Extract frame_system SignedExtensions into separate files. (#6474)

* Split the code.

* Restructure.

* Split tests.

* Self-review.

* Break lines.

* Move tests out.

* Rename CheckEra -> CheckMortality but keep backwards compatibility

* Update frame/system/src/extensions/check_mortality.rs

* Don't rename the IDENTIFIER for now.

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/frame/system/src/extensions/check_nonce.rs

@@ -0,0 +1,145 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2017-2020 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 codec::{Encode, Decode};
+use crate::Trait;
+use frame_support::{
+	weights::DispatchInfo,
+	StorageMap,
+};
+use sp_runtime::{
+	traits::{SignedExtension, DispatchInfoOf, Dispatchable, One},
+	transaction_validity::{
+		ValidTransaction, TransactionValidityError, InvalidTransaction, TransactionValidity,
+		TransactionLongevity, TransactionPriority,
+	},
+};
+use sp_std::vec;
+
+/// Nonce check and increment to give replay protection for transactions.
+#[derive(Encode, Decode, Clone, Eq, PartialEq)]
+pub struct CheckNonce<T: Trait>(#[codec(compact)] T::Index);
+
+impl<T: Trait> CheckNonce<T> {
+	/// utility constructor. Used only in client/factory code.
+	pub fn from(nonce: T::Index) -> Self {
+		Self(nonce)
+	}
+}
+
+impl<T: Trait> sp_std::fmt::Debug for CheckNonce<T> {
+	#[cfg(feature = "std")]
+	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
+		write!(f, "CheckNonce({})", self.0)
+	}
+
+	#[cfg(not(feature = "std"))]
+	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
+		Ok(())
+	}
+}
+
+impl<T: Trait> SignedExtension for CheckNonce<T> where
+	T::Call: Dispatchable<Info=DispatchInfo>
+{
+	type AccountId = T::AccountId;
+	type Call = T::Call;
+	type AdditionalSigned = ();
+	type Pre = ();
+	const IDENTIFIER: &'static str = "CheckNonce";
+
+	fn additional_signed(&self) -> sp_std::result::Result<(), TransactionValidityError> { Ok(()) }
+
+	fn pre_dispatch(
+		self,
+		who: &Self::AccountId,
+		_call: &Self::Call,
+		_info: &DispatchInfoOf<Self::Call>,
+		_len: usize,
+	) -> Result<(), TransactionValidityError> {
+		let mut account = crate::Account::<T>::get(who);
+		if self.0 != account.nonce {
+			return Err(
+				if self.0 < account.nonce {
+					InvalidTransaction::Stale
+				} else {
+					InvalidTransaction::Future
+				}.into()
+			)
+		}
+		account.nonce += T::Index::one();
+		crate::Account::<T>::insert(who, account);
+		Ok(())
+	}
+
+	fn validate(
+		&self,
+		who: &Self::AccountId,
+		_call: &Self::Call,
+		info: &DispatchInfoOf<Self::Call>,
+		_len: usize,
+	) -> TransactionValidity {
+		// check index
+		let account = crate::Account::<T>::get(who);
+		if self.0 < account.nonce {
+			return InvalidTransaction::Stale.into()
+		}
+
+		let provides = vec![Encode::encode(&(who, self.0))];
+		let requires = if account.nonce < self.0 {
+			vec![Encode::encode(&(who, self.0 - One::one()))]
+		} else {
+			vec![]
+		};
+
+		Ok(ValidTransaction {
+			priority: info.weight as TransactionPriority,
+			requires,
+			provides,
+			longevity: TransactionLongevity::max_value(),
+			propagate: true,
+		})
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use crate::mock::{Test, new_test_ext, CALL};
+
+	#[test]
+	fn signed_ext_check_nonce_works() {
+		new_test_ext().execute_with(|| {
+			crate::Account::<Test>::insert(1, crate::AccountInfo {
+				nonce: 1,
+				refcount: 0,
+				data: 0,
+			});
+			let info = DispatchInfo::default();
+			let len = 0_usize;
+			// stale
+			assert!(CheckNonce::<Test>(0).validate(&1, CALL, &info, len).is_err());
+			assert!(CheckNonce::<Test>(0).pre_dispatch(&1, CALL, &info, len).is_err());
+			// correct
+			assert!(CheckNonce::<Test>(1).validate(&1, CALL, &info, len).is_ok());
+			assert!(CheckNonce::<Test>(1).pre_dispatch(&1, CALL, &info, len).is_ok());
+			// future
+			assert!(CheckNonce::<Test>(5).validate(&1, CALL, &info, len).is_ok());
+			assert!(CheckNonce::<Test>(5).pre_dispatch(&1, CALL, &info, len).is_err());
+		})
+	}
+}