Move sc-client into sc-service (#5502)

* Drop client from sc-network and sc-client-db, move LongestChain to sc-client-api

* move leaves, cht, in_mem to sc-client-api, drop client from sc-finality-grandpa

* drop sc-service from sc-rpc

* drop sc-service from sc-consensus-aura

* drop sc-client from manual-seal and babe

* drop sc-client from utils/frame/rpc/system and utils/frame/benchmarking-cli

* drop sc-client from bin/node and bin/node-template

* drop sc-client

* fix tests

* remove check -p sc-client from gitlab.yml

* fix warnings

* fixes ui test

* fix light client tests

* adds associated Client type to AbstractService

* adds UsageProvider to Client

* fixed ui test, again

* tried and failed to get node-cli to compile for wasm

* thanks to tomaka for helping me get node-cli to compile for wasmm

* ui test pls pas 🙏🏾

* all tests passing 🪄

* no_run documentation code

* rm -f documentation code

* ClientProvider

* fix mega trait

* move LongestChain to sc-consensus, use adds minimal bounds to AbstractService::Client

* adds license to sc-consensus

Co-authored-by: Benjamin Kampmann <ben@parity.io>

substrate/client/service/src/builder.rs

@@ -20,14 +20,11 @@ use crate::status_sinks;
 use crate::config::{Configuration, KeystoreConfig, PrometheusConfig, OffchainWorkerConfig};
 use crate::metrics::MetricsService;
 use sc_client_api::{
-	self,
-	BlockchainEvents,
-	backend::RemoteBackend, light::RemoteBlockchain,
-	execution_extensions::ExtensionsFactory,
-	ExecutorProvider, CallExecutor
+	self, BlockchainEvents, backend::RemoteBackend, light::RemoteBlockchain, execution_extensions::ExtensionsFactory,
+	ExecutorProvider, CallExecutor, ForkBlocks, BadBlocks, CloneableSpawn, UsageProvider,
 };
+use crate::client::{Client, ClientConfig};
 use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedSender};
-use sc_client::{Client, ClientConfig};
 use sc_chain_spec::get_extension;
 use sp_consensus::{
 	block_validation::{BlockAnnounceValidator, DefaultBlockAnnounceValidator},
@@ -47,7 +44,7 @@ use sp_runtime::traits::{
 	Block as BlockT, NumberFor, SaturatedConversion, HashFor,
 };
 use sp_api::ProvideRuntimeApi;
-use sc_executor::{NativeExecutor, NativeExecutionDispatch};
+use sc_executor::{NativeExecutor, NativeExecutionDispatch, RuntimeInfo};
 use std::{
 	collections::HashMap,
 	io::{Read, Write, Seek},
@@ -57,7 +54,11 @@ use wasm_timer::SystemTime;
 use sc_telemetry::{telemetry, SUBSTRATE_INFO};
 use sp_transaction_pool::{MaintainedTransactionPool, ChainEvent};
 use sp_blockchain;
-use prometheus_endpoint::Registry as PrometheusRegistry;
+use prometheus_endpoint::Registry;
+use sc_client_db::{Backend, DatabaseSettings};
+use sp_core::traits::CodeExecutor;
+use sp_runtime::BuildStorage;
+use sc_client_api::execution_extensions::ExecutionExtensions;
 
 pub type BackgroundTask = Pin<Box<dyn Future<Output=()> + Send>>;
 
@@ -111,7 +112,7 @@ pub type TFullClient<TBl, TRtApi, TExecDisp> = Client<
 pub type TFullBackend<TBl> = sc_client_db::Backend<TBl>;
 
 /// Full client call executor type.
-pub type TFullCallExecutor<TBl, TExecDisp> = sc_client::LocalCallExecutor<
+pub type TFullCallExecutor<TBl, TExecDisp> = crate::client::LocalCallExecutor<
 	sc_client_db::Backend<TBl>,
 	NativeExecutor<TExecDisp>,
 >;
@@ -125,19 +126,19 @@ pub type TLightClient<TBl, TRtApi, TExecDisp> = Client<
 >;
 
 /// Light client backend type.
-pub type TLightBackend<TBl> = sc_client::light::backend::Backend<
+pub type TLightBackend<TBl> = crate::client::light::backend::Backend<
 	sc_client_db::light::LightStorage<TBl>,
 	HashFor<TBl>,
 >;
 
 /// Light call executor type.
-pub type TLightCallExecutor<TBl, TExecDisp> = sc_client::light::call_executor::GenesisCallExecutor<
-	sc_client::light::backend::Backend<
+pub type TLightCallExecutor<TBl, TExecDisp> = crate::client::light::call_executor::GenesisCallExecutor<
+	crate::client::light::backend::Backend<
 		sc_client_db::light::LightStorage<TBl>,
 		HashFor<TBl>
 	>,
-	sc_client::LocalCallExecutor<
-		sc_client::light::backend::Backend<
+	crate::client::LocalCallExecutor<
+		crate::client::light::backend::Backend<
 			sc_client_db::light::LightStorage<TBl>,
 			HashFor<TBl>
 		>,
@@ -188,11 +189,11 @@ fn new_full_parts<TBl, TRtApi, TExecDisp>(
 	);
 
 	let chain_spec = &config.chain_spec;
-	let fork_blocks = get_extension::<sc_client::ForkBlocks<TBl>>(chain_spec.extensions())
+	let fork_blocks = get_extension::<ForkBlocks<TBl>>(chain_spec.extensions())
 		.cloned()
 		.unwrap_or_default();
 
-	let bad_blocks = get_extension::<sc_client::BadBlocks<TBl>>(chain_spec.extensions())
+	let bad_blocks = get_extension::<BadBlocks<TBl>>(chain_spec.extensions())
 		.cloned()
 		.unwrap_or_default();
 
@@ -210,7 +211,7 @@ fn new_full_parts<TBl, TRtApi, TExecDisp>(
 			Some(keystore.clone()),
 		);
 
-		sc_client_db::new_client(
+		new_client(
 			db_config,
 			executor,
 			chain_spec.as_storage_builder(),
@@ -229,6 +230,52 @@ fn new_full_parts<TBl, TRtApi, TExecDisp>(
 	Ok((client, backend, keystore, task_manager))
 }
 
+
+/// Create an instance of db-backed client.
+pub fn new_client<E, Block, RA>(
+	settings: DatabaseSettings,
+	executor: E,
+	genesis_storage: &dyn BuildStorage,
+	fork_blocks: ForkBlocks<Block>,
+	bad_blocks: BadBlocks<Block>,
+	execution_extensions: ExecutionExtensions<Block>,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	prometheus_registry: Option<Registry>,
+	config: ClientConfig,
+) -> Result<(
+	crate::client::Client<
+		Backend<Block>,
+		crate::client::LocalCallExecutor<Backend<Block>, E>,
+		Block,
+		RA,
+	>,
+	Arc<Backend<Block>>,
+),
+	sp_blockchain::Error,
+>
+	where
+		Block: BlockT,
+		E: CodeExecutor + RuntimeInfo,
+{
+	const CANONICALIZATION_DELAY: u64 = 4096;
+
+	let backend = Arc::new(Backend::new(settings, CANONICALIZATION_DELAY)?);
+	let executor = crate::client::LocalCallExecutor::new(backend.clone(), executor, spawn_handle, config.clone());
+	Ok((
+		crate::client::Client::new(
+			backend.clone(),
+			executor,
+			genesis_storage,
+			fork_blocks,
+			bad_blocks,
+			execution_extensions,
+			prometheus_registry,
+			config,
+		)?,
+		backend,
+	))
+}
+
 impl ServiceBuilder<(), (), (), (), (), (), (), (), (), (), ()> {
 	/// Start the service builder with a configuration.
 	pub fn new_full<TBl: BlockT, TRtApi, TExecDisp: NativeExecutionDispatch + 'static>(
@@ -315,18 +362,18 @@ impl ServiceBuilder<(), (), (), (), (), (), (), (), (), (), ()> {
 			};
 			sc_client_db::light::LightStorage::new(db_settings)?
 		};
-		let light_blockchain = sc_client::light::new_light_blockchain(db_storage);
+		let light_blockchain = crate::client::light::new_light_blockchain(db_storage);
 		let fetch_checker = Arc::new(
-			sc_client::light::new_fetch_checker::<_, TBl, _>(
+			crate::client::light::new_fetch_checker::<_, TBl, _>(
 				light_blockchain.clone(),
 				executor.clone(),
 				Box::new(task_manager.spawn_handle()),
 			),
 		);
 		let fetcher = Arc::new(sc_network::config::OnDemand::new(fetch_checker));
-		let backend = sc_client::light::new_light_backend(light_blockchain);
+		let backend = crate::client::light::new_light_backend(light_blockchain);
 		let remote_blockchain = backend.remote_blockchain();
-		let client = Arc::new(sc_client::light::new_light(
+		let client = Arc::new(crate::client::light::new_light(
 			backend.clone(),
 			config.chain_spec.as_storage_builder(),
 			executor,
@@ -601,7 +648,7 @@ impl<TBl, TRtApi, TCl, TFchr, TSc, TImpQu, TFprb, TFpp, TExPool, TRpc, Backend>
 			sc_transaction_pool::txpool::Options,
 			Arc<TCl>,
 			Option<TFchr>,
-			Option<&PrometheusRegistry>,
+			Option<&Registry>,
 		) -> Result<(UExPool, Option<BackgroundTask>), Error>
 	) -> Result<ServiceBuilder<TBl, TRtApi, TCl, TFchr, TSc, TImpQu, TFprb, TFpp,
 		UExPool, TRpc, Backend>, Error>
@@ -757,7 +804,7 @@ ServiceBuilder<
 	TBl: BlockT,
 	TRtApi: 'static + Send + Sync,
 	TBackend: 'static + sc_client_api::backend::Backend<TBl> + Send,
-	TExec: 'static + sc_client::CallExecutor<TBl> + Send + Sync + Clone,
+	TExec: 'static + CallExecutor<TBl> + Send + Sync + Clone,
 	TSc: Clone,
 	TImpQu: 'static + ImportQueue<TBl>,
 	TExPool: MaintainedTransactionPool<Block=TBl, Hash = <TBl as BlockT>::Hash> + MallocSizeOfWasm + 'static,

substrate/client/service/src/chain_ops.rs

@@ -27,7 +27,7 @@ use sp_runtime::traits::{
 };
 use sp_runtime::generic::{BlockId, SignedBlock};
 use codec::{Decode, Encode, IoReader};
-use sc_client::{Client, LocalCallExecutor};
+use crate::client::{Client, LocalCallExecutor};
 use sp_consensus::{
 	BlockOrigin,
 	import_queue::{IncomingBlock, Link, BlockImportError, BlockImportResult, ImportQueue},

