// Copyright 2017-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

use crate::{DiscoveryNetBehaviour, config::ProtocolId};
use crate::legacy_proto::{LegacyProto, LegacyProtoOut};
use bytes::BytesMut;
use futures::prelude::*;
use futures03::{StreamExt as _, TryStreamExt as _};
use libp2p::{Multiaddr, PeerId};
use libp2p::core::{ConnectedPoint, nodes::Substream, muxing::StreamMuxerBox};
use libp2p::swarm::{ProtocolsHandler, IntoProtocolsHandler};
use libp2p::swarm::{NetworkBehaviour, NetworkBehaviourAction, PollParameters};
use primitives::storage::StorageKey;
use consensus::{
	BlockOrigin,
	block_validation::BlockAnnounceValidator,
	import_queue::{BlockImportResult, BlockImportError, IncomingBlock, Origin}
};
use codec::{Decode, Encode};
use sr_primitives::{generic::BlockId, ConsensusEngineId, Justification};
use sr_primitives::traits::{
	Block as BlockT, Header as HeaderT, NumberFor, One, Zero,
	CheckedSub, SaturatedConversion
};
use message::{BlockAnnounce, BlockAttributes, Direction, FromBlock, Message, RequestId};
use message::generic::{Message as GenericMessage, ConsensusMessage};
use consensus_gossip::{ConsensusGossip, MessageRecipient as GossipMessageRecipient};
use light_dispatch::{LightDispatch, LightDispatchNetwork, RequestData};
use specialization::NetworkSpecialization;
use sync::{ChainSync, SyncState};
use crate::service::{TransactionPool, ExHashT};
use crate::config::{BoxFinalityProofRequestBuilder, Roles};
use rustc_hex::ToHex;
use std::collections::{BTreeMap, HashMap};
use std::sync::Arc;
use std::fmt::Write;
use std::{cmp, num::NonZeroUsize, time};
use log::{trace, debug, warn, error};
use crate::chain::{Client, FinalityProofProvider};
use client::light::fetcher::{FetchChecker, ChangesProof, StorageProof};
use crate::error;
use util::LruHashSet;

mod util;
pub mod consensus_gossip;
pub mod message;
pub mod event;
pub mod light_dispatch;
pub mod specialization;
pub mod sync;

const REQUEST_TIMEOUT_SEC: u64 = 40;
/// Interval at which we perform time based maintenance
const TICK_TIMEOUT: time::Duration = time::Duration::from_millis(1100);
/// Interval at which we propagate exstrinsics;
const PROPAGATE_TIMEOUT: time::Duration = time::Duration::from_millis(2900);

/// Current protocol version.
pub(crate) const CURRENT_VERSION: u32 = 4;
/// Lowest version we support
pub(crate) const MIN_VERSION: u32 = 3;

// Maximum allowed entries in `BlockResponse`
const MAX_BLOCK_DATA_RESPONSE: u32 = 128;
/// When light node connects to the full node and the full node is behind light node
/// for at least `LIGHT_MAXIMAL_BLOCKS_DIFFERENCE` blocks, we consider it unuseful
/// and disconnect to free connection slot.
const LIGHT_MAXIMAL_BLOCKS_DIFFERENCE: u64 = 8192;

/// Reputation change when a peer is "clogged", meaning that it's not fast enough to process our
/// messages.
const CLOGGED_PEER_REPUTATION_CHANGE: i32 = -(1 << 12);
/// Reputation change when a peer doesn't respond in time to our messages.
const TIMEOUT_REPUTATION_CHANGE: i32 = -(1 << 10);
/// Reputation change when a peer sends us a status message while we already received one.
const UNEXPECTED_STATUS_REPUTATION_CHANGE: i32 = -(1 << 20);
/// Reputation change when we are a light client and a peer is behind us.
const PEER_BEHIND_US_LIGHT_REPUTATION_CHANGE: i32 = -(1 << 8);
/// Reputation change when a peer sends us an extrinsic that we didn't know about.
const GOOD_EXTRINSIC_REPUTATION_CHANGE: i32 = 1 << 7;
/// Reputation change when a peer sends us a bad extrinsic.
const BAD_EXTRINSIC_REPUTATION_CHANGE: i32 = -(1 << 12);
/// We sent an RPC query to the given node, but it failed.
const RPC_FAILED_REPUTATION_CHANGE: i32 = -(1 << 12);
/// We received a message that failed to decode.
const BAD_MESSAGE_REPUTATION_CHANGE: i32 = -(1 << 12);

// Lock must always be taken in order declared here.
pub struct Protocol<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> {
	/// Interval at which we call `tick`.
	tick_timeout: Box<dyn Stream<Item = (), Error = ()> + Send>,
	/// Interval at which we call `propagate_extrinsics`.
	propagate_timeout: Box<dyn Stream<Item = (), Error = ()> + Send>,
	config: ProtocolConfig,
	/// Handler for light client requests.
	light_dispatch: LightDispatch<B>,
	genesis_hash: B::Hash,
	sync: ChainSync<B>,
	specialization: S,
	consensus_gossip: ConsensusGossip<B>,
	context_data: ContextData<B, H>,
	// Connected peers pending Status message.
	handshaking_peers: HashMap<PeerId, HandshakingPeer>,
	/// Used to report reputation changes.
	peerset_handle: peerset::PeersetHandle,
	transaction_pool: Arc<dyn TransactionPool<H, B>>,
	/// When asked for a proof of finality, we use this struct to build one.
	finality_proof_provider: Option<Arc<dyn FinalityProofProvider<B>>>,
	/// Handles opening the unique substream and sending and receiving raw messages.
	behaviour: LegacyProto<Substream<StreamMuxerBox>>,
}

#[derive(Default)]
struct PacketStats {
	bytes_in: u64,
	bytes_out: u64,
	count_in: u64,
	count_out: u64,
}

/// A peer that we are connected to
/// and from whom we have not yet received a Status message.
struct HandshakingPeer {
	timestamp: time::Instant,
}

/// Peer information
#[derive(Debug, Clone)]
struct Peer<B: BlockT, H: ExHashT> {
	info: PeerInfo<B>,
	/// Current block request, if any.
	block_request: Option<(time::Instant, message::BlockRequest<B>)>,
	/// Requests we are no longer insterested in.
	obsolete_requests: HashMap<message::RequestId, time::Instant>,
	/// Holds a set of transactions known to this peer.
	known_extrinsics: LruHashSet<H>,
	/// Holds a set of blocks known to this peer.
	known_blocks: LruHashSet<B::Hash>,
	/// Request counter,
	next_request_id: message::RequestId,
}

/// Info about a peer's known state.
#[derive(Clone, Debug)]
pub struct PeerInfo<B: BlockT> {
	/// Roles
	pub roles: Roles,
	/// Protocol version
	pub protocol_version: u32,
	/// Peer best block hash
	pub best_hash: B::Hash,
	/// Peer best block number
	pub best_number: <B::Header as HeaderT>::Number,
}

struct LightDispatchIn<'a> {
	behaviour: &'a mut LegacyProto<Substream<StreamMuxerBox>>,
	peerset: peerset::PeersetHandle,
}

impl<'a, B: BlockT> LightDispatchNetwork<B> for LightDispatchIn<'a> {
	fn report_peer(&mut self, who: &PeerId, reputation: i32) {
		self.peerset.report_peer(who.clone(), reputation)
	}

	fn disconnect_peer(&mut self, who: &PeerId) {
		self.behaviour.disconnect_peer(who)
	}

	fn send_header_request(&mut self, who: &PeerId, id: RequestId, block: <<B as BlockT>::Header as HeaderT>::Number) {
		let message: Message<B> = message::generic::Message::RemoteHeaderRequest(message::RemoteHeaderRequest {
			id,
			block,
		});

