openethereum/util/network/src/host.rs

// Copyright 2015-2017 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::net::{SocketAddr, SocketAddrV4, Ipv4Addr};
use std::collections::{HashMap, HashSet};
use std::str::FromStr;
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, AtomicBool, Ordering as AtomicOrdering};
use std::ops::*;
use std::cmp::min;
use std::path::{Path, PathBuf};
use std::io::{Read, Write, ErrorKind};
use std::fs;
use ethkey::{KeyPair, Secret, Random, Generator};
use mio::*;
use mio::deprecated::{EventLoop};
use mio::tcp::*;
use util::hash::*;
use util::Hashable;
use util::version;
use rlp::*;
use session::{Session, SessionInfo, SessionData};
use error::*;
use io::*;
use {NetworkProtocolHandler, NonReservedPeerMode, AllowIP, PROTOCOL_VERSION};
use node_table::*;
use stats::NetworkStats;
use discovery::{Discovery, TableUpdates, NodeEntry};
use ip_utils::{map_external_address, select_public_address};
use path::restrict_permissions_owner;
use parking_lot::{Mutex, RwLock};

type Slab<T> = ::slab::Slab<T, usize>;

const MAX_SESSIONS: usize = 1024 + MAX_HANDSHAKES;
const MAX_HANDSHAKES: usize = 1024;

const DEFAULT_PORT: u16 = 30303;

// Tokens
const TCP_ACCEPT: usize = SYS_TIMER + 1;
const IDLE: usize = SYS_TIMER + 2;
const DISCOVERY: usize = SYS_TIMER + 3;
const DISCOVERY_REFRESH: usize = SYS_TIMER + 4;
const DISCOVERY_ROUND: usize = SYS_TIMER + 5;
const NODE_TABLE: usize = SYS_TIMER + 6;
const FIRST_SESSION: usize = 0;
const LAST_SESSION: usize = FIRST_SESSION + MAX_SESSIONS - 1;
const USER_TIMER: usize = LAST_SESSION + 256;
const SYS_TIMER: usize = LAST_SESSION + 1;

// Timeouts
const MAINTENANCE_TIMEOUT: u64 = 1000;
const DISCOVERY_REFRESH_TIMEOUT: u64 = 60_000;
const DISCOVERY_ROUND_TIMEOUT: u64 = 300;
const NODE_TABLE_TIMEOUT: u64 = 300_000;

#[derive(Debug, PartialEq, Clone)]
/// Network service configuration
pub struct NetworkConfiguration {
	/// Directory path to store general network configuration. None means nothing will be saved
	pub config_path: Option<String>,
	/// Directory path to store network-specific configuration. None means nothing will be saved
	pub net_config_path: Option<String>,
	/// IP address to listen for incoming connections. Listen to all connections by default
	pub listen_address: Option<SocketAddr>,
	/// IP address to advertise. Detected automatically if none.
	pub public_address: Option<SocketAddr>,
	/// Port for UDP connections, same as TCP by default
	pub udp_port: Option<u16>,
	/// Enable NAT configuration
	pub nat_enabled: bool,
	/// Enable discovery
	pub discovery_enabled: bool,
	/// List of initial node addresses
	pub boot_nodes: Vec<String>,
	/// Use provided node key instead of default
	pub use_secret: Option<Secret>,
	/// Minimum number of connected peers to maintain
	pub min_peers: u32,
	/// Maximum allowed number of peers
	pub max_peers: u32,
	/// Maximum handshakes
	pub max_handshakes: u32,
	/// Reserved protocols. Peers with <key> protocol get additional <value> connection slots.
	pub reserved_protocols: HashMap<ProtocolId, u32>,
	/// List of reserved node addresses.
	pub reserved_nodes: Vec<String>,
	/// The non-reserved peer mode.
	pub non_reserved_mode: NonReservedPeerMode,
	/// IP filter
	pub allow_ips: AllowIP,
}

impl Default for NetworkConfiguration {
	fn default() -> Self {
		NetworkConfiguration::new()
	}
}

impl NetworkConfiguration {
	/// Create a new instance of default settings.
	pub fn new() -> Self {
		NetworkConfiguration {
			config_path: None,
			net_config_path: None,
			listen_address: None,
			public_address: None,
			udp_port: None,
			nat_enabled: true,
			discovery_enabled: true,
			boot_nodes: Vec::new(),
			use_secret: None,
			min_peers: 25,
			max_peers: 50,
			max_handshakes: 64,
			reserved_protocols: HashMap::new(),
			allow_ips: AllowIP::All,
			reserved_nodes: Vec::new(),
			non_reserved_mode: NonReservedPeerMode::Accept,
		}
	}

