Initial: Offchain Workers (#1942)

* Refactor state-machine stuff.

* Fix tests.

* WiP

* WiP2

* Service support for offchain workers.

* Service support for offchain workers.

* Testing offchain worker.

* Initial version working.

* Pass side effects in call.

* Pass OffchainExt in context.

* Submit extrinsics to the pool.

* Support inherents.

* Insert to inherents pool.

* Inserting to the pool asynchronously.

* Add test to offchain worker.

* Implement convenience syntax for modules.

* Dispatching offchain worker through executive.

* Fix offchain test.

* Remove offchain worker from timestamp.

* Update Cargo.lock.

* Address review comments.

* Use latest patch version for futures.

* Add CLI parameter for offchain worker.

* Fix compilation.

* Fix test.

* Fix extrinsics format for tests.

* Fix RPC test.

* Bump spec version.

* Fix executive.

* Fix support macro.

* Address grumbles.

* Bump runtime

substrate/Cargo.lock

@@ -1974,6 +1974,7 @@ dependencies = [
  "substrate-client 0.1.0",
  "substrate-consensus-aura-primitives 0.1.0",
  "substrate-keyring 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
 ]
 
@@ -2029,6 +2030,7 @@ dependencies = [
  "srml-timestamp 0.1.0",
  "substrate-client 0.1.0",
  "substrate-consensus-aura-primitives 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
 ]
 
@@ -3978,6 +3980,33 @@ dependencies = [
  "void 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "substrate-offchain"
+version = "0.1.0"
+dependencies = [
+ "env_logger 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.1.25 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-codec 3.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sr-primitives 0.1.0",
+ "substrate-client 0.1.0",
+ "substrate-consensus-common 0.1.0",
+ "substrate-inherents 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
+ "substrate-primitives 0.1.0",
+ "substrate-test-client 0.1.0",
+ "substrate-transaction-pool 0.1.0",
+ "tokio 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "substrate-offchain-primitives"
+version = "0.1.0"
+dependencies = [
+ "sr-primitives 0.1.0",
+ "substrate-client 0.1.0",
+]
+
 [[package]]
 name = "substrate-panic-handler"
 version = "0.1.0"
@@ -4110,8 +4139,10 @@ dependencies = [
  "substrate-client-db 0.1.0",
  "substrate-consensus-common 0.1.0",
  "substrate-executor 0.1.0",
+ "substrate-inherents 0.1.0",
  "substrate-keystore 0.1.0",
  "substrate-network 0.1.0",
+ "substrate-offchain 0.1.0",
  "substrate-primitives 0.1.0",
  "substrate-rpc-servers 0.1.0",
  "substrate-telemetry 0.3.1",
@@ -4222,6 +4253,7 @@ dependencies = [
  "substrate-executor 0.1.0",
  "substrate-inherents 0.1.0",
  "substrate-keyring 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
  "substrate-test-client 0.1.0",
 ]

substrate/core/basic-authorship/src/basic_authorship.rs

@@ -20,7 +20,7 @@
 //
 use std::{self, time, sync::Arc};
 
-use log::{info, debug};
+use log::{info, debug, warn};
 
 use client::{
 	self, error, Client as SubstrateClient, CallExecutor,
@@ -28,15 +28,14 @@ use client::{
 };
 use codec::Decode;
 use consensus_common::{self, evaluation};
-use primitives::{H256, Blake2Hasher};
+use primitives::{H256, Blake2Hasher, ExecutionContext};
 use runtime_primitives::traits::{
 	Block as BlockT, Hash as HashT, Header as HeaderT, ProvideRuntimeApi, AuthorityIdFor
 };
-use runtime_primitives::ExecutionContext;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::ApplyError;
 use transaction_pool::txpool::{self, Pool as TransactionPool};
-use inherents::InherentData;
+use inherents::{InherentData, pool::InherentsPool};
 use substrate_telemetry::{telemetry, CONSENSUS_INFO};
 
 /// Build new blocks.
@@ -115,6 +114,8 @@ pub struct ProposerFactory<C, A> where A: txpool::ChainApi {
 	pub client: Arc<C>,
 	/// The transaction pool.
 	pub transaction_pool: Arc<TransactionPool<A>>,
+	/// The inherents pool
+	pub inherents_pool: Arc<InherentsPool<<A::Block as BlockT>::Extrinsic>>,
 }
 
 impl<C, A> consensus_common::Environment<<C as AuthoringApi>::Block> for ProposerFactory<C, A> where
@@ -144,6 +145,7 @@ impl<C, A> consensus_common::Environment<<C as AuthoringApi>::Block> for Propose
 			parent_id: id,
 			parent_number: *parent_header.number(),
 			transaction_pool: self.transaction_pool.clone(),
+			inherents_pool: self.inherents_pool.clone(),
 			now: Box::new(time::Instant::now),
 		};
 
@@ -158,6 +160,7 @@ pub struct Proposer<Block: BlockT, C, A: txpool::ChainApi> {
 	parent_id: BlockId<Block>,
 	parent_number: <<Block as BlockT>::Header as HeaderT>::Number,
 	transaction_pool: Arc<TransactionPool<A>>,
+	inherents_pool: Arc<InherentsPool<<Block as BlockT>::Extrinsic>>,
 	now: Box<Fn() -> time::Instant>,
 }
 
@@ -201,11 +204,23 @@ impl<Block, C, A> Proposer<Block, C, A>	where
 			&self.parent_id,
 			inherent_data,
 			|block_builder| {
+				// Add inherents from the internal pool
+
+				let inherents = self.inherents_pool.drain();
+				debug!("Pushing {} queued inherents.", inherents.len());
+				for i in inherents {
+					if let Err(e) = block_builder.push_extrinsic(i) {
+						warn!("Error while pushing inherent extrinsic from the pool: {:?}", e);
+					}
+				}
+
+				// proceed with transactions
 				let mut is_first = true;
 				let mut skipped = 0;
 				let mut unqueue_invalid = Vec::new();
 				let pending_iterator = self.transaction_pool.ready();
 
+				debug!("Attempting to push transactions from the pool.");
 				for pending in pending_iterator {
 					if (self.now)() > deadline {
 						debug!("Consensus deadline reached when pushing block transactions, proceeding with proposing.");
@@ -303,6 +318,7 @@ mod tests {
 		let proposer_factory = ProposerFactory {
 			client: client.clone(),
 			transaction_pool: txpool.clone(),
+			inherents_pool: Default::default(),
 		};
 
 		let mut proposer = proposer_factory.init(
@@ -325,4 +341,32 @@ mod tests {
 		assert_eq!(txpool.ready().count(), 2);
 	}
 
+	#[test]
+	fn should_include_inherents_from_the_pool() {
+		// given
+		let client = Arc::new(test_client::new());
+		let chain_api = transaction_pool::ChainApi::new(client.clone());
+		let txpool = Arc::new(TransactionPool::new(Default::default(), chain_api));
+		let inpool = Arc::new(InherentsPool::default());
+
+		let proposer_factory = ProposerFactory {
+			client: client.clone(),
+			transaction_pool: txpool.clone(),
+			inherents_pool: inpool.clone(),
+		};
+
+		inpool.add(extrinsic(0));
+
+		let proposer = proposer_factory.init(
+			&client.header(&BlockId::number(0)).unwrap().unwrap(),
+			&[]
+		).unwrap();
+
+		// when
+		let deadline = time::Duration::from_secs(3);
+		let block = proposer.propose(Default::default(), deadline).unwrap();
+
+		// then
+		assert_eq!(block.extrinsics().len(), 1);
+	}
 }

substrate/core/cli/src/lib.rs

@@ -419,11 +419,20 @@ where
 			service::Roles::FULL
 		};
 
+	let exec = cli.execution_strategies;
 	config.execution_strategies = ExecutionStrategies {
-		syncing: cli.syncing_execution.into(),
-		importing: cli.importing_execution.into(),
-		block_construction: cli.block_construction_execution.into(),
-		other: cli.other_execution.into(),
+		syncing: exec.syncing_execution.into(),
+		importing: exec.importing_execution.into(),
+		block_construction: exec.block_construction_execution.into(),
+		offchain_worker: exec.offchain_worker_execution.into(),
+		other: exec.other_execution.into(),
+	};
+
+	config.offchain_worker = match (cli.offchain_worker, role) {
+		(params::OffchainWorkerEnabled::WhenValidating, service::Roles::AUTHORITY) => true,
+		(params::OffchainWorkerEnabled::Always, _) => true,
+		(params::OffchainWorkerEnabled::Never, _) => false,
+		(params::OffchainWorkerEnabled::WhenValidating, _) => false,
 	};
 
 	config.roles = role;

substrate/core/cli/src/params.rs

@@ -53,6 +53,16 @@ impl Into<client::ExecutionStrategy> for ExecutionStrategy {
 	}
 }
 
+arg_enum! {
+	/// How to execute blocks
+	#[derive(Debug, Clone)]
+	pub enum OffchainWorkerEnabled {
+		Always,
+		Never,
+		WhenValidating,
+	}
+}
+
 /// Shared parameters used by all `CoreParams`.
 #[derive(Debug, StructOpt, Clone)]
 pub struct SharedParams {
@@ -205,6 +215,70 @@ pub struct TransactionPoolParams {
 	pub pool_kbytes: usize,
 }
 
+/// Execution strategies parameters.
+#[derive(Debug, StructOpt, Clone)]
+pub struct ExecutionStrategies {
+	/// The means of execution used when calling into the runtime while syncing blocks.
+	#[structopt(
+		long = "syncing-execution",
+		value_name = "STRATEGY",
+		raw(
+			possible_values = "&ExecutionStrategy::variants()",
+			case_insensitive = "true",
+			default_value = r#""NativeElseWasm""#
+		)
+	)]
+	pub syncing_execution: ExecutionStrategy,
+
+	/// The means of execution used when calling into the runtime while importing blocks.
+	#[structopt(
+		long = "importing-execution",
+		value_name = "STRATEGY",
+		raw(
+			possible_values = "&ExecutionStrategy::variants()",
+			case_insensitive = "true",
+			default_value = r#""NativeElseWasm""#
+		)
+	)]
+	pub importing_execution: ExecutionStrategy,
+
+	/// The means of execution used when calling into the runtime while constructing blocks.
+	#[structopt(
+		long = "block-construction-execution",
+		value_name = "STRATEGY",
+		raw(
+			possible_values = "&ExecutionStrategy::variants()",
+			case_insensitive = "true",
+			default_value = r#""Wasm""#
+		)
+	)]
+	pub block_construction_execution: ExecutionStrategy,
+
+	/// The means of execution used when calling into the runtime while constructing blocks.
+	#[structopt(
+		long = "offchain-worker-execution",
+		value_name = "STRATEGY",
+		raw(
+			possible_values = "&ExecutionStrategy::variants()",
+			case_insensitive = "true",
+			default_value = r#""NativeWhenPossible""#
+		)
+	)]
+	pub offchain_worker_execution: ExecutionStrategy,
+
+	/// The means of execution used when calling into the runtime while not syncing, importing or constructing blocks.
+	#[structopt(
+		long = "other-execution",
+		value_name = "STRATEGY",
+		raw(
+			possible_values = "&ExecutionStrategy::variants()",
+			case_insensitive = "true",
+			default_value = r#""Wasm""#
+		)
+	)]
+	pub other_execution: ExecutionStrategy,
+}
+
 /// The `run` command used to run a node.
 #[derive(Debug, StructOpt, Clone)]
 pub struct RunCmd {
@@ -266,53 +340,22 @@ pub struct RunCmd {
 	#[structopt(long = "telemetry-url", value_name = "URL VERBOSITY", parse(try_from_str = "parse_telemetry_endpoints"))]
 	pub telemetry_endpoints: Vec<(String, u8)>,
 
-	/// The means of execution used when calling into the runtime while syncing blocks.
+	/// Should execute offchain workers on every block. By default it's only enabled for nodes that are authoring new
+	/// blocks.
 	#[structopt(
-		long = "syncing-execution",
-		value_name = "STRATEGY",
+		long = "offchain-worker",
+		value_name = "ENABLED",
 		raw(
-			possible_values = "&ExecutionStrategy::variants()",
+			possible_values = "&OffchainWorkerEnabled::variants()",
 			case_insensitive = "true",
-			default_value = r#""NativeElseWasm""#
+			default_value = r#""WhenValidating""#
 		)
 	)]
-	pub syncing_execution: ExecutionStrategy,
+	pub offchain_worker: OffchainWorkerEnabled,
 
-	/// The means of execution used when calling into the runtime while importing blocks.
-	#[structopt(
-		long = "importing-execution",
-		value_name = "STRATEGY",
-		raw(
-			possible_values = "&ExecutionStrategy::variants()",
-			case_insensitive = "true",
-			default_value = r#""NativeElseWasm""#
-		)
-	)]
-	pub importing_execution: ExecutionStrategy,
-
-	/// The means of execution used when calling into the runtime while constructing blocks.
-	#[structopt(
-		long = "block-construction-execution",
-		value_name = "STRATEGY",
-		raw(
-			possible_values = "&ExecutionStrategy::variants()",
-			case_insensitive = "true",
-			default_value = r#""Wasm""#
-		)
-	)]
-	pub block_construction_execution: ExecutionStrategy,
-
-	/// The means of execution used when calling into the runtime while not syncing, importing or constructing blocks.
-	#[structopt(
-		long = "other-execution",
-		value_name = "STRATEGY",
-		raw(
-			possible_values = "&ExecutionStrategy::variants()",
-			case_insensitive = "true",
-			default_value = r#""Wasm""#
-		)
-	)]
-	pub other_execution: ExecutionStrategy,
+	#[allow(missing_docs)]
+	#[structopt(flatten)]
+	pub execution_strategies: ExecutionStrategies,
 
 	#[allow(missing_docs)]
 	#[structopt(flatten)]

substrate/core/client/src/block_builder/block_builder.rs

@@ -17,15 +17,15 @@
 use super::api::BlockBuilder as BlockBuilderApi;
 use std::vec::Vec;
 use parity_codec::Encode;
-use crate::blockchain::HeaderBackend;
+use runtime_primitives::ApplyOutcome;
+use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{
 	Header as HeaderT, Hash, Block as BlockT, One, HashFor, ProvideRuntimeApi, ApiRef
 };
-use primitives::H256;
-use runtime_primitives::generic::BlockId;
+use primitives::{H256, ExecutionContext};
+use crate::blockchain::HeaderBackend;
 use crate::runtime_api::Core;
 use crate::error;
-use runtime_primitives::{ApplyOutcome, ExecutionContext};
 