		self.behaviour.send_packet(who, message.encode())
	}

	fn send_read_request(
		&mut self,
		who: &PeerId,
		id: RequestId,
		block: <B as BlockT>::Hash,
		keys: Vec<Vec<u8>>,
	) {
		let message: Message<B> = message::generic::Message::RemoteReadRequest(message::RemoteReadRequest {
			id,
			block,
			keys,
		});

		self.behaviour.send_packet(who, message.encode())
	}

	fn send_read_child_request(
		&mut self,
		who: &PeerId,
		id: RequestId,
		block: <B as BlockT>::Hash,
		storage_key: Vec<u8>,
		keys: Vec<Vec<u8>>,
	) {
		let message: Message<B> = message::generic::Message::RemoteReadChildRequest(message::RemoteReadChildRequest {
			id,
			block,
			storage_key,
			keys,
		});

		self.behaviour.send_packet(who, message.encode())
	}

	fn send_call_request(
		&mut self,
		who: &PeerId,
		id: RequestId,
		block: <B as BlockT>::Hash,
		method: String,
		data: Vec<u8>
	) {
		let message: Message<B> = message::generic::Message::RemoteCallRequest(message::RemoteCallRequest {
			id,
			block,
			method,
			data,
		});

		self.behaviour.send_packet(who, message.encode())
	}

	fn send_changes_request(
		&mut self,
		who: &PeerId,
		id: RequestId,
		first: <B as BlockT>::Hash,
		last: <B as BlockT>::Hash,
		min: <B as BlockT>::Hash,
		max: <B as BlockT>::Hash,
		storage_key: Option<Vec<u8>>,
		key: Vec<u8>,
	) {
		let message: Message<B> = message::generic::Message::RemoteChangesRequest(message::RemoteChangesRequest {
			id,
			first,
			last,
			min,
			max,
			storage_key,
			key,
		});

		self.behaviour.send_packet(who, message.encode())
	}

	fn send_body_request(
		&mut self,
		who: &PeerId,
		id: RequestId,
		fields: BlockAttributes,
		from: FromBlock<<B as BlockT>::Hash, <<B as BlockT>::Header as HeaderT>::Number>,
		to: Option<<B as BlockT>::Hash>,
		direction: Direction,
		max: Option<u32>
	) {
		let message: Message<B> = message::generic::Message::BlockRequest(message::BlockRequest::<B> {
			id,
			fields,
			from,
			to,
			direction,
			max,
		});

		self.behaviour.send_packet(who, message.encode())
	}
}

/// Context for a network-specific handler.
pub trait Context<B: BlockT> {
	/// Adjusts the reputation of the peer. Use this to point out that a peer has been malign or
	/// irresponsible or appeared lazy.
	fn report_peer(&mut self, who: PeerId, reputation: i32);

	/// Force disconnecting from a peer. Use this when a peer misbehaved.
	fn disconnect_peer(&mut self, who: PeerId);

	/// Send a consensus message to a peer.
	fn send_consensus(&mut self, who: PeerId, consensus: ConsensusMessage);

	/// Send a chain-specific message to a peer.
	fn send_chain_specific(&mut self, who: PeerId, message: Vec<u8>);
}

/// Protocol context.
struct ProtocolContext<'a, B: 'a + BlockT, H: 'a + ExHashT> {
	behaviour: &'a mut LegacyProto<Substream<StreamMuxerBox>>,
	context_data: &'a mut ContextData<B, H>,
	peerset_handle: &'a peerset::PeersetHandle,
}

impl<'a, B: BlockT + 'a, H: 'a + ExHashT> ProtocolContext<'a, B, H> {
	fn new(
		context_data: &'a mut ContextData<B, H>,
		behaviour: &'a mut LegacyProto<Substream<StreamMuxerBox>>,
		peerset_handle: &'a peerset::PeersetHandle,
	) -> Self {
		ProtocolContext { context_data, peerset_handle, behaviour }
	}
}

impl<'a, B: BlockT + 'a, H: ExHashT + 'a> Context<B> for ProtocolContext<'a, B, H> {
	fn report_peer(&mut self, who: PeerId, reputation: i32) {
		self.peerset_handle.report_peer(who, reputation)
	}

	fn disconnect_peer(&mut self, who: PeerId) {
		self.behaviour.disconnect_peer(&who)
	}

	fn send_consensus(&mut self, who: PeerId, consensus: ConsensusMessage) {
		send_message::<B> (
			self.behaviour,
			&mut self.context_data.stats,
			&who,
			GenericMessage::Consensus(consensus)
		)
	}

	fn send_chain_specific(&mut self, who: PeerId, message: Vec<u8>) {
		send_message::<B> (
			self.behaviour,
			&mut self.context_data.stats,
			&who,
			GenericMessage::ChainSpecific(message)
		)
	}
}

/// Data necessary to create a context.
struct ContextData<B: BlockT, H: ExHashT> {
	// All connected peers
	peers: HashMap<PeerId, Peer<B, H>>,
	stats: HashMap<&'static str, PacketStats>,
	pub chain: Arc<dyn Client<B>>,
}

/// Configuration for the Substrate-specific part of the networking layer.
#[derive(Clone)]
pub struct ProtocolConfig {
	/// Assigned roles.
	pub roles: Roles,
}

impl Default for ProtocolConfig {
	fn default() -> ProtocolConfig {
		ProtocolConfig {
			roles: Roles::FULL,
		}
	}
}

impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> Protocol<B, S, H> {
	/// Create a new instance.
	pub fn new(
		config: ProtocolConfig,
		chain: Arc<dyn Client<B>>,
		checker: Arc<dyn FetchChecker<B>>,
		specialization: S,
		transaction_pool: Arc<dyn TransactionPool<H, B>>,
		finality_proof_provider: Option<Arc<dyn FinalityProofProvider<B>>>,
		finality_proof_request_builder: Option<BoxFinalityProofRequestBuilder<B>>,
		protocol_id: ProtocolId,
		peerset_config: peerset::PeersetConfig,
		block_announce_validator: Box<dyn BlockAnnounceValidator<B> + Send>
	) -> error::Result<(Protocol<B, S, H>, peerset::PeersetHandle)> {
		let info = chain.info();
		let sync = ChainSync::new(
			config.roles,
			chain.clone(),
			&info,
			finality_proof_request_builder,
			block_announce_validator,
		);
		let (peerset, peerset_handle) = peerset::Peerset::from_config(peerset_config);
		let versions = &((MIN_VERSION as u8)..=(CURRENT_VERSION as u8)).collect::<Vec<u8>>();
		let behaviour = LegacyProto::new(protocol_id, versions, peerset);

		let protocol = Protocol {
			tick_timeout: Box::new(futures_timer::Interval::new(TICK_TIMEOUT).map(|v| Ok::<_, ()>(v)).compat()),
			propagate_timeout: Box::new(futures_timer::Interval::new(PROPAGATE_TIMEOUT).map(|v| Ok::<_, ()>(v)).compat()),
			config,
			context_data: ContextData {
				peers: HashMap::new(),
				stats: HashMap::new(),
				chain,
			},
			light_dispatch: LightDispatch::new(checker),
			genesis_hash: info.chain.genesis_hash,
			sync,
			specialization,
			consensus_gossip: ConsensusGossip::new(),
			handshaking_peers: HashMap::new(),
			transaction_pool,
			finality_proof_provider,
			peerset_handle: peerset_handle.clone(),
			behaviour,
		};

		Ok((protocol, peerset_handle))
	}

	/// Returns the list of all the peers we have an open channel to.
	pub fn open_peers(&self) -> impl Iterator<Item = &PeerId> {
		self.behaviour.open_peers()
	}

	/// Returns true if we have a channel open with this node.
	pub fn is_open(&self, peer_id: &PeerId) -> bool {
		self.behaviour.is_open(peer_id)
	}

	/// Disconnects the given peer if we are connected to it.
	pub fn disconnect_peer(&mut self, peer_id: &PeerId) {
		self.behaviour.disconnect_peer(peer_id)
	}

