pallet_hyperbridge/

lib.rs

// Copyright (C) Polytope Labs Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! # Pallet Hyperbridge
//!
//! Pallet hyperbridge mediates the connection between hyperbridge and substrate-based chains. This
//! pallet provides:
//!
//!  - An [`IsmpDispatcher`] implementation which collects hyperbridge's protocol fees and commits
//!    the reciepts for these fees to child storage. Hyperbridge will only accept messages that have
//!    been paid for using this module.
//!  - An [`IsmpModule`] which recieves and processes requests from hyperbridge. These requests are
//!    dispatched by hyperbridge governance and may adjust fees or request payouts for both relayers
//!    and protocol revenue.
//!
//! This pallet contains no calls and dispatches no requests. Substrate based chains should use this
//! to dispatch requests that should be processed by hyperbridge.
//!
//! ## Usage
//!
//! This module must be configured as an [`IsmpModule`] in your
//! [`IsmpRouter`](ismp::router::IsmpRouter) implementation so that it may receive important
//! messages from hyperbridge such as paramter updates or relayer fee withdrawals.
//!
//! ```rust,ignore
//! use ismp::module::IsmpModule;
//! use ismp::router::IsmpRouter;
//!
//! #[derive(Default)]
//! struct ModuleRouter;
//!
//! impl IsmpRouter for ModuleRouter {
//!     fn module_for_id(&self, id: Vec<u8>) -> Result<Box<dyn IsmpModule>, anyhow::Error> {
//!         return match id.as_slice() {
//!             pallet_hyperbridge::PALLET_HYPERBRIDGE_ID => Ok(Box::new(pallet_hyperbridge::Pallet::<Runtime>::default())),
//!             _ => Err(Error::ModuleNotFound(id)),
//!         };
//!     }
//! }
//! ```

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

extern crate alloc;

use alloc::{collections::BTreeMap, format};
use codec::{Decode, DecodeWithMemTracking, Encode};
use frame_support::{
	sp_runtime::traits::AccountIdConversion,
	traits::{fungible::Mutate, tokens::Preservation, Get},
};
use ismp::{
	dispatcher::{DispatchRequest, FeeMetadata, IsmpDispatcher},
	host::StateMachine,
	module::IsmpModule,
	router::{PostRequest, PostResponse, Response, Timeout},
};
pub use pallet::*;
use pallet_ismp::RELAYER_FEE_ACCOUNT;
use polkadot_sdk::{sp_runtime::Weight, *};
use primitive_types::H256;

pub mod child_trie;

/// Host params for substrate based chains
#[derive(
	Debug,
	Clone,
	Encode,
	Decode,
	DecodeWithMemTracking,
	scale_info::TypeInfo,
	PartialEq,
	Eq,
	Default,
)]
pub struct SubstrateHostParams<B> {
	/// The default per byte fee
	pub default_per_byte_fee: B,
	/// Per byte fee configured for specific chains
	pub per_byte_fees: BTreeMap<StateMachine, B>,
	/// Asset registration fee
	pub asset_registration_fee: B,
}

/// Parameters that govern the working operations of this module. Versioned for ease of migration.
#[derive(
	Debug, Clone, Encode, Decode, DecodeWithMemTracking, scale_info::TypeInfo, PartialEq, Eq,
)]
pub enum VersionedHostParams<Balance> {
	/// The per-byte fee that hyperbridge charges for outgoing requests and responses.
	V1(SubstrateHostParams<Balance>),
}

impl<Balance: Default> Default for VersionedHostParams<Balance> {
	fn default() -> Self {
		VersionedHostParams::V1(Default::default())
	}
}

#[frame_support::pallet]
pub mod pallet {
	use super::*;
	use frame_support::{pallet_prelude::*, PalletId};

	/// [`IsmpModule`] module identifier for incoming requests from hyperbridge
	pub const PALLET_HYPERBRIDGE_ID: &'static [u8] = b"HYPR-FEE";