substrate/client/service/src/client/block_rules.rs

@@ -0,0 +1,72 @@
+// Copyright 2020 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/>.
+
+//! Client fixed chain specification rules
+
+use std::collections::{HashMap, HashSet};
+
+use sp_runtime::{
+	traits::{Block as BlockT, NumberFor},
+};
+
+use sc_client_api::{ForkBlocks, BadBlocks};
+
+/// Chain specification rules lookup result.
+pub enum LookupResult<B: BlockT> {
+	/// Specification rules do not contain any special rules about this block
+	NotSpecial,
+	/// The bock is known to be bad and should not be imported
+	KnownBad,
+	/// There is a specified canonical block hash for the given height
+	Expected(B::Hash)
+}
+
+/// Chain-specific block filtering rules.
+///
+/// This holds known bad blocks and known good forks, and
+/// is usually part of the chain spec.
+pub struct BlockRules<B: BlockT> {
+	bad: HashSet<B::Hash>,
+	forks: HashMap<NumberFor<B>, B::Hash>,
+}
+
+impl<B: BlockT> BlockRules<B> {
+	/// New block rules with provided black and white lists.
+	pub fn new(
+		fork_blocks: ForkBlocks<B>,
+		bad_blocks: BadBlocks<B>,
+	) -> Self {
+		Self {
+			bad: bad_blocks.unwrap_or(HashSet::new()),
+			forks: fork_blocks.unwrap_or(vec![]).into_iter().collect(),
+		}
+	}
+
+	/// Check if there's any rule affecting the given block.
+	pub fn lookup(&self, number: NumberFor<B>, hash: &B::Hash) -> LookupResult<B> {
+		if let Some(hash_for_height) = self.forks.get(&number) {
+			if hash_for_height != hash {
+				return LookupResult::Expected(hash_for_height.clone());
+			}
+		}
+
+		if self.bad.contains(hash) {
+			return LookupResult::KnownBad;
+		}
+
+		LookupResult::NotSpecial
+	}
+}

substrate/client/service/src/client/call_executor.rs

@@ -0,0 +1,276 @@
+// Copyright 2017-2020 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, panic::UnwindSafe, result, cell::RefCell};
+use codec::{Encode, Decode};
+use sp_runtime::{
+	generic::BlockId, traits::{Block as BlockT, HashFor, NumberFor},
+};
+use sp_state_machine::{
+	self, OverlayedChanges, Ext, ExecutionManager, StateMachine, ExecutionStrategy,
+	backend::Backend as _, StorageProof,
+};
+use sc_executor::{RuntimeVersion, RuntimeInfo, NativeVersion};
+use sp_externalities::Extensions;
+use sp_core::{NativeOrEncoded, NeverNativeValue, traits::CodeExecutor, offchain::storage::OffchainOverlayedChanges};
+use sp_api::{ProofRecorder, InitializeBlock, StorageTransactionCache};
+use sc_client_api::{backend, call_executor::CallExecutor, CloneableSpawn};
+use super::client::ClientConfig;
+
+/// Call executor that executes methods locally, querying all required
+/// data from local backend.
+pub struct LocalCallExecutor<B, E> {
+	backend: Arc<B>,
+	executor: E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	client_config: ClientConfig,
+}
+
+impl<B, E> LocalCallExecutor<B, E> {
+	/// Creates new instance of local call executor.
+	pub fn new(
+		backend: Arc<B>,
+		executor: E,
+		spawn_handle: Box<dyn CloneableSpawn>,
+		client_config: ClientConfig,
+	) -> Self {
+		LocalCallExecutor {
+			backend,
+			executor,
+			spawn_handle,
+			client_config,
+		}
+	}
+}
+
+impl<B, E> Clone for LocalCallExecutor<B, E> where E: Clone {
+	fn clone(&self) -> Self {
+		LocalCallExecutor {
+			backend: self.backend.clone(),
+			executor: self.executor.clone(),
+			spawn_handle: self.spawn_handle.clone(),
+			client_config: self.client_config.clone(),
+		}
+	}
+}
+
+impl<B, E, Block> CallExecutor<Block> for LocalCallExecutor<B, E>
+where
+	B: backend::Backend<Block>,
+	E: CodeExecutor + RuntimeInfo + Clone + 'static,
+	Block: BlockT,
+{
+	type Error = E::Error;
+
+	type Backend = B;
+
+	fn call(
+		&self,
+		id: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		strategy: ExecutionStrategy,
+		extensions: Option<Extensions>,
+	) -> sp_blockchain::Result<Vec<u8>> {
+		let mut changes = OverlayedChanges::default();
+		let mut offchain_changes = if self.client_config.offchain_indexing_api {
+			OffchainOverlayedChanges::enabled()
+		} else {
+			OffchainOverlayedChanges::disabled()
+		};
+		let changes_trie = backend::changes_tries_state_at_block(
+			id, self.backend.changes_trie_storage()
+		)?;
+		let state = self.backend.state_at(*id)?;
+		let state_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&state);
+		let return_data = StateMachine::new(
+			&state,
+			changes_trie,
+			&mut changes,
+			&mut offchain_changes,
+			&self.executor,
+			method,
+			call_data,
+			extensions.unwrap_or_default(),
+			&state_runtime_code.runtime_code()?,
+			self.spawn_handle.clone(),
+		).execute_using_consensus_failure_handler::<_, NeverNativeValue, fn() -> _>(
+			strategy.get_manager(),
+			None,
+		)?;
+
+		Ok(return_data.into_encoded())
+	}
+
+	fn contextual_call<
+		'a,
+		IB: Fn() -> sp_blockchain::Result<()>,
+		EM: Fn(
+			Result<NativeOrEncoded<R>, Self::Error>,
+			Result<NativeOrEncoded<R>, Self::Error>
+		) -> Result<NativeOrEncoded<R>, Self::Error>,
+		R: Encode + Decode + PartialEq,
+		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+	>(
+		&self,
+		initialize_block_fn: IB,
+		at: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		changes: &RefCell<OverlayedChanges>,
+		offchain_changes: &RefCell<OffchainOverlayedChanges>,
+		storage_transaction_cache: Option<&RefCell<
+			StorageTransactionCache<Block, B::State>
+		>>,
+		initialize_block: InitializeBlock<'a, Block>,
+		execution_manager: ExecutionManager<EM>,
+		native_call: Option<NC>,
+		recorder: &Option<ProofRecorder<Block>>,
+		extensions: Option<Extensions>,
+	) -> Result<NativeOrEncoded<R>, sp_blockchain::Error> where ExecutionManager<EM>: Clone {
+		match initialize_block {
+			InitializeBlock::Do(ref init_block)
+				if init_block.borrow().as_ref().map(|id| id != at).unwrap_or(true) => {
+				initialize_block_fn()?;
+			},
+			// We don't need to initialize the runtime at a block.
+			_ => {},
+		}
+
+		let changes_trie_state = backend::changes_tries_state_at_block(at, self.backend.changes_trie_storage())?;
+		let mut storage_transaction_cache = storage_transaction_cache.map(|c| c.borrow_mut());
+
+		let mut state = self.backend.state_at(*at)?;
+
+		let changes = &mut *changes.borrow_mut();
+		let offchain_changes = &mut *offchain_changes.borrow_mut();
+
+		match recorder {
+			Some(recorder) => {
+				let trie_state = state.as_trie_backend()
+					.ok_or_else(||
+						Box::new(sp_state_machine::ExecutionError::UnableToGenerateProof) as Box<dyn sp_state_machine::Error>
+					)?;
+
+				let state_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&trie_state);
+				// It is important to extract the runtime code here before we create the proof
+				// recorder.
+				let runtime_code = state_runtime_code.runtime_code()?;
+
+				let backend = sp_state_machine::ProvingBackend::new_with_recorder(
+					trie_state,
+					recorder.clone(),
+				);
+
+				let mut state_machine = StateMachine::new(
+					&backend,
+					changes_trie_state,
+					changes,
+					offchain_changes,
+					&self.executor,
+					method,
+					call_data,
+					extensions.unwrap_or_default(),
+					&runtime_code,
+					self.spawn_handle.clone(),
+				);
+				// TODO: https://github.com/paritytech/substrate/issues/4455
+				// .with_storage_transaction_cache(storage_transaction_cache.as_mut().map(|c| &mut **c))
+				state_machine.execute_using_consensus_failure_handler(execution_manager, native_call)
+			},
+			None => {
+				let state_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&state);
+				let runtime_code = state_runtime_code.runtime_code()?;
+				let mut state_machine = StateMachine::new(
+					&state,
+					changes_trie_state,
+					changes,
+					offchain_changes,
+					&self.executor,
+					method,
+					call_data,
+					extensions.unwrap_or_default(),
+					&runtime_code,
+					self.spawn_handle.clone(),
+				).with_storage_transaction_cache(storage_transaction_cache.as_mut().map(|c| &mut **c));
+				state_machine.execute_using_consensus_failure_handler(execution_manager, native_call)
+			}
+		}.map_err(Into::into)
+	}
+
+	fn runtime_version(&self, id: &BlockId<Block>) -> sp_blockchain::Result<RuntimeVersion> {
+		let mut overlay = OverlayedChanges::default();
+		let mut offchain_overlay = OffchainOverlayedChanges::default();
+		let changes_trie_state = backend::changes_tries_state_at_block(
+			id,
+			self.backend.changes_trie_storage(),
+		)?;
+		let state = self.backend.state_at(*id)?;
+		let mut cache = StorageTransactionCache::<Block, B::State>::default();
+		let mut ext = Ext::new(
+			&mut overlay,
+			&mut offchain_overlay,
+			&mut cache,
+			&state,
+			changes_trie_state,
+			None,
+		);
+		let state_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&state);
+		self.executor.runtime_version(&mut ext, &state_runtime_code.runtime_code()?)
+			.map_err(|e| sp_blockchain::Error::VersionInvalid(format!("{:?}", e)).into())
+	}
+
+	fn prove_at_trie_state<S: sp_state_machine::TrieBackendStorage<HashFor<Block>>>(
+		&self,
+		trie_state: &sp_state_machine::TrieBackend<S, HashFor<Block>>,
+		overlay: &mut OverlayedChanges,
+		method: &str,
+		call_data: &[u8]
+	) -> Result<(Vec<u8>, StorageProof), sp_blockchain::Error> {
+		sp_state_machine::prove_execution_on_trie_backend::<_, _, NumberFor<Block>, _>(
+			trie_state,
+			overlay,
+			&self.executor,
+			self.spawn_handle.clone(),
+			method,
+			call_data,
+			&sp_state_machine::backend::BackendRuntimeCode::new(trie_state).runtime_code()?,
+		)
+		.map_err(Into::into)
+	}
+
+	fn native_runtime_version(&self) -> Option<&NativeVersion> {
+		Some(self.executor.native_version())
+	}
+}
+
+impl<B, E, Block> sp_version::GetRuntimeVersion<Block> for LocalCallExecutor<B, E>
+	where
+		B: backend::Backend<Block>,
+		E: CodeExecutor + RuntimeInfo + Clone + 'static,
+		Block: BlockT,
+{
+	fn native_version(&self) -> &sp_version::NativeVersion {
+		self.executor.native_version()
+	}
+
+	fn runtime_version(
+		&self,
+		at: &BlockId<Block>,
+	) -> Result<sp_version::RuntimeVersion, String> {
+		CallExecutor::runtime_version(self, at).map_err(|e| format!("{:?}", e))
+	}
+}