	/// Returns true if we try to open protocols with the given peer.
	pub fn is_enabled(&self, peer_id: &PeerId) -> bool {
		self.behaviour.is_enabled(peer_id)
	}

	/// Returns the state of the peerset manager, for debugging purposes.
	pub fn peerset_debug_info(&mut self) -> serde_json::Value {
		self.behaviour.peerset_debug_info()
	}

	/// Returns the number of peers we're connected to.
	pub fn num_connected_peers(&self) -> usize {
		self.context_data.peers.values().count()
	}

	/// Returns the number of peers we're connected to and that are being queried.
	pub fn num_active_peers(&self) -> usize {
		self.context_data
			.peers
			.values()
			.filter(|p| p.block_request.is_some())
			.count()
	}

	/// Current global sync state.
	pub fn sync_state(&self) -> SyncState {
		self.sync.status().state
	}

	/// Target sync block number.
	pub fn best_seen_block(&self) -> Option<NumberFor<B>> {
		self.sync.status().best_seen_block
	}

	/// Number of peers participating in syncing.
	pub fn num_sync_peers(&self) -> u32 {
		self.sync.status().num_peers
	}

	/// Number of blocks in the import queue.
	pub fn num_queued_blocks(&self) -> u32 {
		self.sync.status().queued_blocks
	}

	/// Starts a new data demand request.
	///
	/// The parameter contains a `Sender` where the result, once received, must be sent.
	pub(crate) fn add_light_client_request(&mut self, rq: RequestData<B>) {
		self.light_dispatch.add_request(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, rq);
	}

	fn is_light_response(&self, who: &PeerId, response_id: message::RequestId) -> bool {
		self.light_dispatch.is_light_response(&who, response_id)
	}

	fn handle_response(
		&mut self,
		who: PeerId,
		response: &message::BlockResponse<B>
	) -> Option<message::BlockRequest<B>> {
		if let Some(ref mut peer) = self.context_data.peers.get_mut(&who) {
			if let Some(_) = peer.obsolete_requests.remove(&response.id) {
				trace!(target: "sync", "Ignoring obsolete block response packet from {} ({})", who, response.id);
				return None;
			}
			// Clear the request. If the response is invalid peer will be disconnected anyway.
			let request = peer.block_request.take();
			if request.as_ref().map_or(false, |(_, r)| r.id == response.id) {
				return request.map(|(_, r)| r)
			}
			trace!(target: "sync", "Unexpected response packet from {} ({})", who, response.id);
			self.peerset_handle.report_peer(who.clone(), i32::min_value());
			self.behaviour.disconnect_peer(&who);
		}
		None
	}

	fn update_peer_info(&mut self, who: &PeerId) {
		if let Some(info) = self.sync.peer_info(who) {
			if let Some(ref mut peer) = self.context_data.peers.get_mut(who) {
				peer.info.best_hash = info.best_hash;
				peer.info.best_number = info.best_number;
			}
		}
	}

	/// Returns information about all the peers we are connected to after the handshake message.
	pub fn peers_info(&self) -> impl Iterator<Item = (&PeerId, &PeerInfo<B>)> {
		self.context_data.peers.iter().map(|(id, peer)| (id, &peer.info))
	}

	pub fn on_custom_message(
		&mut self,
		who: PeerId,
		data: BytesMut,
	) -> CustomMessageOutcome<B> {

		let message = match <Message<B> as Decode>::decode(&mut &data[..]) {
			Ok(message) => message,
			Err(err) => {
				debug!(target: "sync", "Couldn't decode packet sent by {}: {:?}: {}", who, data, err.what());
				self.peerset_handle.report_peer(who.clone(), BAD_MESSAGE_REPUTATION_CHANGE);
				return CustomMessageOutcome::None;
			}
		};

		let mut stats = self.context_data.stats.entry(message.id()).or_default();
		stats.bytes_in += data.len() as u64;
		stats.count_in += 1;

		match message {
			GenericMessage::Status(s) => self.on_status_message(who, s),
			GenericMessage::BlockRequest(r) => self.on_block_request(who, r),
			GenericMessage::BlockResponse(r) => {
				// Note, this is safe because only `ordinary bodies` and `remote bodies` are received in this matter.
				if self.is_light_response(&who, r.id) {
					self.on_remote_body_response(who, r);
				} else {
					if let Some(request) = self.handle_response(who.clone(), &r) {
						let outcome = self.on_block_response(who.clone(), request, r);
						self.update_peer_info(&who);
						return outcome
					}
				}
			},
			GenericMessage::BlockAnnounce(announce) => {
				let outcome = self.on_block_announce(who.clone(), announce);
				self.update_peer_info(&who);
				return outcome;
			},
			GenericMessage::Transactions(m) =>
				self.on_extrinsics(who, m),
			GenericMessage::RemoteCallRequest(request) => self.on_remote_call_request(who, request),
			GenericMessage::RemoteCallResponse(response) =>
				self.on_remote_call_response(who, response),
			GenericMessage::RemoteReadRequest(request) =>
				self.on_remote_read_request(who, request),
			GenericMessage::RemoteReadResponse(response) =>
				self.on_remote_read_response(who, response),
			GenericMessage::RemoteHeaderRequest(request) =>
				self.on_remote_header_request(who, request),
			GenericMessage::RemoteHeaderResponse(response) =>
				self.on_remote_header_response(who, response),
			GenericMessage::RemoteChangesRequest(request) =>
				self.on_remote_changes_request(who, request),
			GenericMessage::RemoteChangesResponse(response) =>
				self.on_remote_changes_response(who, response),
			GenericMessage::FinalityProofRequest(request) =>
				self.on_finality_proof_request(who, request),
			GenericMessage::FinalityProofResponse(response) =>
				return self.on_finality_proof_response(who, response),
			GenericMessage::RemoteReadChildRequest(request) =>
				self.on_remote_read_child_request(who, request),
			GenericMessage::Consensus(msg) => {
				if self.context_data.peers.get(&who).map_or(false, |peer| peer.info.protocol_version > 2) {
					self.consensus_gossip.on_incoming(
						&mut ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle),
						who,
						msg,
					);
				}
			}
			GenericMessage::ChainSpecific(msg) => self.specialization.on_message(
				&mut ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle),
				who,
				msg,
			),
		}

		CustomMessageOutcome::None
	}

	fn send_request(&mut self, who: &PeerId, message: Message<B>) {
		send_request::<B, H>(
			&mut self.behaviour,
			&mut self.context_data.stats,
			&mut self.context_data.peers,
			who,
			message,
		);
	}

	fn send_message(&mut self, who: &PeerId, message: Message<B>) {
		send_message::<B>(
			&mut self.behaviour,
			&mut self.context_data.stats,
			who,
			message,
		);
	}

	/// Locks `self` and returns a context plus the `ConsensusGossip` struct.
	pub fn consensus_gossip_lock<'a>(
		&'a mut self,
	) -> (impl Context<B> + 'a, &'a mut ConsensusGossip<B>) {
		let context = ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle);
		(context, &mut self.consensus_gossip)
	}

	/// Locks `self` and returns a context plus the network specialization.
	pub fn specialization_lock<'a>(
		&'a mut self,
	) -> (impl Context<B> + 'a, &'a mut S) {
		let context = ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle);
		(context, &mut self.specialization)
	}

	/// Gossip a consensus message to the network.
	pub fn gossip_consensus_message(
		&mut self,
		topic: B::Hash,
		engine_id: ConsensusEngineId,
		message: Vec<u8>,
		recipient: GossipMessageRecipient,
	) {
		let mut context = ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle);
		let message = ConsensusMessage { data: message, engine_id };
		match recipient {
			GossipMessageRecipient::BroadcastToAll =>
				self.consensus_gossip.multicast(&mut context, topic, message, true),
			GossipMessageRecipient::BroadcastNew =>
				self.consensus_gossip.multicast(&mut context, topic, message, false),
			GossipMessageRecipient::Peer(who) =>
				self.send_message(&who, GenericMessage::Consensus(message)),
		}
	}

