Transaction Fee Module (#1648)

* wip

* Split bytes fee charging and charging by amount into different traits.

* Move to edition 2018.

* Implemented charge fee traits for fees module.

* Implemented 'on_finalise' for fee module.

* Updated fees finalize impl.

* Renaming and documentation update.

* Added overflow & underflow check for fee calculation.

* Added mock and unit tests for fee module.

* More unit tests for fees module.

* Fixed srml-executive unit tests.

* Remove transaction base/bytes fee from balances module, fix unit tests.

* fix compile error

* Fixed unit test.

* Minor fixes.

* Bump spec version.

* Bump spec version.

* Updated fees module and runtime wasm.

* Fees module code style improvement; updated runtime wasm.

* Bump spec and impl version.

substrate/core/sr-primitives/src/traits.rs

@@ -126,15 +126,57 @@ pub trait BlockNumberToHash {
 	}
 }
 
-/// Simple payment making trait, operating on a single generic `AccountId` type.
-pub trait MakePayment<AccountId> {
-	/// Make some sort of payment concerning `who` for an extrinsic (transaction) of encoded length
-	/// `encoded_len` bytes. Return true iff the payment was successful.
-	fn make_payment(who: &AccountId, encoded_len: usize) -> Result<(), &'static str>;
+/// Charge bytes fee trait
+pub trait ChargeBytesFee<AccountId> {
+	/// Charge fees from `transactor` for an extrinsic (transaction) of encoded length
+	/// `encoded_len` bytes. Return Ok iff the payment was successful.
+	fn charge_base_bytes_fee(transactor: &AccountId, encoded_len: usize) -> Result<(), &'static str>;
 }
 
-impl<T> MakePayment<T> for () {
-	fn make_payment(_: &T, _: usize) -> Result<(), &'static str> { Ok(()) }
+/// Charge fee trait
+pub trait ChargeFee<AccountId>: ChargeBytesFee<AccountId> {
+	/// The type of fee amount.
+	type Amount;
+
+	/// Charge `amount` of fees from `transactor`. Return Ok iff the payment was successful.
+	fn charge_fee(transactor: &AccountId, amount: Self::Amount) -> Result<(), &'static str>;
+
+	/// Refund `amount` of previous charged fees from `transactor`. Return Ok iff the refund was successful.
+	fn refund_fee(transactor: &AccountId, amount: Self::Amount) -> Result<(), &'static str>;
+}
+
+/// Transfer fungible asset trait
+pub trait TransferAsset<AccountId> {
+	/// The type of asset amount.
+	type Amount;
+
+	/// Transfer asset from `from` account to `to` account with `amount` of asset.
+	fn transfer(from: &AccountId, to: &AccountId, amount: Self::Amount) -> Result<(), &'static str>;
+
+	/// Remove asset from `who` account by deducing `amount` in the account balances.
+	fn remove_from(who: &AccountId, amount: Self::Amount) -> Result<(), &'static str>;
+
+	/// Add asset to `who` account by increasing `amount` in the account balances.
+	fn add_to(who: &AccountId, amount: Self::Amount) -> Result<(), &'static str>;
+}
+
+impl<T> ChargeBytesFee<T> for () {
+	fn charge_base_bytes_fee(_: &T, _: usize) -> Result<(), &'static str> { Ok(()) }
+}
+
+impl<T> ChargeFee<T> for () {
+	type Amount = ();
+
+	fn charge_fee(_: &T, _: Self::Amount) -> Result<(), &'static str> { Ok(()) }
+	fn refund_fee(_: &T, _: Self::Amount) -> Result<(), &'static str> { Ok(()) }
+}
+
+impl<T> TransferAsset<T> for () {
+	type Amount = ();
+
+	fn transfer(_: &T, _: &T, _: Self::Amount) -> Result<(), &'static str> { Ok(()) }
+	fn remove_from(_: &T, _: Self::Amount) -> Result<(), &'static str> { Ok(()) }
+	fn add_to(_: &T, _: Self::Amount) -> Result<(), &'static str> { Ok(()) }
 }
 
 /// Extensible conversion trait. Generic over both source and destination types.