 
 /// Utility for building new (valid) blocks from a stream of extrinsics.

substrate/core/client/src/call_executor.rs

@@ -19,12 +19,12 @@ use parity_codec::{Encode, Decode};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::Block as BlockT;
 use state_machine::{
-	self, OverlayedChanges, Ext, CodeExecutor, ExecutionManager, ExecutionStrategy
+	self, OverlayedChanges, Ext, CodeExecutor, ExecutionManager, ExecutionStrategy, NeverOffchainExt,
 };
 use executor::{RuntimeVersion, RuntimeInfo, NativeVersion};
 use hash_db::Hasher;
 use trie::MemoryDB;
-use primitives::{H256, Blake2Hasher, NativeOrEncoded, NeverNativeValue};
+use primitives::{H256, Blake2Hasher, NativeOrEncoded, NeverNativeValue, OffchainExt};
 
 use crate::backend;
 use crate::error;
@@ -42,12 +42,15 @@ where
 	/// Execute a call to a contract on top of state in a block of given hash.
 	///
 	/// No changes are made.
-	fn call(
+	fn call<
+		O: OffchainExt,
+	>(
 		&self,
 		id: &BlockId<B>,
 		method: &str,
 		call_data: &[u8],
 		strategy: ExecutionStrategy,
+		side_effects_handler: Option<&mut O>,
 	) -> Result<Vec<u8>, error::Error>;
 
 	/// Execute a contextual call on top of state in a block of a given hash.
@@ -56,6 +59,7 @@ where
 	/// Before executing the method, passed header is installed as the current header
 	/// of the execution context.
 	fn contextual_call<
+		O: OffchainExt,
 		PB: Fn() -> error::Result<B::Header>,
 		EM: Fn(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -73,6 +77,7 @@ where
 		prepare_environment_block: PB,
 		execution_manager: ExecutionManager<EM>,
 		native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> error::Result<NativeOrEncoded<R>> where ExecutionManager<EM>: Clone;
 
 	/// Extract RuntimeVersion of given block
@@ -84,6 +89,7 @@ where
 	///
 	/// No changes are made.
 	fn call_at_state<
+		O: OffchainExt,
 		S: state_machine::Backend<H>,
 		F: FnOnce(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -98,6 +104,7 @@ where
 		call_data: &[u8],
 		manager: ExecutionManager<F>,
 		native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> Result<(NativeOrEncoded<R>, S::Transaction, Option<MemoryDB<H>>), error::Error>;
 
 	/// Execute a call to a contract on top of given state, gathering execution proof.
@@ -140,7 +147,10 @@ pub struct LocalCallExecutor<B, E> {
 impl<B, E> LocalCallExecutor<B, E> {
 	/// Creates new instance of local call executor.
 	pub fn new(backend: Arc<B>, executor: E) -> Self {
-		LocalCallExecutor { backend, executor }
+		LocalCallExecutor {
+			backend,
+			executor,
+		}
 	}
 }
 
@@ -161,17 +171,19 @@ where
 {
 	type Error = E::Error;
 
-	fn call(&self,
+	fn call<O: OffchainExt>(&self,
 		id: &BlockId<Block>,
 		method: &str,
 		call_data: &[u8],
-		strategy: ExecutionStrategy
+		strategy: ExecutionStrategy,
+		side_effects_handler: Option<&mut O>,
 	) -> error::Result<Vec<u8>> {
 		let mut changes = OverlayedChanges::default();
 		let state = self.backend.state_at(*id)?;
 		let return_data = state_machine::new(
 			&state,
 			self.backend.changes_trie_storage(),
+			side_effects_handler,
 			&mut changes,
 			&self.executor,
 			method,
@@ -187,6 +199,7 @@ where
 	}
 
 	fn contextual_call<
+		O: OffchainExt,
 		PB: Fn() -> error::Result<Block::Header>,
 		EM: Fn(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -204,6 +217,7 @@ where
 		prepare_environment_block: PB,
 		execution_manager: ExecutionManager<EM>,
 		native_call: Option<NC>,
+		mut side_effects_handler: Option<&mut O>,
 	) -> Result<NativeOrEncoded<R>, error::Error> where ExecutionManager<EM>: Clone {
 		let state = self.backend.state_at(*at)?;
 		if method != "Core_initialise_block" && initialised_block.map(|id| id != *at).unwrap_or(true) {
@@ -211,6 +225,7 @@ where
 			state_machine::new(
 				&state,
 				self.backend.changes_trie_storage(),
+				side_effects_handler.as_mut().map(|x| &mut **x),
 				changes,
 				&self.executor,
 				"Core_initialise_block",
@@ -226,6 +241,7 @@ where
 		let result = state_machine::new(
 			&state,
 			self.backend.changes_trie_storage(),
+			side_effects_handler,
 			changes,
 			&self.executor,
 			method,
@@ -248,12 +264,13 @@ where
 	fn runtime_version(&self, id: &BlockId<Block>) -> error::Result<RuntimeVersion> {
 		let mut overlay = OverlayedChanges::default();
 		let state = self.backend.state_at(*id)?;
-		let mut ext = Ext::new(&mut overlay, &state, self.backend.changes_trie_storage());
+		let mut ext = Ext::new(&mut overlay, &state, self.backend.changes_trie_storage(), NeverOffchainExt::new());
 		self.executor.runtime_version(&mut ext)
 			.ok_or(error::ErrorKind::VersionInvalid.into())
 	}
 
 	fn call_at_state<
+		O: OffchainExt,
 		S: state_machine::Backend<Blake2Hasher>,
 		F: FnOnce(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -268,10 +285,12 @@ where
 		call_data: &[u8],
 		manager: ExecutionManager<F>,
 		native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> error::Result<(NativeOrEncoded<R>, S::Transaction, Option<MemoryDB<Blake2Hasher>>)> {
 		state_machine::new(
 			state,
 			self.backend.changes_trie_storage(),
+			side_effects_handler,
 			changes,
 			&self.executor,
 			method,

substrate/core/client/src/client.rs

@@ -33,9 +33,9 @@ use runtime_primitives::traits::{
 	Block as BlockT, Header as HeaderT, Zero, As, NumberFor, CurrentHeight, BlockNumberToHash,
 	ApiRef, ProvideRuntimeApi, Digest, DigestItem, AuthorityIdFor
 };
-use runtime_primitives::{BuildStorage, ExecutionContext};
+use runtime_primitives::BuildStorage;
 use crate::runtime_api::{CallRuntimeAt, ConstructRuntimeApi};
-use primitives::{Blake2Hasher, H256, ChangesTrieConfiguration, convert_hash, NeverNativeValue};
+use primitives::{Blake2Hasher, H256, ChangesTrieConfiguration, convert_hash, NeverNativeValue, ExecutionContext};
 use primitives::storage::{StorageKey, StorageData};
 use primitives::storage::well_known_keys;
 use parity_codec::{Encode, Decode};
@@ -43,7 +43,7 @@ use state_machine::{
 	DBValue, Backend as StateBackend, CodeExecutor, ChangesTrieAnchorBlockId,
 	ExecutionStrategy, ExecutionManager, prove_read,
 	ChangesTrieRootsStorage, ChangesTrieStorage,
-	key_changes, key_changes_proof, OverlayedChanges,
+	key_changes, key_changes_proof, OverlayedChanges, NeverOffchainExt,
 };
 use hash_db::Hasher;
 
@@ -84,6 +84,8 @@ pub struct ExecutionStrategies {
 	pub importing: ExecutionStrategy,
 	/// Execution strategy used when constructing blocks.
 	pub block_construction: ExecutionStrategy,
+	/// Execution strategy used for offchain workers.
+	pub offchain_worker: ExecutionStrategy,
 	/// Execution strategy used in other cases.
 	pub other: ExecutionStrategy,
 }
@@ -94,6 +96,7 @@ impl Default for ExecutionStrategies {
 			syncing: ExecutionStrategy::NativeElseWasm,
 			importing: ExecutionStrategy::NativeElseWasm,
 			block_construction: ExecutionStrategy::AlwaysWasm,
+			offchain_worker: ExecutionStrategy::NativeWhenPossible,
 			other: ExecutionStrategy::NativeElseWasm,
 		}
 	}
@@ -343,7 +346,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 	pub fn authorities_at(&self, id: &BlockId<Block>) -> error::Result<Vec<AuthorityIdFor<Block>>> {
 		match self.backend.blockchain().cache().and_then(|cache| cache.authorities_at(*id)) {
 			Some(cached_value) => Ok(cached_value),
-			None => self.executor.call(id, "Core_authorities", &[], ExecutionStrategy::NativeElseWasm)
+			None => self.executor.call(id, "Core_authorities", &[], ExecutionStrategy::NativeElseWasm, NeverOffchainExt::new())
 				.and_then(|r| Vec::<AuthorityIdFor<Block>>::decode(&mut &r[..])
 					.ok_or_else(|| error::ErrorKind::InvalidAuthoritiesSet.into()))
 		}
@@ -871,7 +874,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 						}),
 					}
 				};
-				let (_, storage_update, changes_update) = self.executor.call_at_state::<_, _, NeverNativeValue, fn() -> _>(
+				let (_, storage_update, changes_update) = self.executor.call_at_state::<_, _, _, NeverNativeValue, fn() -> _>(
 					transaction_state,
 					&mut overlay,
 					"Core_execute_block",
@@ -881,6 +884,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 						_ => get_execution_manager(self.execution_strategies().importing),
 					},
 					None,
+					NeverOffchainExt::new(),
 				)?;
 
 				overlay.commit_prospective();
@@ -1339,7 +1343,8 @@ impl<B, E, Block, RA> CallRuntimeAt<Block> for Client<B, E, Block, RA> where
 	Block: BlockT<Hash=H256>
 {
 	fn call_api_at<
-		R: Encode + Decode + PartialEq, NC: FnOnce() -> result::Result<R, &'static str> + UnwindSafe
+		R: Encode + Decode + PartialEq,
+		NC: FnOnce() -> result::Result<R, &'static str> + UnwindSafe,
 	>(
 		&self,
 		at: &BlockId<Block>,
@@ -1348,15 +1353,22 @@ impl<B, E, Block, RA> CallRuntimeAt<Block> for Client<B, E, Block, RA> where
 		changes: &mut OverlayedChanges,
 		initialised_block: &mut Option<BlockId<Block>>,
 		native_call: Option<NC>,
-		context: ExecutionContext
+		context: ExecutionContext,
 	) -> error::Result<NativeOrEncoded<R>> {
 		let manager = match context {
 			ExecutionContext::BlockConstruction => self.execution_strategies.block_construction.get_manager(),
 			ExecutionContext::Syncing => self.execution_strategies.syncing.get_manager(),
 			ExecutionContext::Importing => self.execution_strategies.importing.get_manager(),
+			ExecutionContext::OffchainWorker(_) => self.execution_strategies.offchain_worker.get_manager(),
 			ExecutionContext::Other => self.execution_strategies.other.get_manager(),
 		};
-		self.executor.contextual_call::<_, fn(_,_) -> _,_,_>(
+
+		let mut offchain_extensions = match context {
+			ExecutionContext::OffchainWorker(ext) => Some(ext),
+			_ => None,
+		};
+
+		self.executor.contextual_call::<_, _, fn(_,_) -> _,_,_>(
 			at,
 			function,
 			&args,
@@ -1365,6 +1377,7 @@ impl<B, E, Block, RA> CallRuntimeAt<Block> for Client<B, E, Block, RA> where
 			|| self.prepare_environment_block(at),
 			manager,
 			native_call,
+			offchain_extensions.as_mut(),
 		)
 	}
 

substrate/core/client/src/genesis.rs

@@ -90,6 +90,7 @@ mod tests {
 		state_machine::new(
 			backend,
 			Some(&InMemoryChangesTrieStorage::new()),
+			state_machine::NeverOffchainExt::new(),
 			&mut overlay,
 			&executor(),
 			"Core_initialise_block",
@@ -102,6 +103,7 @@ mod tests {
 			state_machine::new(
 				backend,
 				Some(&InMemoryChangesTrieStorage::new()),
+				state_machine::NeverOffchainExt::new(),
 				&mut overlay,
 				&executor(),
 				"BlockBuilder_apply_extrinsic",
@@ -114,6 +116,7 @@ mod tests {
 		let (ret_data, _, _) = state_machine::new(
 			backend,
 			Some(&InMemoryChangesTrieStorage::new()),
+			state_machine::NeverOffchainExt::new(),
 			&mut overlay,
 			&executor(),
 			"BlockBuilder_finalise_block",
@@ -160,6 +163,7 @@ mod tests {
 		let _ = state_machine::new(
 			&backend,
 			Some(&InMemoryChangesTrieStorage::new()),
+			state_machine::NeverOffchainExt::new(),
 			&mut overlay,
 			&executor(),
 			"Core_execute_block",
@@ -188,6 +192,7 @@ mod tests {
 		let _ = state_machine::new(
 			&backend,
 			Some(&InMemoryChangesTrieStorage::new()),
+			state_machine::NeverOffchainExt::new(),
 			&mut overlay,
 			&executor(),
 			"Core_execute_block",
@@ -216,6 +221,7 @@ mod tests {
 		let r = state_machine::new(
 			&backend,
 			Some(&InMemoryChangesTrieStorage::new()),
+			state_machine::NeverOffchainExt::new(),
 			&mut overlay,
 			&Executor::new(None),
 			"Core_execute_block",

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

@@ -21,11 +21,11 @@ use std::{collections::HashSet, sync::Arc, panic::UnwindSafe, result, marker::Ph
 use futures::{IntoFuture, Future};
 
 use parity_codec::{Encode, Decode};
-use primitives::{H256, Blake2Hasher, convert_hash, NativeOrEncoded};
+use primitives::{H256, Blake2Hasher, convert_hash, NativeOrEncoded, OffchainExt};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{As, Block as BlockT, Header as HeaderT};
 use state_machine::{self, Backend as StateBackend, CodeExecutor, OverlayedChanges, ExecutionStrategy,
-	create_proof_check_backend, execution_proof_check_on_trie_backend, ExecutionManager};
+	create_proof_check_backend, execution_proof_check_on_trie_backend, ExecutionManager, NeverOffchainExt};
 use hash_db::Hasher;
 
 use crate::backend::RemoteBackend;
@@ -80,7 +80,16 @@ where
 {
 	type Error = ClientError;
 