	/// Called when a new peer is connected
	pub fn on_peer_connected(&mut self, who: PeerId) {
		trace!(target: "sync", "Connecting {}", who);
		self.handshaking_peers.insert(who.clone(), HandshakingPeer { timestamp: time::Instant::now() });
		self.send_status(who);
	}

	/// Called by peer when it is disconnecting
	pub fn on_peer_disconnected(&mut self, peer: PeerId) {
		trace!(target: "sync", "Disconnecting {}", peer);
		// lock all the the peer lists so that add/remove peer events are in order
		let removed = {
			self.handshaking_peers.remove(&peer);
			self.context_data.peers.remove(&peer)
		};
		if let Some(peer_data) = removed {
			let mut context = ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle);
			if peer_data.info.protocol_version > 2 {
				self.consensus_gossip.peer_disconnected(&mut context, peer.clone());
			}
			self.sync.peer_disconnected(peer.clone());
			self.specialization.on_disconnect(&mut context, peer.clone());
			self.light_dispatch.on_disconnect(LightDispatchIn {
				behaviour: &mut self.behaviour,
				peerset: self.peerset_handle.clone(),
			}, peer);
		}
	}

	/// Called as a back-pressure mechanism if the networking detects that the peer cannot process
	/// our messaging rate fast enough.
	pub fn on_clogged_peer(&self, who: PeerId, _msg: Option<Message<B>>) {
		self.peerset_handle.report_peer(who.clone(), CLOGGED_PEER_REPUTATION_CHANGE);

		// Print some diagnostics.
		if let Some(peer) = self.context_data.peers.get(&who) {
			debug!(target: "sync", "Clogged peer {} (protocol_version: {:?}; roles: {:?}; \
				known_extrinsics: {:?}; known_blocks: {:?}; best_hash: {:?}; best_number: {:?})",
				who, peer.info.protocol_version, peer.info.roles, peer.known_extrinsics, peer.known_blocks,
				peer.info.best_hash, peer.info.best_number);
		} else {
			debug!(target: "sync", "Peer clogged before being properly connected");
		}
	}

	fn on_block_request(
		&mut self,
		peer: PeerId,
		request: message::BlockRequest<B>
	) {
		trace!(target: "sync", "BlockRequest {} from {}: from {:?} to {:?} max {:?}",
			request.id,
			peer,
			request.from,
			request.to,
			request.max);

		// sending block requests to the node that is unable to serve it is considered a bad behavior
		if !self.config.roles.is_full() {
			trace!(target: "sync", "Peer {} is trying to sync from the light node", peer);
			self.behaviour.disconnect_peer(&peer);
			self.peerset_handle.report_peer(peer, i32::min_value());
			return;
		}

		let mut blocks = Vec::new();
		let mut id = match request.from {
			message::FromBlock::Hash(h) => BlockId::Hash(h),
			message::FromBlock::Number(n) => BlockId::Number(n),
		};
		let max = cmp::min(request.max.unwrap_or(u32::max_value()), MAX_BLOCK_DATA_RESPONSE) as usize;
		let get_header = request.fields.contains(message::BlockAttributes::HEADER);
		let get_body = request.fields.contains(message::BlockAttributes::BODY);
		let get_justification = request
			.fields
			.contains(message::BlockAttributes::JUSTIFICATION);
		while let Some(header) = self.context_data.chain.header(&id).unwrap_or(None) {
			if blocks.len() >= max {
				break;
			}
			let number = header.number().clone();
			let hash = header.hash();
			let parent_hash = header.parent_hash().clone();
			let justification = if get_justification {
				self.context_data.chain.justification(&BlockId::Hash(hash)).unwrap_or(None)
			} else {
				None
			};
			let block_data = message::generic::BlockData {
				hash: hash,
				header: if get_header { Some(header) } else { None },
				body: if get_body {
					self.context_data
						.chain
						.body(&BlockId::Hash(hash))
						.unwrap_or(None)
				} else {
					None
				},
				receipt: None,
				message_queue: None,
				justification,
			};
			blocks.push(block_data);
			match request.direction {
				message::Direction::Ascending => id = BlockId::Number(number + One::one()),
				message::Direction::Descending => {
					if number.is_zero() {
						break;
					}
					id = BlockId::Hash(parent_hash)
				}
			}
		}
		let response = message::generic::BlockResponse {
			id: request.id,
			blocks: blocks,
		};
		trace!(target: "sync", "Sending BlockResponse with {} blocks", response.blocks.len());
		self.send_message(&peer, GenericMessage::BlockResponse(response))
	}

	/// Adjusts the reputation of a node.
	pub fn report_peer(&self, who: PeerId, reputation: i32) {
		self.peerset_handle.report_peer(who, reputation)
	}

	fn on_block_response(
		&mut self,
		peer: PeerId,
		request: message::BlockRequest<B>,
		response: message::BlockResponse<B>,
	) -> CustomMessageOutcome<B> {
		let blocks_range = match (
			response.blocks.first().and_then(|b| b.header.as_ref().map(|h| h.number())),
			response.blocks.last().and_then(|b| b.header.as_ref().map(|h| h.number())),
		) {
			(Some(first), Some(last)) if first != last => format!(" ({}..{})", first, last),
			(Some(first), Some(_)) => format!(" ({})", first),
			_ => Default::default(),
		};
		trace!(target: "sync", "BlockResponse {} from {} with {} blocks {}",
			response.id,
			peer,
			response.blocks.len(),
			blocks_range
		);

		// TODO [andre]: move this logic to the import queue so that
		// justifications are imported asynchronously (#1482)
		if request.fields == message::BlockAttributes::JUSTIFICATION {
			match self.sync.on_block_justification(peer, response) {
				Ok(sync::OnBlockJustification::Nothing) => CustomMessageOutcome::None,
				Ok(sync::OnBlockJustification::Import { peer, hash, number, justification }) =>
					CustomMessageOutcome::JustificationImport(peer, hash, number, justification),
				Err(sync::BadPeer(id, repu)) => {
					self.behaviour.disconnect_peer(&id);
					self.peerset_handle.report_peer(id, repu);
					CustomMessageOutcome::None
				}
			}
		} else {
			match self.sync.on_block_data(peer, request, response) {
				Ok(sync::OnBlockData::Import(origin, blocks)) =>
					CustomMessageOutcome::BlockImport(origin, blocks),
				Ok(sync::OnBlockData::Request(peer, req)) => {
					self.send_request(&peer, GenericMessage::BlockRequest(req));
					CustomMessageOutcome::None
				}
				Err(sync::BadPeer(id, repu)) => {
					self.behaviour.disconnect_peer(&id);
					self.peerset_handle.report_peer(id, repu);
					CustomMessageOutcome::None
				}
			}
		}
	}

	/// Perform time based maintenance.
	///
	/// > **Note**: This method normally doesn't have to be called except for testing purposes.
	pub fn tick(&mut self) {
		self.consensus_gossip.tick(
			&mut ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle)
		);
		self.maintain_peers();
		self.light_dispatch.maintain_peers(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		});
	}

	fn maintain_peers(&mut self) {
		let tick = time::Instant::now();
		let mut aborting = Vec::new();
		{
			for (who, peer) in self.context_data.peers.iter() {
				if peer.block_request.as_ref().map_or(false, |(t, _)| (tick - *t).as_secs() > REQUEST_TIMEOUT_SEC) {
					trace!(target: "sync", "Request timeout {}", who);
					aborting.push(who.clone());
				} else if peer.obsolete_requests.values().any(|t| (tick - *t).as_secs() > REQUEST_TIMEOUT_SEC) {
					trace!(target: "sync", "Obsolete timeout {}", who);
					aborting.push(who.clone());
				}
			}
			for (who, _) in self.handshaking_peers.iter()
				.filter(|(_, handshaking)| (tick - handshaking.timestamp).as_secs() > REQUEST_TIMEOUT_SEC)
			{
				trace!(target: "sync", "Handshake timeout {}", who);
				aborting.push(who.clone());
			}
		}

		self.specialization.maintain_peers(
			&mut ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle)
		);
		for p in aborting {
			self.behaviour.disconnect_peer(&p);
			self.peerset_handle.report_peer(p, TIMEOUT_REPUTATION_CHANGE);
		}
	}

