Dual execution (#311)

* Initial logic

* Remove accidental file

* Config

* Remove accidental

* Apply CLI config

* Additional work. Sadly pointless.

* Rearrange everything

* Loop into CLI param

* Implement dual execution

* typo

* fix tests.

* Better docs

* Fix bug

* Add some tests

* Report block information on consensus failure, tests

* Fix test

substrate/Cargo.lock

@@ -337,6 +337,7 @@ dependencies = [
  "substrate-executor 0.1.0",
  "substrate-keyring 0.1.0",
  "substrate-primitives 0.1.0",
+ "substrate-runtime-consensus 0.1.0",
  "substrate-runtime-io 0.1.0",
  "substrate-runtime-primitives 0.1.0",
  "substrate-runtime-staking 0.1.0",

substrate/demo/executor/Cargo.toml

@@ -22,3 +22,4 @@ substrate-keyring = { path = "../../substrate/keyring" }
 substrate-runtime-primitives = { path = "../../substrate/runtime/primitives" }
 substrate-runtime-staking = { path = "../../substrate/runtime/staking" }
 substrate-runtime-system = { path = "../../substrate/runtime/system" }
+substrate-runtime-consensus = { path = "../../substrate/runtime/consensus" }

substrate/demo/executor/src/lib.rs

@@ -32,6 +32,7 @@ extern crate triehash;
 #[cfg(test)] extern crate substrate_runtime_support as runtime_support;
 #[cfg(test)] extern crate substrate_runtime_staking as staking;
 #[cfg(test)] extern crate substrate_runtime_system as system;
+#[cfg(test)] extern crate substrate_runtime_consensus as consensus;
 #[cfg(test)] #[macro_use] extern crate hex_literal;
 
 native_executor_instance!(pub Executor, demo_runtime::api::dispatch, demo_runtime::VERSION, include_bytes!("../../runtime/wasm/target/wasm32-unknown-unknown/release/demo_runtime.compact.wasm"));
@@ -49,7 +50,7 @@ mod tests {
 	use demo_primitives::{Hash, BlockNumber, AccountId};
 	use runtime_primitives::traits::Header as HeaderT;
 	use runtime_primitives::{ApplyOutcome, ApplyError, ApplyResult, MaybeUnsigned};
-	use {staking, system};
+	use {staking, system, consensus};
 	use demo_runtime::{Header, Block, UncheckedExtrinsic, Extrinsic, Call, Concrete, Staking,
 		BuildStorage, GenesisConfig, SessionConfig, StakingConfig, BareExtrinsic};
 	use ed25519::{Public, Pair};
@@ -104,9 +105,9 @@ mod tests {
 			twox_128(&<system::BlockHash<Concrete>>::key_for(0)).to_vec() => vec![0u8; 32]
 		];
 
-		let r = Executor::new().call(&mut t, BLOATY_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = Executor::new().call(&mut t, BLOATY_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let v = Executor::new().call(&mut t, BLOATY_CODE, "apply_extrinsic", &vec![].and(&xt())).unwrap();
+		let v = Executor::new().call(&mut t, BLOATY_CODE, "apply_extrinsic", &vec![].and(&xt()), true).0.unwrap();
 		let r = ApplyResult::decode(&mut &v[..]).unwrap();
 		assert_eq!(r, Err(ApplyError::CantPay));
 	}
@@ -123,9 +124,9 @@ mod tests {
 			twox_128(&<system::BlockHash<Concrete>>::key_for(0)).to_vec() => vec![0u8; 32]
 		];
 
-		let r = Executor::new().call(&mut t, COMPACT_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = Executor::new().call(&mut t, COMPACT_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let v = Executor::new().call(&mut t, COMPACT_CODE, "apply_extrinsic", &vec![].and(&xt())).unwrap();
+		let v = Executor::new().call(&mut t, COMPACT_CODE, "apply_extrinsic", &vec![].and(&xt()), true).0.unwrap();
 		let r = ApplyResult::decode(&mut &v[..]).unwrap();
 		assert_eq!(r, Err(ApplyError::CantPay));
 	}
@@ -142,9 +143,9 @@ mod tests {
 			twox_128(&<system::BlockHash<Concrete>>::key_for(0)).to_vec() => vec![0u8; 32]
 		];
 
-		let r = Executor::new().call(&mut t, COMPACT_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = Executor::new().call(&mut t, COMPACT_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let r = Executor::new().call(&mut t, COMPACT_CODE, "apply_extrinsic", &vec![].and(&xt()));
+		let r = Executor::new().call(&mut t, COMPACT_CODE, "apply_extrinsic", &vec![].and(&xt()), true).0;
 		assert!(r.is_ok());
 
 		runtime_io::with_externalities(&mut t, || {
@@ -165,9 +166,9 @@ mod tests {
 			twox_128(&<system::BlockHash<Concrete>>::key_for(0)).to_vec() => vec![0u8; 32]
 		];
 
-		let r = Executor::new().call(&mut t, BLOATY_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = Executor::new().call(&mut t, BLOATY_CODE, "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let r = Executor::new().call(&mut t, BLOATY_CODE, "apply_extrinsic", &vec![].and(&xt()));
+		let r = Executor::new().call(&mut t, BLOATY_CODE, "apply_extrinsic", &vec![].and(&xt()), true).0;
 		assert!(r.is_ok());
 
 		runtime_io::with_externalities(&mut t, || {
@@ -271,18 +272,31 @@ mod tests {
 		)
 	}
 
+	fn block1big() -> (Vec<u8>, Hash) {
+		construct_block(
+			1,
+			[69u8; 32].into(),
+			hex!("d95fc2cf4541b97ed2cd381fe7a486af8aebad9ed0480c30e9cca184bb207e95").into(),
+			vec![BareExtrinsic {
+				signed: alice(),
+				index: 0,
+				function: Call::Consensus(consensus::Call::remark(vec![0; 60000])),
+			}]
+		)
+	}
+
 	#[test]
 	fn full_native_block_import_works() {
 		let mut t = new_test_ext();
 
-		Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block1().0).unwrap();
+		Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block1().0, true).0.unwrap();
 
 		runtime_io::with_externalities(&mut t, || {
 			assert_eq!(Staking::voting_balance(&alice()), 41);
 			assert_eq!(Staking::voting_balance(&bob()), 69);
 		});
 
-		Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block2().0).unwrap();
+		Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block2().0, true).0.unwrap();
 
 		runtime_io::with_externalities(&mut t, || {
 			assert_eq!(Staking::voting_balance(&alice()), 30);
@@ -294,14 +308,14 @@ mod tests {
 	fn full_wasm_block_import_works() {
 		let mut t = new_test_ext();
 
-		WasmExecutor.call(&mut t, COMPACT_CODE, "execute_block", &block1().0).unwrap();
+		WasmExecutor{heap_pages: 8}.call(&mut t, COMPACT_CODE, "execute_block", &block1().0, true).0.unwrap();
 
 		runtime_io::with_externalities(&mut t, || {
 			assert_eq!(Staking::voting_balance(&alice()), 41);
 			assert_eq!(Staking::voting_balance(&bob()), 69);
 		});
 