-	fn call(&self, id: &BlockId<Block>, method: &str, call_data: &[u8], _strategy: ExecutionStrategy)
+	fn call<
+		O: OffchainExt,
+	>(
+		&self,
+		id: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		_strategy: ExecutionStrategy,
+		_side_effects_handler: Option<&mut O>,
+	)
 		-> ClientResult<Vec<u8>> {
 		let block_hash = self.blockchain.expect_block_hash_from_id(id)?;
 		let block_header = self.blockchain.expect_header(id.clone())?;
@@ -95,6 +104,7 @@ where
 	}
 
 	fn contextual_call<
+		O: OffchainExt,
 		PB: Fn() -> ClientResult<Block::Header>,
 		EM: Fn(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -112,22 +122,24 @@ where
 		_prepare_environment_block: PB,
 		execution_manager: ExecutionManager<EM>,
 		_native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> ClientResult<NativeOrEncoded<R>> where ExecutionManager<EM>: Clone {
 		// it is only possible to execute contextual call if changes are empty
 		if !changes.is_empty() || initialised_block.is_some() {
 			return Err(ClientErrorKind::NotAvailableOnLightClient.into());
 		}
 
-		self.call(at, method, call_data, (&execution_manager).into()).map(NativeOrEncoded::Encoded)
+		self.call(at, method, call_data, (&execution_manager).into(), side_effects_handler).map(NativeOrEncoded::Encoded)
 	}
 
 	fn runtime_version(&self, id: &BlockId<Block>) -> ClientResult<RuntimeVersion> {
-		let call_result = self.call(id, "version", &[], ExecutionStrategy::NativeElseWasm)?;
+		let call_result = self.call(id, "version", &[], ExecutionStrategy::NativeElseWasm, NeverOffchainExt::new())?;
 		RuntimeVersion::decode(&mut call_result.as_slice())
 			.ok_or_else(|| ClientErrorKind::VersionInvalid.into())
 	}
 
 	fn call_at_state<
+		O: OffchainExt,
 		S: StateBackend<Blake2Hasher>,
 		FF: FnOnce(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -142,6 +154,7 @@ where
 		_call_data: &[u8],
 		_m: ExecutionManager<FF>,
 		_native_call: Option<NC>,
+		_side_effects_handler: Option<&mut O>,
 	) -> ClientResult<(NativeOrEncoded<R>, S::Transaction, Option<MemoryDB<Blake2Hasher>>)> {
 		Err(ClientErrorKind::NotAvailableOnLightClient.into())
 	}
@@ -201,15 +214,24 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 {
 	type Error = ClientError;
 
-	fn call(&self, id: &BlockId<Block>, method: &str, call_data: &[u8], strategy: ExecutionStrategy)
-		-> ClientResult<Vec<u8>> {
+	fn call<
+		O: OffchainExt,
+	>(
+		&self,
+		id: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		strategy: ExecutionStrategy,
+		side_effects_handler: Option<&mut O>,
+	) -> ClientResult<Vec<u8>> {
 		match self.backend.is_local_state_available(id) {
-			true => self.local.call(id, method, call_data, strategy),
-			false => self.remote.call(id, method, call_data, strategy),
+			true => self.local.call(id, method, call_data, strategy, side_effects_handler),
+			false => self.remote.call(id, method, call_data, strategy, side_effects_handler),
 		}
 	}
 
 	fn contextual_call<
+		O: OffchainExt,
 		PB: Fn() -> ClientResult<Block::Header>,
 		EM: Fn(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -227,12 +249,14 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 		prepare_environment_block: PB,
 		_manager: ExecutionManager<EM>,
 		native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> ClientResult<NativeOrEncoded<R>> where ExecutionManager<EM>: Clone {
 		// there's no actual way/need to specify native/wasm execution strategy on light node
 		// => we can safely ignore passed values
 
 		match self.backend.is_local_state_available(at) {
 			true => CallExecutor::contextual_call::<
+				_,
 				_,
 				fn(
 					Result<NativeOrEncoded<R>, Local::Error>,
@@ -250,8 +274,10 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 				prepare_environment_block,
 				ExecutionManager::NativeWhenPossible,
 				native_call,
+				side_effects_handler,
 			).map_err(|e| ClientErrorKind::Execution(Box::new(e.to_string())).into()),
 			false => CallExecutor::contextual_call::<
+				_,
 				_,
 				fn(
 					Result<NativeOrEncoded<R>, Remote::Error>,
@@ -269,6 +295,7 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 				prepare_environment_block,
 				ExecutionManager::NativeWhenPossible,
 				native_call,
+				side_effects_handler,
 			).map_err(|e| ClientErrorKind::Execution(Box::new(e.to_string())).into()),
 		}
 	}
@@ -281,6 +308,7 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 	}
 
 	fn call_at_state<
+		O: OffchainExt,
 		S: StateBackend<Blake2Hasher>,
 		FF: FnOnce(
 			Result<NativeOrEncoded<R>, Self::Error>,
@@ -295,11 +323,13 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 		call_data: &[u8],
 		_manager: ExecutionManager<FF>,
 		native_call: Option<NC>,
+		side_effects_handler: Option<&mut O>,
 	) -> ClientResult<(NativeOrEncoded<R>, S::Transaction, Option<MemoryDB<Blake2Hasher>>)> {
 		// there's no actual way/need to specify native/wasm execution strategy on light node
 		// => we can safely ignore passed values
 
 		CallExecutor::call_at_state::<
+				_,
 				_,
 				fn(
 					Result<NativeOrEncoded<R>, Remote::Error>,
@@ -315,6 +345,7 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 				call_data,
 				ExecutionManager::NativeWhenPossible,
 				native_call,
+				side_effects_handler,
 			).map_err(|e| ClientErrorKind::Execution(Box::new(e.to_string())).into())
 	}
 
@@ -509,7 +540,7 @@ mod tests {
 		let local_executor = RemoteCallExecutor::new(Arc::new(backend.blockchain().clone()), Arc::new(OkCallFetcher::new(vec![1])));
 		let remote_executor = RemoteCallExecutor::new(Arc::new(backend.blockchain().clone()), Arc::new(OkCallFetcher::new(vec![2])));
 		let remote_or_local = RemoteOrLocalCallExecutor::new(backend, remote_executor, local_executor);
-		assert_eq!(remote_or_local.call(&BlockId::Number(0), "test_method", &[], ExecutionStrategy::NativeElseWasm).unwrap(), vec![1]);
-		assert_eq!(remote_or_local.call(&BlockId::Number(1), "test_method", &[], ExecutionStrategy::NativeElseWasm).unwrap(), vec![2]);
+		assert_eq!(remote_or_local.call(&BlockId::Number(0), "test_method", &[], ExecutionStrategy::NativeElseWasm, NeverOffchainExt::new()).unwrap(), vec![1]);
+		assert_eq!(remote_or_local.call(&BlockId::Number(1), "test_method", &[], ExecutionStrategy::NativeElseWasm, NeverOffchainExt::new()).unwrap(), vec![2]);
 	}
 }

substrate/core/client/src/runtime_api.rs

@@ -24,10 +24,12 @@ pub use state_machine::OverlayedChanges;
 pub use primitives::NativeOrEncoded;
 #[doc(hidden)]
 pub use runtime_primitives::{
-	traits::{AuthorityIdFor, Block as BlockT, GetNodeBlockType, GetRuntimeBlockType, ApiRef, RuntimeApiInfo},
-	generic::BlockId, transaction_validity::TransactionValidity, ExecutionContext,
+	traits::{AuthorityIdFor, Block as BlockT, GetNodeBlockType, GetRuntimeBlockType, Header as HeaderT, ApiRef, RuntimeApiInfo},
+	generic::BlockId, transaction_validity::TransactionValidity,
 };
 #[doc(hidden)]
+pub use primitives::{ExecutionContext, OffchainExt};
+#[doc(hidden)]
 pub use runtime_version::{ApiId, RuntimeVersion, ApisVec, create_apis_vec};
 #[doc(hidden)]
 pub use rstd::{slice, mem};
@@ -91,7 +93,10 @@ pub trait ApiExt<Block: BlockT> {
 pub trait CallRuntimeAt<Block: BlockT> {
 	/// Calls the given api function with the given encoded arguments at the given block
 	/// and returns the encoded result.
-	fn call_api_at<R: Encode + Decode + PartialEq, NC: FnOnce() -> result::Result<R, &'static str> + UnwindSafe>(
+	fn call_api_at<
+		R: Encode + Decode + PartialEq,
+		NC: FnOnce() -> result::Result<R, &'static str> + UnwindSafe,
+	>(
 		&self,
 		at: &BlockId<Block>,
 		function: &'static str,
@@ -99,7 +104,7 @@ pub trait CallRuntimeAt<Block: BlockT> {
 		changes: &mut OverlayedChanges,
 		initialised_block: &mut Option<BlockId<Block>>,
 		native_call: Option<NC>,
-		context: ExecutionContext
+		context: ExecutionContext,
 	) -> error::Result<NativeOrEncoded<R>>;
 
 	/// Returns the runtime version at the given block.
@@ -132,3 +137,4 @@ decl_runtime_apis! {
 		fn validate_transaction(tx: <Block as BlockT>::Extrinsic) -> TransactionValidity;
 	}
 }
+

substrate/core/executor/src/wasm_executor.rs

@@ -520,6 +520,15 @@ impl_function_executor!(this: FunctionExecutor<'e, E>,
 
 		Ok(0)
 	},
+	ext_submit_extrinsic(msg_data: *const u8, len: u32) => {
+		let extrinsic = this.memory.get(msg_data, len as usize)
+			.map_err(|_| UserError("OOB while ext_submit_extrinsic: wasm"))?;
+
+		this.ext.submit_extrinsic(extrinsic)
+			.map_err(|_| UserError("Calling unavailable API ext_submit_extrinsic: wasm"))?;
+
+		Ok(())
+	},
 	ext_sandbox_instantiate(
 		dispatch_thunk_idx: usize,
 		wasm_ptr: *const u8,

substrate/core/finality-grandpa/src/tests.rs

@@ -35,8 +35,7 @@ use std::collections::{HashMap, HashSet};
 use std::result;
 use runtime_primitives::traits::{ApiRef, ProvideRuntimeApi};
 use runtime_primitives::generic::BlockId;
-use runtime_primitives::ExecutionContext;
-use substrate_primitives::NativeOrEncoded;
+use substrate_primitives::{NativeOrEncoded, ExecutionContext};
 
 use authorities::AuthoritySet;
 use consensus_changes::ConsensusChanges;

substrate/core/inherents/src/lib.rs

@@ -31,6 +31,7 @@
 //! information on how that is done.
 
 #![cfg_attr(not(feature = "std"), no_std)]
+#![warn(missing_docs)]
 
 use parity_codec as codec;
 use codec::{Encode, Decode};
@@ -43,6 +44,9 @@ use parking_lot::RwLock;
 #[cfg(feature = "std")]
 use std::{sync::Arc, format};
 
+#[cfg(feature = "std")]
+pub mod pool;
+
 pub use runtime_primitives::RuntimeString;
 
 /// An identifier for an inherent.

substrate/core/inherents/src/pool.rs

@@ -0,0 +1,75 @@
+// Copyright 2019 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/>.
+
+//! Inherents Pool
+
+use std::{fmt, mem, vec};
+use parking_lot::Mutex;
+
+/// Inherents Pool
+///
+/// The pool is responsible to collect inherents asynchronously generated
+/// by some other parts of the code and make them ready for the next block production.
+pub struct InherentsPool<T> {
+	data: Mutex<Vec<T>>,
+}
+
+impl<T> Default for InherentsPool<T> {
+	fn default() -> Self {
+		InherentsPool {
+			data: Default::default(),
+		}
+	}
+}
+
+impl<T: fmt::Debug> fmt::Debug for InherentsPool<T> {
+	fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+		let mut builder = fmt.debug_struct("InherentsPool");
+		if let Some(data) = self.data.try_lock() {
+			builder.field("data", &*data);
+		}
+		builder.finish()
+	}
+}
+
+impl<T> InherentsPool<T> {
+	/// Add inherent extrinsic to the pool.
+	///
+	/// This inherent will be appended to the next produced block.
+	pub fn add(&self, extrinsic: T) {
+		self.data.lock().push(extrinsic);
+	}
+
+	/// Drain all currently queued inherents.
+	pub fn drain(&self) -> Vec<T> {
+		mem::replace(&mut *self.data.lock(), vec![])
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn should_drain_inherents_to_given_data() {
+		let pool = InherentsPool::default();
+		pool.add(5);
+		pool.add(7);
+
+		assert_eq!(pool.drain(), vec![5, 7]);
+		assert_eq!(pool.drain(), vec![]);
+	}
+}

substrate/core/offchain/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+description = "Substrate offchain workers"
+name = "substrate-offchain"
+version = "0.1.0"
+license = "GPL-3.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+client = { package = "substrate-client", path = "../../core/client" }
+consensus = { package = "substrate-consensus-common", path = "../../core/consensus/common" }
+futures = "0.1.25"
+inherents = { package = "substrate-inherents", path = "../../core/inherents" }
+log = "0.4"
+offchain-primitives = { package = "substrate-offchain-primitives", path = "./primitives" }
+parity-codec = { version = "3.1", features = ["derive"] }
+primitives = { package = "substrate-primitives", path = "../../core/primitives" }
+runtime_primitives = { package = "sr-primitives", path = "../../core/sr-primitives" }
+tokio = "0.1.7"
+transaction_pool = { package = "substrate-transaction-pool", path = "../../core/transaction-pool" }
+
+[dev-dependencies]
+env_logger = "0.6"
+test_client = { package = "substrate-test-client", path = "../../core/test-client" }
+
+[features]
+default = []

substrate/core/offchain/primitives/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+description = "Substrate offchain workers primitives"
+name = "substrate-offchain-primitives"
+version = "0.1.0"
+license = "GPL-3.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+client = { package = "substrate-client", path = "../../client", default-features = false }
+runtime_primitives = { package = "sr-primitives", path = "../../sr-primitives", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"client/std",
+	"runtime_primitives/std"
+]

substrate/core/offchain/primitives/src/lib.rs

@@ -0,0 +1,31 @@
+// Copyright 2018 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/>.
+
+//! The Offchain Worker runtime api primitives.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![warn(missing_docs)]
+
+use client::decl_runtime_apis;
+use runtime_primitives::traits::NumberFor;
+
+decl_runtime_apis! {
+	/// The offchain worker api.
+	pub trait OffchainWorkerApi {
+		/// Starts the off-chain task for given block number.
+		fn offchain_worker(number: NumberFor<Block>);
+	}
+}

