common_runtime/extensions/
check_nonce.rs

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// This file overrides the default Substrate CheckNonce for Frequency.
// It only creates the token account for paid extrinsics.

// Copyright (C) 2017-2022 Parity Technologies (UK) 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.

use frame_system::Config;
use parity_scale_codec::{Decode, DecodeWithMemTracking, Encode};

use frame_support::{
	dispatch::{DispatchInfo, Pays},
	sp_runtime, RuntimeDebugNoBound,
};
use scale_info::TypeInfo;
use sp_runtime::{
	traits::{
		AsSystemOriginSigner, DispatchInfoOf, Dispatchable, One, PostDispatchInfoOf,
		TransactionExtension, ValidateResult,
	},
	transaction_validity::{
		InvalidTransaction, TransactionLongevity, TransactionSource, TransactionValidityError,
		ValidTransaction,
	},
	DispatchResult, Weight,
};
extern crate alloc;
use alloc::vec;

/// Nonce check and increment to give replay protection for transactions.
///
/// # Transaction Validity
///
/// This extension affects `requires` and `provides` tags of validity, but DOES NOT
/// set the `priority` field. Make sure that AT LEAST one of the signed extension sets
/// some kind of priority upon validating transactions.
#[derive(Encode, Decode, DecodeWithMemTracking, Clone, Eq, PartialEq, TypeInfo)]
#[scale_info(skip_type_params(T))]
pub struct CheckNonce<T: Config>(#[codec(compact)] pub T::Nonce);

impl<T: Config> CheckNonce<T> {
	/// utility constructor. Used only in client/factory code.
	pub fn from(nonce: T::Nonce) -> Self {
		Self(nonce)
	}
}

impl<T: Config> core::fmt::Debug for CheckNonce<T> {
	#[cfg(feature = "std")]
	fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
		write!(f, "CheckNonce({})", self.0)
	}

	#[cfg(not(feature = "std"))]
	fn fmt(&self, _: &mut core::fmt::Formatter) -> core::fmt::Result {
		Ok(())
	}
}

/// Transaction operations from `validate` to `post_dispatch` for the `CheckNonce` extension.
/// This is used to determine whether the transaction extension weight should be refunded or not.
#[derive(RuntimeDebugNoBound)]
pub enum Val<T: Config> {
	/// Account and its nonce to check for.
	CheckNonce((T::AccountId, T::Nonce)),
	/// Weight to refund.
	Refund(Weight),
}

/// Transaction operations from `prepare` to `post_dispatch` for the `CheckNonce` extension.
/// This is used to determine whether the transaction extension weight should be refunded or not.
#[derive(RuntimeDebugNoBound)]
pub enum Pre {
	/// No nonce check was performed
	NonceChecked,
	/// Weight to refund.
	Refund(Weight),
}

impl<T: Config> TransactionExtension<T::RuntimeCall> for CheckNonce<T>
where
	T::RuntimeCall: Dispatchable<Info = DispatchInfo>,
	<T::RuntimeCall as Dispatchable>::RuntimeOrigin: AsSystemOriginSigner<T::AccountId> + Clone,
{
	const IDENTIFIER: &'static str = "CheckNonce";
	type Implicit = ();
	type Val = Val<T>;
	type Pre = Pre;

	fn weight(&self, _call: &T::RuntimeCall) -> Weight {
		<T::ExtensionsWeightInfo as frame_system::ExtensionsWeightInfo>::check_nonce()
	}

	fn validate(
		&self,
		origin: <T as Config>::RuntimeOrigin,
		call: &T::RuntimeCall,
		_info: &DispatchInfoOf<T::RuntimeCall>,
		_len: usize,
		_self_implicit: Self::Implicit,
		_inherited_implication: &impl Encode,
		_source: TransactionSource,
	) -> ValidateResult<Self::Val, T::RuntimeCall> {
		// Only check for signed origin
		let Some(who) = origin.as_system_origin_signer() else {
			return Ok((ValidTransaction::default(), Val::Refund(self.weight(call)), origin));
		};

		let (valid_transaction, account_nonce) = validate_nonce::<T>(who, self.0)?;