	/// Called by peer to report status
	fn on_status_message(&mut self, who: PeerId, status: message::Status<B>) {
		trace!(target: "sync", "New peer {} {:?}", who, status);
		let protocol_version = {
			if self.context_data.peers.contains_key(&who) {
				debug!("Unexpected status packet from {}", who);
				self.peerset_handle.report_peer(who, UNEXPECTED_STATUS_REPUTATION_CHANGE);
				return;
			}
			if status.genesis_hash != self.genesis_hash {
				trace!(
					target: "protocol",
					"Peer is on different chain (our genesis: {} theirs: {})",
					self.genesis_hash, status.genesis_hash
				);
				self.peerset_handle.report_peer(who.clone(), i32::min_value());
				self.behaviour.disconnect_peer(&who);
				return;
			}
			if status.version < MIN_VERSION && CURRENT_VERSION < status.min_supported_version {
				trace!(target: "protocol", "Peer {:?} using unsupported protocol version {}", who, status.version);
				self.peerset_handle.report_peer(who.clone(), i32::min_value());
				self.behaviour.disconnect_peer(&who);
				return;
			}

			if self.config.roles.is_light() {
				// we're not interested in light peers
				if status.roles.is_light() {
					debug!(target: "sync", "Peer {} is unable to serve light requests", who);
					self.peerset_handle.report_peer(who.clone(), i32::min_value());
					self.behaviour.disconnect_peer(&who);
					return;
				}

				// we don't interested in peers that are far behind us
				let self_best_block = self
					.context_data
					.chain
					.info()
					.chain.best_number;
				let blocks_difference = self_best_block
					.checked_sub(&status.best_number)
					.unwrap_or_else(Zero::zero)
					.saturated_into::<u64>();
				if blocks_difference > LIGHT_MAXIMAL_BLOCKS_DIFFERENCE {
					debug!(target: "sync", "Peer {} is far behind us and will unable to serve light requests", who);
					self.peerset_handle.report_peer(who.clone(), PEER_BEHIND_US_LIGHT_REPUTATION_CHANGE);
					self.behaviour.disconnect_peer(&who);
					return;
				}
			}

			let cache_limit = NonZeroUsize::new(1_000_000).expect("1_000_000 > 0; qed");

			let info = match self.handshaking_peers.remove(&who) {
				Some(_handshaking) => {
					PeerInfo {
						protocol_version: status.version,
						roles: status.roles,
						best_hash: status.best_hash,
						best_number: status.best_number
					}
				},
				None => {
					error!(target: "sync", "Received status from previously unconnected node {}", who);
					return;
				},
			};

			let peer = Peer {
				info,
				block_request: None,
				known_extrinsics: LruHashSet::new(cache_limit),
				known_blocks: LruHashSet::new(cache_limit),
				next_request_id: 0,
				obsolete_requests: HashMap::new(),
			};
			self.context_data.peers.insert(who.clone(), peer);

			debug!(target: "sync", "Connected {}", who);
			status.version
		};

		let info = self.context_data.peers.get(&who).expect("We just inserted above; QED").info.clone();
		self.light_dispatch.on_connect(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who.clone(), status.roles, status.best_number);
		match self.sync.new_peer(who.clone(), info) {
			Ok(None) => (),
			Ok(Some(req)) => self.send_request(&who, GenericMessage::BlockRequest(req)),
			Err(sync::BadPeer(id, repu)) => {
				self.behaviour.disconnect_peer(&id);
				self.peerset_handle.report_peer(id, repu)
			}
		}
		let mut context = ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle);
		if protocol_version > 2 {
			self.consensus_gossip.new_peer(&mut context, who.clone(), status.roles);
		}
		self.specialization.on_connect(&mut context, who, status);
	}

	/// Called when peer sends us new extrinsics
	fn on_extrinsics(
		&mut self,
		who: PeerId,
		extrinsics: message::Transactions<B::Extrinsic>
	) {
		// sending extrinsic to light node is considered a bad behavior
		if !self.config.roles.is_full() {
			trace!(target: "sync", "Peer {} is trying to send extrinsic to the light node", who);
			self.behaviour.disconnect_peer(&who);
			self.peerset_handle.report_peer(who, i32::min_value());
			return;
		}

		// Accept extrinsics only when fully synced
		if self.sync.status().state != SyncState::Idle {
			trace!(target: "sync", "{} Ignoring extrinsics while syncing", who);
			return;
		}
		trace!(target: "sync", "Received {} extrinsics from {}", extrinsics.len(), who);
		if let Some(ref mut peer) = self.context_data.peers.get_mut(&who) {
			for t in extrinsics {
				let hash = self.transaction_pool.hash_of(&t);
				peer.known_extrinsics.insert(hash);

				self.transaction_pool.import(
					self.peerset_handle.clone().into(),
					who.clone(),
					GOOD_EXTRINSIC_REPUTATION_CHANGE,
					BAD_EXTRINSIC_REPUTATION_CHANGE,
					t,
				);
			}
		}
	}

	/// Call when we must propagate ready extrinsics to peers.
	pub fn propagate_extrinsics(
		&mut self,
	) {
		debug!(target: "sync", "Propagating extrinsics");

		// Accept transactions only when fully synced
		if self.sync.status().state != SyncState::Idle {
			return;
		}

		let extrinsics = self.transaction_pool.transactions();
		let mut propagated_to = HashMap::new();
		for (who, peer) in self.context_data.peers.iter_mut() {
			// never send extrinsics to the light node
			if !peer.info.roles.is_full() {
				continue;
			}

			let (hashes, to_send): (Vec<_>, Vec<_>) = extrinsics
				.iter()
				.filter(|&(ref hash, _)| peer.known_extrinsics.insert(hash.clone()))
				.cloned()
				.unzip();

			if !to_send.is_empty() {
				for hash in hashes {
					propagated_to
						.entry(hash)
						.or_insert_with(Vec::new)
						.push(who.to_base58());
				}
				trace!(target: "sync", "Sending {} transactions to {}", to_send.len(), who);
				send_message::<B> (
					&mut self.behaviour,
					&mut self.context_data.stats,
					&who,
					GenericMessage::Transactions(to_send)
				)
			}
		}

		self.transaction_pool.on_broadcasted(propagated_to);
	}

	/// Make sure an important block is propagated to peers.
	///
	/// In chain-based consensus, we often need to make sure non-best forks are
	/// at least temporarily synced.
	pub fn announce_block(&mut self, hash: B::Hash, data: Vec<u8>) {
		let header = match self.context_data.chain.header(&BlockId::Hash(hash)) {
			Ok(Some(header)) => header,
			Ok(None) => {
				warn!("Trying to announce unknown block: {}", hash);
				return;
			}
			Err(e) => {
				warn!("Error reading block header {}: {:?}", hash, e);
				return;
			}
		};

		// don't announce genesis block since it will be ignored
		if header.number().is_zero() {
			return;
		}

		let is_best = self.context_data.chain.info().chain.best_hash == hash;
		debug!(target: "sync", "Reannouncing block {:?}", hash);
		self.send_announcement(&header, data, is_best, true)
	}

	fn send_announcement(&mut self, header: &B::Header, data: Vec<u8>, is_best: bool, force: bool) {
		let hash = header.hash();

		for (who, ref mut peer) in self.context_data.peers.iter_mut() {
			trace!(target: "sync", "Announcing block {:?} to {}", hash, who);
			let inserted = peer.known_blocks.insert(hash);
			if inserted || force {
				let message: Message<B> = GenericMessage::BlockAnnounce(message::BlockAnnounce {
					header: header.clone(),
					state: if peer.info.protocol_version >= 4  {
						if is_best {
							Some(message::BlockState::Best)
						} else {
							Some(message::BlockState::Normal)
						}
					} else  {
						None
					},
					data: if peer.info.protocol_version >= 4 {
						Some(data.clone())
					} else {
						None
					},
				});

				send_message::<B> (
					&mut self.behaviour,
					&mut self.context_data.stats,
					&who,
					message,
				)
			}
		}
	}