substrate/core/offchain/src/api.rs

@@ -0,0 +1,99 @@
+// Copyright 2019 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/>.
+
+use std::sync::Arc;
+use futures::{Stream, Future, sync::mpsc};
+use inherents::pool::InherentsPool;
+use log::{info, debug, warn};
+use parity_codec::Decode;
+use primitives::OffchainExt;
+use runtime_primitives::{
+	generic::BlockId,
+	traits::{self, Extrinsic},
+};
+use transaction_pool::txpool::{Pool, ChainApi};
+
+/// A message between the offchain extension and the processing thread.
+enum ExtMessage {
+	SubmitExtrinsic(Vec<u8>),
+}
+
+/// Asynchronous offchain API.
+///
+/// NOTE this is done to prevent recursive calls into the runtime (which are not supported currently).
+pub(crate) struct AsyncApi(mpsc::UnboundedSender<ExtMessage>);
+
+impl OffchainExt for AsyncApi {
+	fn submit_extrinsic(&mut self, ext: Vec<u8>) {
+		let _ = self.0.unbounded_send(ExtMessage::SubmitExtrinsic(ext));
+	}
+}
+
+/// Offchain extensions implementation API
+pub(crate) struct Api<A: ChainApi> {
+	receiver: Option<mpsc::UnboundedReceiver<ExtMessage>>,
+	transaction_pool: Arc<Pool<A>>,
+	inherents_pool: Arc<InherentsPool<<A::Block as traits::Block>::Extrinsic>>,
+	at: BlockId<A::Block>,
+}
+
+impl<A: ChainApi> Api<A> {
+	pub fn new(
+		transaction_pool: Arc<Pool<A>>,
+		inherents_pool: Arc<InherentsPool<<A::Block as traits::Block>::Extrinsic>>,
+		at: BlockId<A::Block>,
+	) -> (AsyncApi, Self) {
+		let (tx, rx) = mpsc::unbounded();
+		let api = Self {
+			receiver: Some(rx),
+			transaction_pool,
+			inherents_pool,
+			at,
+		};
+		(AsyncApi(tx), api)
+	}
+
+	/// Run a processing task for the API
+	pub fn process(mut self) -> impl Future<Item=(), Error=()> {
+		let receiver = self.receiver.take().expect("Take invoked only once.");
+
+		receiver.for_each(move |msg| {
+			match msg {
+				ExtMessage::SubmitExtrinsic(ext) => self.submit_extrinsic(ext),
+			}
+			Ok(())
+		})
+	}
+
+	fn submit_extrinsic(&mut self, ext: Vec<u8>) {
+		let xt = match <A::Block as traits::Block>::Extrinsic::decode(&mut &*ext) {
+			Some(xt) => xt,
+			None => {
+				warn!("Unable to decode extrinsic: {:?}", ext);
+				return
+			},
+		};
+
+		info!("Submitting to the pool: {:?} (isSigned: {:?})", xt, xt.is_signed());
+		match self.transaction_pool.submit_one(&self.at, xt.clone()) {
+			Ok(hash) => debug!("[{:?}] Offchain transaction added to the pool.", hash),
+			Err(_) => {
+				debug!("Offchain inherent added to the pool.");
+				self.inherents_pool.add(xt);
+			},
+		}
+	}
+}

substrate/core/offchain/src/lib.rs

@@ -0,0 +1,132 @@
+// Copyright 2019 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/>.
+
+//! Substrate offchain workers.
+//!
+//! The offchain workers is a special function of the runtime that
+//! gets executed after block is imported. During execution
+//! it's able to asynchronously submit extrinsics that will either
+//! be propagated to other nodes (transactions) or will be
+//! added to the next block produced by the node as inherents.
+//!
+//! Offchain workers can be used for computation-heavy tasks
+//! that are not feasible for execution during regular block processing.
+//! It can either be tasks that no consensus is required for,
+//! or some form of consensus over the data can be built on-chain
+//! for instance via:
+//! 1. Challenge period for incorrect computations
+//! 2. Majority voting for results
+//! 3. etc
+
+#![warn(missing_docs)]
+
+use std::{
+	marker::PhantomData,
+	sync::Arc,
+};
+
+use client::runtime_api::ApiExt;
+use inherents::pool::InherentsPool;
+use log::{debug, warn};
+use primitives::ExecutionContext;
+use runtime_primitives::{
+	generic::BlockId,
+	traits::{self, ProvideRuntimeApi},
+};
+use tokio::runtime::TaskExecutor;
+use transaction_pool::txpool::{Pool, ChainApi};
+
+mod api;
+
+pub use offchain_primitives::OffchainWorkerApi;
+
+/// An offchain workers manager.
+#[derive(Debug)]
+pub struct OffchainWorkers<C, Block: traits::Block> {
+	client: Arc<C>,
+	inherents_pool: Arc<InherentsPool<<Block as traits::Block>::Extrinsic>>,
+	executor: TaskExecutor,
+	_block: PhantomData<Block>,
+}
+
+impl<C, Block: traits::Block> OffchainWorkers<C, Block> {
+	/// Creates new `OffchainWorkers`.
+	pub fn new(
+		client: Arc<C>,
+		inherents_pool: Arc<InherentsPool<<Block as traits::Block>::Extrinsic>>,
+		executor: TaskExecutor,
+	) -> Self {
+		Self {
+			client,
+			inherents_pool,
+			executor,
+			_block: PhantomData,
+		}
+	}
+}
+
+impl<C, Block> OffchainWorkers<C, Block> where
+	Block: traits::Block,
+	C: ProvideRuntimeApi,
+	C::Api: OffchainWorkerApi<Block>,
+{
+	/// Start the offchain workers after given block.
+	pub fn on_block_imported<A>(
+		&self,
+		number: &<Block::Header as traits::Header>::Number,
+		pool: &Arc<Pool<A>>,
+	) where
+		A: ChainApi<Block=Block> + 'static,
+	{
+		let runtime = self.client.runtime_api();
+		let at = BlockId::number(*number);
+		let has_api = runtime.has_api::<OffchainWorkerApi<Block>>(&at);
+		debug!("Checking offchain workers at {:?}: {:?}", at, has_api);
+
+		if has_api.unwrap_or(false) {
+			let (api, runner) = api::Api::new(pool.clone(), self.inherents_pool.clone(), at.clone());
+			self.executor.spawn(runner.process());
+
+			debug!("Running offchain workers at {:?}", at);
+			let api = Box::new(api);
+			runtime.offchain_worker_with_context(&at, ExecutionContext::OffchainWorker(api), *number).unwrap();
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use futures::Future;
+
+	#[test]
+	fn should_call_into_runtime_and_produce_extrinsic() {
+		// given
+		let _ = env_logger::try_init();
+		let runtime = tokio::runtime::Runtime::new().unwrap();
+		let client = Arc::new(test_client::new());
+		let pool = Arc::new(Pool::new(Default::default(), ::transaction_pool::ChainApi::new(client.clone())));
+		let inherents = Arc::new(InherentsPool::default());
+
+		// when
+		let offchain = OffchainWorkers::new(client, inherents.clone(), runtime.executor());
+		offchain.on_block_imported(&0u64, &pool);
+
+		// then
+		runtime.shutdown_on_idle().wait().unwrap();
+		assert_eq!(inherents.drain().len(), 1);
+	}
+}

substrate/core/primitives/src/lib.rs

@@ -76,6 +76,35 @@ pub use hash_db::Hasher;
 // pub use self::hasher::blake::BlakeHasher;
 pub use self::hasher::blake2::Blake2Hasher;
 
+/// Context for executing a call into the runtime.
+#[repr(u8)]
+pub enum ExecutionContext {
+	/// Context for general importing (including own blocks).
+	Importing,
+	/// Context used when syncing the blockchain.
+	Syncing,
+	/// Context used for block construction.
+	BlockConstruction,
+	/// Offchain worker context.
+	OffchainWorker(Box<OffchainExt>),
+	/// Context used for other calls.
+	Other,
+}
+
+/// An extended externalities for offchain workers.
+pub trait OffchainExt {
+	/// Submits an extrinsics.
+	///
+	/// The extrinsic will either go to the pool (signed)
+	/// or to the next produced block (inherent).
+	fn submit_extrinsic(&mut self, extrinsic: Vec<u8>);
+}
+impl<T: OffchainExt + ?Sized> OffchainExt for Box<T> {
+	fn submit_extrinsic(&mut self, ex: Vec<u8>) {
+		(&mut **self).submit_extrinsic(ex)
+	}
+}
+
 /// Hex-serialised shim for `Vec<u8>`.
 #[derive(PartialEq, Eq, Clone)]
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug, Hash, PartialOrd, Ord))]

substrate/core/rpc/src/state/mod.rs

@@ -35,7 +35,7 @@ use crate::rpc::futures::{stream, Future, Sink, Stream};
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Block as BlockT, Header, ProvideRuntimeApi, As, NumberFor};
 use runtime_version::RuntimeVersion;
-use state_machine::ExecutionStrategy;
+use state_machine::{self, ExecutionStrategy};
 
 use crate::subscriptions::Subscriptions;
 
@@ -298,7 +298,7 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 			.executor()
 			.call(
 				&BlockId::Hash(block),
-				&method, &data.0, ExecutionStrategy::NativeElseWasm
+				&method, &data.0, ExecutionStrategy::NativeElseWasm, state_machine::NeverOffchainExt::new(),
 			)?;
 		Ok(Bytes(return_data))
 	}

substrate/core/rpc/src/state/tests.rs

@@ -221,7 +221,7 @@ fn should_return_runtime_version() {
 
 	assert_eq!(
 		::serde_json::to_string(&api.runtime_version(None.into()).unwrap()).unwrap(),
-		r#"{"specName":"test","implName":"parity-test","authoringVersion":1,"specVersion":1,"implVersion":1,"apis":[["0xdf6acb689907609b",1],["0x37e397fc7c91f5e4",1],["0xd2bc9897eed08f15",1],["0x40fe3ad401f8959a",2],["0xc6e9a76309f39b09",1],["0xdd718d5cc53262d4",1]]}"#
+		r#"{"specName":"test","implName":"parity-test","authoringVersion":1,"specVersion":1,"implVersion":1,"apis":[["0xdf6acb689907609b",1],["0x37e397fc7c91f5e4",1],["0xd2bc9897eed08f15",1],["0x40fe3ad401f8959a",2],["0xc6e9a76309f39b09",1],["0xdd718d5cc53262d4",1],["0xf78b278be53f454c",1]]}"#
 	);
 }
 

substrate/core/service/Cargo.toml

@@ -17,6 +17,7 @@ serde = "1.0"
 serde_json = "1.0"
 serde_derive = "1.0"
 target_info = "0.1"
+inherents = { package = "substrate-inherents", path = "../../core/inherents" }
 keystore = { package = "substrate-keystore", path = "../../core/keystore" }
 sr-io = { path = "../../core/sr-io" }
 runtime_primitives = { package = "sr-primitives", path = "../../core/sr-primitives" }
@@ -30,6 +31,7 @@ substrate-executor = { path = "../../core/executor" }
 transaction_pool = { package = "substrate-transaction-pool", path = "../../core/transaction-pool" }
 rpc = { package = "substrate-rpc-servers", path = "../../core/rpc-servers" }
 tel = { package = "substrate-telemetry", path = "../../core/telemetry" }
+offchain = { package = "substrate-offchain", path = "../../core/offchain" }
 
 [dev-dependencies]
 substrate-test-client = { path = "../test-client" }

substrate/core/service/src/chain_spec.rs

@@ -116,35 +116,43 @@ impl<G: RuntimeGenesis> Clone for ChainSpec<G> {
 }
 
 impl<G: RuntimeGenesis> ChainSpec<G> {
+	/// A list of bootnode addresses.
 	pub fn boot_nodes(&self) -> &[String] {
 		&self.spec.boot_nodes
 	}
 
+	/// Spec name.
 	pub fn name(&self) -> &str {
 		&self.spec.name
 	}
 
+	/// Spec id.
 	pub fn id(&self) -> &str {
 		&self.spec.id
 	}
 
+	/// Telemetry endpoints (if any)
 	pub fn telemetry_endpoints(&self) -> &Option<TelemetryEndpoints> {
 		&self.spec.telemetry_endpoints
 	}
 
+	/// Network protocol id.
 	pub fn protocol_id(&self) -> Option<&str> {
 		self.spec.protocol_id.as_ref().map(String::as_str)
 	}
 
+	/// Name of the consensus engine.
 	pub fn consensus_engine(&self) -> Option<&str> {
 		self.spec.consensus_engine.as_ref().map(String::as_str)
 	}
 
+	/// Additional loosly-typed properties of the chain.
 	pub fn properties(&self) -> Properties {
 		// Return an empty JSON object if 'properties' not defined in config
 		self.spec.properties.as_ref().unwrap_or(&json::map::Map::new()).clone()
 	}
 
+	/// Add a bootnode to the list.
 	pub fn add_boot_node(&mut self, addr: Multiaddr) {
 		self.spec.boot_nodes.push(addr.to_string())
 	}

substrate/core/service/src/components.rs

@@ -21,7 +21,7 @@ use serde::{Serialize, de::DeserializeOwned};
 use tokio::runtime::TaskExecutor;
 use crate::chain_spec::ChainSpec;
 use client_db;
-use client::{self, Client, runtime_api::{Metadata, TaggedTransactionQueue}};
+use client::{self, Client, runtime_api};
 use crate::{error, Service, maybe_start_server};
 use consensus_common::import_queue::ImportQueue;
 use network::{self, OnDemand};
@@ -150,7 +150,7 @@ pub trait StartRPC<C: Components> {
 
 impl<C: Components> StartRPC<Self> for C where
 	ComponentClient<C>: ProvideRuntimeApi,
-	<ComponentClient<C> as ProvideRuntimeApi>::Api: Metadata<ComponentBlock<C>>,
+	<ComponentClient<C> as ProvideRuntimeApi>::Api: runtime_api::Metadata<ComponentBlock<C>>,
 {
 	type ServersHandle = (Option<rpc::HttpServer>, Option<Mutex<rpc::WsServer>>);
 
@@ -192,14 +192,14 @@ impl<C: Components> StartRPC<Self> for C where
 
 /// Something that can maintain transaction pool on every imported block.
 pub trait MaintainTransactionPool<C: Components> {
-	fn on_block_imported(
+	fn maintain_transaction_pool(
 		id: &BlockId<ComponentBlock<C>>,
 		client: &ComponentClient<C>,
 		transaction_pool: &TransactionPool<C::TransactionPoolApi>,
 	) -> error::Result<()>;
 }
 