-		WasmExecutor.call(&mut t, COMPACT_CODE, "execute_block", &block2().0).unwrap();
+		WasmExecutor{heap_pages: 8}.call(&mut t, COMPACT_CODE, "execute_block", &block2().0, true).0.unwrap();
 
 		runtime_io::with_externalities(&mut t, || {
 			assert_eq!(Staking::voting_balance(&alice()), 30);
@@ -309,6 +323,30 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn wasm_big_block_import_fails() {
+		let mut t = new_test_ext();
+
+		let r = WasmExecutor{heap_pages: 8}.call(&mut t, COMPACT_CODE, "execute_block", &block1big().0, true).0;
+		assert!(!r.is_ok());
+	}
+
+	#[test]
+	fn native_big_block_import_succeeds() {
+		let mut t = new_test_ext();
+
+		let r = Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block1big().0, true).0;
+		assert!(r.is_ok());
+	}
+
+	#[test]
+	fn native_big_block_import_fails_on_fallback() {
+		let mut t = new_test_ext();
+
+		let r = Executor::new().call(&mut t, COMPACT_CODE, "execute_block", &block1big().0, false).0;
+		assert!(!r.is_ok());
+	}
+
 	#[test]
 	fn panic_execution_gives_error() {
 		let mut t: TestExternalities = map![
@@ -322,9 +360,9 @@ mod tests {
 		];
 
 		let foreign_code = include_bytes!("../../runtime/wasm/target/wasm32-unknown-unknown/release/demo_runtime.wasm");
-		let r = WasmExecutor.call(&mut t, &foreign_code[..], "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = WasmExecutor{heap_pages: 8}.call(&mut t, &foreign_code[..], "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let r = WasmExecutor.call(&mut t, &foreign_code[..], "apply_extrinsic", &vec![].and(&xt())).unwrap();
+		let r = WasmExecutor{heap_pages: 8}.call(&mut t, &foreign_code[..], "apply_extrinsic", &vec![].and(&xt()), true).0.unwrap();
 		let r = ApplyResult::decode(&mut &r[..]).unwrap();
 		assert_eq!(r, Err(ApplyError::CantPay));
 	}
@@ -342,9 +380,9 @@ mod tests {
 		];
 
 		let foreign_code = include_bytes!("../../runtime/wasm/target/wasm32-unknown-unknown/release/demo_runtime.compact.wasm");
-		let r = WasmExecutor.call(&mut t, &foreign_code[..], "initialise_block", &vec![].and(&from_block_number(1u64)));
+		let r = WasmExecutor{heap_pages: 8}.call(&mut t, &foreign_code[..], "initialise_block", &vec![].and(&from_block_number(1u64)), true).0;
 		assert!(r.is_ok());
-		let r = WasmExecutor.call(&mut t, &foreign_code[..], "apply_extrinsic", &vec![].and(&xt())).unwrap();
+		let r = WasmExecutor{heap_pages: 8}.call(&mut t, &foreign_code[..], "apply_extrinsic", &vec![].and(&xt()), true).0.unwrap();
 		let r = ApplyResult::decode(&mut &r[..]).unwrap();
 		assert_eq!(r, Ok(ApplyOutcome::Success));
 

substrate/polkadot/cli/src/cli.yml

@@ -74,7 +74,7 @@ args:
   - pruning:
       long: pruning
       value_name: PRUNING_MODE
-      help: Specify the pruning mode. (a number of blocks to keep or "archive"). Default is 256.
+      help: Specify the pruning mode, a number of blocks to keep or "archive". Default is 256.
       takes_value: true
   - name:
       long: name
@@ -95,6 +95,10 @@ args:
       value_name: TELEMETRY_URL
       help: The URL of the telemetry server. Implies --telemetry
       takes_value: true
+  - execution:
+      long: execution
+      value_name: STRATEGY
+      help: The means of execution used when calling into the runtime. Can be either wasm, native or both.
 subcommands:
   - build-spec:
       about: Build a spec.json file, outputing to stdout

substrate/polkadot/cli/src/lib.rs

@@ -218,18 +218,32 @@ pub fn run<I, T, W>(args: I, worker: W) -> error::Result<()> where
 		if matches.is_present("collator") {
 			info!("Starting collator");
 			// TODO [rob]: collation node implementation
-			service::Role::FULL
+			// This isn't a thing. Different parachains will have their own collator executables and
+			// maybe link to libpolkadot to get a light-client. 
+			service::Role::LIGHT
 		} else if matches.is_present("light") {
 			info!("Starting (light)");
+			config.execution_strategy = service::ExecutionStrategy::NativeWhenPossible;
 			service::Role::LIGHT
 		} else if matches.is_present("validator") || matches.is_present("dev") {
 			info!("Starting validator");
+			config.execution_strategy = service::ExecutionStrategy::Both;
 			service::Role::AUTHORITY
 		} else {
 			info!("Starting (heavy)");
+			config.execution_strategy = service::ExecutionStrategy::NativeWhenPossible;
 			service::Role::FULL
 		};
 
+	if let Some(s) = matches.value_of("execution") {
+		config.execution_strategy = match s {
+			"both" => service::ExecutionStrategy::Both,
+			"native" => service::ExecutionStrategy::NativeWhenPossible,
+			"wasm" => service::ExecutionStrategy::AlwaysWasm,
+			_ => return Err(error::ErrorKind::Input("Invalid execution mode specified".to_owned()).into()),
+		};
+	}
+
 	config.roles = role;
 	{
 		config.network.boot_nodes.extend(matches

substrate/polkadot/service/src/components.rs

@@ -30,7 +30,7 @@ use polkadot_api;
 use polkadot_executor::Executor as LocalDispatch;
 use polkadot_network::NetworkService;
 use polkadot_primitives::{Block, BlockId, Hash};
-use state_machine;
+use state_machine::{self, ExecutionStrategy};
 use substrate_executor::NativeExecutor;
 use transaction_pool::{self, TransactionPool};
 use tokio::runtime::TaskExecutor;
@@ -50,7 +50,7 @@ pub trait Components {
 	type Executor: 'static + client::CallExecutor<Block> + Send + Sync;
 
 	/// Create client.
-	fn build_client(&self, settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec)
+	fn build_client(&self, settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec, execution_strategy: ExecutionStrategy)
 		-> Result<(Arc<Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error>;
 
 	/// Create api.
@@ -83,9 +83,9 @@ impl Components for FullComponents {
 	type Api = Client<Self::Backend, Self::Executor, Block>;
 	type Executor = client::LocalCallExecutor<client_db::Backend<Block>, NativeExecutor<LocalDispatch>>;
 
-	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec)
+	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, chain_spec: &ChainSpec, execution_strategy: ExecutionStrategy)
 		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error> {
-		Ok((Arc::new(client_db::new_client(db_settings, executor, chain_spec)?), None))
+		Ok((Arc::new(client_db::new_client(db_settings, executor, chain_spec, execution_strategy)?), None))
 	}
 
 	fn build_api(&self, client: Arc<client::Client<Self::Backend, Self::Executor, Block>>) -> Arc<Self::Api> {
@@ -142,7 +142,7 @@ impl Components for LightComponents {
 		client::light::blockchain::Blockchain<client_db::light::LightStorage<Block>, network::OnDemand<Block, NetworkService>>,
 		network::OnDemand<Block, NetworkService>>;
 
-	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, spec: &ChainSpec)
+	fn build_client(&self, db_settings: client_db::DatabaseSettings, executor: CodeExecutor, spec: &ChainSpec, _execution_strategy: ExecutionStrategy)
 		-> Result<(Arc<client::Client<Self::Backend, Self::Executor, Block>>, Option<Arc<OnDemand<Block, NetworkService>>>), error::Error> {
 		let db_storage = client_db::light::LightStorage::new(db_settings)?;
 		let light_blockchain = client::light::new_light_blockchain(db_storage);

substrate/polkadot/service/src/config.rs

@@ -18,6 +18,7 @@
 
 use transaction_pool;
 use chain_spec::ChainSpec;
+pub use state_machine::ExecutionStrategy;
 pub use network::Role;
 pub use network::NetworkConfiguration;
 pub use client_db::PruningMode;
@@ -44,6 +45,8 @@ pub struct Configuration {
 	pub telemetry: Option<String>,
 	/// Node name.
 	pub name: String,
+	/// Execution strategy.
+	pub execution_strategy: ExecutionStrategy,
 }
 
 impl Configuration {
@@ -60,6 +63,7 @@ impl Configuration {
 			keys: Default::default(),
 			telemetry: Default::default(),
 			pruning: PruningMode::ArchiveAll,
+			execution_strategy: ExecutionStrategy::Both,
 		};
 		configuration.network.boot_nodes = configuration.chain_spec.boot_nodes().to_vec();
 		configuration

substrate/polkadot/service/src/lib.rs

@@ -73,7 +73,7 @@ use tokio::runtime::TaskExecutor;
 
 pub use self::error::{ErrorKind, Error};
 pub use self::components::{Components, FullComponents, LightComponents};
-pub use config::{Configuration, Role, PruningMode};
+pub use config::{Configuration, Role, PruningMode, ExecutionStrategy};
 pub use chain_spec::ChainSpec;
 