	/// Create new default configuration with sepcified listen port.
	pub fn new_with_port(port: u16) -> NetworkConfiguration {
		let mut config = NetworkConfiguration::new();
		config.listen_address = Some(SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(0, 0, 0, 0), port)));
		config
	}

	/// Create new default configuration for localhost-only connection with random port (usefull for testing)
	pub fn new_local() -> NetworkConfiguration {
		let mut config = NetworkConfiguration::new();
		config.listen_address = Some(SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 0)));
		config.nat_enabled = false;
		config
	}
}

/// Protocol handler level packet id
pub type PacketId = u8;
/// Protocol / handler id
pub type ProtocolId = [u8; 3];

/// Messages used to communitate with the event loop from other threads.
#[derive(Clone)]
pub enum NetworkIoMessage {
	/// Register a new protocol handler.
	AddHandler {
		/// Handler shared instance.
		handler: Arc<NetworkProtocolHandler + Sync>,
		/// Protocol Id.
		protocol: ProtocolId,
		/// Supported protocol versions.
		versions: Vec<u8>,
		/// Number of packet IDs reserved by the protocol.
		packet_count: u8,
	},
	/// Register a new protocol timer
	AddTimer {
		/// Protocol Id.
		protocol: ProtocolId,
		/// Timer token.
		token: TimerToken,
		/// Timer delay in milliseconds.
		delay: u64,
	},
	/// Initliaze public interface.
	InitPublicInterface,
	/// Disconnect a peer.
	Disconnect(PeerId),
	/// Disconnect and temporary disable peer.
	DisablePeer(PeerId),
	/// Network has been started with the host as the given enode.
	NetworkStarted(String),
}

/// Local (temporary) peer session ID.
pub type PeerId = usize;

#[derive(Debug, PartialEq, Eq)]
/// Protocol info
pub struct CapabilityInfo {
	pub protocol: ProtocolId,
	pub version: u8,
	/// Total number of packet IDs this protocol support.
	pub packet_count: u8,
}

impl Encodable for CapabilityInfo {
	fn rlp_append(&self, s: &mut RlpStream) {
		s.begin_list(2);
		s.append(&&self.protocol[..]);
		s.append(&self.version);
	}
}

/// IO access point. This is passed to all IO handlers and provides an interface to the IO subsystem.
pub struct NetworkContext<'s> {
	io: &'s IoContext<NetworkIoMessage>,
	protocol: ProtocolId,
	sessions: Arc<RwLock<Slab<SharedSession>>>,
	session: Option<SharedSession>,
	session_id: Option<StreamToken>,
	_reserved_peers: &'s HashSet<NodeId>,
}

impl<'s> NetworkContext<'s> {
	/// Create a new network IO access point. Takes references to all the data that can be updated within the IO handler.
	fn new(io: &'s IoContext<NetworkIoMessage>,
		protocol: ProtocolId,
		session: Option<SharedSession>, sessions: Arc<RwLock<Slab<SharedSession>>>,
		reserved_peers: &'s HashSet<NodeId>) -> NetworkContext<'s> {
		let id = session.as_ref().map(|s| s.lock().token());
		NetworkContext {
			io: io,
			protocol: protocol,
			session_id: id,
			session: session,
			sessions: sessions,
			_reserved_peers: reserved_peers,
		}
	}

	fn resolve_session(&self, peer: PeerId) -> Option<SharedSession> {
		match self.session_id {
			Some(id) if id == peer => self.session.clone(),
			_ => self.sessions.read().get(peer).cloned(),
		}
	}

	/// Send a packet over the network to another peer.
	pub fn send(&self, peer: PeerId, packet_id: PacketId, data: Vec<u8>) -> Result<(), NetworkError> {
		self.send_protocol(self.protocol, peer, packet_id, data)
	}

	/// Send a packet over the network to another peer using specified protocol.
	pub fn send_protocol(&self, protocol: ProtocolId, peer: PeerId, packet_id: PacketId, data: Vec<u8>) -> Result<(), NetworkError> {
		let session = self.resolve_session(peer);
		if let Some(session) = session {
			session.lock().send_packet(self.io, protocol, packet_id as u8, &data)?;
		} else  {
			trace!(target: "network", "Send: Peer no longer exist")
		}
		Ok(())
	}