-fn on_block_imported<Api, Backend, Block, Executor, PoolApi>(
+fn maintain_transaction_pool<Api, Backend, Block, Executor, PoolApi>(
 	id: &BlockId<Block>,
 	client: &Client<Backend, Executor, Block, Api>,
 	transaction_pool: &TransactionPool<PoolApi>,
@@ -207,7 +207,7 @@ fn on_block_imported<Api, Backend, Block, Executor, PoolApi>(
 	Block: BlockT<Hash = <Blake2Hasher as ::primitives::Hasher>::Out>,
 	Backend: client::backend::Backend<Block, Blake2Hasher>,
 	Client<Backend, Executor, Block, Api>: ProvideRuntimeApi,
-	<Client<Backend, Executor, Block, Api> as ProvideRuntimeApi>::Api: TaggedTransactionQueue<Block>,
+	<Client<Backend, Executor, Block, Api> as ProvideRuntimeApi>::Api: runtime_api::TaggedTransactionQueue<Block>,
 	Executor: client::CallExecutor<Block, Blake2Hasher>,
 	PoolApi: txpool::ChainApi<Hash = Block::Hash, Block = Block>,
 {
@@ -227,14 +227,35 @@ fn on_block_imported<Api, Backend, Block, Executor, PoolApi>(
 
 impl<C: Components> MaintainTransactionPool<Self> for C where
 	ComponentClient<C>: ProvideRuntimeApi,
-	<ComponentClient<C> as ProvideRuntimeApi>::Api: TaggedTransactionQueue<ComponentBlock<C>>,
+	<ComponentClient<C> as ProvideRuntimeApi>::Api: runtime_api::TaggedTransactionQueue<ComponentBlock<C>>,
 {
-	fn on_block_imported(
+	fn maintain_transaction_pool(
 		id: &BlockId<ComponentBlock<C>>,
 		client: &ComponentClient<C>,
 		transaction_pool: &TransactionPool<C::TransactionPoolApi>,
 	) -> error::Result<()> {
-		on_block_imported(id, client, transaction_pool)
+		maintain_transaction_pool(id, client, transaction_pool)
+	}
+}
+
+pub trait OffchainWorker<C: Components> {
+	fn offchain_workers(
+		number: &FactoryBlockNumber<C::Factory>,
+		offchain: &offchain::OffchainWorkers<ComponentClient<C>, ComponentBlock<C>>,
+		pool: &Arc<TransactionPool<C::TransactionPoolApi>>,
+	) -> error::Result<()>;
+}
+
+impl<C: Components> OffchainWorker<Self> for C where
+	ComponentClient<C>: ProvideRuntimeApi,
+	<ComponentClient<C> as ProvideRuntimeApi>::Api: offchain::OffchainWorkerApi<ComponentBlock<C>>,
+{
+	fn offchain_workers(
+		number: &FactoryBlockNumber<C::Factory>,
+		offchain: &offchain::OffchainWorkers<ComponentClient<C>, ComponentBlock<C>>,
+		pool: &Arc<TransactionPool<C::TransactionPoolApi>>,
+	) -> error::Result<()> {
+		Ok(offchain.on_block_imported(number, pool))
 	}
 }
 
@@ -246,9 +267,16 @@ pub trait ServiceTrait<C: Components>:
 	+ 'static
 	+ StartRPC<C>
 	+ MaintainTransactionPool<C>
+	+ OffchainWorker<C>
 {}
 impl<C: Components, T> ServiceTrait<C> for T where
-	T: Deref<Target = Service<C>> + Send + Sync + 'static + StartRPC<C> + MaintainTransactionPool<C>
+	T: Deref<Target = Service<C>>
+	+ Send
+	+ Sync
+	+ 'static
+	+ StartRPC<C>
+	+ MaintainTransactionPool<C>
+	+ OffchainWorker<C>
 {}
 
 /// A collection of types and methods to build a service on top of the substrate service.
@@ -338,17 +366,14 @@ pub trait Components: Sized + 'static {
 	type Executor: 'static + client::CallExecutor<FactoryBlock<Self::Factory>, Blake2Hasher> + Send + Sync + Clone;
 	/// The type that implements the runtime API.
 	type RuntimeApi: Send + Sync;
-	/// A type that can start the RPC.
-	type RPC: StartRPC<Self>;
+	/// A type that can start all runtime-dependent services.
+	type RuntimeServices: ServiceTrait<Self>;
 	// TODO: Traitify transaction pool and allow people to implement their own. (#1242)
-	/// A type that can maintain transaction pool.
-	type TransactionPool: MaintainTransactionPool<Self>;
 	/// Extrinsic pool type.
 	type TransactionPoolApi: 'static + txpool::ChainApi<
 		Hash = <FactoryBlock<Self::Factory> as BlockT>::Hash,
 		Block = FactoryBlock<Self::Factory>
 	>;
-
 	/// Our Import Queue
 	type ImportQueue: ImportQueue<FactoryBlock<Self::Factory>> + 'static;
 
@@ -382,6 +407,7 @@ pub struct FullComponents<Factory: ServiceFactory> {
 }
 
 impl<Factory: ServiceFactory> FullComponents<Factory> {
+	/// Create new `FullComponents`
 	pub fn new(
 		config: FactoryFullConfiguration<Factory>,
 		task_executor: TaskExecutor
@@ -416,8 +442,7 @@ impl<Factory: ServiceFactory> Components for FullComponents<Factory> {
 	type TransactionPoolApi = <Factory as ServiceFactory>::FullTransactionPoolApi;
 	type ImportQueue = Factory::FullImportQueue;
 	type RuntimeApi = Factory::RuntimeApi;
-	type RPC = Factory::FullService;
-	type TransactionPool = Factory::FullService;
+	type RuntimeServices = Factory::FullService;
 
 	fn build_client(
 		config: &FactoryFullConfiguration<Factory>,
@@ -462,6 +487,7 @@ pub struct LightComponents<Factory: ServiceFactory> {
 }
 
 impl<Factory: ServiceFactory> LightComponents<Factory> {
+	/// Create new `LightComponents`
 	pub fn new(
 		config: FactoryFullConfiguration<Factory>,
 		task_executor: TaskExecutor
@@ -490,8 +516,7 @@ impl<Factory: ServiceFactory> Components for LightComponents<Factory> {
 	type TransactionPoolApi = <Factory as ServiceFactory>::LightTransactionPoolApi;
 	type ImportQueue = <Factory as ServiceFactory>::LightImportQueue;
 	type RuntimeApi = Factory::RuntimeApi;
-	type RPC = Factory::LightService;
-	type TransactionPool = Factory::LightService;
+	type RuntimeServices = Factory::LightService;
 
 	fn build_client(
 		config: &FactoryFullConfiguration<Factory>,
@@ -564,7 +589,7 @@ mod tests {
 
 		// fire notification - this should clean up the queue
 		assert_eq!(pool.status().ready, 1);
-		on_block_imported(
+		maintain_transaction_pool(
 			&id,
 			&client,
 			&pool,

substrate/core/service/src/config.rs

@@ -68,6 +68,8 @@ pub struct Configuration<C, G: Serialize + DeserializeOwned + BuildStorage> {
 	pub telemetry_endpoints: Option<TelemetryEndpoints>,
 	/// The default number of 64KB pages to allocate for Wasm execution
 	pub default_heap_pages: Option<u64>,
+	/// Should offchain workers be executed.
+	pub offchain_worker: bool,
 	/// Enable authoring even when offline.
 	pub force_authoring: bool,
 	/// Disable GRANDPA when running in validator mode
@@ -97,6 +99,7 @@ impl<C: Default, G: Serialize + DeserializeOwned + BuildStorage> Configuration<C
 			rpc_ws: None,
 			telemetry_endpoints: None,
 			default_heap_pages: None,
+			offchain_worker: Default::default(),
 			force_authoring: false,
 			disable_grandpa: false,
 		};

substrate/core/service/src/lib.rs

@@ -17,7 +17,7 @@
 //! Substrate service. Starts a thread that spins up the network, client, and extrinsic pool.
 //! Manages communication between them.
 
-#![warn(unused_extern_crates)]
+#![warn(missing_docs)]
 
 mod components;
 mod error;
@@ -28,20 +28,18 @@ pub mod chain_ops;
 use std::io;
 use std::net::SocketAddr;
 use std::collections::HashMap;
-#[doc(hidden)]
-pub use std::{ops::Deref, result::Result, sync::Arc};
-use log::{info, warn, debug};
-use futures::prelude::*;
-use keystore::Store as Keystore;
+
 use client::BlockchainEvents;
+use exit_future::Signal;
+use futures::prelude::*;
+use inherents::pool::InherentsPool;
+use keystore::Store as Keystore;
+use log::{info, warn, debug};
+use parity_codec::{Encode, Decode};
 use primitives::Pair;
 use runtime_primitives::generic::BlockId;
 use runtime_primitives::traits::{Header, As};
-use exit_future::Signal;
-#[doc(hidden)]
-pub use tokio::runtime::TaskExecutor;
 use substrate_executor::NativeExecutor;
-use parity_codec::{Encode, Decode};
 use tel::{telemetry, SUBSTRATE_INFO};
 
 pub use self::error::{ErrorKind, Error};
@@ -59,9 +57,13 @@ pub use components::{ServiceFactory, FullBackend, FullExecutor, LightBackend,
 	FactoryFullConfiguration, RuntimeGenesis, FactoryGenesis,
 	ComponentExHash, ComponentExtrinsic, FactoryExtrinsic
 };
-use components::{StartRPC, MaintainTransactionPool};
+use components::{StartRPC, MaintainTransactionPool, OffchainWorker};
+#[doc(hidden)]
+pub use std::{ops::Deref, result::Result, sync::Arc};
 #[doc(hidden)]
 pub use network::OnDemand;
+#[doc(hidden)]
+pub use tokio::runtime::TaskExecutor;
 
 const DEFAULT_PROTOCOL_ID: &str = "sup";
 
@@ -70,6 +72,7 @@ pub struct Service<Components: components::Components> {
 	client: Arc<ComponentClient<Components>>,
 	network: Option<Arc<components::NetworkService<Components::Factory>>>,
 	transaction_pool: Arc<TransactionPool<Components::TransactionPoolApi>>,
+	inherents_pool: Arc<InherentsPool<ComponentExtrinsic<Components>>>,
 	keystore: Keystore,
 	exit: ::exit_future::Exit,
 	signal: Option<Signal>,
@@ -77,6 +80,7 @@ pub struct Service<Components: components::Components> {
 	pub config: FactoryFullConfiguration<Components::Factory>,
 	_rpc: Box<::std::any::Any + Send + Sync>,
 	_telemetry: Option<Arc<tel::Telemetry>>,
+	_offchain_workers: Option<Arc<offchain::OffchainWorkers<ComponentClient<Components>, ComponentBlock<Components>>>>,
 }
 
 /// Creates bare client without any networking.
@@ -96,9 +100,7 @@ impl<Components: components::Components> Service<Components> {
 	pub fn new(
 		mut config: FactoryFullConfiguration<Components::Factory>,
 		task_executor: TaskExecutor,
-	)
-		-> Result<Self, error::Error>
-	{
+	) -> Result<Self, error::Error> {
 		let (signal, exit) = ::exit_future::signal();
 
 		// Create client
@@ -169,24 +171,48 @@ impl<Components: components::Components> Service<Components> {
 		)?;
 		on_demand.map(|on_demand| on_demand.set_network_sender(network_chan));
 
+		let inherents_pool = Arc::new(InherentsPool::default());
+		let offchain_workers =  if config.offchain_worker {
+			Some(Arc::new(offchain::OffchainWorkers::new(
+				client.clone(),
+				inherents_pool.clone(),
+				task_executor.clone(),
+			)))
+		} else {
+			None
+		};
+
 		{
 			// block notifications
 			let network = Arc::downgrade(&network);
 			let txpool = Arc::downgrade(&transaction_pool);
 			let wclient = Arc::downgrade(&client);
+			let offchain = offchain_workers.as_ref().map(Arc::downgrade);
 
 			let events = client.import_notification_stream()
 				.for_each(move |notification| {
+					let number = *notification.header.number();
+
 					if let Some(network) = network.upgrade() {
 						network.on_block_imported(notification.hash, notification.header);
 					}
+
 					if let (Some(txpool), Some(client)) = (txpool.upgrade(), wclient.upgrade()) {
-						Components::TransactionPool::on_block_imported(
+						Components::RuntimeServices::maintain_transaction_pool(
 							&BlockId::hash(notification.hash),
 							&*client,
 							&*txpool,
 						).map_err(|e| warn!("Pool error processing new block: {:?}", e))?;
 					}
+
+					if let (Some(txpool), Some(offchain)) = (txpool.upgrade(), offchain.as_ref().and_then(|o| o.upgrade())) {
+						Components::RuntimeServices::offchain_workers(
+							&number,
+							&offchain,
+							&txpool,
+						).map_err(|e| warn!("Offchain workers error processing new block: {:?}", e))?;
+					}
+
 					Ok(())
 				})
 				.select(exit.clone())
@@ -264,7 +290,7 @@ impl<Components: components::Components> Service<Components> {
 			impl_version: config.impl_version.into(),
 			properties: config.chain_spec.properties(),
 		};
-		let rpc = Components::RPC::start_rpc(
+		let rpc = Components::RuntimeServices::start_rpc(
 			client.clone(), network.clone(), has_bootnodes, system_info, config.rpc_http,
 			config.rpc_ws, task_executor.clone(), transaction_pool.clone(),
 		)?;
@@ -299,12 +325,14 @@ impl<Components: components::Components> Service<Components> {
 			client,
 			network: Some(network),
 			transaction_pool,
+			inherents_pool,
 			signal: Some(signal),
 			keystore,
 			config,
 			exit,
 			_rpc: Box::new(rpc),
 			_telemetry: telemetry,
+			_offchain_workers: offchain_workers,
 		})
 	}
 
@@ -321,6 +349,7 @@ impl<Components: components::Components> Service<Components> {
 		}
 	}
 
+	/// return a shared instance of Telemtry (if enabled)
 	pub fn telemetry(&self) -> Option<Arc<tel::Telemetry>> {
 		self._telemetry.as_ref().map(|t| t.clone())
 	}
@@ -337,11 +366,16 @@ impl<Components> Service<Components> where Components: components::Components {
 		self.network.as_ref().expect("self.network always Some").clone()
 	}
 
