Introduce Minimal Header Chain: Proving Interface (#287)

* Add header-chain primitive crate

* Make MinimalHeaderChain functionaly the same as PeerBlockchain

* Use a better doc comment for MinimalHeaderChain

* Fix benchmark compilation

* Rust Fmt

* Remove Substrate based dependencies

* Rename MinimalHeaderChain to BaseHeaderChain

bridges/primitives/header-chain/src/lib.rs

@@ -0,0 +1,44 @@
+// Copyright 2019-2020 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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.
+
+// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Defines traits which represent a common interface for Substrate pallets which want to
+//! incorporate bridge functionality.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use core::clone::Clone;
+use core::cmp::Eq;
+use core::fmt::Debug;
+use parity_scale_codec::{Codec, EncodeLike};
+
+/// A type that can be used as a parameter in a dispatchable function.
+///
+/// When using `decl_module` all arguments for call functions must implement this trait.
+pub trait Parameter: Codec + EncodeLike + Clone + Eq + Debug {}
+impl<T> Parameter for T where T: Codec + EncodeLike + Clone + Eq + Debug {}
+
+/// A base trait for pallets which want to keep track of a full set of headers from a bridged chain.
+pub trait BaseHeaderChain {
+	/// Transaction type.
+	type Transaction: Parameter;
+	/// Transaction inclusion proof type.
+	type TransactionInclusionProof: Parameter;
+
+	/// Verify that transaction is a part of given block.
+	///
+	/// Returns Some(transaction) if proof is valid and None otherwise.
+	fn verify_transaction_inclusion_proof(proof: &Self::TransactionInclusionProof) -> Option<Self::Transaction>;
+}