 /// Polkadot service.
@@ -112,7 +112,7 @@ pub fn new_client(config: Configuration) -> Result<Arc<Client<
 	let executor = polkadot_executor::Executor::new();
 	let is_validator = (config.roles & Role::AUTHORITY) == Role::AUTHORITY;
 	let components = components::FullComponents { is_validator };
-	let (client, _) = components.build_client(db_settings, executor, &config.chain_spec)?;
+	let (client, _) = components.build_client(db_settings, executor, &config.chain_spec, config.execution_strategy)?;
 	Ok(client)
 }
 
@@ -126,7 +126,7 @@ impl<Components> Service<Components>
 		let (signal, exit) = ::exit_future::signal();
 
 		// Create client
-		let executor = polkadot_executor::Executor::new();
+		let executor = polkadot_executor::Executor::with_heap_pages(128);
 
 		let mut keystore = Keystore::open(config.keystore_path.into())?;
 		for seed in &config.keys {
@@ -144,7 +144,7 @@ impl<Components> Service<Components>
 			pruning: config.pruning,
 		};
 
-		let (client, on_demand) = components.build_client(db_settings, executor, &config.chain_spec)?;
+		let (client, on_demand) = components.build_client(db_settings, executor, &config.chain_spec, config.execution_strategy)?;
 		let api = components.build_api(client.clone());
 		let best_header = client.best_block_header()?;
 

substrate/substrate/client/db/src/lib.rs

@@ -54,7 +54,7 @@ use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, As, Hash, H
 use runtime_primitives::BuildStorage;
 use state_machine::backend::Backend as StateBackend;
 use executor::RuntimeInfo;
-use state_machine::{CodeExecutor, TrieH256, DBValue};
+use state_machine::{CodeExecutor, TrieH256, DBValue, ExecutionStrategy};
 use utils::{Meta, db_err, meta_keys, number_to_db_key, open_database, read_db, read_id, read_meta};
 use state_db::StateDb;
 pub use state_db::PruningMode;
@@ -79,6 +79,7 @@ pub fn new_client<E, S, Block>(
 	settings: DatabaseSettings,
 	executor: E,
 	genesis_storage: S,
+	execution_strategy: ExecutionStrategy,
 ) -> Result<client::Client<Backend<Block>, client::LocalCallExecutor<Backend<Block>, E>, Block>, client::error::Error>
 	where
 		Block: BlockT,
@@ -89,7 +90,7 @@ pub fn new_client<E, S, Block>(
 {
 	let backend = Arc::new(Backend::new(settings, FINALIZATION_WINDOW)?);
 	let executor = client::LocalCallExecutor::new(backend.clone(), executor);
-	Ok(client::Client::new(backend, executor, genesis_storage)?)
+	Ok(client::Client::new(backend, executor, genesis_storage, execution_strategy)?)
 }
 
 mod columns {

substrate/substrate/client/src/block_builder.rs

@@ -18,7 +18,7 @@
 
 use std::vec::Vec;
 use codec::Slicable;
-use state_machine;
+use state_machine::{self, native_when_possible};
 use runtime_primitives::traits::{Header as HeaderT, Hash, Block as BlockT, One, HashFor};
 use runtime_primitives::generic::BlockId;
 use {backend, error, Client, CallExecutor};
@@ -69,7 +69,7 @@ impl<B, E, Block> BlockBuilder<B, E, Block> where
 			Default::default()
 		);
 
-		executor.call_at_state(&state, &mut changes, "initialise_block", &header.encode())?;
+		executor.call_at_state(&state, &mut changes, "initialise_block", &header.encode(), native_when_possible())?;
 
 		Ok(BlockBuilder {
 			header,
@@ -84,7 +84,7 @@ impl<B, E, Block> BlockBuilder<B, E, Block> where
 	/// can be validly executed (by executing it); if it is invalid, it'll be returned along with
 	/// the error. Otherwise, it will return a mutable reference to self (in order to chain).
 	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> error::Result<()> {
-		match self.executor.call_at_state(&self.state, &mut self.changes, "apply_extrinsic", &xt.encode()) {
+		match self.executor.call_at_state(&self.state, &mut self.changes, "apply_extrinsic", &xt.encode(), native_when_possible()) {
 			Ok(_) => {
 				self.extrinsics.push(xt);
 				Ok(())
@@ -103,6 +103,7 @@ impl<B, E, Block> BlockBuilder<B, E, Block> where
 			&mut self.changes,
 			"finalise_block",
 			&[],
+			native_when_possible(),
 		)?;
 		self.header = <<Block as BlockT>::Header as Slicable>::decode(&mut &output[..])
 			.expect("Header came straight out of runtime so must be valid");

substrate/substrate/client/src/call_executor.rs

@@ -17,7 +17,8 @@
 use std::sync::Arc;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::Block as BlockT;
-use state_machine::{self, OverlayedChanges, Ext, Backend as StateBackend, CodeExecutor};
+use state_machine::{self, OverlayedChanges, Ext, Backend as StateBackend,
+	CodeExecutor, ExecutionManager, native_when_possible};
 use runtime_io::Externalities;
 use executor::{RuntimeVersion, RuntimeInfo};
 
@@ -41,7 +42,11 @@ pub trait CallExecutor<B: BlockT> {
 	/// Execute a call to a contract on top of state in a block of given hash.
 	///
 	/// No changes are made.
-	fn call(&self, id: &BlockId<B>, method: &str, call_data: &[u8]) -> Result<CallResult, error::Error>;
+	fn call(&self,
+		id: &BlockId<B>,
+		method: &str,
+		call_data: &[u8],
+	) -> Result<CallResult, error::Error>;
 
 	/// Extract RuntimeVersion of given block
 	///
@@ -51,12 +56,26 @@ pub trait CallExecutor<B: BlockT> {
 	/// Execute a call to a contract on top of given state.
 	///
 	/// No changes are made.
-	fn call_at_state<S: state_machine::Backend>(&self, state: &S, overlay: &mut OverlayedChanges, method: &str, call_data: &[u8]) -> Result<(Vec<u8>, S::Transaction), error::Error>;
+	fn call_at_state<
+		S: state_machine::Backend,
+		F: FnOnce(Result<Vec<u8>, Self::Error>, Result<Vec<u8>, Self::Error>) -> Result<Vec<u8>, Self::Error>,
+	>(&self,
+		state: &S,
+		overlay: &mut OverlayedChanges,
+		method: &str,
+		call_data: &[u8],
+		manager: ExecutionManager<F>
+	) -> Result<(Vec<u8>, S::Transaction), error::Error>;
 
 	/// Execute a call to a contract on top of given state, gathering execution proof.
 	///
 	/// No changes are made.
-	fn prove_at_state<S: state_machine::Backend>(&self, state: S, overlay: &mut OverlayedChanges, method: &str, call_data: &[u8]) -> Result<(Vec<u8>, Vec<Vec<u8>>), error::Error>;
+	fn prove_at_state<S: state_machine::Backend>(&self,
+		state: S,
+		overlay: &mut OverlayedChanges,
+		method: &str,
+		call_data: &[u8]
+	) -> Result<(Vec<u8>, Vec<Vec<u8>>), error::Error>;
 
