Re-introduce zero copy codec and add minimal polkadot client API which uses linked native runtime (#65)

* client-api type and move duty roster types to primitives

* tuple implementation for slicable

* mild cleanup of deserialization code

* stubs which handle encoding and decoding themselves

* fancier impl_stubs macro

* zero-copy slicable API

* minimal polkadot-client API

* fix WASM API generation

* move native environment stuff to substrate executor

* fix warnings and grumbles

substrate/polkadot/api/src/lib.rs

@@ -0,0 +1,118 @@
+// 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/>.
+
+//! Strongly typed API for Polkadot based around the locally-compiled native
+//! runtime.
+
+extern crate polkadot_executor as polkadot_executor;
+extern crate polkadot_runtime ;
+extern crate polkadot_primitives as primitives;
+extern crate substrate_client as client;
+extern crate substrate_executor as substrate_executor;
+extern crate substrate_state_machine as state_machine;
+
+#[macro_use]
+extern crate error_chain;
+
+use client::backend::Backend;
+use client::blockchain::BlockId;
+use client::Client;
+use polkadot_runtime::runtime;
+use polkadot_executor::LocalNativeExecutionDispatch as LocalDispatch;
+use substrate_executor::{NativeExecutionDispatch, NativeExecutor};
+use primitives::{AccountId, SessionKey};
+use primitives::parachain::DutyRoster;
+
+error_chain! {
+	errors {
+		/// Unknown runtime code.
+		UnknownRuntime {
+			description("Unknown runtime code")
+			display("Unknown runtime code")
+		}
+		UnknownBlock(b: BlockId) {
+			description("Unknown block")
+			display("Unknown block")
+		}
+		/// Some other error.
+		// TODO: allow to be specified as associated type of PolkadotApi
+		Other(e: Box<::std::error::Error + Send>) {
+			description("Other error")
+			display("Other error: {}", e.description())
+		}
+	}
+
+	links {
+		Executor(substrate_executor::error::Error, substrate_executor::error::ErrorKind);
+	}
+}
+
+/// Trait encapsulating the Polkadot API.
+///
+/// All calls should fail when the exact runtime is unknown.
+pub trait PolkadotApi {
+	/// Get authorities at a given block.
+	fn authorities(&self, at: &BlockId) -> Result<Vec<SessionKey>>;
+
+	/// Get validators at a given block.
+	fn validators(&self, at: &BlockId) -> Result<Vec<AccountId>>;
+
+	/// Get the authority duty roster at a block.
+	fn duty_roster(&self, at: &BlockId) -> Result<DutyRoster>;
+}
+
+fn convert_client_error(e: client::error::Error) -> Error {
+	match e {
+		client::error::Error(client::error::ErrorKind::UnknownBlock(b), _) => Error::from_kind(ErrorKind::UnknownBlock(b)),
+		other => Error::from_kind(ErrorKind::Other(Box::new(other) as Box<_>)),
+	}
+}
+
+// set up the necessary scaffolding to execute the runtime.
+macro_rules! with_runtime {
+	($client: ident, $at: expr, $exec: expr) => {{
+		// bail if the code is not the same as the natively linked.
+		if $client.code_at($at).map_err(convert_client_error)? != LocalDispatch::native_equivalent() {
+			bail!(ErrorKind::UnknownRuntime);
+		}
+
+		$client.state_at($at).map_err(convert_client_error).and_then(|state| {
+			let mut changes = Default::default();
+			let mut ext = state_machine::Ext {
+				overlay: &mut changes,
+				backend: &state,
+			};
+
+			::substrate_executor::with_native_environment(&mut ext, $exec).map_err(Into::into)
+		})
+	}}
+}
+
+impl<B: Backend> PolkadotApi for Client<B, NativeExecutor<LocalDispatch>>
+	where ::client::error::Error: From<<<B as Backend>::State as state_machine::backend::Backend>::Error>
+{
+	fn authorities(&self, at: &BlockId) -> Result<Vec<SessionKey>> {
+		with_runtime!(self, at, ::runtime::consensus::authorities)
+	}
+
+	fn validators(&self, at: &BlockId) -> Result<Vec<AccountId>> {
+		with_runtime!(self, at, ::runtime::session::validators)
+	}
+
+	fn duty_roster(&self, at: &BlockId) -> Result<DutyRoster> {
+		with_runtime!(self, at, ::runtime::parachains::calculate_duty_roster)
+	}
+}