-	/// Get shared extrinsic pool instance.
+	/// Get shared transaction pool instance.
 	pub fn transaction_pool(&self) -> Arc<TransactionPool<Components::TransactionPoolApi>> {
 		self.transaction_pool.clone()
 	}
 
+	/// Get shared inherents pool instance.
+	pub fn inherents_pool(&self) -> Arc<InherentsPool<ComponentExtrinsic<Components>>> {
+		self.inherents_pool.clone()
+	}
+
 	/// Get shared keystore.
 	pub fn keystore(&self) -> &Keystore {
 		&self.keystore

substrate/core/service/test/src/lib.rs

@@ -120,6 +120,7 @@ fn node_config<F: ServiceFactory> (
 		rpc_ws: None,
 		telemetry_endpoints: None,
 		default_heap_pages: None,
+		offchain_worker: false,
 		force_authoring: false,
 		disable_grandpa: false,
 	}

substrate/core/sr-api-macros/src/impl_runtime_apis.rs

@@ -469,7 +469,7 @@ impl<'a> Fold for ApiRuntimeImplToApiRuntimeApiImpl<'a> {
 			};
 
 			let context_arg: syn::FnArg = parse_quote!( context: #crate_::runtime_api::ExecutionContext );
-	
+
 			// Rewrite the input parameters.
 			input.sig.decl.inputs = parse_quote! {
 				&self, at: &#block_id, #context_arg, params: Option<( #( #param_types ),* )>, params_encoded: Vec<u8>
@@ -615,7 +615,7 @@ fn generate_runtime_api_versions(impls: &[ItemImpl]) -> Result<TokenStream> {
 pub fn impl_runtime_apis_impl(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 	// Parse all impl blocks
 	let RuntimeApiImpls { impls: api_impls } = parse_macro_input!(input as RuntimeApiImpls);
-	
+
 	let dispatch_impl = unwrap_or_error(generate_dispatch_function(&api_impls));
 	let api_impls_for_runtime = unwrap_or_error(generate_api_impl_for_runtime(&api_impls));
 	let base_runtime_api = unwrap_or_error(generate_runtime_api_base_structures(&api_impls));

substrate/core/sr-io/with_std.rs

@@ -218,6 +218,14 @@ pub fn secp256k1_ecdsa_recover(sig: &[u8; 65], msg: &[u8; 32]) -> Result<[u8; 64
 	Ok(res)
 }
 
+/// Submit extrinsic.
+pub fn submit_extrinsic<T: codec::Encode>(data: &T) {
+	ext::with(|ext| ext
+		.submit_extrinsic(codec::Encode::encode(data))
+		.expect("submit_extrinsic can be called only in offchain worker context")
+	).expect("submit_extrinsic cannot be called outside of an Externalities-provided environment.")
+}
+
 /// Execute the given closure with global function available whose functionality routes into the
 /// externalities `ext`. Forwards the value that the closure returns.
 // NOTE: need a concrete hasher here due to limitations of the `environmental!` macro, otherwise a type param would have been fine I think.

substrate/core/sr-io/without_std.rs

@@ -283,6 +283,13 @@ extern_functions! {
 	fn ext_sr25519_verify(msg_data: *const u8, msg_len: u32, sig_data: *const u8, pubkey_data: *const u8) -> u32;
 	/// Note: ext_secp256k1_ecdsa_recover returns 0 if the signature is correct, nonzero otherwise.
 	fn ext_secp256k1_ecdsa_recover(msg_data: *const u8, sig_data: *const u8, pubkey_data: *mut u8) -> u32;
+
+	//================================
+	// Offchain-worker Context
+	//================================
+
+	/// Submit extrinsic.
+	fn ext_submit_extrinsic(data: *const u8, len: u32);
 }
 
 /// Ensures we use the right crypto when calling into native
@@ -594,6 +601,18 @@ pub fn secp256k1_ecdsa_recover(sig: &[u8; 65], msg: &[u8; 32]) -> Result<[u8; 64
 	}
 }
 
+/// Submit extrinsic from the runtime.
+///
+/// Depending on the kind of extrinsic it will either be:
+/// 1. scheduled to be included in the next produced block (inherent)
+/// 2. added to the pool and propagated (transaction)
+pub fn submit_extrinsic<T: codec::Encode>(data: &T) {
+	let encoded_data = codec::Encode::encode(data);
+	unsafe {
+		ext_submit_extrinsic.get()(encoded_data.as_ptr(), encoded_data.len() as u32)
+	}
+}
+
 /// Trait for things which can be printed.
 pub trait Printable {
 	fn print(self);

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

@@ -393,21 +393,6 @@ impl From<sr25519::Signature> for AnySignature {
 	}
 }
 
-/// Context for executing a call into the runtime.
-#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode)]
-#[cfg_attr(feature = "std", derive(Debug, Serialize))]
-#[repr(u8)]
-pub enum ExecutionContext {
-	/// Context for general importing (including own blocks).
-	Importing,
-	/// Context used when syncing the blockchain.
-	Syncing,
-	/// Context used for block construction.
-	BlockConstruction,
-	/// Context used for other calls.
-	Other,
-}
-
 #[derive(Eq, PartialEq, Clone, Copy, Decode)]
 #[cfg_attr(feature = "std", derive(Debug, Serialize))]
 #[repr(u8)]

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

@@ -270,6 +270,24 @@ pub trait OnInitialise<BlockNumber> {
 
 impl<N> OnInitialise<N> for () {}
 
+/// Off-chain computation trait.
+///
+/// Implementing this trait on a module allows you to perform a long-running tasks
+/// that make validators generate extrinsics (either transactions or inherents)
+/// with results of those long-running computations.
+///
+/// NOTE: This function runs off-chain, so it can access the block state,
+/// but cannot preform any alterations.
+pub trait OffchainWorker<BlockNumber> {
+	/// This function is being called on every block.
+	///
+	/// Implement this and use special `extern`s to generate transactions or inherents.
+	/// Any state alterations are lost and are not persisted.
+	fn generate_extrinsics(_n: BlockNumber) {}
+}
+
+impl<N> OffchainWorker<N> for () {}
+
 macro_rules! tuple_impl {
 	($one:ident,) => {
 		impl<Number: Copy, $one: OnFinalise<Number>> OnFinalise<Number> for ($one,) {
@@ -282,6 +300,11 @@ macro_rules! tuple_impl {
 				$one::on_initialise(n);
 			}
 		}
+		impl<Number: Copy, $one: OffchainWorker<Number>> OffchainWorker<Number> for ($one,) {
+			fn generate_extrinsics(n: Number) {
+				$one::generate_extrinsics(n);
+			}
+		}
 	};
 	($first:ident, $($rest:ident,)+) => {
 		impl<
@@ -304,6 +327,16 @@ macro_rules! tuple_impl {
 				$($rest::on_initialise(n);)+
 			}
 		}
+		impl<
+			Number: Copy,
+			$first: OffchainWorker<Number>,
+			$($rest: OffchainWorker<Number>),+
+		> OffchainWorker<Number> for ($first, $($rest),+) {
+			fn generate_extrinsics(n: Number) {
+				$first::generate_extrinsics(n);
+				$($rest::generate_extrinsics(n);)+
+			}
+		}
 		tuple_impl!($($rest,)+);
 	}
 }

substrate/core/state-machine/src/basic.rs

@@ -24,6 +24,7 @@ use trie::trie_root;
 use primitives::storage::well_known_keys::{CHANGES_TRIE_CONFIG, CODE, HEAP_PAGES};
 use parity_codec::Encode;
 use super::{Externalities, OverlayedChanges};
+use log::warn;
 
 /// Simple HashMap-based Externalities impl.
 pub struct BasicExternalities {
@@ -151,6 +152,11 @@ impl<H: Hasher> Externalities<H> for BasicExternalities where H::Out: Ord + Heap
 	fn storage_changes_root(&mut self, _parent: H::Out, _parent_num: u64) -> Option<H::Out> {
 		None
 	}
+
+	fn submit_extrinsic(&mut self, _extrinsic: Vec<u8>) -> Result<(), ()> {
+		warn!("Call to submit_extrinsic without offchain externalities set.");
+		Err(())
+	}
 }
 
 #[cfg(test)]

substrate/core/state-machine/src/ext.rs

@@ -20,7 +20,7 @@ use std::{error, fmt, cmp::Ord};
 use log::warn;
 use crate::backend::{Backend, Consolidate};
 use crate::changes_trie::{AnchorBlockId, Storage as ChangesTrieStorage, compute_changes_trie_root};
-use crate::{Externalities, OverlayedChanges};
+use crate::{Externalities, OverlayedChanges, OffchainExt};
 use hash_db::Hasher;
 use primitives::storage::well_known_keys::is_child_storage_key;
 use trie::{MemoryDB, TrieDBMut, TrieMut, default_child_trie_root, is_child_trie_key_valid};
@@ -58,12 +58,11 @@ impl<B: error::Error, E: error::Error> error::Error for Error<B, E> {
 }
 
 /// Wraps a read-only backend, call executor, and current overlayed changes.
-pub struct Ext<'a, H, B, T>
+pub struct Ext<'a, H, B, T, O>
 where
 	H: Hasher,
 
 	B: 'a + Backend<H>,
-	T: 'a + ChangesTrieStorage<H>,
 {
 	/// The overlayed changes to write to.
 	overlay: &'a mut OverlayedChanges,
@@ -81,23 +80,34 @@ where
 	/// `storage_changes_root` is called matters + we need to remember additional
 	/// data at this moment (block number).
 	changes_trie_transaction: Option<(u64, MemoryDB<H>, H::Out)>,
+	/// Additional externalities for offchain workers.
+	///
+	/// If None, some methods from the trait might not supported.
+	offchain_externalities: Option<&'a mut O>,
 }
 
-impl<'a, H, B, T> Ext<'a, H, B, T>
+impl<'a, H, B, T, O> Ext<'a, H, B, T, O>
 where
 	H: Hasher,
 	B: 'a + Backend<H>,
 	T: 'a + ChangesTrieStorage<H>,
+	O: 'a + OffchainExt,
 	H::Out: Ord + HeapSizeOf,
 {
 	/// Create a new `Ext` from overlayed changes and read-only backend
-	pub fn new(overlay: &'a mut OverlayedChanges, backend: &'a B, changes_trie_storage: Option<&'a T>) -> Self {
+	pub fn new(
+		overlay: &'a mut OverlayedChanges,
+		backend: &'a B,
+		changes_trie_storage: Option<&'a T>,
+		offchain_externalities: Option<&'a mut O>,
+	) -> Self {
 		Ext {
 			overlay,
 			backend,
 			storage_transaction: None,
 			changes_trie_storage,
 			changes_trie_transaction: None,
+			offchain_externalities,
 		}
 	}
 
@@ -152,12 +162,13 @@ where
 }
 
 #[cfg(test)]
-impl<'a, H, B, T> Ext<'a, H, B, T>
+impl<'a, H, B, T, O> Ext<'a, H, B, T, O>
 where
 	H: Hasher,
 
 	B: 'a + Backend<H>,
 	T: 'a + ChangesTrieStorage<H>,
+	O: 'a + OffchainExt,
 {
 	pub fn storage_pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
 		use std::collections::HashMap;
@@ -173,11 +184,12 @@ where
 	}
 }
 
-impl<'a, B: 'a, T: 'a, H> Externalities<H> for Ext<'a, H, B, T>
+impl<'a, B, T, H, O> Externalities<H> for Ext<'a, H, B, T, O>
 where
 	H: Hasher,
 	B: 'a + Backend<H>,
 	T: 'a + ChangesTrieStorage<H>,
+	O: 'a + OffchainExt,
 	H::Out: Ord + HeapSizeOf,
 {
 	fn storage(&self, key: &[u8]) -> Option<Vec<u8>> {
@@ -329,6 +341,17 @@ where
 		self.changes_trie_transaction = root_and_tx;
 		root
 	}
+
+	fn submit_extrinsic(&mut self, extrinsic: Vec<u8>) -> Result<(), ()> {
+		let _guard = panic_handler::AbortGuard::new(true);
+		if let Some(ext) = self.offchain_externalities.as_mut() {
+			ext.submit_extrinsic(extrinsic);
+			Ok(())
+		} else {
+			warn!("Call to submit_extrinsic without offchain externalities set.");
+			Err(())
+		}
+	}
 }
 
 #[cfg(test)]
@@ -345,7 +368,7 @@ mod tests {
 
 	type TestBackend = InMemory<Blake2Hasher>;
 	type TestChangesTrieStorage = InMemoryChangesTrieStorage<Blake2Hasher>;
-	type TestExt<'a> = Ext<'a, Blake2Hasher, TestBackend, TestChangesTrieStorage>;
+	type TestExt<'a> = Ext<'a, Blake2Hasher, TestBackend, TestChangesTrieStorage, crate::NeverOffchainExt>;
 
 	fn prepare_overlay_with_changes() -> OverlayedChanges {
 		OverlayedChanges {
@@ -371,7 +394,7 @@ mod tests {
 	fn storage_changes_root_is_none_when_storage_is_not_provided() {
 		let mut overlay = prepare_overlay_with_changes();
 		let backend = TestBackend::default();
-		let mut ext = TestExt::new(&mut overlay, &backend, None);
+		let mut ext = TestExt::new(&mut overlay, &backend, None, None);
 		assert_eq!(ext.storage_changes_root(Default::default(), 100), None);
 	}
 
@@ -381,7 +404,7 @@ mod tests {
 		overlay.changes_trie_config = None;
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
-		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
+		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage), None);
 		assert_eq!(ext.storage_changes_root(Default::default(), 100), None);
 	}
 
@@ -390,7 +413,7 @@ mod tests {
 		let mut overlay = prepare_overlay_with_changes();
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
-		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
+		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage), None);
 		assert_eq!(ext.storage_changes_root(Default::default(), 99),
 			Some(hex!("5b829920b9c8d554a19ee2a1ba593c4f2ee6fc32822d083e04236d693e8358d5").into()));
 	}
@@ -401,7 +424,7 @@ mod tests {
 		overlay.prospective.top.get_mut(&vec![1]).unwrap().value = None;
 		let storage = TestChangesTrieStorage::new();
 		let backend = TestBackend::default();
-		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage));
+		let mut ext = TestExt::new(&mut overlay, &backend, Some(&storage), None);
 		assert_eq!(ext.storage_changes_root(Default::default(), 99),
 			Some(hex!("bcf494e41e29a15c9ae5caa053fe3cb8b446ee3e02a254efbdec7a19235b76e4").into()));
 	}