	/// Respond to a current network message. Panics if no there is no packet in the context. If the session is expired returns nothing.
	pub fn respond(&self, packet_id: PacketId, data: Vec<u8>) -> Result<(), NetworkError> {
		assert!(self.session.is_some(), "Respond called without network context");
		self.session_id.map_or_else(|| Err(NetworkError::Expired), |id| self.send(id, packet_id, data))
	}

	/// Get an IoChannel.
	pub fn io_channel(&self) -> IoChannel<NetworkIoMessage> {
		self.io.channel()
	}

	/// Disconnect a peer and prevent it from connecting again.
	pub fn disable_peer(&self, peer: PeerId) {
		self.io.message(NetworkIoMessage::DisablePeer(peer))
			.unwrap_or_else(|e| warn!("Error sending network IO message: {:?}", e));
	}

	/// Disconnect peer. Reconnect can be attempted later.
	pub fn disconnect_peer(&self, peer: PeerId) {
		self.io.message(NetworkIoMessage::Disconnect(peer))
			.unwrap_or_else(|e| warn!("Error sending network IO message: {:?}", e));
	}

	/// Check if the session is still active.
	pub fn is_expired(&self) -> bool {
		self.session.as_ref().map_or(false, |s| s.lock().expired())
	}

	/// Register a new IO timer. 'IoHandler::timeout' will be called with the token.
	pub fn register_timer(&self, token: TimerToken, ms: u64) -> Result<(), NetworkError> {
		self.io.message(NetworkIoMessage::AddTimer {
			token: token,
			delay: ms,
			protocol: self.protocol,
		}).unwrap_or_else(|e| warn!("Error sending network IO message: {:?}", e));
		Ok(())
	}

	/// Returns peer identification string
	pub fn peer_client_version(&self, peer: PeerId) -> String {
		self.resolve_session(peer).map_or("unknown".to_owned(), |s| s.lock().info.client_version.clone())
	}

	/// Returns information on p2p session
	pub fn session_info(&self, peer: PeerId) -> Option<SessionInfo> {
		self.resolve_session(peer).map(|s| s.lock().info.clone())
	}

	/// Returns max version for a given protocol.
	pub fn protocol_version(&self, protocol: ProtocolId, peer: PeerId) -> Option<u8> {
		let session = self.resolve_session(peer);
		session.and_then(|s| s.lock().capability_version(protocol))
	}

	/// Returns this object's subprotocol name.
	pub fn subprotocol_name(&self) -> ProtocolId { self.protocol }
}

/// Shared host information
pub struct HostInfo {
	/// Our private and public keys.
	keys: KeyPair,
	/// Current network configuration
	config: NetworkConfiguration,
	/// Connection nonce.
	nonce: H256,
	/// RLPx protocol version
	pub protocol_version: u32,
	/// Client identifier
	pub client_version: String,
	/// Registered capabilities (handlers)
	pub capabilities: Vec<CapabilityInfo>,
	/// Local address + discovery port
	pub local_endpoint: NodeEndpoint,
	/// Public address + discovery port
	pub public_endpoint: Option<NodeEndpoint>,
}

impl HostInfo {
	/// Returns public key
	pub fn id(&self) -> &NodeId {
		self.keys.public()
	}

	/// Returns secret key
	pub fn secret(&self) -> &Secret {
		self.keys.secret()
	}

	/// Increments and returns connection nonce.
	pub fn next_nonce(&mut self) -> H256 {
		self.nonce = self.nonce.sha3();
		self.nonce.clone()
	}
}

type SharedSession = Arc<Mutex<Session>>;

#[derive(Copy, Clone)]
struct ProtocolTimer {
	pub protocol: ProtocolId,
	pub token: TimerToken, // Handler level token
}