substrate/client/service/src/client/genesis.rs

@@ -0,0 +1,41 @@
+// Copyright 2017-2020 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/>.
+
+//! Tool for creating the genesis block.
+
+use sp_runtime::traits::{Block as BlockT, Header as HeaderT, Hash as HashT, Zero};
+
+/// Create a genesis block, given the initial storage.
+pub fn construct_genesis_block<
+	Block: BlockT
+> (
+	state_root: Block::Hash
+) -> Block {
+	let extrinsics_root = <<<Block as BlockT>::Header as HeaderT>::Hashing as HashT>::trie_root(
+		Vec::new(),
+	);
+
+	Block::new(
+		<<Block as BlockT>::Header as HeaderT>::new(
+			Zero::zero(),
+			extrinsics_root,
+			state_root,
+			Default::default(),
+			Default::default()
+		),
+		Default::default()
+	)
+}

substrate/client/service/src/client/light/backend.rs

@@ -0,0 +1,515 @@
+// Copyright 2017-2020 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/>.
+
+//! Light client backend. Only stores headers and justifications of blocks.
+//! Everything else is requested from full nodes on demand.
+
+use std::collections::HashMap;
+use std::sync::Arc;
+use parking_lot::RwLock;
+
+use codec::{Decode, Encode};
+
+use sp_core::ChangesTrieConfiguration;
+use sp_core::storage::{well_known_keys, ChildInfo};
+use sp_core::offchain::storage::InMemOffchainStorage;
+use sp_state_machine::{
+	Backend as StateBackend, TrieBackend, InMemoryBackend, ChangesTrieTransaction,
+	StorageCollection, ChildStorageCollection,
+};
+use sp_runtime::{generic::BlockId, Justification, Storage};
+use sp_runtime::traits::{Block as BlockT, NumberFor, Zero, Header, HashFor};
+use sp_blockchain::{Error as ClientError, Result as ClientResult};
+use sc_client_api::{
+	backend::{
+		AuxStore, Backend as ClientBackend, BlockImportOperation, RemoteBackend, NewBlockState,
+		PrunableStateChangesTrieStorage,
+	},
+	blockchain::{
+		HeaderBackend as BlockchainHeaderBackend, well_known_cache_keys,
+	},
+	light::Storage as BlockchainStorage,
+	in_mem::check_genesis_storage,
+	UsageInfo,
+};
+use super::blockchain::Blockchain;
+use hash_db::Hasher;
+
+const IN_MEMORY_EXPECT_PROOF: &str = "InMemory state backend has Void error type and always succeeds; qed";
+
+/// Light client backend.
+pub struct Backend<S, H: Hasher> {
+	blockchain: Arc<Blockchain<S>>,
+	genesis_state: RwLock<Option<InMemoryBackend<H>>>,
+	import_lock: RwLock<()>,
+}
+
+/// Light block (header and justification) import operation.
+pub struct ImportOperation<Block: BlockT, S> {
+	header: Option<Block::Header>,
+	cache: HashMap<well_known_cache_keys::Id, Vec<u8>>,
+	leaf_state: NewBlockState,
+	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
+	finalized_blocks: Vec<BlockId<Block>>,
+	set_head: Option<BlockId<Block>>,
+	storage_update: Option<InMemoryBackend<HashFor<Block>>>,
+	changes_trie_config_update: Option<Option<ChangesTrieConfiguration>>,
+	_phantom: std::marker::PhantomData<S>,
+}
+
+/// Either in-memory genesis state, or locally-unavailable state.
+pub enum GenesisOrUnavailableState<H: Hasher> {
+	/// Genesis state - storage values are stored in-memory.
+	Genesis(InMemoryBackend<H>),
+	/// We know that state exists, but all calls will fail with error, because it
+	/// isn't locally available.
+	Unavailable,
+}
+
+impl<S, H: Hasher> Backend<S, H> {
+	/// Create new light backend.
+	pub fn new(blockchain: Arc<Blockchain<S>>) -> Self {
+		Self {
+			blockchain,
+			genesis_state: RwLock::new(None),
+			import_lock: Default::default(),
+		}
+	}
+
+	/// Get shared blockchain reference.
+	pub fn blockchain(&self) -> &Arc<Blockchain<S>> {
+		&self.blockchain
+	}
+}
+
+impl<S: AuxStore, H: Hasher> AuxStore for Backend<S, H> {
+	fn insert_aux<
+		'a,
+		'b: 'a,
+		'c: 'a,
+		I: IntoIterator<Item=&'a(&'c [u8], &'c [u8])>,
+		D: IntoIterator<Item=&'a &'b [u8]>,
+	>(&self, insert: I, delete: D) -> ClientResult<()> {
+		self.blockchain.storage().insert_aux(insert, delete)
+	}
+
+	fn get_aux(&self, key: &[u8]) -> ClientResult<Option<Vec<u8>>> {
+		self.blockchain.storage().get_aux(key)
+	}
+}
+
+impl<S, Block> ClientBackend<Block> for Backend<S, HashFor<Block>>
+	where
+		Block: BlockT,
+		S: BlockchainStorage<Block>,
+		Block::Hash: Ord,
+{
+	type BlockImportOperation = ImportOperation<Block, S>;
+	type Blockchain = Blockchain<S>;
+	type State = GenesisOrUnavailableState<HashFor<Block>>;
+	type OffchainStorage = InMemOffchainStorage;
+
+	fn begin_operation(&self) -> ClientResult<Self::BlockImportOperation> {
+		Ok(ImportOperation {
+			header: None,
+			cache: Default::default(),
+			leaf_state: NewBlockState::Normal,
+			aux_ops: Vec::new(),
+			finalized_blocks: Vec::new(),
+			set_head: None,
+			storage_update: None,
+			changes_trie_config_update: None,
+			_phantom: Default::default(),
+		})
+	}
+
+	fn begin_state_operation(
+		&self,
+		_operation: &mut Self::BlockImportOperation,
+		_block: BlockId<Block>
+	) -> ClientResult<()> {
+		Ok(())
+	}
+
+	fn commit_operation(&self, mut operation: Self::BlockImportOperation) -> ClientResult<()> {
+		if !operation.finalized_blocks.is_empty() {
+			for block in operation.finalized_blocks {
+				self.blockchain.storage().finalize_header(block)?;
+			}
+		}
+
+		if let Some(header) = operation.header {
+			let is_genesis_import = header.number().is_zero();
+			if let Some(new_config) = operation.changes_trie_config_update {
+				operation.cache.insert(well_known_cache_keys::CHANGES_TRIE_CONFIG, new_config.encode());
+			}
+			self.blockchain.storage().import_header(
+				header,
+				operation.cache,
+				operation.leaf_state,
+				operation.aux_ops,
+			)?;
+
+			// when importing genesis block => remember its state
+			if is_genesis_import {
+				*self.genesis_state.write() = operation.storage_update.take();
+			}
+		} else {
+			for (key, maybe_val) in operation.aux_ops {
+				match maybe_val {
+					Some(val) => self.blockchain.storage().insert_aux(
+						&[(&key[..], &val[..])],
+						std::iter::empty(),
+					)?,
+					None => self.blockchain.storage().insert_aux(std::iter::empty(), &[&key[..]])?,
+				}
+			}
+		}
+
+		if let Some(set_head) = operation.set_head {
+			self.blockchain.storage().set_head(set_head)?;
+		}
+
+		Ok(())
+	}
+
+	fn finalize_block(
+		&self,
+		block: BlockId<Block>,
+		_justification: Option<Justification>,
+	) -> ClientResult<()> {
+		self.blockchain.storage().finalize_header(block)
+	}
+
+	fn blockchain(&self) -> &Blockchain<S> {
+		&self.blockchain
+	}
+
+	fn usage_info(&self) -> Option<UsageInfo> {
+		self.blockchain.storage().usage_info()
+	}
+
+	fn changes_trie_storage(&self) -> Option<&dyn PrunableStateChangesTrieStorage<Block>> {
+		None
+	}
+
+	fn offchain_storage(&self) -> Option<Self::OffchainStorage> {
+		None
+	}
+
+	fn state_at(&self, block: BlockId<Block>) -> ClientResult<Self::State> {
+		let block_number = self.blockchain.expect_block_number_from_id(&block)?;
+
+		// special case for genesis block
+		if block_number.is_zero() {
+			if let Some(genesis_state) = self.genesis_state.read().clone() {
+				return Ok(GenesisOrUnavailableState::Genesis(genesis_state));
+			}
+		}
+
+		// else return unavailable state. We do not return error here, because error
+		// would mean that we do not know this state at all. But we know that it exists
+		Ok(GenesisOrUnavailableState::Unavailable)
+	}
+
+	fn revert(
+		&self,
+		_n: NumberFor<Block>,
+		_revert_finalized: bool,
+	) -> ClientResult<NumberFor<Block>> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+
+	fn get_import_lock(&self) -> &RwLock<()> {
+		&self.import_lock
+	}
+}
+
+impl<S, Block> RemoteBackend<Block> for Backend<S, HashFor<Block>>
+where
+	Block: BlockT,
+	S: BlockchainStorage<Block> + 'static,
+	Block::Hash: Ord,
+{
+	fn is_local_state_available(&self, block: &BlockId<Block>) -> bool {
+		self.genesis_state.read().is_some()
+			&& self.blockchain.expect_block_number_from_id(block)
+				.map(|num| num.is_zero())
+				.unwrap_or(false)
+	}
+
+	fn remote_blockchain(&self) -> Arc<dyn super::blockchain::RemoteBlockchain<Block>> {
+		self.blockchain.clone()
+	}
+}
+
+impl<S, Block> BlockImportOperation<Block> for ImportOperation<Block, S>
+	where
+		Block: BlockT,
+		S: BlockchainStorage<Block>,
+		Block::Hash: Ord,
+{
+	type State = GenesisOrUnavailableState<HashFor<Block>>;
+
+	fn state(&self) -> ClientResult<Option<&Self::State>> {
+		// None means 'locally-stateless' backend
+		Ok(None)
+	}
+
+	fn set_block_data(
+		&mut self,
+		header: Block::Header,
+		_body: Option<Vec<Block::Extrinsic>>,
+		_justification: Option<Justification>,
+		state: NewBlockState,
+	) -> ClientResult<()> {
+		self.leaf_state = state;
+		self.header = Some(header);
+		Ok(())
+	}
+
+	fn update_cache(&mut self, cache: HashMap<well_known_cache_keys::Id, Vec<u8>>) {
+		self.cache = cache;
+	}
+
+	fn update_db_storage(
+		&mut self,
+		_update: <Self::State as StateBackend<HashFor<Block>>>::Transaction,
+	) -> ClientResult<()> {
+		// we're not storing anything locally => ignore changes
+		Ok(())
+	}
+
+	fn update_changes_trie(
+		&mut self,
+		_update: ChangesTrieTransaction<HashFor<Block>, NumberFor<Block>>,
+	) -> ClientResult<()> {
+		// we're not storing anything locally => ignore changes
+		Ok(())
+	}
+
+	fn reset_storage(&mut self, input: Storage) -> ClientResult<Block::Hash> {
+		check_genesis_storage(&input)?;
+
+		// changes trie configuration
+		let changes_trie_config = input.top.iter()
+			.find(|(k, _)| &k[..] == well_known_keys::CHANGES_TRIE_CONFIG)
+			.map(|(_, v)| Decode::decode(&mut &v[..])
+				.expect("changes trie configuration is encoded properly at genesis"));
+		self.changes_trie_config_update = Some(changes_trie_config);
+
+		// this is only called when genesis block is imported => shouldn't be performance bottleneck
+		let mut storage: HashMap<Option<ChildInfo>, _> = HashMap::new();
+		storage.insert(None, input.top);
+
+		// create a list of children keys to re-compute roots for
+		let child_delta = input.children_default.iter()
+			.map(|(_storage_key, storage_child)| (storage_child.child_info.clone(), None))
+			.collect::<Vec<_>>();
+
+		// make sure to persist the child storage
+		for (_child_key, storage_child) in input.children_default {
+			storage.insert(Some(storage_child.child_info), storage_child.data);
+		}
+
+		let storage_update = InMemoryBackend::from(storage);
+		let (storage_root, _) = storage_update.full_storage_root(std::iter::empty(), child_delta);
+		self.storage_update = Some(storage_update);
+
+		Ok(storage_root)
+	}
+
+	fn insert_aux<I>(&mut self, ops: I) -> ClientResult<()>
+		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		self.aux_ops.append(&mut ops.into_iter().collect());
+		Ok(())
+	}
+
+	fn update_storage(
+		&mut self,
+		_update: StorageCollection,
+		_child_update: ChildStorageCollection,
+	) -> ClientResult<()> {
+		// we're not storing anything locally => ignore changes
+		Ok(())
+	}
+
+	fn mark_finalized(&mut self, block: BlockId<Block>, _justification: Option<Justification>) -> ClientResult<()> {
+		self.finalized_blocks.push(block);
+		Ok(())
+	}
+
+	fn mark_head(&mut self, block: BlockId<Block>) -> ClientResult<()> {
+		self.set_head = Some(block);
+		Ok(())
+	}
+}
+
+impl<H: Hasher> std::fmt::Debug for GenesisOrUnavailableState<H> {
+	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => state.fmt(f),
+			GenesisOrUnavailableState::Unavailable => write!(f, "Unavailable"),
+		}
+	}
+}
+
+impl<H: Hasher> StateBackend<H> for GenesisOrUnavailableState<H>
+	where
+		H::Out: Ord + codec::Codec,
+{
+	type Error = ClientError;
+	type Transaction = <InMemoryBackend<H> as StateBackend<H>>::Transaction;
+	type TrieBackendStorage = <InMemoryBackend<H> as StateBackend<H>>::TrieBackendStorage;
+
+	fn storage(&self, key: &[u8]) -> ClientResult<Option<Vec<u8>>> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				Ok(state.storage(key).expect(IN_MEMORY_EXPECT_PROOF)),
+			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn child_storage(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> ClientResult<Option<Vec<u8>>> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				Ok(state.child_storage(child_info, key).expect(IN_MEMORY_EXPECT_PROOF)),
+			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				Ok(state.next_storage_key(key).expect(IN_MEMORY_EXPECT_PROOF)),
+			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn next_child_storage_key(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> Result<Option<Vec<u8>>, Self::Error> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => Ok(
+				state.next_child_storage_key(child_info, key)
+					.expect(IN_MEMORY_EXPECT_PROOF)
+			),
+			GenesisOrUnavailableState::Unavailable => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn for_keys_with_prefix<A: FnMut(&[u8])>(&self, prefix: &[u8], action: A) {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => state.for_keys_with_prefix(prefix, action),
+			GenesisOrUnavailableState::Unavailable => (),
+		}
+	}
+
+	fn for_key_values_with_prefix<A: FnMut(&[u8], &[u8])>(&self, prefix: &[u8], action: A) {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => state.for_key_values_with_prefix(prefix, action),
+			GenesisOrUnavailableState::Unavailable => (),
+		}
+	}
+
+	fn for_keys_in_child_storage<A: FnMut(&[u8])>(
+		&self,
+		child_info: &ChildInfo,
+		action: A,
+	) {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				state.for_keys_in_child_storage(child_info, action),
+			GenesisOrUnavailableState::Unavailable => (),
+		}
+	}
+
+	fn for_child_keys_with_prefix<A: FnMut(&[u8])>(
+		&self,
+		child_info: &ChildInfo,
+		prefix: &[u8],
+		action: A,
+	) {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				state.for_child_keys_with_prefix(child_info, prefix, action),
+			GenesisOrUnavailableState::Unavailable => (),
+		}
+	}
+
+	fn storage_root<I>(&self, delta: I) -> (H::Out, Self::Transaction)
+	where
+		I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) =>
+				state.storage_root(delta),
+			GenesisOrUnavailableState::Unavailable => Default::default(),
+		}
+	}
+
+	fn child_storage_root<I>(
+		&self,
+		child_info: &ChildInfo,
+		delta: I,
+	) -> (H::Out, bool, Self::Transaction)
+	where
+		I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
+	{
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => {
+				let (root, is_equal, _) = state.child_storage_root(child_info, delta);
+				(root, is_equal, Default::default())
+			},
+			GenesisOrUnavailableState::Unavailable =>
+				(H::Out::default(), true, Default::default()),
+		}
+	}
+
+	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => state.pairs(),
+			GenesisOrUnavailableState::Unavailable => Vec::new(),
+		}
+	}
+
+	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
+		match *self {
+			GenesisOrUnavailableState::Genesis(ref state) => state.keys(prefix),
+			GenesisOrUnavailableState::Unavailable => Vec::new(),
+		}
+	}
+
+	fn register_overlay_stats(&mut self, _stats: &sp_state_machine::StateMachineStats) { }
+
+	fn usage_info(&self) -> sp_state_machine::UsageInfo {
+		sp_state_machine::UsageInfo::empty()
+	}
+
+	fn as_trie_backend(&mut self) -> Option<&TrieBackend<Self::TrieBackendStorage, H>> {
+		match self {
+			GenesisOrUnavailableState::Genesis(ref mut state) => state.as_trie_backend(),
+			GenesisOrUnavailableState::Unavailable => None,
+		}
+	}
+}