	/// Send Status message
	fn send_status(&mut self, who: PeerId) {
		let info = self.context_data.chain.info();
		let status = message::generic::Status {
			version: CURRENT_VERSION,
			min_supported_version: MIN_VERSION,
			genesis_hash: info.chain.genesis_hash,
			roles: self.config.roles.into(),
			best_number: info.chain.best_number,
			best_hash: info.chain.best_hash,
			chain_status: self.specialization.status(),
		};

		self.send_message(&who, GenericMessage::Status(status))
	}

	fn on_block_announce(&mut self, who: PeerId, announce: BlockAnnounce<B::Header>) -> CustomMessageOutcome<B> {
		let hash = announce.header.hash();
		if let Some(ref mut peer) = self.context_data.peers.get_mut(&who) {
			peer.known_blocks.insert(hash.clone());
		}
		self.light_dispatch.update_best_number(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who.clone(), *announce.header.number());

		let is_their_best = match announce.state.unwrap_or(message::BlockState::Best) {
			message::BlockState::Best => true,
			message::BlockState::Normal => false,
		};

		match self.sync.on_block_announce(who.clone(), hash, &announce, is_their_best) {
			sync::OnBlockAnnounce::Nothing => {
				// `on_block_announce` returns `OnBlockAnnounce::ImportHeader`
				// when we have all data required to import the block
				// in the BlockAnnounce message. This is only when:
				// 1) we're on light client;
				// AND
				// 2) parent block is already imported and not pruned.
				return CustomMessageOutcome::None
			}
			sync::OnBlockAnnounce::ImportHeader => () // We proceed with the import.
		}

		// to import header from announced block let's construct response to request that normally would have
		// been sent over network (but it is not in our case)
		let blocks_to_import = self.sync.on_block_data(
			who.clone(),
			message::generic::BlockRequest {
				id: 0,
				fields: BlockAttributes::HEADER,
				from: message::FromBlock::Hash(hash),
				to: None,
				direction: message::Direction::Ascending,
				max: Some(1),
			},
			message::generic::BlockResponse {
				id: 0,
				blocks: vec![
					message::generic::BlockData {
						hash: hash,
						header: Some(announce.header),
						body: None,
						receipt: None,
						message_queue: None,
						justification: None,
					},
				],
			},
		);
		match blocks_to_import {
			Ok(sync::OnBlockData::Import(origin, blocks)) => CustomMessageOutcome::BlockImport(origin, blocks),
			Ok(sync::OnBlockData::Request(peer, req)) => {
				self.send_request(&peer, GenericMessage::BlockRequest(req));
				CustomMessageOutcome::None
			}
			Err(sync::BadPeer(id, repu)) => {
				self.behaviour.disconnect_peer(&id);
				self.peerset_handle.report_peer(id, repu);
				CustomMessageOutcome::None
			}
		}
	}

	/// Call this when a block has been imported in the import queue and we should announce it on
	/// the network.
	pub fn on_block_imported(&mut self, hash: B::Hash, header: &B::Header, data: Vec<u8>, is_best: bool) {
		if is_best {
			self.sync.update_chain_info(header);
		}
		self.specialization.on_block_imported(
			&mut ProtocolContext::new(&mut self.context_data, &mut self.behaviour, &self.peerset_handle),
			hash.clone(),
			header,
		);

		// blocks are not announced by light clients
		if self.config.roles.is_light() {
			return;
		}

		// send out block announcements
		self.send_announcement(header, data, is_best, false);
	}

	/// Call this when a block has been finalized. The sync layer may have some additional
	/// requesting to perform.
	pub fn on_block_finalized(&mut self, hash: B::Hash, header: &B::Header) {
		self.sync.on_block_finalized(&hash, *header.number())
	}

	fn on_remote_call_request(
		&mut self,
		who: PeerId,
		request: message::RemoteCallRequest<B::Hash>,
	) {
		trace!(target: "sync", "Remote call request {} from {} ({} at {})",
			request.id,
			who,
			request.method,
			request.block
		);
		let proof = match self.context_data.chain.execution_proof(
			&request.block,
			&request.method,
			&request.data,
		) {
			Ok((_, proof)) => proof,
			Err(error) => {
				trace!(target: "sync", "Remote call request {} from {} ({} at {}) failed with: {}",
					request.id,
					who,
					request.method,
					request.block,
					error
				);
				self.peerset_handle.report_peer(who.clone(), RPC_FAILED_REPUTATION_CHANGE);
				StorageProof::empty()
			}
		};

		self.send_message(
			&who,
			GenericMessage::RemoteCallResponse(message::RemoteCallResponse {
				id: request.id,
				proof,
			}),
		);
	}

	/// Request a justification for the given block.
	///
	/// Uses `protocol` to queue a new justification request and tries to dispatch all pending
	/// requests.
	pub fn request_justification(&mut self, hash: &B::Hash, number: NumberFor<B>) {
		self.sync.request_justification(&hash, number)
	}

	/// Request syncing for the given block from given set of peers.
	/// Uses `protocol` to queue a new block download request and tries to dispatch all pending
	/// requests.
	pub fn set_sync_fork_request(&mut self, peers: Vec<PeerId>, hash: &B::Hash, number: NumberFor<B>) {
		self.sync.set_sync_fork_request(peers, hash, number)
	}

	/// A batch of blocks have been processed, with or without errors.
	/// Call this when a batch of blocks have been processed by the importqueue, with or without
	/// errors.
	pub fn blocks_processed(
		&mut self,
		imported: usize,
		count: usize,
		results: Vec<(Result<BlockImportResult<NumberFor<B>>, BlockImportError>, B::Hash)>
	) {
		let peers = self.context_data.peers.clone();
		let results = self.sync.on_blocks_processed(
			imported,
			count,
			results,
			|peer_id| peers.get(peer_id).map(|i| i.info.clone())
		);
		for result in results {
			match result {
				Ok((id, req)) => {
					let msg = GenericMessage::BlockRequest(req);
					send_request(
						&mut self.behaviour,
						&mut self.context_data.stats,
						&mut self.context_data.peers,
						&id,
						msg
					)
				}
				Err(sync::BadPeer(id, repu)) => {
					self.behaviour.disconnect_peer(&id);
					self.peerset_handle.report_peer(id, repu)
				}
			}
		}
	}

	/// Call this when a justification has been processed by the import queue, with or without
	/// errors.
	pub fn justification_import_result(&mut self, hash: B::Hash, number: NumberFor<B>, success: bool) {
		self.sync.on_justification_import(hash, number, success)
	}

