count - 1) / parachain_count;
+
+	let mut roles_val = (0..validator_count).map(|i| match i {
+		i if i < parachain_count * validators_per_parachain => Chain::Parachain(i / validators_per_parachain as u32),
+		_ => Chain::Relay,
+	}).collect::<Vec<_>>();
+	let mut roles_gua = roles_val.clone();
+
+	let h = with_env(|e| e.parent_hash.clone());
+	let mut seed = Vec::<u8>::new().join(&h).join(b"validator_role_pairs").blake2_256();
+
+	// 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::from_slice(&mut &seed[offset..offset + 4]).expect("using 4 bytes for a 32-bit quantity") as usize % remaining;
+		let gua_index = u32::from_slice(&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 = seed.blake2_256();
+		}
+
+		// 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,
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use runtime_std::{with_externalities, twox_128, TestExternalities};
+	use codec::{KeyedVec, Joiner};
+	use support::{one, two, with_env};
+	use runtime::{consensus, session};
+
+	fn simple_setup() -> TestExternalities {
+		TestExternalities { storage: map![
+			twox_128(b"ses:val:len").to_vec() => vec![].join(&8u32),
+			twox_128(b"par:cou").to_vec() => vec![].join(&2u32)
+		], }
+	}
+
+	#[test]
+	fn should_work() {
+		let mut t = simple_setup();
+		with_externalities(&mut t, || {
+			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 {
+					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);
+			};
+
+			with_env(|e| e.parent_hash = [0u8; 32].into());
+			let duty_roster_0 = calculate_duty_roster();
+			check_roster(&duty_roster_0);
+
+			with_env(|e| e.parent_hash = [1u8; 32].into());
+			let duty_roster_1 = calculate_duty_roster();
+			check_roster(&duty_roster_1);
+			assert!(duty_roster_0 != duty_roster_1);
+
+			with_env(|e| e.parent_hash = [2u8; 32].into());
+			let duty_roster_2 = calculate_duty_roster();
+			check_roster(&duty_roster_2);
+			assert!(duty_roster_0 != duty_roster_2);
+			assert!(duty_roster_1 != duty_roster_2);
+		});
+	}
+}