Signed extension to refund relayer at the target chain #1657
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| // Copyright 2021 Parity Technologies (UK) Ltd. | ||
| // This file is part of Parity Bridges Common. | ||
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| // Parity Bridges Common 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. | ||
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| // Parity Bridges Common 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. | ||
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| // You should have received a copy of the GNU General Public License | ||
| // along with Parity Bridges Common. If not, see <http://www.gnu.org/licenses/>. | ||
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| //! Signed extension that refunds relayer if he has delivered some new messages. | ||
| //! It also refunds transacation cost if the transaction is an `utility.batchAll()` | ||
| //! with calls that are: delivering new messsage and all necessary underlying headers | ||
| //! (parachain or relay chain). | ||
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| use bp_messages::{LaneId, MessageNonce}; | ||
| use bp_polkadot_core::parachains::ParaId; | ||
| use codec::{Decode, Encode}; | ||
| use frame_support::{ | ||
| dispatch::{DispatchInfo, Dispatchable, PostDispatchInfo}, | ||
| RuntimeDebugNoBound, | ||
| }; | ||
| use pallet_bridge_parachains::RelayBlockNumber; | ||
| use pallet_transaction_payment::OnChargeTransaction; | ||
| use scale_info::TypeInfo; | ||
| use sp_runtime::{ | ||
| traits::{DispatchInfoOf, PostDispatchInfoOf, SignedExtension, Zero}, | ||
| transaction_validity::{TransactionValidity, TransactionValidityError, ValidTransaction}, | ||
| DispatchResult, FixedPointOperand, | ||
| }; | ||
| use sp_std::marker::PhantomData; | ||
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| // TODO: is it possible to impl it for several bridges at once? Like what we have in | ||
| // `BridgeRejectObsoleteHeadersAndMessages`? If it is hard to do now - just submit an issue | ||
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| #[derive(Decode, Encode, RuntimeDebugNoBound, TypeInfo)] | ||
| #[scale_info(skip_type_params(Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance))] | ||
| pub struct RefundRelayerForMessagesDeliveryFromParachain< | ||
| Runtime, | ||
| GrandpaInstance, | ||
| ParachainsInstance, | ||
| MessagesInstance, | ||
| >(PhantomData<(Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance)>); | ||
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| impl<Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance> Clone | ||
| for RefundRelayerForMessagesDeliveryFromParachain< | ||
| Runtime, | ||
| GrandpaInstance, | ||
| ParachainsInstance, | ||
| MessagesInstance, | ||
| > | ||
| { | ||
| fn clone(&self) -> Self { | ||
| RefundRelayerForMessagesDeliveryFromParachain(PhantomData) | ||
| } | ||
| } | ||
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| impl<Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance> Eq | ||
| for RefundRelayerForMessagesDeliveryFromParachain< | ||
| Runtime, | ||
| GrandpaInstance, | ||
| ParachainsInstance, | ||
| MessagesInstance, | ||
| > | ||
| { | ||
| } | ||
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| impl<Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance> PartialEq | ||
| for RefundRelayerForMessagesDeliveryFromParachain< | ||
| Runtime, | ||
| GrandpaInstance, | ||
| ParachainsInstance, | ||
| MessagesInstance, | ||
| > | ||
| { | ||
| fn eq(&self, _other: &Self) -> bool { | ||
| true | ||
| } | ||
| } | ||
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| /// Data that is crafted in `pre_dispatch` method and used at `post_dispatch`. | ||
| #[derive(PartialEq)] | ||
| pub struct PreDispatchData<AccountId> { | ||
| /// Transaction submitter (relayer) account. | ||
| pub relayer: AccountId, | ||
| /// Type of the call. | ||
| pub call_type: CallType, | ||
| } | ||
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| /// Type of the call that the extension recognizing. | ||
| #[derive(Clone, Copy, PartialEq)] | ||
| pub enum CallType { | ||
| /// Relay chain finality + parachain finality + message delivery calls. | ||
| AllFinalityAndDelivery(ExpectedRelayChainState, ExpectedParachainState, MessagesState), | ||
| /// Parachain finality + message delivery calls. | ||
| ParachainFinalityAndDelivery(ExpectedParachainState, MessagesState), | ||
| /// Standalone message delivery call. | ||
| Delivery(MessagesState), | ||
| } | ||
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| impl CallType { | ||