substrate/client/service/src/client/light/blockchain.rs

@@ -0,0 +1,174 @@
+// Copyright 2017-2020 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/>.
+
+//! Light client blockchain backend. Only stores headers and justifications of recent
+//! blocks. CHT roots are stored for headers of ancient blocks.
+
+use std::sync::Arc;
+
+use sp_runtime::{Justification, generic::BlockId};
+use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero};
+
+use sp_blockchain::{
+	HeaderMetadata, CachedHeaderMetadata,
+	Error as ClientError, Result as ClientResult,
+};
+pub use sc_client_api::{
+	backend::{
+		AuxStore, NewBlockState
+	},
+	blockchain::{
+		Backend as BlockchainBackend, BlockStatus, Cache as BlockchainCache,
+		HeaderBackend as BlockchainHeaderBackend, Info as BlockchainInfo, ProvideCache,
+		well_known_cache_keys,
+	},
+	light::{
+		RemoteBlockchain, LocalOrRemote, Storage
+	},
+	cht,
+};
+use super::fetcher::RemoteHeaderRequest;
+
+/// Light client blockchain.
+pub struct Blockchain<S> {
+	storage: S,
+}
+
+impl<S> Blockchain<S> {
+	/// Create new light blockchain backed with given storage.
+	pub fn new(storage: S) -> Self {
+		Self {
+			storage,
+		}
+	}
+
+	/// Get storage reference.
+	pub fn storage(&self) -> &S {
+		&self.storage
+	}
+}
+
+impl<S, Block> BlockchainHeaderBackend<Block> for Blockchain<S> where Block: BlockT, S: Storage<Block> {
+	fn header(&self, id: BlockId<Block>) -> ClientResult<Option<Block::Header>> {
+		match RemoteBlockchain::header(self, id)? {
+			LocalOrRemote::Local(header) => Ok(Some(header)),
+			LocalOrRemote::Remote(_) => Err(ClientError::NotAvailableOnLightClient),
+			LocalOrRemote::Unknown => Ok(None),
+		}
+	}
+
+	fn info(&self) -> BlockchainInfo<Block> {
+		self.storage.info()
+	}
+
+	fn status(&self, id: BlockId<Block>) -> ClientResult<BlockStatus> {
+		self.storage.status(id)
+	}
+
+	fn number(&self, hash: Block::Hash) -> ClientResult<Option<NumberFor<Block>>> {
+		self.storage.number(hash)
+	}
+
+	fn hash(&self, number: <<Block as BlockT>::Header as HeaderT>::Number) -> ClientResult<Option<Block::Hash>> {
+		self.storage.hash(number)
+	}
+}
+
+impl<S, Block> HeaderMetadata<Block> for Blockchain<S> where Block: BlockT, S: Storage<Block> {
+	type Error = ClientError;
+
+	fn header_metadata(&self, hash: Block::Hash) -> Result<CachedHeaderMetadata<Block>, Self::Error> {
+		self.storage.header_metadata(hash)
+	}
+
+	fn insert_header_metadata(&self, hash: Block::Hash, metadata: CachedHeaderMetadata<Block>) {
+		self.storage.insert_header_metadata(hash, metadata)
+	}
+
+	fn remove_header_metadata(&self, hash: Block::Hash) {
+		self.storage.remove_header_metadata(hash)
+	}
+}
+
+impl<S, Block> BlockchainBackend<Block> for Blockchain<S> where Block: BlockT, S: Storage<Block> {
+	fn body(&self, _id: BlockId<Block>) -> ClientResult<Option<Vec<Block::Extrinsic>>> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+
+	fn justification(&self, _id: BlockId<Block>) -> ClientResult<Option<Justification>> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+
+	fn last_finalized(&self) -> ClientResult<Block::Hash> {
+		self.storage.last_finalized()
+	}
+
+	fn cache(&self) -> Option<Arc<dyn BlockchainCache<Block>>> {
+		self.storage.cache()
+	}
+
+	fn leaves(&self) -> ClientResult<Vec<Block::Hash>> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+
+	fn children(&self, _parent_hash: Block::Hash) -> ClientResult<Vec<Block::Hash>> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+}
+
+impl<S: Storage<Block>, Block: BlockT> ProvideCache<Block> for Blockchain<S> {
+	fn cache(&self) -> Option<Arc<dyn BlockchainCache<Block>>> {
+		self.storage.cache()
+	}
+}
+
+impl<S, Block: BlockT> RemoteBlockchain<Block> for Blockchain<S>
+	where
+		S: Storage<Block>,
+{
+	fn header(&self, id: BlockId<Block>) -> ClientResult<LocalOrRemote<
+		Block::Header,
+		RemoteHeaderRequest<Block::Header>,
+	>> {
+		// first, try to read header from local storage
+		if let Some(local_header) = self.storage.header(id)? {
+			return Ok(LocalOrRemote::Local(local_header));
+		}
+
+		// we need to know block number to check if it's a part of CHT
+		let number = match id {
+			BlockId::Hash(hash) => match self.storage.number(hash)? {
+				Some(number) => number,
+				None => return Ok(LocalOrRemote::Unknown),
+			},
+			BlockId::Number(number) => number,
+		};
+
+		// if the header is genesis (never pruned), non-canonical, or from future => return
+		if number.is_zero() || self.storage.status(BlockId::Number(number))? == BlockStatus::Unknown {
+			return Ok(LocalOrRemote::Unknown);
+		}
+
+		Ok(LocalOrRemote::Remote(RemoteHeaderRequest {
+			cht_root: match self.storage.header_cht_root(cht::size(), number)? {
+				Some(cht_root) => cht_root,
+				None => return Ok(LocalOrRemote::Unknown),
+			},
+			block: number,
+			retry_count: None,
+		}))
+	}
+}

