client.rs

// Copyright 2015-2018 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity 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.

// Parity 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 Parity.  If not, see <http://www.gnu.org/licenses/>.

use std::collections::{HashSet, BTreeMap, BTreeSet, VecDeque};
use std::fmt;
use std::str::FromStr;
use std::sync::atomic::{AtomicUsize, AtomicBool, Ordering as AtomicOrdering};
use std::sync::{Arc, Weak};
use std::time::{Instant, Duration};

// util
use hash::keccak;
use bytes::Bytes;
use itertools::Itertools;
use journaldb;
use trie::{TrieSpec, TrieFactory, Trie};
use kvdb::{DBValue, KeyValueDB, DBTransaction};
use util_error::UtilError;

// other
use ethereum_types::{H256, Address, U256};
use block::{IsBlock, LockedBlock, Drain, ClosedBlock, OpenBlock, enact_verified, SealedBlock};
use blockchain::{BlockChain, BlockProvider, TreeRoute, ImportRoute, TransactionAddress, ExtrasInsert};
use client::ancient_import::AncientVerifier;
use client::Error as ClientError;
use client::{
	Nonce, Balance, ChainInfo, BlockInfo, CallContract, TransactionInfo,
	RegistryInfo, ReopenBlock, PrepareOpenBlock, ScheduleInfo, ImportSealedBlock,
	BroadcastProposalBlock, ImportBlock, StateOrBlock, StateInfo, StateClient, Call,
	AccountData, BlockChain as BlockChainTrait, BlockProducer, SealedBlockImporter,
	ClientIoMessage
};
use client::{
	BlockId, TransactionId, UncleId, TraceId, ClientConfig, BlockChainClient,
	TraceFilter, CallAnalytics, BlockImportError, Mode,
	ChainNotify, ChainRoute, PruningInfo, ProvingBlockChainClient, EngineInfo, ChainMessageType,
	IoClient,
};
use encoded;
use engines::{EthEngine, EpochTransition, ForkChoice};
use error::{ImportErrorKind, BlockImportErrorKind, ExecutionError, CallError, BlockError, ImportResult, Error as EthcoreError};
use vm::{EnvInfo, LastHashes};
use evm::Schedule;
use executive::{Executive, Executed, TransactOptions, contract_address};
use factory::{Factories, VmFactory};
use header::{BlockNumber, Header, ExtendedHeader};
use io::{IoChannel, IoError};
use log_entry::LocalizedLogEntry;
use miner::{Miner, MinerService};
use ethcore_miner::pool::VerifiedTransaction;
use parking_lot::{Mutex, RwLock};
use rand::OsRng;
use receipt::{Receipt, LocalizedReceipt};
use snapshot::{self, io as snapshot_io};
use spec::Spec;
use state_db::StateDB;
use state::{self, State};
use trace;
use trace::{TraceDB, ImportRequest as TraceImportRequest, LocalizedTrace, Database as TraceDatabase};
use transaction::{self, LocalizedTransaction, UnverifiedTransaction, SignedTransaction, Transaction, Action};
use types::filter::Filter;
use types::mode::Mode as IpcMode;
use types::ancestry_action::AncestryAction;
use verification;
use verification::{PreverifiedBlock, Verifier};
use verification::queue::BlockQueue;
use views::BlockView;
use parity_machine::{Finalizable, WithMetadata};

// re-export
pub use types::blockchain_info::BlockChainInfo;
pub use types::block_status::BlockStatus;
pub use blockchain::CacheSize as BlockChainCacheSize;
pub use verification::queue::QueueInfo as BlockQueueInfo;

use_contract!(registry, "Registry", "res/contracts/registrar.json");

const MAX_TX_QUEUE_SIZE: usize = 4096;
const MAX_ANCIENT_BLOCKS_QUEUE_SIZE: usize = 4096;
// Max number of blocks imported at once.
const MAX_ANCIENT_BLOCKS_TO_IMPORT: usize = 4;
const MAX_QUEUE_SIZE_TO_SLEEP_ON: usize = 2;
const MIN_HISTORY_SIZE: u64 = 8;