	/// [`PalletId`] where protocol fees will be collected
	pub const PALLET_HYPERBRIDGE: PalletId = PalletId(*b"HYPR-FEE");

	#[pallet::config]
	pub trait Config: polkadot_sdk::frame_system::Config + pallet_ismp::Config {
		/// The underlying [`IsmpHost`] implementation
		type IsmpHost: IsmpDispatcher<Account = Self::AccountId, Balance = Self::Balance> + Default;
	}

	#[pallet::pallet]
	#[pallet::without_storage_info]
	pub struct Pallet<T>(_);

	/// The host parameters of the pallet-hyperbridge.
	#[pallet::storage]
	#[pallet::getter(fn host_params)]
	pub type HostParams<T> =
		StorageValue<_, VersionedHostParams<<T as pallet_ismp::Config>::Balance>, ValueQuery>;

	#[pallet::event]
	#[pallet::generate_deposit(pub(super) fn deposit_event)]
	pub enum Event<T: Config> {
		/// Hyperbridge governance has now updated it's host params on this chain.
		HostParamsUpdated {
			/// The old host params
			old: VersionedHostParams<<T as pallet_ismp::Config>::Balance>,
			/// The new host params
			new: VersionedHostParams<<T as pallet_ismp::Config>::Balance>,
		},
		/// A relayer has withdrawn some fees
		RelayerFeeWithdrawn {
			/// The amount that was withdrawn
			amount: <T as pallet_ismp::Config>::Balance,
			/// The withdrawal beneficiary
			account: T::AccountId,
		},
	}

	// Errors encountered by pallet-hyperbridge
	#[pallet::error]
	pub enum Error<T> {}

	// Hack for implementing the [`Default`] bound needed for
	// [`IsmpDispatcher`](ismp::dispatcher::IsmpDispatcher) and
	// [`IsmpModule`](ismp::module::IsmpModule)
	impl<T> Default for Pallet<T> {
		fn default() -> Self {
			Self(PhantomData)
		}
	}
}

/// [`IsmpDispatcher`] implementation for dispatching requests to the hyperbridge coprocessor.
/// Charges the hyperbridge protocol fee on a per-byte basis.
///
/// **NOTE** Hyperbridge WILL NOT accept requests that were not dispatched through this
/// implementation.
impl<T> IsmpDispatcher for Pallet<T>
where
	T: Config,
	T::Balance: Into<u128> + From<u128>,
{
	type Account = T::AccountId;
	type Balance = T::Balance;

	fn dispatch_request(
		&self,
		request: DispatchRequest,
		fee: FeeMetadata<Self::Account, Self::Balance>,
	) -> Result<H256, anyhow::Error> {
		let fees = match request {
			DispatchRequest::Post(ref post) => {
				let VersionedHostParams::V1(params) = Self::host_params();
				let per_byte_fee: u128 =
					(*params.per_byte_fees.get(&post.dest).unwrap_or(&params.default_per_byte_fee))
						.into();
				// minimum fee is 32 bytes
				let fees = if post.body.len() < 32 {
					per_byte_fee * 32u128
				} else {
					per_byte_fee * post.body.len() as u128
				};

				// collect protocol fees
				if fees != 0 {
					T::Currency::transfer(
						&fee.payer,
						&RELAYER_FEE_ACCOUNT.into_account_truncating(),
						fees.into(),
						Preservation::Expendable,
					)
					.map_err(|err| {
						ismp::Error::Custom(format!("Error withdrawing request fees: {err:?}"))
					})?;
				}

				fees
			},
			DispatchRequest::Get(_) => Default::default(),
		};

		let host = <T as Config>::IsmpHost::default();
		let commitment = host.dispatch_request(request, fee)?;

		// commit the fee collected to child-trie
		child_trie::RequestPayments::insert(commitment, fees);