	/// Request a finality proof for the given block.
	///
	/// Queues a new finality proof request and tries to dispatch all pending requests.
	pub fn request_finality_proof(&mut self, hash: &B::Hash, number: NumberFor<B>) {
		self.sync.request_finality_proof(&hash, number)
	}

	pub fn finality_proof_import_result(
		&mut self,
		request_block: (B::Hash, NumberFor<B>),
		finalization_result: Result<(B::Hash, NumberFor<B>), ()>,
	) {
		self.sync.on_finality_proof_import(request_block, finalization_result)
	}

	fn on_remote_call_response(
		&mut self,
		who: PeerId,
		response: message::RemoteCallResponse
	) {
		trace!(target: "sync", "Remote call response {} from {}", response.id, who);
		self.light_dispatch.on_remote_call_response(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who, response);
	}

	fn on_remote_read_request(
		&mut self,
		who: PeerId,
		request: message::RemoteReadRequest<B::Hash>,
	) {
		let keys_str = || match request.keys.len() {
			1 => request.keys[0].to_hex::<String>(),
			_ => format!(
				"{}..{}",
				request.keys[0].to_hex::<String>(),
				request.keys[request.keys.len() - 1].to_hex::<String>(),
			),
		};

		trace!(target: "sync", "Remote read request {} from {} ({} at {})",
			request.id, who, keys_str(), request.block);
		let proof = match self.context_data.chain.read_proof(&request.block, &request.keys) {
			Ok(proof) => proof,
			Err(error) => {
				trace!(target: "sync", "Remote read request {} from {} ({} at {}) failed with: {}",
					request.id,
					who,
					keys_str(),
					request.block,
					error
				);
				StorageProof::empty()
			}
		};
		self.send_message(
			&who,
			GenericMessage::RemoteReadResponse(message::RemoteReadResponse {
				id: request.id,
				proof,
			}),
		);
	}

	fn on_remote_read_child_request(
		&mut self,
		who: PeerId,
		request: message::RemoteReadChildRequest<B::Hash>,
	) {
		let keys_str = || match request.keys.len() {
			1 => request.keys[0].to_hex::<String>(),
			_ => format!(
				"{}..{}",
				request.keys[0].to_hex::<String>(),
				request.keys[request.keys.len() - 1].to_hex::<String>(),
			),
		};

		trace!(target: "sync", "Remote read child request {} from {} ({} {} at {})",
			request.id, who, request.storage_key.to_hex::<String>(), keys_str(), request.block);
		let proof = match self.context_data.chain.read_child_proof(
			&request.block,
			&request.storage_key,
			&request.keys,
		) {
			Ok(proof) => proof,
			Err(error) => {
				trace!(target: "sync", "Remote read child request {} from {} ({} {} at {}) failed with: {}",
					request.id,
					who,
					request.storage_key.to_hex::<String>(),
					keys_str(),
					request.block,
					error
				);
				StorageProof::empty()
			}
		};
		self.send_message(
			&who,
			GenericMessage::RemoteReadResponse(message::RemoteReadResponse {
				id: request.id,
				proof,
			}),
		);
	}

	fn on_remote_read_response(
		&mut self,
		who: PeerId,
		response: message::RemoteReadResponse
	) {
		trace!(target: "sync", "Remote read response {} from {}", response.id, who);
		self.light_dispatch.on_remote_read_response(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who, response);
	}

	fn on_remote_header_request(
		&mut self,
		who: PeerId,
		request: message::RemoteHeaderRequest<NumberFor<B>>,
	) {
		trace!(target: "sync", "Remote header proof request {} from {} ({})",
			request.id, who, request.block);
		let (header, proof) = match self.context_data.chain.header_proof(request.block) {
			Ok((header, proof)) => (Some(header), proof),
			Err(error) => {
				trace!(target: "sync", "Remote header proof request {} from {} ({}) failed with: {}",
					request.id,
					who,
					request.block,
					error
				);
				(Default::default(), StorageProof::empty())
			}
		};
		self.send_message(
			&who,
			GenericMessage::RemoteHeaderResponse(message::RemoteHeaderResponse {
				id: request.id,
				header,
				proof,
			}),
		);
	}

	fn on_remote_header_response(
		&mut self,
		who: PeerId,
		response: message::RemoteHeaderResponse<B::Header>,
	) {
		trace!(target: "sync", "Remote header proof response {} from {}", response.id, who);
		self.light_dispatch.on_remote_header_response(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who, response);
	}

	fn on_remote_changes_request(
		&mut self,
		who: PeerId,
		request: message::RemoteChangesRequest<B::Hash>,
	) {
		trace!(target: "sync", "Remote changes proof request {} from {} for key {} ({}..{})",
			request.id,
			who,
			if let Some(sk) = request.storage_key.as_ref() {
				format!("{} : {}", sk.to_hex::<String>(), request.key.to_hex::<String>())
			} else {
				request.key.to_hex::<String>()
			},
			request.first,
			request.last
		);
		let storage_key = request.storage_key.map(|sk| StorageKey(sk));
		let key = StorageKey(request.key);
		let proof = match self.context_data.chain.key_changes_proof(
			request.first,
			request.last,
			request.min,
			request.max,
			storage_key.as_ref(),
			&key,
		) {
			Ok(proof) => proof,
			Err(error) => {
				trace!(target: "sync", "Remote changes proof request {} from {} for key {} ({}..{}) failed with: {}",
					request.id,
					who,
					if let Some(sk) = storage_key {
						format!("{} : {}", sk.0.to_hex::<String>(), key.0.to_hex::<String>())
					} else {
						key.0.to_hex::<String>()
					},
					request.first,
					request.last,
					error
				);
				ChangesProof::<B::Header> {
					max_block: Zero::zero(),
					proof: vec![],
					roots: BTreeMap::new(),
					roots_proof: StorageProof::empty(),
				}
			}
		};
		self.send_message(
			&who,
			GenericMessage::RemoteChangesResponse(message::RemoteChangesResponse {
				id: request.id,
				max: proof.max_block,
				proof: proof.proof,
				roots: proof.roots.into_iter().collect(),
				roots_proof: proof.roots_proof,
			}),
		);
	}

	fn on_remote_changes_response(
		&mut self,
		who: PeerId,
		response: message::RemoteChangesResponse<NumberFor<B>, B::Hash>,
	) {
		trace!(target: "sync", "Remote changes proof response {} from {} (max={})",
			response.id,
			who,
			response.max
		);
		self.light_dispatch.on_remote_changes_response(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, who, response);
	}

	fn on_finality_proof_request(
		&mut self,
		who: PeerId,
		request: message::FinalityProofRequest<B::Hash>,
	) {
		trace!(target: "sync", "Finality proof request from {} for {}", who, request.block);
		let finality_proof = self.finality_proof_provider.as_ref()
			.ok_or_else(|| String::from("Finality provider is not configured"))
			.and_then(|provider|
				provider.prove_finality(request.block, &request.request).map_err(|e| e.to_string())
			);
		let finality_proof = match finality_proof {
			Ok(finality_proof) => finality_proof,
			Err(error) => {
				trace!(target: "sync", "Finality proof request from {} for {} failed with: {}",
					who,
					request.block,
					error
				);
				None
			},
		};
 		self.send_message(
			&who,
			GenericMessage::FinalityProofResponse(message::FinalityProofResponse {
				id: 0,
				block: request.block,
				proof: finality_proof,
			}),
		);
	}

	fn on_finality_proof_response(
		&mut self,
		who: PeerId,
		response: message::FinalityProofResponse<B::Hash>,
	) -> CustomMessageOutcome<B> {
		trace!(target: "sync", "Finality proof response from {} for {}", who, response.block);
		match self.sync.on_block_finality_proof(who, response) {
			Ok(sync::OnBlockFinalityProof::Nothing) => CustomMessageOutcome::None,
			Ok(sync::OnBlockFinalityProof::Import { peer, hash, number, proof }) =>
				CustomMessageOutcome::FinalityProofImport(peer, hash, number, proof),
			Err(sync::BadPeer(id, repu)) => {
				self.behaviour.disconnect_peer(&id);
				self.peerset_handle.report_peer(id, repu);
				CustomMessageOutcome::None
			}
		}
	}

	fn on_remote_body_response(
		&mut self,
		peer: PeerId,
		response: message::BlockResponse<B>
	) {
		self.light_dispatch.on_remote_body_response(LightDispatchIn {
			behaviour: &mut self.behaviour,
			peerset: self.peerset_handle.clone(),
		}, peer, response);
	}

	fn format_stats(&self) -> String {
		let mut out = String::new();
		for (id, stats) in &self.context_data.stats {
			let _ = writeln!(
				&mut out,
				"{}: In: {} bytes ({}), Out: {} bytes ({})",
				id,
				stats.bytes_in,
				stats.count_in,
				stats.bytes_out,
				stats.count_out,
			);
		}
		out
	}
}