/// Report on the status of a client.
#[derive(Default, Clone, Debug, Eq, PartialEq)]
pub struct ClientReport {
	/// How many blocks have been imported so far.
	pub blocks_imported: usize,
	/// How many transactions have been applied so far.
	pub transactions_applied: usize,
	/// How much gas has been processed so far.
	pub gas_processed: U256,
	/// Memory used by state DB
	pub state_db_mem: usize,
}

impl ClientReport {
	/// Alter internal reporting to reflect the additional `block` has been processed.
	pub fn accrue_block(&mut self, header: &Header, transactions: usize) {
		self.blocks_imported += 1;
		self.transactions_applied += transactions;
		self.gas_processed = self.gas_processed + *header.gas_used();
	}
}

impl<'a> ::std::ops::Sub<&'a ClientReport> for ClientReport {
	type Output = Self;

	fn sub(mut self, other: &'a ClientReport) -> Self {
		let higher_mem = ::std::cmp::max(self.state_db_mem, other.state_db_mem);
		let lower_mem = ::std::cmp::min(self.state_db_mem, other.state_db_mem);

		self.blocks_imported -= other.blocks_imported;
		self.transactions_applied -= other.transactions_applied;
		self.gas_processed = self.gas_processed - other.gas_processed;
		self.state_db_mem = higher_mem - lower_mem;

		self
	}
}

struct SleepState {
	last_activity: Option<Instant>,
	last_autosleep: Option<Instant>,
}

impl SleepState {
	fn new(awake: bool) -> Self {
		SleepState {
			last_activity: match awake { false => None, true => Some(Instant::now()) },
			last_autosleep: match awake { false => Some(Instant::now()), true => None },
		}
	}
}

struct Importer {
	/// Lock used during block import
	pub import_lock: Mutex<()>, // FIXME Maybe wrap the whole `Importer` instead?

	/// Used to verify blocks
	pub verifier: Box<Verifier<Client>>,

	/// Queue containing pending blocks
	pub block_queue: BlockQueue,

	/// Handles block sealing
	pub miner: Arc<Miner>,

	/// Ancient block verifier: import an ancient sequence of blocks in order from a starting epoch
	pub ancient_verifier: AncientVerifier,

	/// Ethereum engine to be used during import
	pub engine: Arc<EthEngine>,
}

/// Blockchain database client backed by a persistent database. Owns and manages a blockchain and a block queue.
/// Call `import_block()` to import a block asynchronously; `flush_queue()` flushes the queue.
pub struct Client {
	/// Flag used to disable the client forever. Not to be confused with `liveness`.
	///
	/// For example, auto-updater will disable client forever if there is a
	/// hard fork registered on-chain that we don't have capability for.
	/// When hard fork block rolls around, the client (if `update` is false)
	/// knows it can't proceed further.
	enabled: AtomicBool,

	/// Operating mode for the client
	mode: Mutex<Mode>,

	chain: RwLock<Arc<BlockChain>>,
	tracedb: RwLock<TraceDB<BlockChain>>,
	engine: Arc<EthEngine>,

	/// Client configuration
	config: ClientConfig,

	/// Database pruning strategy to use for StateDB
	pruning: journaldb::Algorithm,

	/// Client uses this to store blocks, traces, etc.
	db: RwLock<Arc<KeyValueDB>>,

	state_db: RwLock<StateDB>,

	/// Report on the status of client
	report: RwLock<ClientReport>,

	sleep_state: Mutex<SleepState>,

	/// Flag changed by `sleep` and `wake_up` methods. Not to be confused with `enabled`.
	liveness: AtomicBool,
	io_channel: Mutex<IoChannel<ClientIoMessage>>,

	/// List of actors to be notified on certain chain events
	notify: RwLock<Vec<Weak<ChainNotify>>>,

	/// Queued transactions from IO
	queue_transactions: IoChannelQueue,
	/// Ancient blocks import queue
	queue_ancient_blocks: IoChannelQueue,
	/// Queued ancient blocks, make sure they are imported in order.
	queued_ancient_blocks: Arc<RwLock<(
		HashSet<H256>,
		VecDeque<(Header, Bytes, Bytes)>
	)>>,
	ancient_blocks_import_lock: Arc<Mutex<()>>,
	/// Consensus messages import queue
	queue_consensus_message: IoChannelQueue,

	last_hashes: RwLock<VecDeque<H256>>,
	factories: Factories,

	/// Number of eras kept in a journal before they are pruned
	history: u64,

	/// An action to be done if a mode/spec_name change happens
	on_user_defaults_change: Mutex<Option<Box<FnMut(Option<Mode>) + 'static + Send>>>,