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

@@ -0,0 +1,297 @@
+// Copyright 2017-2020 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/>.
+
+//! Methods that light client could use to execute runtime calls.
+
+use std::{
+	sync::Arc, panic::UnwindSafe, result, cell::RefCell,
+};
+
+use codec::{Encode, Decode};
+use sp_core::{convert_hash, NativeOrEncoded, traits::CodeExecutor, offchain::storage::OffchainOverlayedChanges};
+use sp_runtime::{
+	generic::BlockId, traits::{One, Block as BlockT, Header as HeaderT, HashFor},
+};
+use sp_externalities::Extensions;
+use sp_state_machine::{
+	self, Backend as StateBackend, OverlayedChanges, ExecutionStrategy, create_proof_check_backend,
+	execution_proof_check_on_trie_backend, ExecutionManager, StorageProof, CloneableSpawn,
+};
+use hash_db::Hasher;
+
+use sp_api::{ProofRecorder, InitializeBlock, StorageTransactionCache};
+
+use sp_blockchain::{Error as ClientError, Result as ClientResult};
+
+use sc_client_api::{
+	backend::RemoteBackend,
+	light::RemoteCallRequest,
+	call_executor::CallExecutor,
+};
+use sc_executor::{RuntimeVersion, NativeVersion};
+
+/// Call executor that is able to execute calls only on genesis state.
+///
+/// Trying to execute call on non-genesis state leads to error.
+pub struct GenesisCallExecutor<B, L> {
+	backend: Arc<B>,
+	local: L,
+}
+
+impl<B, L> GenesisCallExecutor<B, L> {
+	/// Create new genesis call executor.
+	pub fn new(backend: Arc<B>, local: L) -> Self {
+		Self { backend, local }
+	}
+}
+
+impl<B, L: Clone> Clone for GenesisCallExecutor<B, L> {
+	fn clone(&self) -> Self {
+		GenesisCallExecutor {
+			backend: self.backend.clone(),
+			local: self.local.clone(),
+		}
+	}
+}
+
+impl<Block, B, Local> CallExecutor<Block> for
+	GenesisCallExecutor<B, Local>
+	where
+		Block: BlockT,
+		B: RemoteBackend<Block>,
+		Local: CallExecutor<Block>,
+{
+	type Error = ClientError;
+
+	type Backend = B;
+
+	fn call(
+		&self,
+		id: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		strategy: ExecutionStrategy,
+		extensions: Option<Extensions>,
+	) -> ClientResult<Vec<u8>> {
+		match self.backend.is_local_state_available(id) {
+			true => self.local.call(id, method, call_data, strategy, extensions),
+			false => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn contextual_call<
+		'a,
+		IB: Fn() -> ClientResult<()>,
+		EM: Fn(
+			Result<NativeOrEncoded<R>, Self::Error>,
+			Result<NativeOrEncoded<R>, Self::Error>
+		) -> Result<NativeOrEncoded<R>, Self::Error>,
+		R: Encode + Decode + PartialEq,
+		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+	>(
+		&self,
+		initialize_block_fn: IB,
+		at: &BlockId<Block>,
+		method: &str,
+		call_data: &[u8],
+		changes: &RefCell<OverlayedChanges>,
+		offchain_changes: &RefCell<OffchainOverlayedChanges>,
+		_: Option<&RefCell<StorageTransactionCache<Block, B::State>>>,
+		initialize_block: InitializeBlock<'a, Block>,
+		_manager: ExecutionManager<EM>,
+		native_call: Option<NC>,
+		recorder: &Option<ProofRecorder<Block>>,
+		extensions: Option<Extensions>,
+	) -> 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>,
+					Result<NativeOrEncoded<R>, Local::Error>,
+				) -> Result<NativeOrEncoded<R>, Local::Error>,
+				_,
+				NC
+			>(
+				&self.local,
+				initialize_block_fn,
+				at,
+				method,
+				call_data,
+				changes,
+				offchain_changes,
+				None,
+				initialize_block,
+				ExecutionManager::NativeWhenPossible,
+				native_call,
+				recorder,
+				extensions,
+			).map_err(|e| ClientError::Execution(Box::new(e.to_string()))),
+			false => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn runtime_version(&self, id: &BlockId<Block>) -> ClientResult<RuntimeVersion> {
+		match self.backend.is_local_state_available(id) {
+			true => self.local.runtime_version(id),
+			false => Err(ClientError::NotAvailableOnLightClient),
+		}
+	}
+
+	fn prove_at_trie_state<S: sp_state_machine::TrieBackendStorage<HashFor<Block>>>(
+		&self,
+		_state: &sp_state_machine::TrieBackend<S, HashFor<Block>>,
+		_changes: &mut OverlayedChanges,
+		_method: &str,
+		_call_data: &[u8],
+	) -> ClientResult<(Vec<u8>, StorageProof)> {
+		Err(ClientError::NotAvailableOnLightClient)
+	}
+
+	fn native_runtime_version(&self) -> Option<&NativeVersion> {
+		None
+	}
+}
+
+/// Prove contextual execution using given block header in environment.
+///
+/// Method is executed using passed header as environment' current block.
+/// Proof includes both environment preparation proof and method execution proof.
+pub fn prove_execution<Block, S, E>(
+	mut state: S,
+	header: Block::Header,
+	executor: &E,
+	method: &str,
+	call_data: &[u8],
+) -> ClientResult<(Vec<u8>, StorageProof)>
+	where
+		Block: BlockT,
+		S: StateBackend<HashFor<Block>>,
+		E: CallExecutor<Block>,
+{
+	let trie_state = state.as_trie_backend()
+		.ok_or_else(||
+			Box::new(sp_state_machine::ExecutionError::UnableToGenerateProof) as
+				Box<dyn sp_state_machine::Error>
+		)?;
+
+	// prepare execution environment + record preparation proof
+	let mut changes = Default::default();
+	let (_, init_proof) = executor.prove_at_trie_state(
+		trie_state,
+		&mut changes,
+		"Core_initialize_block",
+		&header.encode(),
+	)?;
+
+	// execute method + record execution proof
+	let (result, exec_proof) = executor.prove_at_trie_state(
+		&trie_state,
+		&mut changes,
+		method,
+		call_data,
+	)?;
+	let total_proof = StorageProof::merge(vec![init_proof, exec_proof]);
+
+	Ok((result, total_proof))
+}
+
+/// Check remote contextual execution proof using given backend.
+///
+/// Method is executed using passed header as environment' current block.
+/// Proof should include both environment preparation proof and method execution proof.
+pub fn check_execution_proof<Header, E, H>(
+	executor: &E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	request: &RemoteCallRequest<Header>,
+	remote_proof: StorageProof,
+) -> ClientResult<Vec<u8>>
+	where
+		Header: HeaderT,
+		E: CodeExecutor + Clone + 'static,
+		H: Hasher,
+		H::Out: Ord + codec::Codec + 'static,
+{
+	check_execution_proof_with_make_header::<Header, E, H, _>(
+		executor,
+		spawn_handle,
+		request,
+		remote_proof,
+		|header| <Header as HeaderT>::new(
+			*header.number() + One::one(),
+			Default::default(),
+			Default::default(),
+			header.hash(),
+			Default::default(),
+		),
+	)
+}
+
+/// Check remote contextual execution proof using given backend and header factory.
+///
+/// Method is executed using passed header as environment' current block.
+/// Proof should include both environment preparation proof and method execution proof.
+pub fn check_execution_proof_with_make_header<Header, E, H, MakeNextHeader>(
+	executor: &E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	request: &RemoteCallRequest<Header>,
+	remote_proof: StorageProof,
+	make_next_header: MakeNextHeader,
+) -> ClientResult<Vec<u8>>
+	where
+		E: CodeExecutor + Clone + 'static,
+		H: Hasher,
+		Header: HeaderT,
+		H::Out: Ord + codec::Codec + 'static,
+		MakeNextHeader: Fn(&Header) -> Header,
+{
+	let local_state_root = request.header.state_root();
+	let root: H::Out = convert_hash(&local_state_root);
+
+	// prepare execution environment + check preparation proof
+	let mut changes = OverlayedChanges::default();
+	let trie_backend = create_proof_check_backend(root, remote_proof)?;
+	let next_header = make_next_header(&request.header);
+
+	// TODO: Remove when solved: https://github.com/paritytech/substrate/issues/5047
+	let backend_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&trie_backend);
+	let runtime_code = backend_runtime_code.runtime_code()?;
+
+	execution_proof_check_on_trie_backend::<H, Header::Number, _>(
+		&trie_backend,
+		&mut changes,
+		executor,
+		spawn_handle.clone(),
+		"Core_initialize_block",
+		&next_header.encode(),
+		&runtime_code,
+	)?;
+
+	// execute method
+	execution_proof_check_on_trie_backend::<H, Header::Number, _>(
+		&trie_backend,
+		&mut changes,
+		executor,
+		spawn_handle,
+		&request.method,
+		&request.call_data,
+		&runtime_code,
+	)
+	.map_err(Into::into)
+}