| /// Returns the pre-dispatch messages pallet state. | ||
| fn pre_dispatch_messages_state(&self) -> MessagesState { | ||
| match *self { | ||
| Self::AllFinalityAndDelivery(_, _, messages_state) => messages_state, | ||
| Self::ParachainFinalityAndDelivery(_, messages_state) => messages_state, | ||
| Self::Delivery(messages_state) => messages_state, | ||
| } | ||
| } | ||
| } | ||
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| /// Expected post-dispatch state of the relay chain pallet. | ||
| #[derive(Clone, Copy, PartialEq)] | ||
| pub struct ExpectedRelayChainState { | ||
| /// Best known relay chain block number. | ||
| pub best_block_number: RelayBlockNumber, | ||
| } | ||
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| /// Expected post-dispatch state of the parachain pallet. | ||
| #[derive(Clone, Copy, PartialEq)] | ||
| pub struct ExpectedParachainState { | ||
| /// Parachain identifier. | ||
| pub para: ParaId, | ||
| /// At which relay block the parachain head has been updated? | ||
| pub at_relay_block_number: RelayBlockNumber, | ||
| } | ||
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| /// Pre-dispatch state of messages pallet. | ||
| /// | ||
| /// This struct is for pre-dispatch state of the pallet, not the expected post-dispatch state. | ||
| /// That's because message delivery transaction may deliver some of messages that it brings. | ||
| /// If this happens, we consider it "helpful" and refund its cost. If transaction fails to | ||
| /// deliver at least one message, it is considered wrong and is not refunded. | ||
| #[derive(Clone, Copy, PartialEq)] | ||
| pub struct MessagesState { | ||
| /// Message lane identifier. | ||
| pub lane: LaneId, | ||
| /// Best delivered message nonce. | ||
| pub last_delivered_nonce: MessageNonce, | ||
| } | ||
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| // without this typedef rustfmt fails with internal err | ||
| type BalanceOf<Runtime> = | ||
| <<Runtime as pallet_transaction_payment::Config>::OnChargeTransaction as OnChargeTransaction< | ||
| Runtime, | ||
| >>::Balance; | ||
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| impl<Runtime, GrandpaInstance, ParachainsInstance, MessagesInstance> SignedExtension | ||
| for RefundRelayerForMessagesDeliveryFromParachain< | ||
| Runtime, | ||
| GrandpaInstance, | ||
| ParachainsInstance, | ||
| MessagesInstance, | ||
| > where | ||
| Runtime: 'static | ||
| + Send | ||
| + Sync | ||
| + frame_system::Config | ||
| + pallet_transaction_payment::Config | ||
| + pallet_bridge_grandpa::Config<GrandpaInstance> | ||
| + pallet_bridge_parachains::Config<ParachainsInstance> | ||
| + pallet_bridge_messages::Config<MessagesInstance> | ||
| + pallet_bridge_relayers::Config<Reward = BalanceOf<Runtime>>, | ||
| GrandpaInstance: 'static + Send + Sync, | ||
| ParachainsInstance: 'static + Send + Sync, | ||
| MessagesInstance: 'static + Send + Sync, | ||
| <Runtime as frame_system::Config>::RuntimeCall: | ||
| Dispatchable<Info = DispatchInfo, PostInfo = PostDispatchInfo>, | ||
| BalanceOf<Runtime>: FixedPointOperand, | ||
| { | ||
| const IDENTIFIER: &'static str = "RefundRelayerForMessagesDeliveryFromParachain"; | ||
| type AccountId = Runtime::AccountId; | ||
| type Call = Runtime::RuntimeCall; | ||
| type AdditionalSigned = (); | ||
| type Pre = PreDispatchData<Runtime::AccountId>; | ||
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| fn additional_signed(&self) -> Result<(), TransactionValidityError> { | ||
| Ok(()) | ||
| } | ||
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| fn validate( | ||
| &self, | ||
| _who: &Self::AccountId, | ||
| _call: &Self::Call, | ||
| _info: &DispatchInfoOf<Self::Call>, | ||
| _len: usize, | ||
| ) -> TransactionValidity { | ||
| Ok(ValidTransaction::default()) | ||
| } | ||
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| fn pre_dispatch( | ||
| self, | ||
| _who: &Self::AccountId, | ||
| _call: &Self::Call, | ||
| _post_info: &DispatchInfoOf<Self::Call>, | ||
| _len: usize, | ||
| ) -> Result<Self::Pre, TransactionValidityError> { | ||
| // TODO: for every call from the batch - call the `BridgesExtension` to ensure that every | ||
| // call transaction brings something new and reject obsolete transactions | ||
| unimplemented!("TODO") // TODO: return actual call type | ||
| } | ||
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| fn post_dispatch( | ||
| pre: Option<Self::Pre>, | ||
| info: &DispatchInfoOf<Self::Call>, | ||
| post_info: &PostDispatchInfoOf<Self::Call>, | ||
| len: usize, | ||
| result: &DispatchResult, | ||
| ) -> Result<(), TransactionValidityError> { | ||