	/// Link to a registry object useful for looking up names
	registrar: registry::Registry,
	registrar_address: Option<Address>,

	/// A closure to call when we want to restart the client
	exit_handler: Mutex<Option<Box<Fn(String) + 'static + Send>>>,

	importer: Importer,
}

impl Importer {
	pub fn new(
		config: &ClientConfig,
		engine: Arc<EthEngine>,
		message_channel: IoChannel<ClientIoMessage>,
		miner: Arc<Miner>,
	) -> Result<Importer, ::error::Error> {
		let block_queue = BlockQueue::new(config.queue.clone(), engine.clone(), message_channel.clone(), config.verifier_type.verifying_seal());

		Ok(Importer {
			import_lock: Mutex::new(()),
			verifier: verification::new(config.verifier_type.clone()),
			block_queue,
			miner,
			ancient_verifier: AncientVerifier::new(engine.clone()),
			engine,
		})
	}

	/// This is triggered by a message coming from a block queue when the block is ready for insertion
	pub fn import_verified_blocks(&self, client: &Client) -> usize {

		// Shortcut out if we know we're incapable of syncing the chain.
		if !client.enabled.load(AtomicOrdering::Relaxed) {
			return 0;
		}

		let max_blocks_to_import = 4;
		let (imported_blocks, import_results, invalid_blocks, imported, proposed_blocks, duration, is_empty) = {
			let mut imported_blocks = Vec::with_capacity(max_blocks_to_import);
			let mut invalid_blocks = HashSet::new();
			let mut proposed_blocks = Vec::with_capacity(max_blocks_to_import);
			let mut import_results = Vec::with_capacity(max_blocks_to_import);

			let _import_lock = self.import_lock.lock();
			let blocks = self.block_queue.drain(max_blocks_to_import);
			if blocks.is_empty() {
				return 0;
			}
			trace_time!("import_verified_blocks");
			let start = Instant::now();

			for block in blocks {
				let header = block.header.clone();
				let bytes = block.bytes.clone();
				let hash = header.hash();

				let is_invalid = invalid_blocks.contains(header.parent_hash());
				if is_invalid {
					invalid_blocks.insert(hash);
					continue;
				}

				if let Ok(closed_block) = self.check_and_close_block(block, client) {
					if self.engine.is_proposal(&header) {
						self.block_queue.mark_as_good(&[hash]);
						proposed_blocks.push(bytes);
					} else {
						imported_blocks.push(hash);

						let transactions_len = closed_block.transactions().len();

						let route = self.commit_block(closed_block, &header, &bytes, client);
						import_results.push(route);

						client.report.write().accrue_block(&header, transactions_len);
					}
				} else {
					invalid_blocks.insert(header.hash());
				}
			}

			let imported = imported_blocks.len();
			let invalid_blocks = invalid_blocks.into_iter().collect::<Vec<H256>>();

			if !invalid_blocks.is_empty() {
				self.block_queue.mark_as_bad(&invalid_blocks);
			}
			let is_empty = self.block_queue.mark_as_good(&imported_blocks);
			(imported_blocks, import_results, invalid_blocks, imported, proposed_blocks, start.elapsed(), is_empty)
		};

		{
			if !imported_blocks.is_empty() && is_empty {
				let route = ChainRoute::from(import_results.as_ref());

				if is_empty {
					self.miner.chain_new_blocks(client, &imported_blocks, &invalid_blocks, route.enacted(), route.retracted(), false);
				}

				client.notify(|notify| {
					notify.new_blocks(
						imported_blocks.clone(),
						invalid_blocks.clone(),
						route.clone(),
						Vec::new(),
						proposed_blocks.clone(),
						duration,
					);
				});
			}
		}

		client.db.read().flush().expect("DB flush failed.");
		imported
	}

	fn check_and_close_block(&self, block: PreverifiedBlock, client: &Client) -> Result<LockedBlock, ()> {
		let engine = &*self.engine;
		let header = block.header.clone();

		// Check the block isn't so old we won't be able to enact it.
		let best_block_number = client.chain.read().best_block_number();
		if client.pruning_info().earliest_state > header.number() {
			warn!(target: "client", "Block import failed for #{} ({})\nBlock is ancient (current best block: #{}).", header.number(), header.hash(), best_block_number);
			return Err(());
		}