/// Outcome of an incoming custom message.
#[derive(Debug)]
pub enum CustomMessageOutcome<B: BlockT> {
	BlockImport(BlockOrigin, Vec<IncomingBlock<B>>),
	JustificationImport(Origin, B::Hash, NumberFor<B>, Justification),
	FinalityProofImport(Origin, B::Hash, NumberFor<B>, Vec<u8>),
	None,
}

fn send_request<B: BlockT, H: ExHashT>(
	behaviour: &mut LegacyProto<Substream<StreamMuxerBox>>,
	stats: &mut HashMap<&'static str, PacketStats>,
	peers: &mut HashMap<PeerId, Peer<B, H>>,
	who: &PeerId,
	mut message: Message<B>,
) {
	if let GenericMessage::BlockRequest(ref mut r) = message {
		if let Some(ref mut peer) = peers.get_mut(who) {
			r.id = peer.next_request_id;
			peer.next_request_id = peer.next_request_id + 1;
			if let Some((timestamp, request)) = peer.block_request.take() {
				trace!(target: "sync", "Request {} for {} is now obsolete.", request.id, who);
				peer.obsolete_requests.insert(request.id, timestamp);
			}
			peer.block_request = Some((time::Instant::now(), r.clone()));
		}
	}
	send_message::<B>(behaviour, stats, who, message)
}

fn send_message<B: BlockT>(
	behaviour: &mut LegacyProto<Substream<StreamMuxerBox>>,
	stats: &mut HashMap<&'static str, PacketStats>,
	who: &PeerId,
	message: Message<B>,
) {
	let encoded = message.encode();
	let mut stats = stats.entry(message.id()).or_default();
	stats.bytes_out += encoded.len() as u64;
	stats.count_out += 1;
	behaviour.send_packet(who, encoded);
}

impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> NetworkBehaviour for
Protocol<B, S, H> {
	type ProtocolsHandler = <LegacyProto<Substream<StreamMuxerBox>> as NetworkBehaviour>::ProtocolsHandler;
	type OutEvent = CustomMessageOutcome<B>;

	fn new_handler(&mut self) -> Self::ProtocolsHandler {
		self.behaviour.new_handler()
	}

	fn addresses_of_peer(&mut self, peer_id: &PeerId) -> Vec<Multiaddr> {
		self.behaviour.addresses_of_peer(peer_id)
	}

	fn inject_connected(&mut self, peer_id: PeerId, endpoint: ConnectedPoint) {
		self.behaviour.inject_connected(peer_id, endpoint)
	}

	fn inject_disconnected(&mut self, peer_id: &PeerId, endpoint: ConnectedPoint) {
		self.behaviour.inject_disconnected(peer_id, endpoint)
	}

	fn inject_node_event(
		&mut self,
		peer_id: PeerId,
		event: <<Self::ProtocolsHandler as IntoProtocolsHandler>::Handler as ProtocolsHandler>::OutEvent,
	) {
		self.behaviour.inject_node_event(peer_id, event)
	}

	fn poll(
		&mut self,
		params: &mut impl PollParameters,
	) -> Async<
		NetworkBehaviourAction<
			<<Self::ProtocolsHandler as IntoProtocolsHandler>::Handler as ProtocolsHandler>::InEvent,
			Self::OutEvent
		>
	> {
		while let Ok(Async::Ready(_)) = self.tick_timeout.poll() {
			self.tick();
		}

		while let Ok(Async::Ready(_)) = self.propagate_timeout.poll() {
			self.propagate_extrinsics();
		}

		for (id, r) in self.sync.block_requests() {
			send_request(
				&mut self.behaviour,
				&mut self.context_data.stats,
				&mut self.context_data.peers,
				&id,
				GenericMessage::BlockRequest(r)
			)
		}
		for (id, r) in self.sync.justification_requests() {
			send_request(
				&mut self.behaviour,
				&mut self.context_data.stats,
				&mut self.context_data.peers,
				&id,
				GenericMessage::BlockRequest(r)
			)
		}
		for (id, r) in self.sync.finality_proof_requests() {
			send_request(
				&mut self.behaviour,
				&mut self.context_data.stats,
				&mut self.context_data.peers,
				&id,
				GenericMessage::FinalityProofRequest(r))
		}

		let event = match self.behaviour.poll(params) {
			Async::NotReady => return Async::NotReady,
			Async::Ready(NetworkBehaviourAction::GenerateEvent(ev)) => ev,
			Async::Ready(NetworkBehaviourAction::DialAddress { address }) =>
				return Async::Ready(NetworkBehaviourAction::DialAddress { address }),
			Async::Ready(NetworkBehaviourAction::DialPeer { peer_id }) =>
				return Async::Ready(NetworkBehaviourAction::DialPeer { peer_id }),
			Async::Ready(NetworkBehaviourAction::SendEvent { peer_id, event }) =>
				return Async::Ready(NetworkBehaviourAction::SendEvent { peer_id, event }),
			Async::Ready(NetworkBehaviourAction::ReportObservedAddr { address }) =>
				return Async::Ready(NetworkBehaviourAction::ReportObservedAddr { address }),
		};

		let outcome = match event {
			LegacyProtoOut::CustomProtocolOpen { peer_id, version, .. } => {
				debug_assert!(
					version <= CURRENT_VERSION as u8
					&& version >= MIN_VERSION as u8
				);
				self.on_peer_connected(peer_id);
				CustomMessageOutcome::None
			}
			LegacyProtoOut::CustomProtocolClosed { peer_id, .. } => {
				self.on_peer_disconnected(peer_id);
				CustomMessageOutcome::None
			},
			LegacyProtoOut::CustomMessage { peer_id, message } =>
				self.on_custom_message(peer_id, message),
			LegacyProtoOut::Clogged { peer_id, messages } => {
				debug!(target: "sync", "{} clogging messages:", messages.len());
				for msg in messages.into_iter().take(5) {
					let message: Option<Message<B>> = Decode::decode(&mut &msg[..]).ok();
					debug!(target: "sync", "{:?}", message);
					self.on_clogged_peer(peer_id.clone(), message);
				}
				CustomMessageOutcome::None
			}
		};

		if let CustomMessageOutcome::None = outcome {
			Async::NotReady
		} else {
			Async::Ready(NetworkBehaviourAction::GenerateEvent(outcome))
		}
	}

	fn inject_replaced(&mut self, peer_id: PeerId, closed_endpoint: ConnectedPoint, new_endpoint: ConnectedPoint) {
		self.behaviour.inject_replaced(peer_id, closed_endpoint, new_endpoint)
	}

	fn inject_addr_reach_failure(
		&mut self,
		peer_id: Option<&PeerId>,
		addr: &Multiaddr,
		error: &dyn std::error::Error
	) {
		self.behaviour.inject_addr_reach_failure(peer_id, addr, error)
	}

	fn inject_dial_failure(&mut self, peer_id: &PeerId) {
		self.behaviour.inject_dial_failure(peer_id)
	}

	fn inject_new_listen_addr(&mut self, addr: &Multiaddr) {
		self.behaviour.inject_new_listen_addr(addr)
	}

	fn inject_expired_listen_addr(&mut self, addr: &Multiaddr) {
		self.behaviour.inject_expired_listen_addr(addr)
	}

	fn inject_new_external_addr(&mut self, addr: &Multiaddr) {
		self.behaviour.inject_new_external_addr(addr)
	}
}

impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> DiscoveryNetBehaviour for Protocol<B, S, H> {
	fn add_discovered_nodes(&mut self, peer_ids: impl Iterator<Item = PeerId>) {
		self.behaviour.add_discovered_nodes(peer_ids)
	}
}

impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> Drop for Protocol<B, S, H> {
	fn drop(&mut self) {
		debug!(target: "sync", "Network stats:\n{}", self.format_stats());
	}
}