 	/// Get runtime version if supported.
 	fn native_runtime_version(&self) -> Option<RuntimeVersion>;
@@ -94,9 +113,19 @@ impl<B, E, Block> CallExecutor<Block> for LocalCallExecutor<B, E>
 {
 	type Error = E::Error;
 
-	fn call(&self, id: &BlockId<Block>, method: &str, call_data: &[u8]) -> error::Result<CallResult> {
+	fn call(&self,
+		id: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+	) -> error::Result<CallResult> {
 		let mut changes = OverlayedChanges::default();
-		let (return_data, _) = self.call_at_state(&self.backend.state_at(*id)?, &mut changes, method, call_data)?;
+		let (return_data, _) = self.call_at_state(
+			&self.backend.state_at(*id)?,
+			&mut changes,
+			method,
+			call_data,
+			native_when_possible(),
+		)?;
 		Ok(CallResult{ return_data, changes })
 	}
 
@@ -111,17 +140,32 @@ impl<B, E, Block> CallExecutor<Block> for LocalCallExecutor<B, E>
 			.ok_or(error::ErrorKind::VersionInvalid.into())
 	}
 
-	fn call_at_state<S: state_machine::Backend>(&self, state: &S, changes: &mut OverlayedChanges, method: &str, call_data: &[u8]) -> error::Result<(Vec<u8>, S::Transaction)> {
-		state_machine::execute(
+	fn call_at_state<
+		S: state_machine::Backend,
+		F: FnOnce(Result<Vec<u8>, Self::Error>, Result<Vec<u8>, Self::Error>) -> Result<Vec<u8>, Self::Error>,
+	>(&self,
+		state: &S,
+		changes: &mut OverlayedChanges,
+		method: &str,
+		call_data: &[u8],
+		manager: ExecutionManager<F>,
+	) -> error::Result<(Vec<u8>, S::Transaction)> {
+		state_machine::execute_using_consensus_failure_handler(
 			state,
 			changes,
 			&self.executor,
 			method,
 			call_data,
+			manager,
 		).map_err(Into::into)
 	}
 
-	fn prove_at_state<S: state_machine::Backend>(&self, state: S, changes: &mut OverlayedChanges, method: &str, call_data: &[u8]) -> Result<(Vec<u8>, Vec<Vec<u8>>), error::Error> {
+	fn prove_at_state<S: state_machine::Backend>(&self,
+		state: S,
+		changes: &mut OverlayedChanges,
+		method: &str,
+		call_data: &[u8]
+	) -> Result<(Vec<u8>, Vec<Vec<u8>>), error::Error> {
 		state_machine::prove_execution(
 			state,
 			changes,

substrate/substrate/client/src/client.rs

@@ -25,7 +25,7 @@ use runtime_primitives::traits::{Block as BlockT, Header as HeaderT, Zero, One,
 use runtime_primitives::BuildStorage;
 use primitives::storage::{StorageKey, StorageData};
 use codec::Slicable;
-use state_machine::{self, Ext, OverlayedChanges, Backend as StateBackend, CodeExecutor};
+use state_machine::{self, Ext, OverlayedChanges, Backend as StateBackend, CodeExecutor, ExecutionStrategy, ExecutionManager};
 
 use backend::{self, BlockImportOperation};
 use blockchain::{self, Info as ChainInfo, Backend as ChainBackend, HeaderBackend as ChainHeaderBackend};
@@ -43,6 +43,7 @@ pub struct Client<B, E, Block> where Block: BlockT {
 	import_notification_sinks: Mutex<Vec<mpsc::UnboundedSender<BlockImportNotification<Block>>>>,
 	import_lock: Mutex<()>,
 	importing_block: RwLock<Option<Block::Hash>>, // holds the block hash currently being imported. TODO: replace this with block queue
+	execution_strategy: ExecutionStrategy,
 }
 
 /// A source of blockchain evenets.
@@ -144,7 +145,7 @@ impl<Block: BlockT> JustifiedHeader<Block> {
 /// Create an instance of in-memory client.
 pub fn new_in_mem<E, Block, S>(
 	executor: E,
-	genesis_storage: S
+	genesis_storage: S,
 ) -> error::Result<Client<in_mem::Backend<Block>, LocalCallExecutor<in_mem::Backend<Block>, E>, Block>>
 	where
 		E: CodeExecutor + RuntimeInfo,
@@ -153,7 +154,7 @@ pub fn new_in_mem<E, Block, S>(
 {
 	let backend = Arc::new(in_mem::Backend::new());
 	let executor = LocalCallExecutor::new(backend.clone(), executor);
-	Client::new(backend, executor, genesis_storage)
+	Client::new(backend, executor, genesis_storage, ExecutionStrategy::NativeWhenPossible)
 }
 
 impl<B, E, Block> Client<B, E, Block> where
@@ -167,6 +168,7 @@ impl<B, E, Block> Client<B, E, Block> where
 		backend: Arc<B>,
 		executor: E,
 		build_genesis_storage: S,
+		execution_strategy: ExecutionStrategy,
 	) -> error::Result<Self> {
 		if backend.blockchain().header(BlockId::Number(Zero::zero()))?.is_none() {
 			let genesis_storage = build_genesis_storage.build_storage()?;
@@ -183,6 +185,7 @@ impl<B, E, Block> Client<B, E, Block> where
 			import_notification_sinks: Mutex::new(Vec::new()),
 			import_lock: Mutex::new(()),
 			importing_block: RwLock::new(None),
+			execution_strategy,
 		})
 	}
 
@@ -327,13 +330,30 @@ impl<B, E, Block> Client<B, E, Block> where
 		let storage_update = match transaction.state()? {
 			Some(transaction_state) => {
 				let mut overlay = Default::default();
-				let (_, storage_update) = self.executor.call_at_state(
+				let mut r = self.executor.call_at_state(
 					transaction_state,
 					&mut overlay,
 					"execute_block",
-					&<Block as BlockT>::new(header.clone(), body.clone().unwrap_or_default()).encode()
-				)?;
-
+					&<Block as BlockT>::new(header.clone(), body.clone().unwrap_or_default()).encode(),
+					match (origin, self.execution_strategy) {
+						(BlockOrigin::NetworkInitialSync, _) | (_, ExecutionStrategy::NativeWhenPossible) =>
+							ExecutionManager::NativeWhenPossible,
+						(_, ExecutionStrategy::AlwaysWasm) => ExecutionManager::AlwaysWasm,
+						_ => ExecutionManager::Both(|wasm_result, native_result| {
+							warn!("Consensus error between wasm and native block execution at block {}", hash);
+							warn!("   Header {:?}", header);
+							warn!("   Native result {:?}", native_result);
+							warn!("   Wasm result {:?}", wasm_result);
+							telemetry!("block.execute.consensus_failure";
+								"hash" => ?hash,
+								"origin" => ?origin,
+								"header" => ?header
+							);
+							wasm_result
+						}),
+					},
+				);
+				let (_, storage_update) = r?;
 				Some(storage_update)
 			},
 			None => None,

substrate/substrate/client/src/genesis.rs

@@ -45,7 +45,7 @@ mod tests {
 	use codec::{Slicable, Joiner};
 	use keyring::Keyring;
 	use executor::WasmExecutor;
-	use state_machine::{execute, OverlayedChanges};
+	use state_machine::{execute, OverlayedChanges, ExecutionStrategy};
 	use state_machine::backend::InMemory;
 	use test_client;
 	use test_client::runtime::genesismap::{GenesisConfig, additional_storage_with_genesis};
@@ -83,6 +83,7 @@ mod tests {
 			&Executor::new(),
 			"initialise_block",
 			&header.encode(),
+			ExecutionStrategy::NativeWhenPossible,
 		).unwrap();
 
 		for tx in transactions.iter() {
@@ -92,6 +93,7 @@ mod tests {
 				&Executor::new(),
 				"apply_extrinsic",
 				&tx.encode(),
+				ExecutionStrategy::NativeWhenPossible,
 			).unwrap();
 		}
 