substrate/client/service/src/client/light/fetcher.rs

@@ -0,0 +1,341 @@
+// Copyright 2017-2020 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/>.
+
+//! Light client data fetcher. Fetches requested data from remote full nodes.
+
+use std::sync::Arc;
+use std::collections::{BTreeMap, HashMap};
+use std::marker::PhantomData;
+
+use hash_db::{HashDB, Hasher, EMPTY_PREFIX};
+use codec::{Decode, Encode};
+use sp_core::{convert_hash, traits::CodeExecutor};
+use sp_core::storage::{ChildInfo, ChildType};
+use sp_runtime::traits::{
+	Block as BlockT, Header as HeaderT, Hash, HashFor, NumberFor,
+	AtLeast32Bit, CheckedConversion,
+};
+use sp_state_machine::{
+	ChangesTrieRootsStorage, ChangesTrieAnchorBlockId, ChangesTrieConfigurationRange,
+	InMemoryChangesTrieStorage, TrieBackend, read_proof_check, key_changes_proof_check_with_db,
+	read_child_proof_check, CloneableSpawn,
+};
+pub use sp_state_machine::StorageProof;
+use sp_blockchain::{Error as ClientError, Result as ClientResult};
+
+pub use sc_client_api::{
+	light::{
+		RemoteCallRequest, RemoteHeaderRequest, RemoteReadRequest, RemoteReadChildRequest,
+		RemoteChangesRequest, ChangesProof, RemoteBodyRequest, Fetcher, FetchChecker,
+		Storage as BlockchainStorage,
+	},
+	cht,
+};
+use super::blockchain::{Blockchain};
+use super::call_executor::check_execution_proof;
+
+/// Remote data checker.
+pub struct LightDataChecker<E, H, B: BlockT, S: BlockchainStorage<B>> {
+	blockchain: Arc<Blockchain<S>>,
+	executor: E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	_hasher: PhantomData<(B, H)>,
+}
+
+impl<E, H, B: BlockT, S: BlockchainStorage<B>> LightDataChecker<E, H, B, S> {
+	/// Create new light data checker.
+	pub fn new(blockchain: Arc<Blockchain<S>>, executor: E, spawn_handle: Box<dyn CloneableSpawn>) -> Self {
+		Self {
+			blockchain, executor, spawn_handle, _hasher: PhantomData
+		}
+	}
+
+	/// Check remote changes query proof assuming that CHT-s are of given size.
+	pub fn check_changes_proof_with_cht_size(
+		&self,
+		request: &RemoteChangesRequest<B::Header>,
+		remote_proof: ChangesProof<B::Header>,
+		cht_size: NumberFor<B>,
+	) -> ClientResult<Vec<(NumberFor<B>, u32)>>
+		where
+			H: Hasher,
+			H::Out: Ord + codec::Codec,
+	{
+		// since we need roots of all changes tries for the range begin..max
+		// => remote node can't use max block greater that one that we have passed
+		if remote_proof.max_block > request.max_block.0 || remote_proof.max_block < request.last_block.0 {
+			return Err(ClientError::ChangesTrieAccessFailed(format!(
+				"Invalid max_block used by the remote node: {}. Local: {}..{}..{}",
+				remote_proof.max_block, request.first_block.0, request.last_block.0, request.max_block.0,
+			)).into());
+		}
+
+		// check if remote node has responded with extra changes trie roots proofs
+		// all changes tries roots must be in range [request.first_block.0; request.tries_roots.0)
+		let is_extra_first_root = remote_proof.roots.keys().next()
+			.map(|first_root| *first_root < request.first_block.0
+				|| *first_root >= request.tries_roots.0)
+			.unwrap_or(false);
+		let is_extra_last_root = remote_proof.roots.keys().next_back()
+			.map(|last_root| *last_root >= request.tries_roots.0)
+			.unwrap_or(false);
+		if is_extra_first_root || is_extra_last_root {
+			return Err(ClientError::ChangesTrieAccessFailed(format!(
+				"Extra changes tries roots proofs provided by the remote node: [{:?}..{:?}]. Expected in range: [{}; {})",
+				remote_proof.roots.keys().next(), remote_proof.roots.keys().next_back(),
+				request.first_block.0, request.tries_roots.0,
+			)).into());
+		}
+
+		// if request has been composed when some required headers were already pruned
+		// => remote node has sent us CHT-based proof of required changes tries roots
+		// => check that this proof is correct before proceeding with changes proof
+		let remote_max_block = remote_proof.max_block;
+		let remote_roots = remote_proof.roots;
+		let remote_roots_proof = remote_proof.roots_proof;
+		let remote_proof = remote_proof.proof;
+		if !remote_roots.is_empty() {
+			self.check_changes_tries_proof(
+				cht_size,
+				&remote_roots,
+				remote_roots_proof,
+			)?;
+		}
+
+		// and now check the key changes proof + get the changes
+		let mut result = Vec::new();
+		let proof_storage = InMemoryChangesTrieStorage::with_proof(remote_proof);
+		for config_range in &request.changes_trie_configs {
+			let result_range = key_changes_proof_check_with_db::<H, _>(
+				ChangesTrieConfigurationRange {
+					config: config_range.config.as_ref().ok_or(ClientError::ChangesTriesNotSupported)?,
+					zero: config_range.zero.0,
+					end: config_range.end.map(|(n, _)| n),
+				},
+				&RootsStorage {
+					roots: (request.tries_roots.0, &request.tries_roots.2),
+					prev_roots: &remote_roots,
+				},
+				&proof_storage,
+				request.first_block.0,
+				&ChangesTrieAnchorBlockId {
+					hash: convert_hash(&request.last_block.1),
+					number: request.last_block.0,
+				},
+				remote_max_block,
+				request.storage_key.as_ref(),
+				&request.key)
+			.map_err(|err| ClientError::ChangesTrieAccessFailed(err))?;
+			result.extend(result_range);
+		}
+
+		Ok(result)
+	}
+
+	/// Check CHT-based proof for changes tries roots.
+	pub fn check_changes_tries_proof(
+		&self,
+		cht_size: NumberFor<B>,
+		remote_roots: &BTreeMap<NumberFor<B>, B::Hash>,
+		remote_roots_proof: StorageProof,
+	) -> ClientResult<()>
+		where
+			H: Hasher,
+			H::Out: Ord + codec::Codec,
+	{
+		// all the checks are sharing the same storage
+		let storage = remote_roots_proof.into_memory_db();
+
+		// remote_roots.keys() are sorted => we can use this to group changes tries roots
+		// that are belongs to the same CHT
+		let blocks = remote_roots.keys().cloned();
+		cht::for_each_cht_group::<B::Header, _, _, _>(cht_size, blocks, |mut storage, _, cht_blocks| {
+			// get local changes trie CHT root for given CHT
+			// it should be there, because it is never pruned AND request has been composed
+			// when required header has been pruned (=> replaced with CHT)
+			let first_block = cht_blocks.first().cloned()
+				.expect("for_each_cht_group never calls callback with empty groups");
+			let local_cht_root = self.blockchain.storage().changes_trie_cht_root(cht_size, first_block)?
+				.ok_or(ClientError::InvalidCHTProof)?;
+
+			// check changes trie root for every block within CHT range
+			for block in cht_blocks {
+				// check if the proofs storage contains the root
+				// normally this happens in when the proving backend is created, but since
+				// we share the storage for multiple checks, do it here
+				let mut cht_root = H::Out::default();
+				cht_root.as_mut().copy_from_slice(local_cht_root.as_ref());
+				if !storage.contains(&cht_root, EMPTY_PREFIX) {
+					return Err(ClientError::InvalidCHTProof.into());
+				}
+
+				// check proof for single changes trie root
+				let proving_backend = TrieBackend::new(storage, cht_root);
+				let remote_changes_trie_root = remote_roots[&block];
+				cht::check_proof_on_proving_backend::<B::Header, H>(
+					local_cht_root,
+					block,
+					remote_changes_trie_root,
+					&proving_backend,
+				)?;
+
+				// and return the storage to use in following checks
+				storage = proving_backend.into_storage();
+			}
+
+			Ok(storage)
+		}, storage)
+	}
+}
+
+impl<E, Block, H, S> FetchChecker<Block> for LightDataChecker<E, H, Block, S>
+	where
+		Block: BlockT,
+		E: CodeExecutor + Clone + 'static,
+		H: Hasher,
+		H::Out: Ord + codec::Codec + 'static,
+		S: BlockchainStorage<Block>,
+{
+	fn check_header_proof(
+		&self,
+		request: &RemoteHeaderRequest<Block::Header>,
+		remote_header: Option<Block::Header>,
+		remote_proof: StorageProof,
+	) -> ClientResult<Block::Header> {
+		let remote_header = remote_header.ok_or_else(||
+			ClientError::from(ClientError::InvalidCHTProof))?;
+		let remote_header_hash = remote_header.hash();
+		cht::check_proof::<Block::Header, H>(
+			request.cht_root,
+			request.block,
+			remote_header_hash,
+			remote_proof,
+		).map(|_| remote_header)
+	}
+
+	fn check_read_proof(
+		&self,
+		request: &RemoteReadRequest<Block::Header>,
+		remote_proof: StorageProof,
+	) -> ClientResult<HashMap<Vec<u8>, Option<Vec<u8>>>> {
+		read_proof_check::<H, _>(
+			convert_hash(request.header.state_root()),
+			remote_proof,
+			request.keys.iter(),
+		).map_err(Into::into)
+	}
+
+	fn check_read_child_proof(
+		&self,
+		request: &RemoteReadChildRequest<Block::Header>,
+		remote_proof: StorageProof,
+	) -> ClientResult<HashMap<Vec<u8>, Option<Vec<u8>>>> {
+		let child_info = match ChildType::from_prefixed_key(&request.storage_key) {
+			Some((ChildType::ParentKeyId, storage_key)) => ChildInfo::new_default(storage_key),
+			None => return Err("Invalid child type".into()),
+		};
+		read_child_proof_check::<H, _>(
+			convert_hash(request.header.state_root()),
+			remote_proof,
+			&child_info,
+			request.keys.iter(),
+		).map_err(Into::into)
+	}
+
+	fn check_execution_proof(
+		&self,
+		request: &RemoteCallRequest<Block::Header>,
+		remote_proof: StorageProof,
+	) -> ClientResult<Vec<u8>> {
+		check_execution_proof::<_, _, H>(
+			&self.executor,
+			self.spawn_handle.clone(),
+			request,
+			remote_proof,
+		)
+	}
+
+	fn check_changes_proof(
+		&self,
+		request: &RemoteChangesRequest<Block::Header>,
+		remote_proof: ChangesProof<Block::Header>
+	) -> ClientResult<Vec<(NumberFor<Block>, u32)>> {
+		self.check_changes_proof_with_cht_size(request, remote_proof, cht::size())
+	}
+
+	fn check_body_proof(
+		&self,
+		request: &RemoteBodyRequest<Block::Header>,
+		body: Vec<Block::Extrinsic>
+	) -> ClientResult<Vec<Block::Extrinsic>> {
+		// TODO: #2621
+		let extrinsics_root = HashFor::<Block>::ordered_trie_root(
+			body.iter().map(Encode::encode).collect(),
+		);
+		if *request.header.extrinsics_root() == extrinsics_root {
+			Ok(body)
+		} else {
+			Err(format!("RemoteBodyRequest: invalid extrinsics root expected: {} but got {}",
+				*request.header.extrinsics_root(),
+				extrinsics_root,
+			).into())
+		}
+
+	}
+}
+
+/// A view of BTreeMap<Number, Hash> as a changes trie roots storage.
+struct RootsStorage<'a, Number: AtLeast32Bit, Hash: 'a> {
+	roots: (Number, &'a [Hash]),
+	prev_roots: &'a BTreeMap<Number, Hash>,
+}
+
+impl<'a, H, Number, Hash> ChangesTrieRootsStorage<H, Number> for RootsStorage<'a, Number, Hash>
+	where
+		H: Hasher,
+		Number: std::fmt::Display + std::hash::Hash + Clone + AtLeast32Bit + Encode + Decode + Send + Sync + 'static,
+		Hash: 'a + Send + Sync + Clone + AsRef<[u8]>,
+{
+	fn build_anchor(
+		&self,
+		_hash: H::Out,
+	) -> Result<sp_state_machine::ChangesTrieAnchorBlockId<H::Out, Number>, String> {
+		Err("build_anchor is only called when building block".into())
+	}
+
+	fn root(
+		&self,
+		_anchor: &ChangesTrieAnchorBlockId<H::Out, Number>,
+		block: Number,
+	) -> Result<Option<H::Out>, String> {
+		// we can't ask for roots from parallel forks here => ignore anchor
+		let root = if block < self.roots.0 {
+			self.prev_roots.get(&Number::unique_saturated_from(block)).cloned()
+		} else {
+			let index: Option<usize> = block.checked_sub(&self.roots.0).and_then(|index| index.checked_into());
+			match index {
+				Some(index) => self.roots.1.get(index as usize).cloned(),
+				None => None,
+			}
+		};
+
+		Ok(root.map(|root| {
+			let mut hasher_root: H::Out = Default::default();
+			hasher_root.as_mut().copy_from_slice(root.as_ref());
+			hasher_root
+		}))
+	}
+}

