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 rstd::collections::btree_map::BTreeMap;
use parity_codec::{Decode, HasCompact};
use srml_support::{decl_storage, decl_module, fail, ensure};

use bitvec::{bitvec, BigEndian};
use sr_primitives::traits::{Hash as HashT, BlakeTwo256, Member, CheckedConversion, Saturating, One};
use primitives::{Hash, Balance, parachain::{
	self, Id as ParaId, Chain, DutyRoster, AttestedCandidate, Statement, AccountIdConversion,
	ParachainDispatchOrigin, UpwardMessage, BlockIngressRoots,
}};
use {system, session};
use srml_support::{
	StorageValue, StorageMap, storage::AppendableStorageMap, Parameter, Dispatchable, dispatch::Result,
	traits::{Currency, WithdrawReason, ExistenceRequirement}
};

#[cfg(feature = "std")]
use srml_support::storage::hashed::generator;

use inherents::{ProvideInherent, InherentData, RuntimeString, MakeFatalError, InherentIdentifier};

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

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

use system::ensure_none;

// ranges for iteration of general block number don't work, so this
// is a utility to get around that.
struct BlockNumberRange<N> {
	low: N,
	high: N,
}

impl<N: Saturating + One + PartialOrd + PartialEq + Clone> Iterator for BlockNumberRange<N> {
	type Item = N;

	fn next(&mut self) -> Option<N> {
		if self.low >= self.high {
			return None
		}

		let item = self.low.clone();
		self.low = self.low.clone().saturating_add(One::one());
		Some(item)
	}
}

// creates a range iterator between `low` and `high`. `low` must be <= `high`.
fn number_range<N>(low: N, high: N) -> BlockNumberRange<N> {
	BlockNumberRange { low, high }
}

/// Parachain registration API.
pub trait ParachainRegistrar<AccountId> {
	/// An identifier for a parachain.
	type ParaId: Member + Parameter + Default + AccountIdConversion<AccountId> + Copy + HasCompact;

	/// Create a new unique parachain identity for later registration.
	fn new_id() -> Self::ParaId;

	/// Register a parachain with given `code` and `initial_head_data`. `id` must not yet be registered or it will
	/// result in a error.
	fn register_parachain(id: Self::ParaId, code: Vec<u8>, initial_head_data: Vec<u8>) -> Result;

	/// Deregister a parachain with given `id`. If `id` is not currently registered, an error is returned.
	fn deregister_parachain(id: Self::ParaId) -> Result;
}

impl<T: Trait> ParachainRegistrar<T::AccountId> for Module<T> {
	type ParaId = ParaId;
	fn new_id() -> ParaId {
		<NextFreeId>::mutate(|n| { let r = *n; *n = ParaId::from(u32::from(*n) + 1); r })
	}
	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>::insert(id, code);
		<Parachains>::put(parachains);
		<Heads>::insert(id, initial_head_data);

		// Because there are no ordering guarantees that inherents
		// are applied before regular transactions, a parachain candidate could
		// be registered before the `UpdateHeads` inherent is processed. If so, messages
		// could be sent to a parachain in the block it is registered.
		<Watermarks<T>>::insert(id, <system::Module<T>>::block_number().saturating_sub(One::one()));

		Ok(())
	}
	fn deregister_parachain(id: ParaId) -> Result {
		let mut parachains = Self::active_parachains();
		match parachains.binary_search(&id) {
			Ok(idx) => { parachains.remove(idx); }
			Err(_) => return Ok(()),
		}

		<Code>::remove(id);
		<Heads>::remove(id);

		let watermark = <Watermarks<T>>::take(id);

		// clear all routing entries _to_. But not those _from_.
		if let Some(watermark) = watermark {
			let now = <system::Module<T>>::block_number();

			// iterate over all blocks between watermark and now + 1 (since messages might
			// have already been sent to `id` in this block.
			for unrouted_block in number_range(watermark, now).map(|n| n.saturating_add(One::one())) {
				<UnroutedIngress<T>>::remove(&(unrouted_block, id));
			}
		}

		<Parachains>::put(parachains);

		Ok(())
	}
}

// wrapper trait because an associated type of `Currency<Self::AccountId,Balance=Balance>`
// doesn't work.`
pub trait ParachainCurrency<AccountId> {
	fn free_balance(para_id: ParaId) -> Balance;
	fn deduct(para_id: ParaId, amount: Balance) -> Result;
}

impl<AccountId, T: Currency<AccountId>> ParachainCurrency<AccountId> for T where
	T::Balance: From<Balance> + Into<Balance>,
	ParaId: AccountIdConversion<AccountId>,
{
	fn free_balance(para_id: ParaId) -> Balance {
		let para_account = para_id.into_account();
		T::free_balance(&para_account).into()
	}

	fn deduct(para_id: ParaId, amount: Balance) -> Result {
		let para_account = para_id.into_account();

		// burn the fee.
		let _ = T::withdraw(
			&para_account,
			amount.into(),
			WithdrawReason::Fee,
			ExistenceRequirement::KeepAlive,
		)?;

		Ok(())
	}
}

pub trait Trait: session::Trait {
	/// The outer origin type.
	type Origin: From<Origin> + From<system::RawOrigin<Self::AccountId>>;

	/// The outer call dispatch type.
	type Call: Parameter + Dispatchable<Origin=<Self as Trait>::Origin>;

	/// Some way of interacting with balances for fees.
	type ParachainCurrency: ParachainCurrency<Self::AccountId>;
}

/// Origin for the parachains module.
#[derive(PartialEq, Eq, Clone)]
#[cfg_attr(feature = "std", derive(Debug))]
pub enum Origin {
	/// It comes from a parachain.
	Parachain(ParaId),
}

// result of <NodeCodec<Blake2Hasher> as trie_db::NodeCodec<Blake2Hasher>>::hashed_null_node()
const EMPTY_TRIE_ROOT: [u8; 32] = [
	3, 23, 10, 46, 117, 151, 183, 183, 227, 216, 76, 5, 57, 29, 19, 154,
	98, 177, 87, 231, 135, 134, 216, 192, 130, 242, 157, 207, 76, 17, 19, 20
];

/// Total number of individual messages allowed in the parachain -> relay-chain message queue.