		// Check if parent is in chain
		let parent = match client.block_header_decoded(BlockId::Hash(*header.parent_hash())) {
			Some(h) => h,
			None => {
				warn!(target: "client", "Block import failed for #{} ({}): Parent not found ({}) ", header.number(), header.hash(), header.parent_hash());
				return Err(());
			}
		};

		let chain = client.chain.read();
		// Verify Block Family
		let verify_family_result = self.verifier.verify_block_family(
			&header,
			&parent,
			engine,
			Some(verification::FullFamilyParams {
				block_bytes: &block.bytes,
				transactions: &block.transactions,
				block_provider: &**chain,
				client
			}),
		);

		if let Err(e) = verify_family_result {
			warn!(target: "client", "Stage 3 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
			return Err(());
		};

		let verify_external_result = self.verifier.verify_block_external(&header, engine);
		if let Err(e) = verify_external_result {
			warn!(target: "client", "Stage 4 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
			return Err(());
		};

		// Enact Verified Block
		let last_hashes = client.build_last_hashes(header.parent_hash());
		let db = client.state_db.read().boxed_clone_canon(header.parent_hash());

		let is_epoch_begin = chain.epoch_transition(parent.number(), *header.parent_hash()).is_some();
		let enact_result = enact_verified(
			block,
			engine,
			client.tracedb.read().tracing_enabled(),
			db,
			&parent,
			last_hashes,
			client.factories.clone(),
			is_epoch_begin,
			&mut chain.ancestry_with_metadata_iter(*header.parent_hash()),
		);

		let mut locked_block = enact_result.map_err(|e| {
			warn!(target: "client", "Block import failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
		})?;

		// Strip receipts for blocks before validate_receipts_transition,
		// if the expected receipts root header does not match.
		// (i.e. allow inconsistency in receipts outcome before the transition block)
		if header.number() < engine.params().validate_receipts_transition
			&& header.receipts_root() != locked_block.block().header().receipts_root()
		{
			locked_block.strip_receipts_outcomes();
		}

		// Final Verification
		if let Err(e) = self.verifier.verify_block_final(&header, locked_block.block().header()) {
			warn!(target: "client", "Stage 5 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
			return Err(());
		}

		Ok(locked_block)
	}

	/// Import a block with transaction receipts.
	///
	/// The block is guaranteed to be the next best blocks in the
	/// first block sequence. Does no sealing or transaction validation.
	fn import_old_block(&self, header: &Header, block_bytes: &[u8], receipts_bytes: &[u8], db: &KeyValueDB, chain: &BlockChain) -> Result<H256, ::error::Error> {
		let receipts = ::rlp::decode_list(receipts_bytes);
		let hash = header.hash();
		let _import_lock = self.import_lock.lock();

		{
			trace_time!("import_old_block");
			// verify the block, passing the chain for updating the epoch verifier.
			let mut rng = OsRng::new().map_err(UtilError::from)?;
			self.ancient_verifier.verify(&mut rng, &header, &chain)?;

			// Commit results
			let mut batch = DBTransaction::new();
			chain.insert_unordered_block(&mut batch, block_bytes, receipts, None, false, true);
			// Final commit to the DB
			db.write_buffered(batch);
			chain.commit();
		}
		db.flush().expect("DB flush failed.");
		Ok(hash)
	}

	// NOTE: the header of the block passed here is not necessarily sealed, as
	// it is for reconstructing the state transition.
	//
	// The header passed is from the original block data and is sealed.
	fn commit_block<B>(&self, block: B, header: &Header, block_data: &[u8], client: &Client) -> ImportRoute where B: IsBlock + Drain {
		let hash = &header.hash();
		let number = header.number();
		let parent = header.parent_hash();
		let chain = client.chain.read();

		// Commit results
		let receipts = block.receipts().to_owned();
		let traces = block.traces().clone().drain();

		assert_eq!(header.hash(), view!(BlockView, block_data).header_view().hash());

		//let traces = From::from(block.traces().clone().unwrap_or_else(Vec::new));

		let mut batch = DBTransaction::new();

		let ancestry_actions = self.engine.ancestry_actions(block.block(), &mut chain.ancestry_with_metadata_iter(*parent));

		let best_hash = chain.best_block_hash();
		let metadata = block.block().metadata().map(Into::into);
		let is_finalized = block.block().is_finalized();

		let new = ExtendedHeader {
			header: header.clone(),
			is_finalized: is_finalized,
			metadata: metadata,
			parent_total_difficulty: chain.block_details(&parent).expect("Parent block is in the database; qed").total_difficulty
		};

		let best = {
			let hash = best_hash;
			let header = chain.block_header_data(&hash)
				.expect("Best block is in the database; qed")
				.decode()
				.expect("Stored block header is valid RLP; qed");
			let details = chain.block_details(&hash)
				.expect("Best block is in the database; qed");

