pezkuwi-subxt/cumulus/primitives/timestamp/src/lib.rs

// Copyright 2021 Parity Technologies (UK) Ltd.
// This file is part of Cumulus.

// Cumulus 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.

// Cumulus 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 Cumulus.  If not, see <http://www.gnu.org/licenses/>.

//! Cumulus timestamp related primitives.
//!
//! Provides a [`InherentDataProvider`] that should be used in the validation phase of the
//! parachain. It will be used to create the inherent data and that will be used to check the
//! inherents inside the parachain block (in this case the timestamp inherent). As we don't have
//! access to any clock from the runtime the timestamp is always passed as an inherent into the
//! runtime. To check this inherent when validating the block, we will use the relay chain slot. As
//! the relay chain slot is derived from a timestamp, we can easily convert it back to a timestamp
//! by muliplying it with the slot duration. By comparing the relay chain slot derived timestamp
//! with the timestamp we can ensure that the parachain timestamp is reasonable.

#![cfg_attr(not(feature = "std"), no_std)]

use cumulus_primitives_core::relay_chain::Slot;
use sp_inherents::{Error, InherentData};
use sp_std::time::Duration;

pub use sp_timestamp::{InherentType, INHERENT_IDENTIFIER};

/// The inherent data provider for the timestamp.
///
/// This should be used in the runtime when checking the inherents in the validation phase of the
/// parachain.
pub struct InherentDataProvider {
	relay_chain_slot: Slot,
	relay_chain_slot_duration: Duration,
}

impl InherentDataProvider {
	/// Create `Self` from the given relay chain slot and slot duration.
	pub fn from_relay_chain_slot_and_duration(
		relay_chain_slot: Slot,
		relay_chain_slot_duration: Duration,
	) -> Self {
		Self { relay_chain_slot, relay_chain_slot_duration }
	}

	/// Create the inherent data.
	pub fn create_inherent_data(&self) -> Result<InherentData, Error> {
		let mut inherent_data = InherentData::new();
		self.provide_inherent_data(&mut inherent_data).map(|_| inherent_data)
	}

	/// Provide the inherent data into the given `inherent_data`.
	pub fn provide_inherent_data(&self, inherent_data: &mut InherentData) -> Result<(), Error> {
		// As the parachain starts building at around `relay_chain_slot + 1` we use that slot to
		// calculate the timestamp.
		let data: InherentType = ((*self.relay_chain_slot + 1) *
			self.relay_chain_slot_duration.as_millis() as u64)
			.into();

		inherent_data.put_data(INHERENT_IDENTIFIER, &data)
	}
}