/// Root IO handler. Manages protocol handlers, IO timers and network connections.
pub struct Host {
	pub info: RwLock<HostInfo>,
	tcp_listener: Mutex<TcpListener>,
	sessions: Arc<RwLock<Slab<SharedSession>>>,
	discovery: Mutex<Option<Discovery>>,
	nodes: RwLock<NodeTable>,
	handlers: RwLock<HashMap<ProtocolId, Arc<NetworkProtocolHandler>>>,
	timers: RwLock<HashMap<TimerToken, ProtocolTimer>>,
	timer_counter: RwLock<usize>,
	stats: Arc<NetworkStats>,
	reserved_nodes: RwLock<HashSet<NodeId>>,
	num_sessions: AtomicUsize,
	stopping: AtomicBool,
}

impl Host {
	/// Create a new instance
	pub fn new(mut config: NetworkConfiguration, stats: Arc<NetworkStats>) -> Result<Host, NetworkError> {
		let mut listen_address = match config.listen_address {
			None => SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(0, 0, 0, 0), DEFAULT_PORT)),
			Some(addr) => addr,
		};

		let keys = if let Some(ref secret) = config.use_secret {
			KeyPair::from_secret(secret.clone())?
		} else {
			config.config_path.clone().and_then(|ref p| load_key(Path::new(&p)))
				.map_or_else(|| {
				let key = Random.generate().expect("Error generating random key pair");
				if let Some(path) = config.config_path.clone() {
					save_key(Path::new(&path), key.secret());
				}
				key
			},
			|s| KeyPair::from_secret(s).expect("Error creating node secret key"))
		};
		let path = config.net_config_path.clone();
		// Setup the server socket
		let tcp_listener = TcpListener::bind(&listen_address)?;
		listen_address = SocketAddr::new(listen_address.ip(), tcp_listener.local_addr()?.port());
		debug!(target: "network", "Listening at {:?}", listen_address);
		let udp_port = config.udp_port.unwrap_or(listen_address.port());
		let local_endpoint = NodeEndpoint { address: listen_address, udp_port: udp_port };

		let boot_nodes = config.boot_nodes.clone();
		let reserved_nodes = config.reserved_nodes.clone();
		config.max_handshakes = min(config.max_handshakes, MAX_HANDSHAKES as u32);

		let mut host = Host {
			info: RwLock::new(HostInfo {
				keys: keys,
				config: config,
				nonce: H256::random(),
				protocol_version: PROTOCOL_VERSION,
				client_version: version(),
				capabilities: Vec::new(),
				public_endpoint: None,
				local_endpoint: local_endpoint,
			}),
			discovery: Mutex::new(None),
			tcp_listener: Mutex::new(tcp_listener),
			sessions: Arc::new(RwLock::new(Slab::new_starting_at(FIRST_SESSION, MAX_SESSIONS))),
			nodes: RwLock::new(NodeTable::new(path)),
			handlers: RwLock::new(HashMap::new()),
			timers: RwLock::new(HashMap::new()),
			timer_counter: RwLock::new(USER_TIMER),
			stats: stats,
			reserved_nodes: RwLock::new(HashSet::new()),
			num_sessions: AtomicUsize::new(0),
			stopping: AtomicBool::new(false),
		};

		for n in boot_nodes {
			host.add_node(&n);
		}

		for n in reserved_nodes {
			if let Err(e) = host.add_reserved_node(&n) {
				debug!(target: "network", "Error parsing node id: {}: {:?}", n, e);
			}
		}
		Ok(host)
	}

	pub fn add_node(&mut self, id: &str) {
		match Node::from_str(id) {
			Err(e) => { debug!(target: "network", "Could not add node {}: {:?}", id, e); },
			Ok(n) => {
				let entry = NodeEntry { endpoint: n.endpoint.clone(), id: n.id.clone() };

				self.nodes.write().add_node(n);
				if let Some(ref mut discovery) = *self.discovery.lock() {
					discovery.add_node(entry);
				}
			}
		}
	}

	pub fn add_reserved_node(&self, id: &str) -> Result<(), NetworkError> {
		let n = Node::from_str(id)?;

		let entry = NodeEntry { endpoint: n.endpoint.clone(), id: n.id.clone() };
		self.reserved_nodes.write().insert(n.id.clone());
		self.nodes.write().add_node(Node::new(entry.id.clone(), entry.endpoint.clone()));

		if let Some(ref mut discovery) = *self.discovery.lock() {
			discovery.add_node(entry);
		}