		Ok(commitment)
	}

	fn dispatch_response(
		&self,
		response: PostResponse,
		fee: FeeMetadata<Self::Account, Self::Balance>,
	) -> Result<H256, anyhow::Error> {
		// collect protocol fees
		let VersionedHostParams::V1(params) = Self::host_params();
		let per_byte_fee: u128 = (*params
			.per_byte_fees
			.get(&response.dest_chain())
			.unwrap_or(&params.default_per_byte_fee))
		.into();
		// minimum fee is 32 bytes
		let fees = if response.response.len() < 32 {
			per_byte_fee * 32u128
		} else {
			per_byte_fee * response.response.len() as u128
		};

		if fees != 0 {
			T::Currency::transfer(
				&fee.payer,
				&RELAYER_FEE_ACCOUNT.into_account_truncating(),
				fees.into(),
				Preservation::Expendable,
			)
			.map_err(|err| {
				ismp::Error::Custom(format!("Error withdrawing request fees: {err:?}"))
			})?;
		}

		let host = <T as Config>::IsmpHost::default();
		let commitment = host.dispatch_response(response, fee)?;

		// commit the collected to child-trie
		child_trie::ResponsePayments::insert(commitment, fees);

		Ok(commitment)
	}
}

/// A request to withdraw some funds. Could either be for protocol revenue or relayer fees.
#[derive(Debug, Clone, Encode, Decode, PartialEq, Eq)]
pub struct WithdrawalRequest<Account, Amount> {
	/// The amount to be withdrawn
	pub amount: Amount,
	/// The withdrawal beneficiary
	pub account: Account,
}

/// Cross-chain messages to this module. This module will only accept messages from the hyperbridge
/// chain. Assumed to be configured in [`pallet_ismp::Config`]
#[derive(Debug, Clone, Encode, Decode, PartialEq, Eq)]
pub enum Message<Account, Balance> {
	/// Set some new host params
	#[codec(index = 0)]
	UpdateHostParams(VersionedHostParams<Balance>),
	/// Withdraw the fees owed to a relayer
	#[codec(index = 2)]
	WithdrawRelayerFees(WithdrawalRequest<Account, Balance>),
}

impl<T> IsmpModule for Pallet<T>
where
	T: Config,
	T::Balance: Into<u128> + From<u128>,
{
	fn on_accept(&self, request: PostRequest) -> Result<Weight, anyhow::Error> {
		// this of course assumes that hyperbridge is configured as the coprocessor.
		let source = request.source;
		if Some(source) != T::Coprocessor::get() {
			Err(ismp::Error::Custom(format!("Invalid request source: {source}")))?
		}

		let message =
			Message::<T::AccountId, T::Balance>::decode(&mut &request.body[..]).map_err(|err| {
				ismp::Error::Custom(format!("Failed to decode per-byte fee: {err:?}"))
			})?;

		let weight = match message {
			Message::UpdateHostParams(new) => {
				let old = HostParams::<T>::get();
				HostParams::<T>::put(new.clone());
				Self::deposit_event(Event::<T>::HostParamsUpdated { old, new });
				T::DbWeight::get().reads_writes(0, 0)
			},
			Message::WithdrawRelayerFees(WithdrawalRequest { account, amount }) => {
				T::Currency::transfer(
					&RELAYER_FEE_ACCOUNT.into_account_truncating(),
					&account,
					amount,
					Preservation::Expendable,
				)
				.map_err(|err| {
					ismp::Error::Custom(format!("Error withdrawing protocol fees: {err:?}"))
				})?;

				Self::deposit_event(Event::<T>::RelayerFeeWithdrawn { account, amount });
				T::DbWeight::get().reads_writes(0, 0)
			},
		};

		Ok(weight)
	}

	fn on_response(&self, _response: Response) -> Result<Weight, anyhow::Error> {
		// this module does not expect responses
		Err(ismp::Error::CannotHandleMessage.into())
	}

	fn on_timeout(&self, _request: Timeout) -> Result<Weight, anyhow::Error> {
		// this module does not dispatch requests
		Err(ismp::Error::CannotHandleMessage.into())
	}
}