			ExtendedHeader {
				parent_total_difficulty: details.total_difficulty - *header.difficulty(),
				is_finalized: details.is_finalized,
				metadata: details.metadata,

				header: header,
			}
		};

		let route = chain.tree_route(best_hash, *parent).expect("forks are only kept when it has common ancestors; tree route from best to prospective's parent always exists; qed");
		let fork_choice = if route.is_from_route_finalized {
			ForkChoice::Old
		} else {
			self.engine.fork_choice(&new, &best)
		};

		// CHECK! I *think* this is fine, even if the state_root is equal to another
		// already-imported block of the same number.
		// TODO: Prove it with a test.
		let mut state = block.drain();

		// check epoch end signal, potentially generating a proof on the current
		// state.
		self.check_epoch_end_signal(
			&header,
			block_data,
			&receipts,
			&state,
			&chain,
			&mut batch,
			client
		);

		state.journal_under(&mut batch, number, hash).expect("DB commit failed");

		for ancestry_action in ancestry_actions {
			let AncestryAction::MarkFinalized(ancestry) = ancestry_action;
			chain.mark_finalized(&mut batch, ancestry).expect("Engine's ancestry action must be known blocks; qed");
		}

		let route = chain.insert_block(&mut batch, block_data, receipts.clone(), ExtrasInsert {
			fork_choice: fork_choice,
			is_finalized: is_finalized,
			metadata: new.metadata,
		});

		client.tracedb.read().import(&mut batch, TraceImportRequest {
			traces: traces.into(),
			block_hash: hash.clone(),
			block_number: number,
			enacted: route.enacted.clone(),
			retracted: route.retracted.len()
		});

		let is_canon = route.enacted.last().map_or(false, |h| h == hash);
		state.sync_cache(&route.enacted, &route.retracted, is_canon);
		// Final commit to the DB
		client.db.read().write_buffered(batch);
		chain.commit();

		self.check_epoch_end(&header, &chain, client);

		client.update_last_hashes(&parent, hash);

		if let Err(e) = client.prune_ancient(state, &chain) {
			warn!("Failed to prune ancient state data: {}", e);
		}

		route
	}

	// check for epoch end signal and write pending transition if it occurs.
	// state for the given block must be available.
	fn check_epoch_end_signal(
		&self,
		header: &Header,
		block_bytes: &[u8],
		receipts: &[Receipt],
		state_db: &StateDB,
		chain: &BlockChain,
		batch: &mut DBTransaction,
		client: &Client,
	) {
		use engines::EpochChange;

		let hash = header.hash();
		let auxiliary = ::machine::AuxiliaryData {
			bytes: Some(block_bytes),
			receipts: Some(&receipts),
		};

		match self.engine.signals_epoch_end(header, auxiliary) {
			EpochChange::Yes(proof) => {
				use engines::epoch::PendingTransition;
				use engines::Proof;

				let proof = match proof {
					Proof::Known(proof) => proof,
					Proof::WithState(with_state) => {
						let env_info = EnvInfo {
							number: header.number(),
							author: header.author().clone(),
							timestamp: header.timestamp(),
							difficulty: header.difficulty().clone(),
							last_hashes: client.build_last_hashes(header.parent_hash()),
							gas_used: U256::default(),
							gas_limit: u64::max_value().into(),
						};

						let call = move |addr, data| {
							let mut state_db = state_db.boxed_clone();
							let backend = ::state::backend::Proving::new(state_db.as_hashdb_mut());

							let transaction =
								client.contract_call_tx(BlockId::Hash(*header.parent_hash()), addr, data);

							let mut state = State::from_existing(
								backend,
								header.state_root().clone(),
								self.engine.account_start_nonce(header.number()),
								client.factories.clone(),
							).expect("state known to be available for just-imported block; qed");

							let options = TransactOptions::with_no_tracing().dont_check_nonce();
							let res = Executive::new(&mut state, &env_info, self.engine.machine())
								.transact(&transaction, options);