@@ -100,7 +102,8 @@ mod tests {
 			&mut overlay,
 			&Executor::new(),
 			"finalise_block",
-			&[]
+			&[],
+			ExecutionStrategy::NativeWhenPossible,
 		).unwrap();
 		header = Header::decode(&mut &ret_data[..]).unwrap();
 		println!("root after: {:?}", header.extrinsics_root);
@@ -141,7 +144,8 @@ mod tests {
 			&mut overlay,
 			&Executor::new(),
 			"execute_block",
-			&b1data
+			&b1data,
+			ExecutionStrategy::NativeWhenPossible,
 		).unwrap();
 	}
 
@@ -161,9 +165,10 @@ mod tests {
 		let _ = execute(
 			&backend,
 			&mut overlay,
-			&WasmExecutor,
+			&WasmExecutor { heap_pages: 8 },
 			"execute_block",
-			&b1data
+			&b1data,
+			ExecutionStrategy::NativeWhenPossible,
 		).unwrap();
 	}
 
@@ -184,9 +189,10 @@ mod tests {
 		let _ = execute(
 			&backend,
 			&mut overlay,
-			&Executor::new(),
+			&Executor::with_heap_pages(8),
 			"execute_block",
-			&b1data
+			&b1data,
+			ExecutionStrategy::NativeWhenPossible,
 		).unwrap();
 	}
 }

substrate/substrate/client/src/light/call_executor.rs

@@ -22,7 +22,7 @@ use futures::{IntoFuture, Future};
 
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header as HeaderT};
-use state_machine::{Backend as StateBackend, CodeExecutor, OverlayedChanges, execution_proof_check};
+use state_machine::{Backend as StateBackend, CodeExecutor, OverlayedChanges, execution_proof_check, ExecutionManager};
 
 use blockchain::Backend as ChainBackend;
 use call_executor::{CallExecutor, CallResult};
@@ -73,7 +73,16 @@ impl<B, F, Block> CallExecutor<Block> for RemoteCallExecutor<B, F>
 			.ok_or_else(|| ClientErrorKind::VersionInvalid.into())
 	}
 
-	fn call_at_state<S: StateBackend>(&self, _state: &S, _changes: &mut OverlayedChanges, _method: &str, _call_data: &[u8]) -> ClientResult<(Vec<u8>, S::Transaction)> {
+	fn call_at_state<
+		S: StateBackend,
+		H: FnOnce(Result<Vec<u8>, Self::Error>, Result<Vec<u8>, Self::Error>) -> Result<Vec<u8>, Self::Error>
+	>(&self,
+		_state: &S,
+		_changes: &mut OverlayedChanges,
+		_method: &str,
+		_call_data: &[u8],
+		_m: ExecutionManager<H>
+	) -> ClientResult<(Vec<u8>, S::Transaction)> {
 		Err(ClientErrorKind::NotAvailableOnLightClient.into())
 	}
 

substrate/substrate/client/src/light/mod.rs

@@ -25,7 +25,7 @@ use std::sync::Arc;
 
 use runtime_primitives::BuildStorage;
 use runtime_primitives::traits::Block as BlockT;
-use state_machine::CodeExecutor;
+use state_machine::{CodeExecutor, ExecutionStrategy};
 
 use client::Client;
 use error::Result as ClientResult;
@@ -58,7 +58,7 @@ pub fn new_light<B, S, F, GS>(
 		GS: BuildStorage,
 {
 	let executor = RemoteCallExecutor::new(backend.blockchain().clone(), fetcher);
-	Client::new(backend, executor, genesis_storage)
+	Client::new(backend, executor, genesis_storage, ExecutionStrategy::NativeWhenPossible)
 }
 
 /// Create an instance of fetch data checker.

substrate/substrate/executor/src/native_executor.rs

@@ -27,14 +27,14 @@ use parking_lot::{Mutex, MutexGuard};
 use RuntimeInfo;
 
 // For the internal Runtime Cache:
-// Do we run this natively or use the given WasmModule
-enum RunWith {
+// Is it compatible enough to run this natively or do we need to fall back on the WasmModule
+enum Compatibility {
 	InvalidVersion(WasmModule),
-	NativeRuntime(RuntimeVersion),
-	WasmRuntime(RuntimeVersion, WasmModule)
+	IsCompatible(RuntimeVersion),
+	NotCompatible(RuntimeVersion, WasmModule)
 }
 
-type CacheType = HashMap<u64, RunWith>;
+type CacheType = HashMap<u64, Compatibility>;
 
 lazy_static! {
 	static ref RUNTIMES_CACHE: Mutex<CacheType> = Mutex::new(HashMap::new());
@@ -51,29 +51,28 @@ fn gen_cache_key(code: &[u8]) -> u64 {
 }
 
 /// fetch a runtime version from the cache or if there is no cached version yet, create
-/// the runtime version entry for `code`, determines whether `RunWith::NativeRuntime`
+/// the runtime version entry for `code`, determines whether `Compatibility::IsCompatible`
 /// can be used by by comparing returned RuntimeVersion to `ref_version`
 fn fetch_cached_runtime_version<'a, E: Externalities>(
 	cache: &'a mut MutexGuard<CacheType>,
 	ext: &mut E,
 	code: &[u8],
 	ref_version: RuntimeVersion
-) -> &'a RunWith {
+) -> &'a Compatibility {
 	cache.entry(gen_cache_key(code))
 		.or_insert_with(|| {
 			let module = WasmModule::from_buffer(code).expect("all modules compiled with rustc are valid wasm code; qed");
-			let version = WasmExecutor.call_in_wasm_module(ext, &module, "version", &[]).ok()
+			let version = WasmExecutor{heap_pages: 8}.call_in_wasm_module(ext, &module, "version", &[]).ok()
 				.and_then(|v| RuntimeVersion::decode(&mut v.as_slice()));
 
-
 			if let Some(v) = version {
 				if ref_version.can_call_with(&v) {
-					RunWith::NativeRuntime(v)
+					Compatibility::IsCompatible(v)
 				} else {
-					RunWith::WasmRuntime(v, module)
+					Compatibility::NotCompatible(v, module)
 				}
 			} else {
-				RunWith::InvalidVersion(module)
+				Compatibility::InvalidVersion(module)
 			}
 	})
 }
@@ -112,18 +111,26 @@ pub trait NativeExecutionDispatch {
 pub struct NativeExecutor<D: NativeExecutionDispatch + Sync + Send> {
 	/// Dummy field to avoid the compiler complaining about us not using `D`.
 	_dummy: ::std::marker::PhantomData<D>,
+	/// The fallback executor in case native isn't available.
+	fallback: WasmExecutor,
 }
 
 impl<D: NativeExecutionDispatch + Sync + Send> NativeExecutor<D> {
-	/// Create new instance.
+	/// Create new instance with 128 pages for the wasm fallback's heap.
 	pub fn new() -> Self {
+		Self::with_heap_pages(128)
+	}
+
+	/// Create new instance with specific number of pages for wasm fallback's heap.
+	pub fn with_heap_pages(heap_pages: usize) -> Self {
 		// FIXME: set this entry at compile time
 		RUNTIMES_CACHE.lock().insert(
 			gen_cache_key(D::native_equivalent()),
-			RunWith::NativeRuntime(D::VERSION));
+			Compatibility::IsCompatible(D::VERSION));
 