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

@@ -0,0 +1,104 @@
+// Copyright 2017-2020 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/>.
+
+//! Light client components.
+
+pub mod backend;
+pub mod blockchain;
+pub mod call_executor;
+pub mod fetcher;
+
+use std::sync::Arc;
+
+use sc_executor::RuntimeInfo;
+use sp_core::traits::CodeExecutor;
+use sp_runtime::BuildStorage;
+use sp_runtime::traits::{Block as BlockT, HashFor};
+use sp_blockchain::Result as ClientResult;
+use prometheus_endpoint::Registry;
+
+use super::call_executor::LocalCallExecutor;
+use super::client::{Client,ClientConfig};
+use sc_client_api::{
+	light::Storage as BlockchainStorage, CloneableSpawn,
+};
+use self::backend::Backend;
+use self::blockchain::Blockchain;
+use self::call_executor::GenesisCallExecutor;
+use self::fetcher::LightDataChecker;
+
+/// Create an instance of light client blockchain backend.
+pub fn new_light_blockchain<B: BlockT, S: BlockchainStorage<B>>(storage: S) -> Arc<Blockchain<S>> {
+	Arc::new(Blockchain::new(storage))
+}
+
+/// Create an instance of light client backend.
+pub fn new_light_backend<B, S>(blockchain: Arc<Blockchain<S>>) -> Arc<Backend<S, HashFor<B>>>
+	where
+		B: BlockT,
+		S: BlockchainStorage<B>,
+{
+	Arc::new(Backend::new(blockchain))
+}
+
+/// Create an instance of light client.
+pub fn new_light<B, S, RA, E>(
+	backend: Arc<Backend<S, HashFor<B>>>,
+	genesis_storage: &dyn BuildStorage,
+	code_executor: E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+	prometheus_registry: Option<Registry>,
+) -> ClientResult<
+		Client<
+			Backend<S, HashFor<B>>,
+			GenesisCallExecutor<
+				Backend<S, HashFor<B>>,
+				LocalCallExecutor<Backend<S, HashFor<B>>, E>
+			>,
+			B,
+			RA
+		>
+	>
+	where
+		B: BlockT,
+		S: BlockchainStorage<B> + 'static,
+		E: CodeExecutor + RuntimeInfo + Clone + 'static,
+{
+	let local_executor = LocalCallExecutor::new(backend.clone(), code_executor, spawn_handle.clone(), ClientConfig::default());
+	let executor = GenesisCallExecutor::new(backend.clone(), local_executor);
+	Client::new(
+		backend,
+		executor,
+		genesis_storage,
+		Default::default(),
+		Default::default(),
+		Default::default(),
+		prometheus_registry,
+		ClientConfig::default(),
+	)
+}
+
+/// Create an instance of fetch data checker.
+pub fn new_fetch_checker<E, B: BlockT, S: BlockchainStorage<B>>(
+	blockchain: Arc<Blockchain<S>>,
+	executor: E,
+	spawn_handle: Box<dyn CloneableSpawn>,
+) -> LightDataChecker<E, HashFor<B>, B, S>
+	where
+		E: CodeExecutor,
+{
+	LightDataChecker::new(blockchain, executor, spawn_handle)
+}

substrate/client/service/src/client/mod.rs

@@ -0,0 +1,54 @@
+// Copyright 2017-2020 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 Client and associated logic.
+//!
+//! The [`Client`] is one of the most important components of Substrate. It mainly comprises two
+//! parts:
+//!
+//! - A database containing the blocks and chain state, generally referred to as
+//! the [`Backend`](sc_client_api::backend::Backend).
+//! - A runtime environment, generally referred to as the [`Executor`](CallExecutor).
+//!
+//! # Initialization
+//!
+//! Creating a [`Client`] is done by calling the `new` method and passing to it a
+//! [`Backend`](sc_client_api::backend::Backend) and an [`Executor`](CallExecutor).
+//!
+//! The former is typically provided by the `sc-client-db` crate.
+//!
+//! The latter typically requires passing one of:
+//!
+//! - A [`LocalCallExecutor`] running the runtime locally.
+//! - A [`RemoteCallExecutor`](light::call_executor::RemoteCallRequest) that will ask a
+//! third-party to perform the executions.
+//! - A [`RemoteOrLocalCallExecutor`](light::call_executor::RemoteOrLocalCallExecutor), combination
+//! of the two.
+//!
+//! Additionally, the fourth generic parameter of the `Client` is a marker type representing
+//! the ways in which the runtime can interface with the outside. Any code that builds a `Client`
+//! is responsible for putting the right marker.
+
+pub mod genesis;
+pub mod light;
+mod call_executor;
+mod client;
+mod block_rules;
+
+pub use self::{
+	call_executor::LocalCallExecutor,
+	client::{new_with_backend, new_in_mem, Client, ClientConfig},
+};

substrate/client/service/src/config.rs

@@ -16,11 +16,11 @@
 
 //! Service configuration.
 
-pub use sc_client::ExecutionStrategies;
 pub use sc_client_db::{Database, PruningMode, DatabaseSettingsSrc as DatabaseConfig};
 pub use sc_network::Multiaddr;
 pub use sc_network::config::{ExtTransport, MultiaddrWithPeerId, NetworkConfiguration, Role, NodeKeyConfig};
 pub use sc_executor::WasmExecutionMethod;
+use sc_client_api::execution_extensions::ExecutionStrategies;
 
 use std::{future::Future, path::{PathBuf, Path}, pin::Pin, net::SocketAddr, sync::Arc};
 pub use sc_transaction_pool::txpool::Options as TransactionPoolOptions;

substrate/client/service/src/lib.rs

@@ -18,6 +18,7 @@
 //! Manages communication between them.
 