| // we never refund anything if that is not bridge transaction or if it is a bridge | ||
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| // transaction that we do not support here | ||
| let (relayer, call_type) = match pre { | ||
| Some(pre) => (pre.relayer, pre.call_type), | ||
| None => return Ok(()), | ||
| }; | ||
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| // we never refund anything if transaction has failed | ||
| if result.is_err() { | ||
| return Ok(()) | ||
| } | ||
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| // check if relay chain state has been updated | ||
| if let CallType::AllFinalityAndDelivery(expected_relay_chain_state, _, _) = call_type { | ||
| let actual_relay_chain_state = relay_chain_state::<Runtime, GrandpaInstance>(); | ||
| if actual_relay_chain_state != expected_relay_chain_state { | ||
| // we only refund relayer if all calls have updated chain state | ||
| return Ok(()) | ||
| } | ||
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| // there's a conflict between how bridge GRANDPA pallet works and the | ||
| // `AllFinalityAndDelivery` transaction. If relay cahin header is mandatory, the GRANDPA | ||
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| // pallet returns `Pays::No`, because such transaction is mandatory for operating the | ||
| // bridge. But `utility.batchAll` transaction always requires payment. But in both cases | ||
| // we'll refund relayer - either explicitly here, or using `Pays::No` if he's choosing | ||
| // to submit dedicated transaction. | ||
| } | ||
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| // check if parachain state has been updated | ||
| match call_type { | ||
| CallType::AllFinalityAndDelivery(_, expected_parachain_state, _) | | ||
| CallType::ParachainFinalityAndDelivery(expected_parachain_state, _) => { | ||
| let actual_parachain_state = parachain_state::<Runtime, ParachainsInstance>(); | ||
| if expected_parachain_state != actual_parachain_state { | ||
| // we only refund relayer if all calls have updated chain state | ||
| return Ok(()) | ||
| } | ||
| }, | ||
| _ => (), | ||
| } | ||
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| // check if messages have been delivered | ||
| let actual_messages_state = messages_state::<Runtime, MessagesInstance>(); | ||
| let pre_dispatch_messages_state = call_type.pre_dispatch_messages_state(); | ||
| if actual_messages_state == pre_dispatch_messages_state { | ||
| // we only refund relayer if all calls have updated chain state | ||
| return Ok(()) | ||
| } | ||
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| // regarding the tip - refund that happens here (at this side of the bridge) isn't the whole | ||
|
There was a problem hiding this comment. That's an important thing - we don't refund the whole transaction cost here. Tip is not included in refund. Reasoning is in the code |
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| // relayer compensation. He'll receive some amount at the other side of the bridge. It shall | ||
| // (in theory) cover the tip here. Otherwise, if we'll be compensating tip here, some | ||
| // malicious relayer may use huge tips, effectively depleting account that pay rewards. The | ||
| // cost of this attack is nothing. Hence we use zero as tip here. | ||
| let tip = Zero::zero(); | ||
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| // compute the relayer reward | ||
| let reward = pallet_transaction_payment::Pallet::<Runtime>::compute_actual_fee( | ||
| len as _, info, post_info, tip, | ||
| ); | ||
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| // finally - regiater reward in relayers pallet | ||
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| pallet_bridge_relayers::Pallet::<Runtime>::register_relayer_reward(&relayer, reward); | ||
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| Ok(()) | ||
| } | ||
| } | ||
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| /// Returns relay chain state that we are interested in. | ||
| fn relay_chain_state<Runtime, GrandpaInstance>() -> ExpectedRelayChainState { | ||
| unimplemented!("TODO") | ||
| } | ||
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| /// Returns parachain state that we are interested in. | ||
| fn parachain_state<Runtime, ParachainsInstance>() -> ExpectedParachainState { | ||
| unimplemented!("TODO") | ||
| } | ||
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| /// Returns messages state that we are interested in. | ||
| fn messages_state<Runtime, MessagesInstance>() -> MessagesState { | ||
| unimplemented!("TODO") | ||
| } | ||
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