 		NativeExecutor {
 			_dummy: Default::default(),
+			fallback: WasmExecutor{heap_pages},
 		}
 	}
 }
@@ -132,6 +139,7 @@ impl<D: NativeExecutionDispatch + Sync + Send> Clone for NativeExecutor<D> {
 	fn clone(&self) -> Self {
 		NativeExecutor {
 			_dummy: Default::default(),
+			fallback: self.fallback.clone(),
 		}
 	}
 }
@@ -146,8 +154,8 @@ impl<D: NativeExecutionDispatch + Sync + Send> RuntimeInfo for NativeExecutor<D>
 	) -> Option<RuntimeVersion> {
 		let mut c = RUNTIMES_CACHE.lock();
 		match fetch_cached_runtime_version(&mut c, ext, code, D::VERSION) {
-			RunWith::NativeRuntime(v) | RunWith::WasmRuntime(v, _) => Some(v.clone()),
-			RunWith::InvalidVersion(_m) => None
+			Compatibility::IsCompatible(v) | Compatibility::NotCompatible(v, _) => Some(v.clone()),
+			Compatibility::InvalidVersion(_m) => None
 		}
 	}
 }
@@ -161,11 +169,15 @@ impl<D: NativeExecutionDispatch + Sync + Send> CodeExecutor for NativeExecutor<D
 		code: &[u8],
 		method: &str,
 		data: &[u8],
-	) -> Result<Vec<u8>> {
+		use_native: bool,
+	) -> (Result<Vec<u8>>, bool) {
 		let mut c = RUNTIMES_CACHE.lock();
-		match fetch_cached_runtime_version(&mut c, ext, code, D::VERSION) {
-			RunWith::NativeRuntime(_v) => D::dispatch(ext, method, data),
-			RunWith::WasmRuntime(_, m) | RunWith::InvalidVersion(m) => WasmExecutor.call_in_wasm_module(ext, m, method, data)
+		match (use_native, fetch_cached_runtime_version(&mut c, ext, code, D::VERSION)) {
+			(_, Compatibility::NotCompatible(_, m)) | (_, Compatibility::InvalidVersion(m)) =>
+				(self.fallback.call_in_wasm_module(ext, m, method, data), false),
+			(false, _) =>
+				(self.fallback.call(ext, code, method, data, false).0, false),
+			_ => (D::dispatch(ext, method, data), true),
 		}
 	}
 }
@@ -200,6 +212,9 @@ macro_rules! native_executor_instance {
 			pub fn new() -> $crate::NativeExecutor<$name> {
 				$crate::NativeExecutor::new()
 			}
+			pub fn with_heap_pages(heap_pages: usize) -> $crate::NativeExecutor<$name> {
+				$crate::NativeExecutor::with_heap_pages(heap_pages)
+			}
 		}
 	}
 }

substrate/substrate/executor/src/sandbox.rs

@@ -554,7 +554,7 @@ mod tests {
 		"#).unwrap();
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_sandbox", &code).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_sandbox", &code, true).0.unwrap(),
 			vec![1],
 		);
 	}
@@ -575,7 +575,7 @@ mod tests {
 		"#).unwrap();
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_sandbox", &code).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_sandbox", &code, true).0.unwrap(),
 			vec![0],
 		);
 	}
@@ -613,7 +613,7 @@ mod tests {
 		"#).unwrap();
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_sandbox", &code).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_sandbox", &code, true).0.unwrap(),
 			vec![1],
 		);
 	}
@@ -647,7 +647,7 @@ mod tests {
 		"#).unwrap();
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_sandbox_args", &code).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_sandbox_args", &code, true).0.unwrap(),
 			vec![1],
 		);
 	}
@@ -669,7 +669,7 @@ mod tests {
 		"#).unwrap();
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_sandbox_return_val", &code).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_sandbox_return_val", &code, true).0.unwrap(),
 			vec![1],
 		);
 	}

substrate/substrate/executor/src/wasm_executor.rs

@@ -37,28 +37,28 @@ struct Heap {
 }
 
 impl Heap {
-	/// Construct new `Heap` struct.
+	/// Construct new `Heap` struct with a given number of pages.
 	///
 	/// Returns `Err` if the heap couldn't allocate required
 	/// number of pages.
 	///
 	/// This could mean that wasm binary specifies memory
 	/// limit and we are trying to allocate beyond that limit.
-	fn new(memory: &MemoryRef) -> Result<Self> {
-		const HEAP_SIZE_IN_PAGES: usize = 1024;
-
+	fn new(memory: &MemoryRef, pages: usize) -> Result<Self> {
 		let prev_page_count = memory
-			.grow(Pages(HEAP_SIZE_IN_PAGES))
+			.grow(Pages(pages))
 			.map_err(|_| Error::from(ErrorKind::Runtime))?;
 		Ok(Heap {
 			end: Bytes::from(prev_page_count).0 as u32,
 		})
 	}
+
 	fn allocate(&mut self, size: u32) -> u32 {
 		let r = self.end;
 		self.end += size;
 		r
 	}
+
 	fn deallocate(&mut self, _offset: u32) {
 	}
 }
@@ -73,10 +73,10 @@ struct FunctionExecutor<'e, E: Externalities + 'e> {
 }
 
 impl<'e, E: Externalities> FunctionExecutor<'e, E> {
-	fn new(m: MemoryRef, t: Option<TableRef>, e: &'e mut E) -> Result<Self> {
+	fn new(m: MemoryRef, heap_pages: usize, t: Option<TableRef>, e: &'e mut E) -> Result<Self> {
 		Ok(FunctionExecutor {
 			sandbox_store: sandbox::Store::new(),
-			heap: Heap::new(&m)?,
+			heap: Heap::new(&m, heap_pages)?,
 			memory: m,
 			table: t,
 			ext: e,
@@ -468,7 +468,10 @@ impl_function_executor!(this: FunctionExecutor<'e, E>,
 ///
 /// Executes the provided code in a sandboxed wasm runtime.
 #[derive(Debug, Default, Clone)]
-pub struct WasmExecutor;
+pub struct WasmExecutor {
+	/// The number of pages to allocate for the heap.
+	pub heap_pages: usize,
+}
 
 impl WasmExecutor {
 
@@ -502,7 +505,7 @@ impl WasmExecutor {
 			.not_started_instance()
 			.export_by_name("table")
 			.and_then(|e| e.as_table().cloned());
-		let mut fec = FunctionExecutor::new(memory.clone(), table, ext)?;
+		let mut fec = FunctionExecutor::new(memory.clone(), self.heap_pages, table, ext)?;
 
 		// finish instantiation by running 'start' function (if any).
 		let instance = intermediate_instance.run_start(&mut fec)?;
@@ -540,9 +543,11 @@ impl CodeExecutor for WasmExecutor {
 		code: &[u8],
 		method: &str,
 		data: &[u8],
-	) -> Result<Vec<u8>> {
-		let module = Module::from_buffer(code)?;
-		self.call_in_wasm_module(ext, &module, method, data)
+		_use_native: bool
+	) -> (Result<Vec<u8>>, bool) {
+		(Module::from_buffer(code).map_err(Into::into).and_then(|module| 
+			self.call_in_wasm_module(ext, &module, method, data)
+		), false)
 	}
 }
 
@@ -565,7 +570,7 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 
-		let output = WasmExecutor.call(&mut ext, &test_code[..], "test_empty_return", &[]).unwrap();
+		let output = WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_empty_return", &[], true).0.unwrap();
 		assert_eq!(output, vec![0u8; 0]);
 	}
 
@@ -574,10 +579,10 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 
-		let output = WasmExecutor.call(&mut ext, &test_code[..], "test_panic", &[]);
+		let output = WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_panic", &[], true).0;
 		assert!(output.is_err());
 
