State machine crate and rust impl of executor (#17)

* Executor.

* Rust contracts implementation.

* Add documentation and fix transfer data.

* Fix auth contract interface.

* Add some executor tests.

* Validator set contract.

substrate/contracts/src/balances.rs

@@ -0,0 +1,64 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot 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.
+
+// Polkadot 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use primitives::Address;
+use primitives::uint::U256;
+use state_machine::Externalities;
+
+use error::Result;
+use executor::RustExecutor;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Transfer {
+	/// Transfer value
+	value: U256,
+	/// Transfer destination
+	to: Address,
+	/// Replay protection
+	nonce: U256,
+	/// Data authorizing the transfer (we can derive sender from it)
+	authentication_data: Vec<u8>,
+}
+
+/// Balances contract rust implementation.
+#[derive(Debug, Default)]
+pub struct Contract;
+impl Contract {
+	/// Returns a balance of given address.
+	pub fn balance_of<E: Externalities<RustExecutor>>(&self, _ext: &E, _data: Address) -> Result<U256> {
+		unimplemented!()
+	}
+
+	/// Returns the next nonce to authorize the transfer from given address.
+	pub fn next_nonce<E: Externalities<RustExecutor>>(&self, _ext: &E, _data: Address) -> Result<U256> {
+		unimplemented!()
+	}
+
+	/// Checks preconditions for transfer.
+	/// Should verify:
+	/// - signature
+	/// - replay protection
+	/// - enough balance
+	pub fn transfer_preconditions<E: Externalities<RustExecutor>>(&self, _db: &E, _data: Transfer) -> Result<bool> {
+		unimplemented!()
+	}
+
+	/// Perform a transfer.
+	/// This should first make sure that precondtions are satisfied and later perform the transfer.
+	pub fn transfer<E: Externalities<RustExecutor>>(&self, _ext: &mut E, _data: Transfer) -> Result<bool> {
+		unimplemented!()
+	}
+}