Generalised Transaction Queue API (#741)

* First effort

* API versioning

* Introduce validate_transaction

* Introduce the API plus fixes.

* Docs

* Typo

* Add longevity parameter to transaction validity info.

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

@@ -58,6 +58,7 @@ pub mod testing;
 pub mod traits;
 pub mod generic;
 pub mod bft;
+pub mod transaction_validity;
 
 use traits::{Verify, Lazy};
 

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

@@ -0,0 +1,37 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Transaction validity interface.
+
+use rstd::prelude::*;
+
+/// Priority for a transaction. Additive. Higher is better.
+pub type TransactionPriority = u64;
+
+/// Minimum number of blocks a transaction will remain valid for.
+/// `TransactionLongevity::max_value()` means "forever".
+pub type TransactionLongevity = u64;
+
+/// Tag for a transaction. No two transactions with the same tag should be placed on-chain.
+pub type TransactionTag = Vec<u8>;
+
+/// Information on a transaction's validity and, if valid, on how it relates to other transactions.
+#[derive(Clone, PartialEq, Eq, Encode, Decode)]
+pub enum TransactionValidity {
+	Invalid,
+	Valid(TransactionPriority, Vec<TransactionTag>, Vec<TransactionTag>, TransactionLongevity),
+	Unknown,
+}