-		let output = WasmExecutor.call(&mut ext, &test_code[..], "test_conditional_panic", &[2]);
+		let output = WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_conditional_panic", &[2], true).0;
 		assert!(output.is_err());
 	}
 
@@ -587,7 +592,7 @@ mod tests {
 		ext.set_storage(b"foo".to_vec(), b"bar".to_vec());
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 
-		let output = WasmExecutor.call(&mut ext, &test_code[..], "test_data_in", b"Hello world").unwrap();
+		let output = WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_data_in", b"Hello world", true).0.unwrap();
 
 		assert_eq!(output, b"all ok!".to_vec());
 
@@ -610,7 +615,7 @@ mod tests {
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 
 		// This will clear all entries which prefix is "ab".
-		let output = WasmExecutor.call(&mut ext, &test_code[..], "test_clear_prefix", b"ab").unwrap();
+		let output = WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_clear_prefix", b"ab", true).0.unwrap();
 
 		assert_eq!(output, b"all ok!".to_vec());
 
@@ -627,11 +632,11 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_blake2_256", &[]).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_blake2_256", &[], true).0.unwrap(),
 			blake2_256(&b""[..]).encode()
 		);
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_blake2_256", b"Hello world!").unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_blake2_256", b"Hello world!", true).0.unwrap(),
 			blake2_256(&b"Hello world!"[..]).encode()
 		);
 	}
@@ -641,11 +646,11 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_twox_256", &[]).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_twox_256", &[], true).0.unwrap(),
 			FromHex::from_hex("99e9d85137db46ef4bbea33613baafd56f963c64b1f3685a4eb4abd67ff6203a").unwrap()
 		);
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_twox_256", b"Hello world!").unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_twox_256", b"Hello world!", true).0.unwrap(),
 			FromHex::from_hex("b27dfd7f223f177f2a13647b533599af0c07f68bda23d96d059da2b451a35a74").unwrap()
 		);
 	}
@@ -655,11 +660,11 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_twox_128", &[]).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_twox_128", &[], true).0.unwrap(),
 			FromHex::from_hex("99e9d85137db46ef4bbea33613baafd5").unwrap()
 		);
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_twox_128", b"Hello world!").unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_twox_128", b"Hello world!", true).0.unwrap(),
 			FromHex::from_hex("b27dfd7f223f177f2a13647b533599af").unwrap()
 		);
 	}
@@ -675,7 +680,7 @@ mod tests {
 		calldata.extend_from_slice(sig.as_ref());
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_ed25519_verify", &calldata).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_ed25519_verify", &calldata, true).0.unwrap(),
 			vec![1]
 		);
 
@@ -685,7 +690,7 @@ mod tests {
 		calldata.extend_from_slice(other_sig.as_ref());
 
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_ed25519_verify", &calldata).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_ed25519_verify", &calldata, true).0.unwrap(),
 			vec![0]
 		);
 	}
@@ -695,7 +700,7 @@ mod tests {
 		let mut ext = TestExternalities::default();
 		let test_code = include_bytes!("../wasm/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
 		assert_eq!(
-			WasmExecutor.call(&mut ext, &test_code[..], "test_enumerated_trie_root", &[]).unwrap(),
+			WasmExecutor{heap_pages: 8}.call(&mut ext, &test_code[..], "test_enumerated_trie_root", &[], true).0.unwrap(),
 			ordered_trie_root(vec![b"zero".to_vec(), b"one".to_vec(), b"two".to_vec()]).0.encode()
 		);
 	}

substrate/substrate/runtime/consensus/src/lib.rs

@@ -69,6 +69,7 @@ decl_module! {
 	#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
 	pub enum Call where aux: T::PublicAux {
 		fn report_misbehavior(aux, report: MisbehaviorReport<T::Hash, T::BlockNumber>) -> Result = 0;
+		fn remark(aux, remark: Vec<u8>) -> Result = 1;
 	}
 
 	#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
@@ -104,6 +105,11 @@ impl<T: Trait> Module<T> {
 		Ok(())
 	}
 
+	/// Make some on-chain remark.
+	fn remark(_aux: &T::PublicAux, _remark: Vec<u8>) -> Result {
+		Ok(())
+	}
+
 	/// Set the current set of authorities' session keys.
 	///
 	/// Called by `next_session` only.

substrate/substrate/state-machine/src/lib.rs

@@ -150,14 +150,57 @@ pub trait CodeExecutor: Sized + Send + Sync {
 	/// Externalities error type.
 	type Error: Error;
 
-	/// Call a given method in the runtime.
+	/// Call a given method in the runtime. Returns a tuple of the result (either the output data
+	/// or an execution error) together with a `bool`, which is true if native execution was used.
 	fn call<E: Externalities>(
 		&self,
 		ext: &mut E,
 		code: &[u8],
 		method: &str,
 		data: &[u8],
-	) -> Result<Vec<u8>, Self::Error>;
+		use_native: bool
+	) -> (Result<Vec<u8>, Self::Error>, bool);
+}
+
+/// Strategy for executing a call into the runtime.
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+pub enum ExecutionStrategy {
+	/// Execute with the native equivalent if it is compatible with the given wasm module; otherwise fall back to the wasm.
+	NativeWhenPossible,
+	/// Use the given wasm module.
+	AlwaysWasm,
+	/// Run with both the wasm and the native variant (if compatible). Report any discrepency as an error.
+	Both,
+}
+
+/// Like `ExecutionStrategy` only it also stores a handler in case of consensus failure.
+pub enum ExecutionManager<F> {
+	/// Execute with the native equivalent if it is compatible with the given wasm module; otherwise fall back to the wasm.
+	NativeWhenPossible,
+	/// Use the given wasm module.
+	AlwaysWasm,
+	/// Run with both the wasm and the native variant (if compatible). Call `F` in the case of any discrepency.
+	Both(F),
+}
+
+impl<'a, F> From<&'a ExecutionManager<F>> for ExecutionStrategy {
+	fn from(s: &'a ExecutionManager<F>) -> Self {
+		match *s {
+			ExecutionManager::NativeWhenPossible => ExecutionStrategy::NativeWhenPossible,
+			ExecutionManager::AlwaysWasm => ExecutionStrategy::AlwaysWasm,
+			ExecutionManager::Both(_) => ExecutionStrategy::Both,
+		}
+	}
+}
+
+/// Evaluate to ExecutionManager::NativeWhenPossible, without having to figure out the type.
+pub fn native_when_possible<E>() -> ExecutionManager<fn(Result<Vec<u8>, E>, Result<Vec<u8>, E>)->Result<Vec<u8>, E>> {
+	ExecutionManager::NativeWhenPossible
+}
+
+/// Evaluate to ExecutionManager::NativeWhenPossible, without having to figure out the type.
+pub fn always_wasm<E>() -> ExecutionManager<fn(Result<Vec<u8>, E>, Result<Vec<u8>, E>)->Result<Vec<u8>, E>> {
+	ExecutionManager::AlwaysWasm
 }
 