		Ok(())
	}

	pub fn set_non_reserved_mode(&self, mode: NonReservedPeerMode, io: &IoContext<NetworkIoMessage>) {
		let mut info = self.info.write();

		if info.config.non_reserved_mode != mode {
			info.config.non_reserved_mode = mode.clone();
			drop(info);
			if let NonReservedPeerMode::Deny = mode {
				// disconnect all non-reserved peers here.
				let reserved: HashSet<NodeId> = self.reserved_nodes.read().clone();
				let mut to_kill = Vec::new();
				for e in self.sessions.write().iter_mut() {
					let mut s = e.lock();
					{
						let id = s.id();
						if id.map_or(false, |id| reserved.contains(id)) {
							continue;
						}
					}

					s.disconnect(io, DisconnectReason::ClientQuit);
					to_kill.push(s.token());
				}
				for p in to_kill {
					trace!(target: "network", "Disconnecting on reserved-only mode: {}", p);
					self.kill_connection(p, io, false);
				}
			}
		}
	}

	pub fn remove_reserved_node(&self, id: &str) -> Result<(), NetworkError> {
		let n = Node::from_str(id)?;
		self.reserved_nodes.write().remove(&n.id);

		Ok(())
	}

	pub fn client_version() -> String {
		version()
	}

	pub fn external_url(&self) -> Option<String> {
		let info = self.info.read();
		info.public_endpoint.as_ref().map(|e| format!("{}", Node::new(info.id().clone(), e.clone())))
	}

	pub fn local_url(&self) -> String {
		let info = self.info.read();
		format!("{}", Node::new(info.id().clone(), info.local_endpoint.clone()))
	}

	pub fn stop(&self, io: &IoContext<NetworkIoMessage>) -> Result<(), NetworkError> {
		self.stopping.store(true, AtomicOrdering::Release);
		let mut to_kill = Vec::new();
		for e in self.sessions.write().iter_mut() {
			let mut s = e.lock();
			s.disconnect(io, DisconnectReason::ClientQuit);
			to_kill.push(s.token());
		}
		for p in to_kill {
			trace!(target: "network", "Disconnecting on shutdown: {}", p);
			self.kill_connection(p, io, true);
		}
		io.unregister_handler()?;
		Ok(())
	}

	/// Get all connected peers.
	pub fn connected_peers(&self) -> Vec<PeerId> {
		let sessions = self.sessions.read();
		let sessions = &*sessions;

		let mut peers = Vec::with_capacity(sessions.count());
		for i in (0..MAX_SESSIONS).map(|x| x + FIRST_SESSION) {
			if sessions.get(i).is_some() {
				peers.push(i);
			}
		}
		peers
	}

	fn init_public_interface(&self, io: &IoContext<NetworkIoMessage>) -> Result<(), NetworkError> {
		if self.info.read().public_endpoint.is_some() {
			return Ok(());
		}
		let local_endpoint = self.info.read().local_endpoint.clone();
		let public_address = self.info.read().config.public_address.clone();
		let allow_ips = self.info.read().config.allow_ips;
		let public_endpoint = match public_address {
			None => {
				let public_address = select_public_address(local_endpoint.address.port());
				let public_endpoint = NodeEndpoint { address: public_address, udp_port: local_endpoint.udp_port };
				if self.info.read().config.nat_enabled {
					match map_external_address(&local_endpoint) {
						Some(endpoint) => {
							info!("NAT mapped to external address {}", endpoint.address);
							endpoint
						},
						None => public_endpoint
					}
				} else {
					public_endpoint
				}
			}
			Some(addr) => NodeEndpoint { address: addr, udp_port: local_endpoint.udp_port }
		};

		self.info.write().public_endpoint = Some(public_endpoint.clone());

		if let Some(url) = self.external_url() {
			io.message(NetworkIoMessage::NetworkStarted(url)).unwrap_or_else(|e| warn!("Error sending IO notification: {:?}", e));
		}

		// Initialize discovery.
		let discovery = {
			let info = self.info.read();
			if info.config.discovery_enabled && info.config.non_reserved_mode == NonReservedPeerMode::Accept {
				let mut udp_addr = local_endpoint.address.clone();
				udp_addr.set_port(local_endpoint.udp_port);
				Some(Discovery::new(&info.keys, udp_addr, public_endpoint, DISCOVERY, allow_ips))
			} else { None }
		};

		if let Some(mut discovery) = discovery {
			discovery.init_node_list(self.nodes.read().unordered_entries());
			discovery.add_node_list(self.nodes.read().unordered_entries());
			*self.discovery.lock() = Some(discovery);
			io.register_stream(DISCOVERY)?;
			io.register_timer(DISCOVERY_REFRESH, DISCOVERY_REFRESH_TIMEOUT)?;
			io.register_timer(DISCOVERY_ROUND, DISCOVERY_ROUND_TIMEOUT)?;
		}
		io.register_timer(NODE_TABLE, NODE_TABLE_TIMEOUT)?;
		io.register_stream(TCP_ACCEPT)?;
		Ok(())
	}