		Ok((valid_transaction, Val::CheckNonce((who.clone(), account_nonce)), origin))
	}

	fn prepare(
		self,
		val: Self::Val,
		_origin: &<T::RuntimeCall as Dispatchable>::RuntimeOrigin,
		_call: &T::RuntimeCall,
		info: &DispatchInfoOf<T::RuntimeCall>,
		_len: usize,
	) -> Result<Self::Pre, TransactionValidityError> {
		let (who, nonce) = match val {
			Val::CheckNonce((who, nonce)) => (who, nonce),
			Val::Refund(weight) => return Ok(Pre::Refund(weight)),
		};

		// Prepare the nonce for the account.
		prepare_nonce::<T>(&who, nonce, info.pays_fee)?;

		Ok(Pre::NonceChecked)
	}

	fn post_dispatch_details(
		pre: Self::Pre,
		_info: &DispatchInfo,
		_post_info: &PostDispatchInfoOf<T::RuntimeCall>,
		_len: usize,
		_result: &DispatchResult,
	) -> Result<Weight, TransactionValidityError> {
		match pre {
			Pre::NonceChecked => Ok(Weight::zero()),
			Pre::Refund(weight) => Ok(weight),
		}
	}
}

/// Helper function to prepare a nonce for a given account.
pub fn prepare_nonce<T: Config>(
	who: &T::AccountId,
	nonce: T::Nonce,
	pays_fee: Pays,
) -> Result<(), TransactionValidityError> {
	let mut account: frame_system::AccountInfo<<T as Config>::Nonce, <T as Config>::AccountData> =
		frame_system::Account::<T>::get(who);
	// The default account (no account) has a nonce of 0.
	// If account nonce is not equal to the tx nonce (self.0), the tx is invalid.  Therefore, check if it is a stale or future tx.
	if nonce != account.nonce {
		return Err(if nonce < account.nonce {
			InvalidTransaction::Stale
		} else {
			InvalidTransaction::Future
		}
		.into());
	}

	// Is this an existing account?
	// extracted from the conditions in which an account gets reaped
	// https://github.com/paritytech/polkadot-sdk/commit/e993f884fc00f359dd8bf9c81422c5161f3447b5#diff-dff2afa7433478e36eb66a9fe319efe28cfbdf95104b30b03afa0a1c4e3239f3R1082
	// Relevant lines: https://github.com/paritytech/polkadot-sdk/blob/495d5a24c8078a0da1eb5e0fe8742a09f1f1bd5c/substrate/frame/system/src/lib.rs#L1642
	let existing_account =
		account.providers > 0 || account.consumers > 0 || account.sufficients > 0;

	// Increment account nonce by 1
	account.nonce += T::Nonce::one();

	// Only create or update the token account if the caller is paying or
	// account already exists
	if pays_fee == Pays::Yes || existing_account {
		frame_system::Account::<T>::insert(who, account);
	}
	Ok(())
}

/// Helper function to validate a nonce for a given account.
pub fn validate_nonce<T: Config>(
	who: &T::AccountId,
	nonce: T::Nonce,
) -> Result<(ValidTransaction, T::Nonce), TransactionValidityError> {
	let account = frame_system::Account::<T>::get(who);

	if nonce < account.nonce {
		return Err(InvalidTransaction::Stale.into());
	}
	let provides = vec![Encode::encode(&(who.clone(), nonce))];
	let requires = if account.nonce < nonce {
		vec![Encode::encode(&(who.clone(), nonce - One::one()))]
	} else {
		vec![]
	};
	Ok((
		ValidTransaction {
			priority: 0,
			requires,
			provides,
			longevity: TransactionLongevity::MAX,
			propagate: true,
		},
		account.nonce,
	))
}