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

@@ -23,7 +23,7 @@ use log::warn;
 use hash_db::Hasher;
 use heapsize::HeapSizeOf;
 use parity_codec::{Decode, Encode};
-use primitives::{storage::well_known_keys, NativeOrEncoded, NeverNativeValue};
+use primitives::{storage::well_known_keys, NativeOrEncoded, NeverNativeValue, OffchainExt};
 
 pub mod backend;
 mod changes_trie;
@@ -153,6 +153,25 @@ pub trait Externalities<H: Hasher> {
 
 	/// Get the change trie root of the current storage overlay at a block with given parent.
 	fn storage_changes_root(&mut self, parent: H::Out, parent_num: u64) -> Option<H::Out> where H::Out: Ord;
+
+	/// Submit extrinsic.
+	///
+	/// Returns an error in case the API is not available.
+	fn submit_extrinsic(&mut self, extrinsic: Vec<u8>) -> Result<(), ()>;
+}
+
+/// An implementation of offchain extensions that should never be triggered.
+pub enum NeverOffchainExt {}
+
+impl NeverOffchainExt {
+	/// Create new offchain extensions.
+	pub fn new<'a>() -> Option<&'a mut Self> {
+		None
+	}
+}
+
+impl OffchainExt for NeverOffchainExt {
+	fn submit_extrinsic(&mut self, _extrinsic: Vec<u8>) { unreachable!() }
 }
 
 /// Code execution engine.
@@ -252,17 +271,19 @@ pub fn always_wasm<E, R: Decode>() -> ExecutionManager<DefaultHandler<R, E>> {
 }
 
 /// Creates new substrate state machine.
-pub fn new<'a, H, B, T, Exec>(
+pub fn new<'a, H, B, T, O, Exec>(
 	backend: &'a B,
 	changes_trie_storage: Option<&'a T>,
+	offchain_ext: Option<&'a mut O>,
 	overlay: &'a mut OverlayedChanges,
 	exec: &'a Exec,
 	method: &'a str,
 	call_data: &'a [u8],
-) -> StateMachine<'a, H, B, T, Exec> {
+) -> StateMachine<'a, H, B, T, O, Exec> {
 	StateMachine {
 		backend,
 		changes_trie_storage,
+		offchain_ext,
 		overlay,
 		exec,
 		method,
@@ -272,9 +293,10 @@ pub fn new<'a, H, B, T, Exec>(
 }
 
 /// The substrate state machine.
-pub struct StateMachine<'a, H, B, T, Exec> {
+pub struct StateMachine<'a, H, B, T, O, Exec> {
 	backend: &'a B,
 	changes_trie_storage: Option<&'a T>,
+	offchain_ext: Option<&'a mut O>,
 	overlay: &'a mut OverlayedChanges,
 	exec: &'a Exec,
 	method: &'a str,
@@ -282,11 +304,12 @@ pub struct StateMachine<'a, H, B, T, Exec> {
 	_hasher: PhantomData<H>,
 }
 
-impl<'a, H, B, T, Exec> StateMachine<'a, H, B, T, Exec> where
+impl<'a, H, B, T, O, Exec> StateMachine<'a, H, B, T, O, Exec> where
 	H: Hasher,
 	Exec: CodeExecutor<H>,
 	B: Backend<H>,
 	T: ChangesTrieStorage<H>,
+	O: OffchainExt,
 	H::Out: Ord + HeapSizeOf,
 {
 	/// Execute a call using the given state backend, overlayed changes, and call executor.
@@ -324,7 +347,13 @@ impl<'a, H, B, T, Exec> StateMachine<'a, H, B, T, Exec> where
 		R: Decode + Encode + PartialEq,
 		NC: FnOnce() -> result::Result<R, &'static str> + UnwindSafe,
 	{
-		let mut externalities = ext::Ext::new(self.overlay, self.backend, self.changes_trie_storage);
+		let offchain = self.offchain_ext.as_mut();
+		let mut externalities = ext::Ext::new(
+			self.overlay,
+			self.backend,
+			self.changes_trie_storage,
+			offchain.map(|x| &mut **x),
+		);
 		let (result, was_native) = self.exec.call(
 			&mut externalities,
 			self.method,
@@ -505,6 +534,7 @@ where
 	let mut sm = StateMachine {
 		backend: &proving_backend,
 		changes_trie_storage: None as Option<&changes_trie::InMemoryStorage<H>>,
+		offchain_ext: NeverOffchainExt::new(),
 		overlay,
 		exec,
 		method,
@@ -554,6 +584,7 @@ where
 	let mut sm = StateMachine {
 		backend: trie_backend,
 		changes_trie_storage: None as Option<&changes_trie::InMemoryStorage<H>>,
+		offchain_ext: NeverOffchainExt::new(),
 		overlay,
 		exec,
 		method,
@@ -730,6 +761,7 @@ mod tests {
 		assert_eq!(new(
 			&trie_backend::tests::test_trie(),
 			Some(&InMemoryChangesTrieStorage::new()),
+			NeverOffchainExt::new(),
 			&mut Default::default(),
 			&DummyCodeExecutor {
 				change_changes_trie_config: false,
@@ -750,6 +782,7 @@ mod tests {
 		assert_eq!(new(
 			&trie_backend::tests::test_trie(),
 			Some(&InMemoryChangesTrieStorage::new()),
+			NeverOffchainExt::new(),
 			&mut Default::default(),
 			&DummyCodeExecutor {
 				change_changes_trie_config: false,
@@ -770,6 +803,7 @@ mod tests {
 		assert!(new(
 			&trie_backend::tests::test_trie(),
 			Some(&InMemoryChangesTrieStorage::new()),
+			NeverOffchainExt::new(),
 			&mut Default::default(),
 			&DummyCodeExecutor {
 				change_changes_trie_config: false,
@@ -838,7 +872,7 @@ mod tests {
 
 		{
 			let changes_trie_storage = InMemoryChangesTrieStorage::new();
-			let mut ext = Ext::new(&mut overlay, &backend, Some(&changes_trie_storage));
+			let mut ext = Ext::new(&mut overlay, &backend, Some(&changes_trie_storage), NeverOffchainExt::new());
 			ext.clear_prefix(b"ab");
 		}
 		overlay.commit_prospective();
@@ -862,7 +896,7 @@ mod tests {
 		let backend = InMemory::<Blake2Hasher>::default().try_into_trie_backend().unwrap();
 		let changes_trie_storage = InMemoryChangesTrieStorage::new();
 		let mut overlay = OverlayedChanges::default();
-		let mut ext = Ext::new(&mut overlay, &backend, Some(&changes_trie_storage));
+		let mut ext = Ext::new(&mut overlay, &backend, Some(&changes_trie_storage), NeverOffchainExt::new());
 
 		assert!(ext.set_child_storage(b":child_storage:testchild".to_vec(), b"abc".to_vec(), b"def".to_vec()));
 		assert_eq!(ext.child_storage(b":child_storage:testchild", b"abc"), Some(b"def".to_vec()));
@@ -889,6 +923,7 @@ mod tests {
 		assert!(new(
 			&trie_backend::tests::test_trie(),
 			Some(&InMemoryChangesTrieStorage::new()),
+			NeverOffchainExt::new(),
 			&mut Default::default(),
 			&DummyCodeExecutor {
 				change_changes_trie_config: true,
@@ -908,6 +943,7 @@ mod tests {
 		assert!(new(
 			&trie_backend::tests::test_trie(),
 			Some(&InMemoryChangesTrieStorage::new()),
+			NeverOffchainExt::new(),
 			&mut Default::default(),
 			&DummyCodeExecutor {
 				change_changes_trie_config: true,

substrate/core/state-machine/src/overlayed_changes.rs

@@ -375,7 +375,12 @@ mod tests {
 		};
 
 		let changes_trie_storage = InMemoryChangesTrieStorage::new();
-		let mut ext = Ext::new(&mut overlay, &backend, Some(&changes_trie_storage));
+		let mut ext = Ext::new(
+			&mut overlay,
+			&backend,
+			Some(&changes_trie_storage),
+			crate::NeverOffchainExt::new(),
+		);
 		const ROOT: [u8; 32] = hex!("0b41e488cccbd67d1f1089592c2c235f5c5399b053f7fe9152dd4b5f279914cd");
 		assert_eq!(ext.storage_root(), H256::from(ROOT));
 	}

substrate/core/state-machine/src/testing.rs

@@ -168,6 +168,10 @@ impl<H: Hasher> Externalities<H> for TestExternalities<H> where H::Out: Ord + He
 			&AnchorBlockId { hash: parent, number: parent_num },
 		).map(|(root, _)| root.clone())
 	}
+
+	fn submit_extrinsic(&mut self, _extrinsic: Vec<u8>) -> Result<(), ()> {
+		unimplemented!()
+	}
 }
 
 #[cfg(test)]

substrate/core/test-client/src/lib.rs

@@ -128,6 +128,7 @@ pub fn new_with_execution_strategy(
 		syncing: execution_strategy,
 		importing: execution_strategy,
 		block_construction: execution_strategy,
+		offchain_worker: execution_strategy,
 		other: execution_strategy,
 	};
 

substrate/core/test-runtime/Cargo.toml

@@ -20,6 +20,7 @@ runtime_io = { package = "sr-io", path = "../sr-io", default-features = false }
 runtime_primitives = { package = "sr-primitives", path = "../sr-primitives", default-features = false }
 runtime_version = { package = "sr-version", path = "../sr-version", default-features = false }
 runtime_support = { package = "srml-support", path = "../../srml/support", default-features = false }
+offchain-primitives = { package = "substrate-offchain-primitives", path = "../offchain/primitives", default-features = false}
 executive = { package = "srml-executive", path = "../../srml/executive", default-features = false }
 cfg-if = "0.1.6"
 
@@ -45,5 +46,6 @@ std = [
 	"runtime_primitives/std",
 	"runtime_version/std",
 	"consensus_aura/std",
+	"offchain-primitives/std",
 	"executive/std",
 ]

substrate/core/test-runtime/src/lib.rs

@@ -94,6 +94,7 @@ impl Transfer {
 pub enum Extrinsic {
 	AuthoritiesChange(Vec<AuthorityId>),
 	Transfer(Transfer, AccountSignature),
+	IncludeData(Vec<u8>),
 }
 
 #[cfg(feature = "std")]
@@ -117,6 +118,7 @@ impl BlindCheckable for Extrinsic {
 					Err(runtime_primitives::BAD_SIGNATURE)
 				}
 			},
+			Extrinsic::IncludeData(data) => Ok(Extrinsic::IncludeData(data)),
 		}
 	}
 }
@@ -377,6 +379,13 @@ cfg_if! {
 			impl consensus_aura::AuraApi<Block> for Runtime {
 				fn slot_duration() -> u64 { 1 }
 			}
+
+			impl offchain_primitives::OffchainWorkerApi<Block> for Runtime {
+				fn offchain_worker(block: u64) {
+					let ex = Extrinsic::IncludeData(block.encode());
+					runtime_io::submit_extrinsic(&ex)
+				}
+			}
 		}
 	} else {
 		impl_runtime_apis! {
@@ -480,6 +489,13 @@ cfg_if! {
 			impl consensus_aura::AuraApi<Block> for Runtime {
 				fn slot_duration() -> u64 { 1 }
 			}
+
+			impl offchain_primitives::OffchainWorkerApi<Block> for Runtime {
+				fn offchain_worker(block: u64) {
+					let ex = Extrinsic::IncludeData(block.encode());
+					runtime_io::submit_extrinsic(&ex)
+				}
+			}
 		}
 	}
 }

substrate/core/test-runtime/src/system.rs

@@ -242,6 +242,7 @@ fn execute_transaction_backend(utx: &Extrinsic) -> ApplyResult {
 	match utx {
 		Extrinsic::Transfer(ref transfer, _) => execute_transfer_backend(transfer),
 		Extrinsic::AuthoritiesChange(ref new_auth) => execute_new_authorities_backend(new_auth),
+		Extrinsic::IncludeData(_) => Ok(ApplyOutcome::Success),
 	}
 }
 

substrate/core/test-runtime/wasm/Cargo.lock

@@ -2346,6 +2346,14 @@ dependencies = [
  "substrate-primitives 0.1.0",
 ]
 
+[[package]]
+name = "substrate-offchain-primitives"
+version = "0.1.0"
+dependencies = [
+ "sr-primitives 0.1.0",
+ "substrate-client 0.1.0",
+]
+
 [[package]]
 name = "substrate-panic-handler"
 version = "0.1.0"
@@ -2446,6 +2454,7 @@ dependencies = [
  "substrate-consensus-aura-primitives 0.1.0",
  "substrate-inherents 0.1.0",
  "substrate-keyring 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
 ]
 

substrate/node-template/runtime/Cargo.toml

@@ -25,6 +25,7 @@ sudo = { package = "srml-sudo", path = "../../srml/sudo", default_features = fal
 runtime-primitives = { package = "sr-primitives", path = "../../core/sr-primitives", default_features = false }
 client = { package = "substrate-client", path = "../../core/client", default_features = false }
 consensus-aura = { package = "substrate-consensus-aura-primitives", path = "../../core/consensus/aura/primitives", default_features = false }
+offchain-primitives = { package = "substrate-offchain-primitives", path = "../../core/offchain/primitives", default-features = false }
 
 [features]
 default = ["std"]
@@ -48,4 +49,5 @@ std = [
 	"serde",
 	"safe-mix/std",
 	"consensus-aura/std",
+	"offchain-primitives/std",
 ]

substrate/node-template/runtime/src/lib.rs

@@ -14,7 +14,7 @@ use primitives::bytes;
 use primitives::{ed25519, OpaqueMetadata};
 use runtime_primitives::{
 	ApplyResult, transaction_validity::TransactionValidity, generic, create_runtime_str,
-	traits::{self, BlakeTwo256, Block as BlockT, StaticLookup, Verify}
+	traits::{self, NumberFor, BlakeTwo256, Block as BlockT, StaticLookup, Verify}
 };
 use client::{
 	block_builder::api::{CheckInherentsResult, InherentData, self as block_builder_api},
@@ -182,7 +182,7 @@ impl sudo::Trait for Runtime {
 }
 
 /// Used for the module template in `./template.rs`
-impl template::Trait for Runtime { 
+impl template::Trait for Runtime {
 	type Event = Event;
 }
 