 #![warn(missing_docs)]
+#![recursion_limit="128"]
 
 pub mod config;
 #[macro_use]
@@ -26,6 +27,10 @@ pub mod error;
 
 mod metrics;
 mod builder;
+#[cfg(feature = "test-helpers")]
+pub mod client;
+#[cfg(not(feature = "test-helpers"))]
+mod client;
 mod status_sinks;
 mod task_manager;
 
@@ -38,7 +43,7 @@ use wasm_timer::Instant;
 use std::task::{Poll, Context};
 use parking_lot::Mutex;
 
-use sc_client::Client;
+use client::Client;
 use futures::{
 	Future, FutureExt, Stream, StreamExt,
 	compat::*,
@@ -49,13 +54,13 @@ use sc_network::{NetworkService, network_state::NetworkState, PeerId, ReportHand
 use log::{log, warn, debug, error, Level};
 use codec::{Encode, Decode};
 use sp_runtime::generic::BlockId;
-use sp_runtime::traits::{NumberFor, Block as BlockT};
+use sp_runtime::traits::{NumberFor, Block as BlockT, BlockIdTo};
 use parity_util_mem::MallocSizeOf;
 use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver,  TracingUnboundedSender};
 
 pub use self::error::Error;
 pub use self::builder::{
-	new_full_client,
+	new_full_client, new_client,
 	ServiceBuilder, ServiceBuilderCommand, TFullClient, TLightClient, TFullBackend, TLightBackend,
 	TFullCallExecutor, TLightCallExecutor,
 };
@@ -66,7 +71,6 @@ pub use sc_chain_spec::{
 };
 pub use sp_transaction_pool::{TransactionPool, InPoolTransaction, error::IntoPoolError};
 pub use sc_transaction_pool::txpool::Options as TransactionPoolOptions;
-pub use sc_client::FinalityNotifications;
 pub use sc_rpc::Metadata as RpcMetadata;
 pub use sc_executor::NativeExecutionDispatch;
 #[doc(hidden)]
@@ -76,6 +80,17 @@ pub use sc_network::config::{FinalityProofProvider, OnDemand, BoxFinalityProofRe
 pub use sc_tracing::TracingReceiver;
 pub use task_manager::SpawnTaskHandle;
 use task_manager::TaskManager;
+use sp_blockchain::{HeaderBackend, HeaderMetadata, ProvideCache};
+use sp_api::{ProvideRuntimeApi, CallApiAt, ApiExt, ConstructRuntimeApi, ApiErrorExt};
+use sc_client_api::{
+	LockImportRun, Backend as BackendT, ProofProvider, ProvideUncles,
+	StorageProvider, ExecutorProvider, Finalizer, AuxStore, Backend,
+	BlockBackend, BlockchainEvents, CallExecutor, TransactionFor,
+	UsageProvider,
+};
+use sc_block_builder::BlockBuilderProvider;
+use sp_consensus::{block_validation::Chain, BlockImport};
+use sp_block_builder::BlockBuilder;
 
 const DEFAULT_PROTOCOL_ID: &str = "sup";
 
@@ -116,21 +131,104 @@ pub struct Service<TBl, TCl, TSc, TNetStatus, TNet, TTxPool, TOc> {
 
 impl<TBl, TCl, TSc, TNetStatus, TNet, TTxPool, TOc> Unpin for Service<TBl, TCl, TSc, TNetStatus, TNet, TTxPool, TOc> {}
 
+/// Client super trait, use this instead of the concrete Client type.
+pub trait ClientProvider<
+	Block: BlockT,
+	Backend: BackendT<Block>,
+	Executor: CallExecutor<Block>,
+	Runtime: ConstructRuntimeApi<Block, Self>,
+>:
+	HeaderBackend<Block>
+	+ ProvideRuntimeApi<
+		Block,
+		Api = <Runtime as ConstructRuntimeApi<Block, Self>>::RuntimeApi
+	>
+	+ LockImportRun<Block, Backend>
+	+ ProofProvider<Block>
+	+ BlockBuilderProvider<Backend, Block, Self>
+	+ ProvideUncles<Block>
+	+ StorageProvider<Block, Backend>
+	+ Chain<Block>
+	+ HeaderMetadata<Block, Error = sp_blockchain::Error>
+	+ ExecutorProvider<Block, Executor = Executor>
+	+ ProvideCache<Block>
+	+ BlockIdTo<Block, Error = sp_blockchain::Error>
+	+ CallApiAt<
+		Block,
+		Error = sp_blockchain::Error,
+		StateBackend = <Backend as BackendT<Block>>::State
+	>
+	+ BlockImport<
+		Block,
+		Error = sp_consensus::Error,
+		Transaction = TransactionFor<Backend, Block>
+	>
+	+ Finalizer<Block, Backend>
+	+ BlockchainEvents<Block>
+	+ BlockBackend<Block>
+	+ UsageProvider<Block>
+	+ AuxStore
+{}
+
+impl<Block, Backend, Executor, Runtime> ClientProvider<Block, Backend, Executor, Runtime>
+	for
+		Client<Backend, Executor, Block, Runtime>
+	where
+		Block: BlockT,
+		Backend: BackendT<Block>,
+		Executor: CallExecutor<Block>,
+		Runtime: ConstructRuntimeApi<Block, Self>,
+		Self: HeaderBackend<Block>
+			+ ProvideRuntimeApi<
+				Block,
+				Api = <Runtime as ConstructRuntimeApi<Block, Self>>::RuntimeApi
+			>
+			+ LockImportRun<Block, Backend>
+			+ ProofProvider<Block>
+			+ BlockBuilderProvider<Backend, Block, Self>
+			+ ProvideUncles<Block>
+			+ StorageProvider<Block, Backend>
+			+ Chain<Block>
+			+ HeaderMetadata<Block, Error = sp_blockchain::Error>
+			+ ExecutorProvider<Block, Executor = Executor>
+			+ ProvideCache<Block>
+			+ BlockIdTo<Block, Error = sp_blockchain::Error>
+			+ CallApiAt<
+				Block,
+				Error = sp_blockchain::Error,
+				StateBackend = <Backend as BackendT<Block>>::State
+			>
+			+ BlockImport<
+				Block,
+				Error = sp_consensus::Error,
+				Transaction = TransactionFor<Backend, Block>
+			>
+			+ Finalizer<Block, Backend>
+			+ BlockchainEvents<Block>
+			+ BlockBackend<Block>
+			+ UsageProvider<Block>
+			+ AuxStore
+{}
+
 /// Abstraction over a Substrate service.
-pub trait AbstractService: 'static + Future<Output = Result<(), Error>> +
-	Spawn + Send + Unpin {
+pub trait AbstractService: Future<Output = Result<(), Error>> + Send + Unpin + Spawn + 'static {
 	/// Type of block of this chain.
 	type Block: BlockT;
 	/// Backend storage for the client.
-	type Backend: 'static + sc_client_api::backend::Backend<Self::Block>;
+	type Backend: 'static + BackendT<Self::Block>;
 	/// How to execute calls towards the runtime.
-	type CallExecutor: 'static + sc_client::CallExecutor<Self::Block> + Send + Sync + Clone;
+	type CallExecutor: 'static + CallExecutor<Self::Block> + Send + Sync + Clone;
 	/// API that the runtime provides.
 	type RuntimeApi: Send + Sync;
 	/// Chain selection algorithm.
 	type SelectChain: sp_consensus::SelectChain<Self::Block>;
 	/// Transaction pool.
 	type TransactionPool: TransactionPool<Block = Self::Block> + MallocSizeOfWasm;
+	/// The generic Client type, the bounds here are the ones specifically required by
+	/// internal crates like sc_informant.
+	type Client:
+		HeaderMetadata<Self::Block, Error = sp_blockchain::Error> + UsageProvider<Self::Block>
+		+ BlockchainEvents<Self::Block> + HeaderBackend<Self::Block> + Send + Sync;
 
 	/// Get event stream for telemetry connection established events.
 	fn telemetry_on_connect_stream(&self) -> TracingUnboundedReceiver<()>;
@@ -170,7 +268,7 @@ pub trait AbstractService: 'static + Future<Output = Result<(), Error>> +
 	fn rpc_query(&self, mem: &RpcSession, request: &str) -> Pin<Box<dyn Future<Output = Option<String>> + Send>>;
 
 	/// Get shared client instance.
-	fn client(&self) -> Arc<sc_client::Client<Self::Backend, Self::CallExecutor, Self::Block, Self::RuntimeApi>>;
+	fn client(&self) -> Arc<Self::Client>;
 
 	/// Get clone of select chain.
 	fn select_chain(&self) -> Option<Self::SelectChain>;
@@ -198,9 +296,14 @@ impl<TBl, TBackend, TExec, TRtApi, TSc, TExPool, TOc> AbstractService for
 		NetworkService<TBl, TBl::Hash>, TExPool, TOc>
 where
 	TBl: BlockT,
-	TBackend: 'static + sc_client_api::backend::Backend<TBl>,
-	TExec: 'static + sc_client::CallExecutor<TBl> + Send + Sync + Clone,
-	TRtApi: 'static + Send + Sync,
+	TBackend: 'static + Backend<TBl>,
+	TExec: 'static + CallExecutor<TBl, Backend = TBackend> + Send + Sync + Clone,
+	TRtApi: 'static + Send + Sync + ConstructRuntimeApi<TBl, Client<TBackend, TExec, TBl, TRtApi>>,
+	<TRtApi as ConstructRuntimeApi<TBl, Client<TBackend, TExec, TBl, TRtApi>>>::RuntimeApi:
+		sp_api::Core<TBl>
+		+ ApiExt<TBl, StateBackend = TBackend::State>
+		+ ApiErrorExt<Error = sp_blockchain::Error>
+		+ BlockBuilder<TBl>,
 	TSc: sp_consensus::SelectChain<TBl> + 'static + Clone + Send + Unpin,
 	TExPool: 'static + TransactionPool<Block = TBl> + MallocSizeOfWasm,
 	TOc: 'static + Send + Sync,
@@ -211,6 +314,7 @@ where
 	type RuntimeApi = TRtApi;
 	type SelectChain = TSc;
 	type TransactionPool = TExPool;
+	type Client = Client<Self::Backend, Self::CallExecutor, Self::Block, Self::RuntimeApi>;
 
 	fn telemetry_on_connect_stream(&self) -> TracingUnboundedReceiver<()> {
 		let (sink, stream) = tracing_unbounded("mpsc_telemetry_on_connect");
@@ -254,7 +358,7 @@ where
 		)
 	}
 
-	fn client(&self) -> Arc<sc_client::Client<Self::Backend, Self::CallExecutor, Self::Block, Self::RuntimeApi>> {
+	fn client(&self) -> Arc<Self::Client> {
 		self.client.clone()
 	}
 
@@ -326,7 +430,7 @@ impl<TBl, TCl, TSc, TNetStatus, TNet, TTxPool, TOc> Spawn for
 /// The `status_sink` contain a list of senders to send a periodic network status to.
 fn build_network_future<
 	B: BlockT,
-	C: sc_client::BlockchainEvents<B>,
+	C: BlockchainEvents<B>,
 	H: sc_network::ExHashT
 > (
 	role: Role,

substrate/client/service/src/metrics.rs

@@ -18,11 +18,11 @@ use std::convert::TryFrom;
 
 use crate::NetworkStatus;
 use prometheus_endpoint::{register, Gauge, U64, F64, Registry, PrometheusError, Opts, GaugeVec};
-use sc_client::ClientInfo;
 use sc_telemetry::{telemetry, SUBSTRATE_INFO};
 use sp_runtime::traits::{NumberFor, Block, SaturatedConversion, UniqueSaturatedInto};
 use sp_transaction_pool::PoolStatus;
 use sp_utils::metrics::register_globals;
+use sc_client_api::ClientInfo;
 
 use sysinfo::{self, ProcessExt, SystemExt};