							let res = match res {
								Err(ExecutionError::Internal(e)) =>
									Err(format!("Internal error: {}", e)),
								Err(e) => {
									trace!(target: "client", "Proved call failed: {}", e);
									Ok((Vec::new(), state.drop().1.extract_proof()))
								}
								Ok(res) => Ok((res.output, state.drop().1.extract_proof())),
							};

							res.map(|(output, proof)| (output, proof.into_iter().map(|x| x.into_vec()).collect()))
						};

						match with_state.generate_proof(&call) {
							Ok(proof) => proof,
							Err(e) => {
								warn!(target: "client", "Failed to generate transition proof for block {}: {}", hash, e);
								warn!(target: "client", "Snapshots produced by this client may be incomplete");
								Vec::new()
							}
						}
					}
				};

				debug!(target: "client", "Block {} signals epoch end.", hash);

				let pending = PendingTransition { proof: proof };
				chain.insert_pending_transition(batch, hash, pending);
			},
			EpochChange::No => {},
			EpochChange::Unsure(_) => {
				warn!(target: "client", "Detected invalid engine implementation.");
				warn!(target: "client", "Engine claims to require more block data, but everything provided.");
			}
		}
	}

	// check for ending of epoch and write transition if it occurs.
	fn check_epoch_end<'a>(&self, header: &'a Header, chain: &BlockChain, client: &Client) {
		let is_epoch_end = self.engine.is_epoch_end(
			header,
			&(|hash| client.block_header_decoded(BlockId::Hash(hash))),
			&(|hash| chain.get_pending_transition(hash)), // TODO: limit to current epoch.
		);

		if let Some(proof) = is_epoch_end {
			debug!(target: "client", "Epoch transition at block {}", header.hash());

			let mut batch = DBTransaction::new();
			chain.insert_epoch_transition(&mut batch, header.number(), EpochTransition {
				block_hash: header.hash(),
				block_number: header.number(),
				proof: proof,
			});

			// always write the batch directly since epoch transition proofs are
			// fetched from a DB iterator and DB iterators are only available on
			// flushed data.
			client.db.read().write(batch).expect("DB flush failed");
		}
	}
}

impl Client {
	/// Create a new client with given parameters.
	/// The database is assumed to have been initialized with the correct columns.
	pub fn new(
		config: ClientConfig,
		spec: &Spec,
		db: Arc<KeyValueDB>,
		miner: Arc<Miner>,
		message_channel: IoChannel<ClientIoMessage>,
	) -> Result<Arc<Client>, ::error::Error> {
		let trie_spec = match config.fat_db {
			true => TrieSpec::Fat,
			false => TrieSpec::Secure,
		};

		let trie_factory = TrieFactory::new(trie_spec);
		let factories = Factories {
			vm: VmFactory::new(config.vm_type.clone(), config.jump_table_size),
			trie: trie_factory,
			accountdb: Default::default(),
		};

		let journal_db = journaldb::new(db.clone(), config.pruning, ::db::COL_STATE);
		let mut state_db = StateDB::new(journal_db, config.state_cache_size);
		if state_db.journal_db().is_empty() {
			// Sets the correct state root.
			state_db = spec.ensure_db_good(state_db, &factories)?;
			let mut batch = DBTransaction::new();
			state_db.journal_under(&mut batch, 0, &spec.genesis_header().hash())?;
			db.write(batch).map_err(ClientError::Database)?;
		}

		let gb = spec.genesis_block();
		let chain = Arc::new(BlockChain::new(config.blockchain.clone(), &gb, db.clone()));
		let tracedb = RwLock::new(TraceDB::new(config.tracing.clone(), db.clone(), chain.clone()));

		trace!("Cleanup journal: DB Earliest = {:?}, Latest = {:?}", state_db.journal_db().earliest_era(), state_db.journal_db().latest_era());

		let history = if config.history < MIN_HISTORY_SIZE {
			info!(target: "client", "Ignoring pruning history parameter of {}\
				, falling back to minimum of {}",
				config.history, MIN_HISTORY_SIZE);
			MIN_HISTORY_SIZE
		} else {
			config.history
		};

		if !chain.block_header_data(&chain.best_block_hash()).map_or(true, |h| state_db.journal_db().contains(&h.state_root())) {
			warn!("State root not found for block #{} ({:x})", chain.best_block_number(), chain.best_block_hash());
		}

		let engine = spec.engine.clone();