@@ -280,4 +280,10 @@ impl_runtime_apis! {
 			Aura::slot_duration()
 		}
 	}
+
+	impl offchain_primitives::OffchainWorkerApi<Block> for Runtime {
+		fn offchain_worker(n: NumberFor<Block>) {
+			Executive::offchain_worker(n)
+		}
+	}
 }

substrate/node-template/runtime/wasm/Cargo.lock

@@ -1273,6 +1273,7 @@ dependencies = [
  "srml-timestamp 0.1.0",
  "substrate-client 0.1.0",
  "substrate-consensus-aura-primitives 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
 ]
 
@@ -2510,6 +2511,14 @@ dependencies = [
  "substrate-primitives 0.1.0",
 ]
 
+[[package]]
+name = "substrate-offchain-primitives"
+version = "0.1.0"
+dependencies = [
+ "sr-primitives 0.1.0",
+ "substrate-client 0.1.0",
+]
+
 [[package]]
 name = "substrate-panic-handler"
 version = "0.1.0"

substrate/node-template/src/service.rs

@@ -62,6 +62,7 @@ construct_service_factory! {
 					let proposer = Arc::new(ProposerFactory {
 						client: service.client(),
 						transaction_pool: service.transaction_pool(),
+						inherents_pool: service.inherents_pool(),
 					});
 					let client = service.client();
 					executor.spawn(start_aura(

substrate/node/cli/src/service.rs

@@ -85,6 +85,7 @@ construct_service_factory! {
 					let proposer = Arc::new(substrate_basic_authorship::ProposerFactory {
 						client: service.client(),
 						transaction_pool: service.transaction_pool(),
+						inherents_pool: service.inherents_pool(),
 					});
 
 					let client = service.client();

substrate/node/runtime/Cargo.toml

@@ -12,6 +12,7 @@ substrate-primitives = { path = "../../core/primitives", default-features = fals
 client = { package = "substrate-client", path = "../../core/client", default-features = false }
 rstd = { package = "sr-std", path = "../../core/sr-std", default-features = false }
 runtime_primitives = { package = "sr-primitives", path = "../../core/sr-primitives", default-features = false }
+offchain-primitives = { package = "substrate-offchain-primitives", path = "../../core/offchain/primitives", default-features = false }
 version = { package = "sr-version", path = "../../core/sr-version", default-features = false }
 support = { package = "srml-support", path = "../../srml/support", default-features = false }
 aura = { package = "srml-aura", path = "../../srml/aura", default-features = false }

substrate/node/runtime/src/lib.rs

@@ -58,8 +58,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	spec_name: create_runtime_str!("node"),
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
-	spec_version: 42,
-	impl_version: 42,
+	spec_version: 43,
+	impl_version: 43,
 	apis: RUNTIME_API_VERSIONS,
 };
 
@@ -288,6 +288,12 @@ impl_runtime_apis! {
 		}
 	}
 
+	impl offchain_primitives::OffchainWorkerApi<Block> for Runtime {
+		fn offchain_worker(number: NumberFor<Block>) {
+			Executive::offchain_worker(number)
+		}
+	}
+
 	impl fg_primitives::GrandpaApi<Block> for Runtime {
 		fn grandpa_pending_change(digest: &DigestFor<Block>)
 			-> Option<ScheduledChange<NumberFor<Block>>>

substrate/node/runtime/wasm/Cargo.lock

@@ -1297,6 +1297,7 @@ dependencies = [
  "substrate-client 0.1.0",
  "substrate-consensus-aura-primitives 0.1.0",
  "substrate-keyring 0.1.0",
+ "substrate-offchain-primitives 0.1.0",
  "substrate-primitives 0.1.0",
 ]
 
@@ -2666,6 +2667,14 @@ dependencies = [
  "substrate-primitives 0.1.0",
 ]
 
+[[package]]
+name = "substrate-offchain-primitives"
+version = "0.1.0"
+dependencies = [
+ "sr-primitives 0.1.0",
+ "substrate-client 0.1.0",
+]
+
 [[package]]
 name = "substrate-panic-handler"
 version = "0.1.0"

substrate/srml/example/src/lib.rs

@@ -214,6 +214,15 @@ decl_module! {
 			// We just kill our dummy storage item.
 			<Dummy<T>>::kill();
 		}
+
+		// A runtime code run after every block and have access to extended set of APIs.
+		//
+		// For instance you can generate extrinsics for the upcoming produced block.
+		fn offchain_worker(_n: T::BlockNumber) {
+			// We don't do anything here.
+			// but we could dispatch extrinsic (transaction/inherent) using
+			// runtime_io::submit_extrinsic
+		}
 	}
 }
 

substrate/srml/executive/src/lib.rs

@@ -23,7 +23,7 @@ use rstd::marker::PhantomData;
 use rstd::result;
 use primitives::traits::{
 	self, Header, Zero, One, Checkable, Applyable, CheckEqual, OnFinalise,
-	OnInitialise, Hash, As, Digest, NumberFor, Block as BlockT
+	OnInitialise, Hash, As, Digest, NumberFor, Block as BlockT, OffchainWorker
 };
 use srml_support::{Dispatchable, traits::MakePayment};
 use parity_codec::{Codec, Encode};
@@ -65,7 +65,7 @@ impl<
 	Block: traits::Block<Header=System::Header, Hash=System::Hash>,
 	Context: Default,
 	Payment: MakePayment<System::AccountId>,
-	AllModules: OnInitialise<System::BlockNumber> + OnFinalise<System::BlockNumber>,
+	AllModules: OnInitialise<System::BlockNumber> + OnFinalise<System::BlockNumber> + OffchainWorker<System::BlockNumber>,
 > ExecuteBlock<Block> for Executive<System, Block, Context, Payment, AllModules> where
 	Block::Extrinsic: Checkable<Context> + Codec,
 	<Block::Extrinsic as Checkable<Context>>::Checked: Applyable<Index=System::Index, AccountId=System::AccountId>,
@@ -73,11 +73,11 @@ impl<
 	<<<Block::Extrinsic as Checkable<Context>>::Checked as Applyable>::Call as Dispatchable>::Origin: From<Option<System::AccountId>>
 {
 	fn execute_block(block: Block) {
-		Self::execute_block(block);
+		Executive::<System, Block, Context, Payment, AllModules>::execute_block(block);
 	}
 
 	fn execute_extrinsics_without_checks(block_number: NumberFor<Block>, extrinsics: Vec<Block::Extrinsic>) {
-		Self::execute_extrinsics_without_checks(block_number, extrinsics);
+		Executive::<System, Block, Context, Payment, AllModules>::execute_extrinsics_without_checks(block_number, extrinsics);
 	}
 }
 
@@ -86,7 +86,7 @@ impl<
 	Block: traits::Block<Header=System::Header, Hash=System::Hash>,
 	Context: Default,
 	Payment: MakePayment<System::AccountId>,
-	AllModules: OnInitialise<System::BlockNumber> + OnFinalise<System::BlockNumber>,
+	AllModules: OnInitialise<System::BlockNumber> + OnFinalise<System::BlockNumber> + OffchainWorker<System::BlockNumber>,
 > Executive<System, Block, Context, Payment, AllModules> where
 	Block::Extrinsic: Checkable<Context> + Codec,
 	<Block::Extrinsic as Checkable<Context>>::Checked: Applyable<Index=System::Index, AccountId=System::AccountId>,
@@ -319,6 +319,11 @@ impl<
 			})
 		}
 	}
+
+	/// Start an offchain worker and generate extrinsics.
+	pub fn offchain_worker(n: System::BlockNumber) {
+		<AllModules as OffchainWorker<System::BlockNumber>>::generate_extrinsics(n)
+	}
 }
 
 #[cfg(test)]

substrate/srml/support/src/dispatch.rs

@@ -117,6 +117,7 @@ macro_rules! decl_module {
 			{}
 			{}
 			{}
+			{}
 			[]
 			$($t)*
 		);
@@ -135,6 +136,7 @@ macro_rules! decl_module {
 			{}
 			{}
 			{}
+			{}
 			[]
 			$($t)*
 		);
@@ -147,6 +149,7 @@ macro_rules! decl_module {
 		{}
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$vis:vis fn deposit_event $(<$dpeg:ident $(, $dpeg_instance:ident)?>)* () = default;
@@ -159,6 +162,7 @@ macro_rules! decl_module {
 			{ $vis fn deposit_event $(<$dpeg $(, $dpeg_instance)?>)* () = default; }
 			{ $( $on_initialise )* }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
 			[ $($t)* ]
 			$($rest)*
 		);
@@ -170,6 +174,7 @@ macro_rules! decl_module {
 		{}
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$vis:vis fn deposit_event $(<$dpeg:ident $(, $dpeg_instance:ident)?>)* (
@@ -184,6 +189,7 @@ macro_rules! decl_module {
 			{ $vis fn deposit_event $(<$dpeg $(, $dpeg_instance)?>)* ($( $param_name: $param ),* ) { $( $impl )* } }
 			{ $( $on_initialise )* }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
 			[ $($t)* ]
 			$($rest)*
 		);
@@ -195,6 +201,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{}
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		fn on_finalise($($param_name:ident : $param:ty),* ) { $( $impl:tt )* }
@@ -207,6 +214,7 @@ macro_rules! decl_module {
 			{ $( $deposit_event )* }
 			{ $( $on_initialise )* }
 			{ fn on_finalise( $( $param_name : $param ),* ) { $( $impl )* } }
+			{ $( $offchain )* }
 			[ $($t)* ]
 			$($rest)*
 		);
@@ -218,6 +226,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{}
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		fn on_initialise($($param_name:ident : $param:ty),* ) { $( $impl:tt )* }
@@ -230,6 +239,32 @@ macro_rules! decl_module {
 			{ $( $deposit_event )* }
 			{ fn on_initialise( $( $param_name : $param ),* ) { $( $impl )* } }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
+			[ $($t)* ]
+			$($rest)*
+		);
+	};
+	(@normalize
+		$(#[$attr:meta])*
+		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident>
+		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $deposit_event:tt )* }
+		{ $( $on_initialise:tt )* }
+		{ $( $on_finalise:tt )* }
+		{ }
+		[ $($t:tt)* ]
+		$(#[doc = $doc_attr:tt])*
+		fn offchain_worker($($param_name:ident : $param:ty),* ) { $( $impl:tt )* }
+		$($rest:tt)*
+	) => {
+		decl_module!(@normalize
+			$(#[$attr])*
+			pub struct $mod_type<$trait_instance: $trait_name>
+			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $deposit_event )* }
+			{ $( $on_initialise )* }
+			{ $( $on_finalise )* }
+			{ fn offchain_worker( $( $param_name : $param ),* ) { $( $impl )* } }
 			[ $($t)* ]
 			$($rest)*
 		);
@@ -241,6 +276,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$fn_vis:vis fn $fn_name:ident(
@@ -255,6 +291,7 @@ macro_rules! decl_module {
 			{ $( $deposit_event )* }
 			{ $( $on_initialise )* }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
 			[
 				$($t)*
 				$(#[doc = $doc_attr])*
@@ -273,6 +310,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$fn_vis:vis fn $fn_name:ident(
@@ -293,6 +331,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$fn_vis:vis fn $fn_name:ident(
@@ -313,6 +352,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 		$(#[doc = $doc_attr:tt])*
 		$fn_vis:vis fn $fn_name:ident(
@@ -327,6 +367,7 @@ macro_rules! decl_module {
 			{ $( $deposit_event )* }
 			{ $( $on_initialise )* }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
 			[
 				$($t)*
 				$(#[doc = $doc_attr])*
@@ -345,6 +386,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 		[ $($t:tt)* ]
 	) => {
 		decl_module!(@imp
@@ -356,6 +398,7 @@ macro_rules! decl_module {
 			{ $( $deposit_event )* }
 			{ $( $on_initialise )* }
 			{ $( $on_finalise )* }
+			{ $( $offchain )* }
 		);
 	};
 
@@ -477,6 +520,39 @@ macro_rules! decl_module {
 		}
 	};
 
+	(@impl_offchain
+		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		fn offchain_worker() { $( $impl:tt )* }
+	) => {
+		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
+			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
+			for $module<$trait_instance$(, $instance)?>
+		{
+			fn generate_extrinsics(_block_number_not_used: $trait_instance::BlockNumber) { $( $impl )* }
+		}
+	};
+
+	(@impl_offchain
+		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		fn offchain_worker($param:ident : $param_ty:ty) { $( $impl:tt )* }
+	) => {
+		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
+			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
+			for $module<$trait_instance$(, $instance)?>
+		{
+			fn generate_extrinsics($param: $param_ty) { $( $impl )* }
+		}
+	};
+
+	(@impl_offchain
+		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+	) => {
+		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
+			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
+			for $module<$trait_instance$(, $instance)?>
+		{}
+	};
+
 	(@impl_function
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
 		$origin_ty:ty;
@@ -556,6 +632,7 @@ macro_rules! decl_module {
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialise:tt )* }
 		{ $( $on_finalise:tt )* }
+		{ $( $offchain:tt )* }
 	) => {
 		// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
 		#[derive(Clone, Copy, PartialEq, Eq)]
@@ -584,6 +661,12 @@ macro_rules! decl_module {
 			$( $on_finalise )*
 		}
 
+		decl_module! {
+			@impl_offchain
+			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
+			$( $offchain )*
+		}
+
 		decl_module! {
 			@impl_deposit_event
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
@@ -1086,6 +1169,7 @@ mod tests {
 
 			fn on_initialise(n: T::BlockNumber) { if n.into() == 42 { panic!("on_initialise") } }
 			fn on_finalise(n: T::BlockNumber) { if n.into() == 42 { panic!("on_finalise") } }
+			fn offchain_worker() {}
 		}
 	}
 

substrate/srml/system/src/lib.rs

@@ -124,8 +124,8 @@ pub struct EventRecord<E: Parameter + Member> {
 	pub event: E,
 }
 
-/// Event for the system module.
 decl_event!(
+	/// Event for the system module.
 	pub enum Event {
 		/// An extrinsic completed successfully.
 		ExtrinsicSuccess,

substrate/srml/timestamp/Cargo.toml

@@ -21,11 +21,11 @@ substrate-primitives = { path = "../../core/primitives" }
 [features]
 default = ["std"]
 std = [
-	"rstd/std",
-	"srml-support/std",
-	"runtime_primitives/std",
-	"serde",
-	"parity-codec/std",
-	"system/std",
 	"inherents/std",
+	"parity-codec/std",
+	"rstd/std",
+	"runtime_primitives/std",
+	"srml-support/std",
+	"serde",
+	"system/std",
 ]