 /// Execute a call using the given state backend, overlayed changes, and call executor.
@@ -174,8 +217,46 @@ pub fn execute<B: backend::Backend, Exec: CodeExecutor>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
-) -> Result<(Vec<u8>, B::Transaction), Box<Error>>
-{
+	strategy: ExecutionStrategy,
+) -> Result<(Vec<u8>, B::Transaction), Box<Error>> {
+	execute_using_consensus_failure_handler(
+		backend,
+		overlay,
+		exec,
+		method,
+		call_data,
+		match strategy {
+			ExecutionStrategy::AlwaysWasm => ExecutionManager::AlwaysWasm,
+			ExecutionStrategy::NativeWhenPossible => ExecutionManager::NativeWhenPossible,
+			ExecutionStrategy::Both => ExecutionManager::Both(|wasm_result, native_result| {
+				warn!("Consensus error between wasm {:?} and native {:?}. Using wasm.", wasm_result, native_result);
+				wasm_result
+			}),
+		},
+	)
+}
+
+/// Execute a call using the given state backend, overlayed changes, and call executor.
+/// Produces a state-backend-specific "transaction" which can be used to apply the changes
+/// to the backing store, such as the disk.
+///
+/// On an error, no prospective changes are written to the overlay.
+///
+/// Note: changes to code will be in place if this call is made again. For running partial
+/// blocks (e.g. a transaction at a time), ensure a different method is used.
+pub fn execute_using_consensus_failure_handler<
+	B: backend::Backend,
+	Exec: CodeExecutor,
+	Handler: FnOnce(Result<Vec<u8>, Exec::Error>, Result<Vec<u8>, Exec::Error>) -> Result<Vec<u8>, Exec::Error>
+>(
+	backend: &B,
+	overlay: &mut OverlayedChanges,
+	exec: &Exec,
+	method: &str,
+	call_data: &[u8],
+	manager: ExecutionManager<Handler>,
+) -> Result<(Vec<u8>, B::Transaction), Box<Error>> {
+	let strategy: ExecutionStrategy = (&manager).into();
 	let result = {
 		let mut externalities = ext::Ext::new(overlay, backend);
 		// make a copy.
@@ -183,12 +264,35 @@ pub fn execute<B: backend::Backend, Exec: CodeExecutor>(
 			.ok_or(Box::new(ExecutionError::CodeEntryDoesNotExist) as Box<Error>)?
 			.to_vec();
 
-		exec.call(
+		let (result, was_native) = exec.call(
 			&mut externalities,
 			&code,
 			method,
 			call_data,
-		).map(move |out| (out, externalities.transaction()))
+			// attempt to run native first, if we're not directed to run wasm only
+			strategy != ExecutionStrategy::AlwaysWasm,
+		);
+		// run wasm separately if we did run native the first time and we're meant to run both
+		let result = if let (true, ExecutionManager::Both(on_consensus_failure)) = (was_native, manager) {
+			let (wasm_result, _) = exec.call(
+				&mut externalities,
+				&code,
+				method,
+				call_data,
+				false
+			);
+			if (result.is_ok() && wasm_result.is_ok() && result.as_ref().unwrap() == wasm_result.as_ref().unwrap())
+				|| (result.is_err() && wasm_result.is_err() && format!("{}", result.as_ref().unwrap_err()) == format!("{}", wasm_result.as_ref().unwrap_err()))
+			{
+				result
+			} else {
+				// Consensus error.
+				on_consensus_failure(wasm_result, result)
+			}
+		} else {
+			result
+		};
+		result.map(move |out| (out, externalities.transaction()))
 	};
 
 	match result {
@@ -218,12 +322,11 @@ pub fn prove_execution<B: TryIntoTrieBackend, Exec: CodeExecutor>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
-) -> Result<(Vec<u8>, Vec<Vec<u8>>, <TrieBackend as Backend>::Transaction), Box<Error>>
-{
+) -> Result<(Vec<u8>, Vec<Vec<u8>>, <TrieBackend as Backend>::Transaction), Box<Error>> {
 	let trie_backend = backend.try_into_trie_backend()
 		.ok_or_else(|| Box::new(ExecutionError::UnableToGenerateProof) as Box<Error>)?;
 	let proving_backend = proving_backend::ProvingBackend::new(trie_backend);
-	let (result, transaction) = execute(&proving_backend, overlay, exec, method, call_data)?;
+	let (result, transaction) = execute(&proving_backend, overlay, exec, method, call_data, ExecutionStrategy::NativeWhenPossible)?;
 	let proof = proving_backend.extract_proof();
 	Ok((result, proof, transaction))
 }
@@ -236,10 +339,9 @@ pub fn execution_proof_check<Exec: CodeExecutor>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
-) -> Result<(Vec<u8>, memorydb::MemoryDB), Box<Error>>
-{
+) -> Result<(Vec<u8>, memorydb::MemoryDB), Box<Error>> {
 	let backend = proving_backend::create_proof_check_backend(root.into(), proof)?;
-	execute(&backend, overlay, exec, method, call_data)
+	execute(&backend, overlay, exec, method, call_data, ExecutionStrategy::NativeWhenPossible)
 }
 
 #[cfg(test)]
@@ -248,7 +350,11 @@ mod tests {
 	use super::backend::InMemory;
 	use super::ext::Ext;
 
-	struct DummyCodeExecutor;
+	struct DummyCodeExecutor {
+		native_available: bool,
+		native_succeeds: bool,
+		fallback_succeeds: bool,
+	}
 
 	impl CodeExecutor for DummyCodeExecutor {
 		type Error = u8;
@@ -259,8 +365,14 @@ mod tests {
 			_code: &[u8],
 			_method: &str,
 			_data: &[u8],
-		) -> Result<Vec<u8>, Self::Error> {
-			Ok(vec![ext.storage(b"value1").unwrap()[0] + ext.storage(b"value2").unwrap()[0]])
+			use_native: bool
+		) -> (Result<Vec<u8>, Self::Error>, bool) {
+			let using_native = use_native && self.native_available;
+			match (using_native, self.native_succeeds, self.fallback_succeeds) {
+				(true, true, _) | (false, _, true) =>
+					(Ok(vec![ext.storage(b"value1").unwrap()[0] + ext.storage(b"value2").unwrap()[0]]), using_native),
+				_ => (Err(0), using_native),
+			}
 		}
 	}
 
@@ -325,21 +437,59 @@ mod tests {
 
 	#[test]
 	fn execute_works() {
-		assert_eq!(execute(&trie_backend::tests::test_trie(),
-			&mut Default::default(), &DummyCodeExecutor, "test", &[]).unwrap().0, vec![66]);
+		assert_eq!(execute(
+			&trie_backend::tests::test_trie(),
+			&mut Default::default(),
+			&DummyCodeExecutor {
+				native_available: true,
+				native_succeeds: true,
+				fallback_succeeds: true,
+			},
+			"test",
+			&[],
+			ExecutionStrategy::NativeWhenPossible
+		).unwrap().0, vec![66]);
+	}
+
+	#[test]
+	fn dual_execution_strategy_detects_consensus_failure() {
+		let mut consensus_failed = false;
+		assert!(execute_using_consensus_failure_handler(
+			&trie_backend::tests::test_trie(),
+			&mut Default::default(),
+			&DummyCodeExecutor {
+				native_available: true,
+				native_succeeds: true,
+				fallback_succeeds: false,
+			},
+			"test",
+			&[],
+			ExecutionManager::Both(|we, _ne| { 
+				consensus_failed = true;
+				println!("HELLO!");
+				we
+			}),
+		).is_err());
+		assert!(consensus_failed);
 	}
 
 	#[test]
 	fn prove_execution_and_proof_check_works() {
+		let executor = DummyCodeExecutor {
+			native_available: true,
+			native_succeeds: true,
+			fallback_succeeds: true,
+		};
+
 		// fetch execution proof from 'remote' full node
 		let remote_backend = trie_backend::tests::test_trie();
 		let remote_root = remote_backend.storage_root(::std::iter::empty()).0;
 		let (remote_result, remote_proof, _) = prove_execution(remote_backend,
-			&mut Default::default(), &DummyCodeExecutor, "test", &[]).unwrap();
+			&mut Default::default(), &executor, "test", &[]).unwrap();
 
 		// check proof locally
 		let (local_result, _) = execution_proof_check(remote_root, remote_proof,
-			&mut Default::default(), &DummyCodeExecutor, "test", &[]).unwrap();
+			&mut Default::default(), &executor, "test", &[]).unwrap();
 
 		// check that both results are correct
 		assert_eq!(remote_result, vec![66]);