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_mortality.rs

@@ -0,0 +1,124 @@
+// 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, Module, BlockHash};
+use frame_support::StorageMap;
+use sp_runtime::{
+	generic::Era,
+	traits::{SignedExtension, DispatchInfoOf, SaturatedConversion},
+	transaction_validity::{
+		ValidTransaction, TransactionValidityError, InvalidTransaction, TransactionValidity,
+	},
+};
+
+/// Check for transaction mortality.
+#[derive(Encode, Decode, Clone, Eq, PartialEq)]
+pub struct CheckMortality<T: Trait + Send + Sync>(Era, sp_std::marker::PhantomData<T>);
+
+impl<T: Trait + Send + Sync> CheckMortality<T> {
+	/// utility constructor. Used only in client/factory code.
+	pub fn from(era: Era) -> Self {
+		Self(era, sp_std::marker::PhantomData)
+	}
+}
+
+impl<T: Trait + Send + Sync> sp_std::fmt::Debug for CheckMortality<T> {
+	#[cfg(feature = "std")]
+	fn fmt(&self, f: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
+		write!(f, "CheckMortality({:?})", self.0)
+	}
+
+	#[cfg(not(feature = "std"))]
+	fn fmt(&self, _: &mut sp_std::fmt::Formatter) -> sp_std::fmt::Result {
+		Ok(())
+	}
+}
+
+impl<T: Trait + Send + Sync> SignedExtension for CheckMortality<T> {
+	type AccountId = T::AccountId;
+	type Call = T::Call;
+	type AdditionalSigned = T::Hash;
+	type Pre = ();
+	// TODO [#6483] rename to CheckMortality
+	const IDENTIFIER: &'static str = "CheckEra";
+
+	fn validate(
+		&self,
+		_who: &Self::AccountId,
+		_call: &Self::Call,
+		_info: &DispatchInfoOf<Self::Call>,
+		_len: usize,
+	) -> TransactionValidity {
+		let current_u64 = <Module<T>>::block_number().saturated_into::<u64>();
+		let valid_till = self.0.death(current_u64);
+		Ok(ValidTransaction {
+			longevity: valid_till.saturating_sub(current_u64),
+			..Default::default()
+		})
+	}
+
+	fn additional_signed(&self) -> Result<Self::AdditionalSigned, TransactionValidityError> {
+		let current_u64 = <Module<T>>::block_number().saturated_into::<u64>();
+		let n = self.0.birth(current_u64).saturated_into::<T::BlockNumber>();
+		if !<BlockHash<T>>::contains_key(n) {
+			Err(InvalidTransaction::AncientBirthBlock.into())
+		} else {
+			Ok(<Module<T>>::block_hash(n))
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use crate::mock::{Test, new_test_ext, System, CALL};
+	use frame_support::weights::{DispatchClass, DispatchInfo, Pays};
+	use sp_core::H256;
+
+	#[test]
+	fn signed_ext_check_era_should_work() {
+		new_test_ext().execute_with(|| {
+			// future
+			assert_eq!(
+				CheckMortality::<Test>::from(Era::mortal(4, 2)).additional_signed().err().unwrap(),
+				InvalidTransaction::AncientBirthBlock.into(),
+			);
+
+			// correct
+			System::set_block_number(13);
+			<BlockHash<Test>>::insert(12, H256::repeat_byte(1));
+			assert!(CheckMortality::<Test>::from(Era::mortal(4, 12)).additional_signed().is_ok());
+		})
+	}
+
+	#[test]
+	fn signed_ext_check_era_should_change_longevity() {
+		new_test_ext().execute_with(|| {
+			let normal = DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
+			let len = 0_usize;
+			let ext = (
+				crate::CheckWeight::<Test>::default(),
+				CheckMortality::<Test>::from(Era::mortal(16, 256)),
+			);
+			System::set_block_number(17);
+			<BlockHash<Test>>::insert(16, H256::repeat_byte(1));
+
+			assert_eq!(ext.validate(&1, CALL, &normal, len).unwrap().longevity, 15);
+		})
+	}
+}