		let awake = match config.mode { Mode::Dark(..) | Mode::Off => false, _ => true };

		let importer = Importer::new(&config, engine.clone(), message_channel.clone(), miner)?;

		let registrar_address = engine.additional_params().get("registrar").and_then(|s| Address::from_str(s).ok());
		if let Some(ref addr) = registrar_address {
			trace!(target: "client", "Found registrar at {}", addr);
		}

		let client = Arc::new(Client {
			enabled: AtomicBool::new(true),
			sleep_state: Mutex::new(SleepState::new(awake)),
			liveness: AtomicBool::new(awake),
			mode: Mutex::new(config.mode.clone()),
			chain: RwLock::new(chain),
			tracedb: tracedb,
			engine: engine,
			pruning: config.pruning.clone(),
			config: config,
			db: RwLock::new(db),
			state_db: RwLock::new(state_db),
			report: RwLock::new(Default::default()),
			io_channel: Mutex::new(message_channel),
			notify: RwLock::new(Vec::new()),
			queue_transactions: IoChannelQueue::new(MAX_TX_QUEUE_SIZE),
			queue_ancient_blocks: IoChannelQueue::new(MAX_ANCIENT_BLOCKS_QUEUE_SIZE),
			queued_ancient_blocks: Default::default(),
			ancient_blocks_import_lock: Default::default(),
			queue_consensus_message: IoChannelQueue::new(usize::max_value()),
			last_hashes: RwLock::new(VecDeque::new()),
			factories: factories,
			history: history,
			on_user_defaults_change: Mutex::new(None),
			registrar: registry::Registry::default(),
			registrar_address,
			exit_handler: Mutex::new(None),
			importer,
		});

		// prune old states.
		{
			let state_db = client.state_db.read().boxed_clone();
			let chain = client.chain.read();
			client.prune_ancient(state_db, &chain)?;
		}

		// ensure genesis epoch proof in the DB.
		{
			let chain = client.chain.read();
			let gh = spec.genesis_header();
			if chain.epoch_transition(0, gh.hash()).is_none() {
				trace!(target: "client", "No genesis transition found.");

				let proof = client.with_proving_caller(
					BlockId::Number(0),
					|call| client.engine.genesis_epoch_data(&gh, call)
				);
				let proof = match proof {
					Ok(proof) => proof,
					Err(e) => {
						warn!(target: "client", "Error generating genesis epoch data: {}. Snapshots generated may not be complete.", e);
						Vec::new()
					}
				};

				debug!(target: "client", "Obtained genesis transition proof: {:?}", proof);

				let mut batch = DBTransaction::new();
				chain.insert_epoch_transition(&mut batch, 0, EpochTransition {
					block_hash: gh.hash(),
					block_number: 0,
					proof: proof,
				});

				client.db.read().write_buffered(batch);
			}
		}

		// ensure buffered changes are flushed.
		client.db.read().flush().map_err(ClientError::Database)?;
		Ok(client)
	}

	/// Wakes up client if it's a sleep.
	pub fn keep_alive(&self) {
		let should_wake = match *self.mode.lock() {
			Mode::Dark(..) | Mode::Passive(..) => true,
			_ => false,
		};
		if should_wake {
			self.wake_up();
			(*self.sleep_state.lock()).last_activity = Some(Instant::now());
		}
	}

	/// Adds an actor to be notified on certain events
	pub fn add_notify(&self, target: Arc<ChainNotify>) {
		self.notify.write().push(Arc::downgrade(&target));
	}

	/// Set a closure to call when the client wants to be restarted.
	///
	/// The parameter passed to the callback is the name of the new chain spec to use after
	/// the restart.
	pub fn set_exit_handler<F>(&self, f: F) where F: Fn(String) + 'static + Send {
		*self.exit_handler.lock() = Some(Box::new(f));
	}

	/// Returns engine reference.
	pub fn engine(&self) -> &EthEngine {
		&*self.engine
	}

	fn notify<F>(&self, f: F) where F: Fn(&ChainNotify) {
		for np in &*self.notify.read() {
			if let Some(n) = np.upgrade() {
				f(&*n);
			}
		}
	}

	/// Register an action to be done if a mode/spec_name change happens.
	pub fn on_user_defaults_change<F>(&self, f: F) where F: 'static + FnMut(Option<Mode>) + Send {
		*self.on_user_defaults_change.lock() = Some(Box::new(f));
	}

	/// Flush the block import queue.
	pub fn flush_queue(&self) {
		self.importer.block_queue.flush();
		while !self.importer.block_queue.queue_info().is_empty() {
			self.import_verified_blocks();
		}
	}

	/// The env info as of the best block.
	pub fn latest_env_info(&self) -> EnvInfo {
		self.env_info(BlockId::Latest).expect("Best block header always stored; qed")
	}

	/// The env info as of a given block.
	/// returns `None` if the block unknown.
	pub fn env_info(&self, id: BlockId) -> Option<EnvInfo> {
		self.block_header(id).map(|header| {
			EnvInfo {
				number: header.number(),
				author: header.author(),
				timestamp: header.timestamp(),
				difficulty: header.difficulty(),
				last_hashes: self.build_last_hashes(&header.parent_hash()),
				gas_used: U256::default(),
				gas_limit: header.gas_limit(),
			}
		})
	}

	fn build_last_hashes(&self, parent_hash: &H256) -> Arc<LastHashes> {
		{
			let hashes = self.last_hashes.read();
			if hashes.front().map_or(false, |h| h == parent_hash) {
				let mut res = Vec::from(hashes.clone());
				res.resize(256, H256::default());
				return Arc::new(res);
			}
		}
		let mut last_hashes = LastHashes::new();
		last_hashes.resize(256, H256::default());
		last_hashes[0] = parent_hash.clone();
		let chain = self.chain.read();
		for i in 0..255 {
			match chain.block_details(&last_hashes[i]) {
				Some(details) => {
					last_hashes[i + 1] = details.parent.clone();
				},
				None => break,
			}
		}
		let mut cached_hashes = self.last_hashes.write();
		*cached_hashes = VecDeque::from(last_hashes.clone());
		Arc::new(last_hashes)
	}

	/// This is triggered by a message coming from a block queue when the block is ready for insertion
	pub fn import_verified_blocks(&self) -> usize {
		self.importer.import_verified_blocks(self)
	}

	// use a state-proving closure for the given block.
	fn with_proving_caller<F, T>(&self, id: BlockId, with_call: F) -> T
		where F: FnOnce(&::machine::Call) -> T
	{
		let call = |a, d| {
			let tx = self.contract_call_tx(id, a, d);
			let (result, items) = self.prove_transaction(tx, id)
				.ok_or_else(|| format!("Unable to make call. State unavailable?"))?;

			let items = items.into_iter().map(|x| x.to_vec()).collect();
			Ok((result, items))
		};

		with_call(&call)
	}

	// prune ancient states until below the memory limit or only the minimum amount remain.
	fn prune_ancient(&self, mut state_db: StateDB, chain: &BlockChain) -> Result<(), ClientError> {
		let number = match state_db.journal_db().latest_era() {
			Some(n) => n,
			None => return Ok(()),
		};

		// prune all ancient eras until we're below the memory target,
		// but have at least the minimum number of states.
		loop {
			let needs_pruning = state_db.journal_db().is_pruned() &&
				state_db.journal_db().journal_size() >= self.config.history_mem;

			if !needs_pruning { break }
			match state_db.journal_db().earliest_era() {
				Some(era) if era + self.history <= number => {
					trace!(target: "client", "Pruning state for ancient era {}", era);
					match chain.block_hash(era) {
						Some(ancient_hash) => {
							let mut batch = DBTransaction::new();
							state_db.mark_canonical(&mut batch, era, &ancient_hash)?;
							self.db.read().write_buffered(batch);
							state_db.journal_db().flush();
						}
						None =>
							debug!(target: "client", "Missing expected hash for block {}", era),
					}
				}
				_ => break, // means that every era is kept, no pruning necessary.
			}
		}

		Ok(())
	}

	fn update_last_hashes(&self, parent: &H256, hash: &H256) {
		let mut hashes = self.last_hashes.write();
		if hashes.front().map_or(false, |h| h == parent) {
			if hashes.len() > 255 {
				hashes.pop_back();
			}
			hashes.push_front(hash.clone());
		}
	}

	/// Get shared miner reference.
	#[cfg(test)]
	pub fn miner(&self) -> Arc<Miner> {
		self.importer.miner.clone()
	}

	/// Replace io channel. Useful for testing.
	pub fn set_io_channel(&self, io_channel: IoChannel<ClientIoMessage>) {
		*self.io_channel.lock() = io_channel;