	fn maintain_network(&self, io: &IoContext<NetworkIoMessage>) {
		self.keep_alive(io);
		self.connect_peers(io);
	}

	fn have_session(&self, id: &NodeId) -> bool {
		self.sessions.read().iter().any(|e| e.lock().info.id == Some(id.clone()))
	}

	fn session_count(&self) -> usize {
		self.num_sessions.load(AtomicOrdering::Relaxed)
	}

	fn connecting_to(&self, id: &NodeId) -> bool {
		self.sessions.read().iter().any(|e| e.lock().id() == Some(id))
	}

	fn handshake_count(&self) -> usize {
		// session_count < total_count is possible because of the data race.
		self.sessions.read().count().saturating_sub(self.session_count())
	}

	fn keep_alive(&self, io: &IoContext<NetworkIoMessage>) {
		let mut to_kill = Vec::new();
		for e in self.sessions.write().iter_mut() {
			let mut s = e.lock();
			if !s.keep_alive(io) {
				s.disconnect(io, DisconnectReason::PingTimeout);
				to_kill.push(s.token());
			}
		}
		for p in to_kill {
			trace!(target: "network", "Ping timeout: {}", p);
			self.kill_connection(p, io, true);
		}
	}

	fn connect_peers(&self, io: &IoContext<NetworkIoMessage>) {
		let (min_peers, mut pin, max_handshakes, allow_ips, self_id) = {
			let info = self.info.read();
			if info.capabilities.is_empty() {
				return;
			}
			let config = &info.config;

			(config.min_peers, config.non_reserved_mode == NonReservedPeerMode::Deny, config.max_handshakes as usize, config.allow_ips, info.id().clone())
		};

		let session_count = self.session_count();
		let reserved_nodes = self.reserved_nodes.read();
		if session_count >= min_peers as usize + reserved_nodes.len() {
			// check if all pinned nodes are connected.
			if reserved_nodes.iter().all(|n| self.have_session(n) && self.connecting_to(n)) {
				return;
			}

			// if not, only attempt connect to reserved peers
			pin = true;
		}

		let handshake_count = self.handshake_count();
		// allow 16 slots for incoming connections
		if handshake_count >= max_handshakes {
			return;
		}

		// iterate over all nodes, reserved ones coming first.
		// if we are pinned to only reserved nodes, ignore all others.
		let nodes = reserved_nodes.iter().cloned().chain(if !pin {
			self.nodes.read().nodes(allow_ips)
		} else {
			Vec::new()
		});

		let max_handshakes_per_round = max_handshakes / 2;
		let mut started: usize = 0;
		for id in nodes.filter(|id| !self.have_session(id) && !self.connecting_to(id) && *id != self_id)
			.take(min(max_handshakes_per_round, max_handshakes - handshake_count)) {
			self.connect_peer(&id, io);
			started += 1;
		}
		debug!(target: "network", "Connecting peers: {} sessions, {} pending, {} started", self.session_count(), self.handshake_count(), started);
	}

	#[cfg_attr(feature="dev", allow(single_match))]
	fn connect_peer(&self, id: &NodeId, io: &IoContext<NetworkIoMessage>) {
		if self.have_session(id) {
			trace!(target: "network", "Aborted connect. Node already connected.");
			return;
		}
		if self.connecting_to(id) {
			trace!(target: "network", "Aborted connect. Node already connecting.");
			return;
		}

		let socket = {
			let address = {
				let mut nodes = self.nodes.write();
				if let Some(node) = nodes.get_mut(id) {
					node.last_attempted = Some(::time::now());
					node.endpoint.address
				}
				else {
					debug!(target: "network", "Connection to expired node aborted");
					return;
				}
			};
			match TcpStream::connect(&address) {
				Ok(socket) => {
					trace!(target: "network", "Connecting to {:?}", address);
					socket
				},
				Err(e) => {
					debug!(target: "network", "Can't connect to address {:?}: {:?}", address, e);
					return;
				}
			}
		};
		if let Err(e) = self.create_connection(socket, Some(id), io) {
			debug!(target: "network", "Can't create connection: {:?}", e);
		}
	}

	#[cfg_attr(feature="dev", allow(block_in_if_condition_stmt))]
	fn create_connection(&self, socket: TcpStream, id: Option<&NodeId>, io: &IoContext<NetworkIoMessage>) -> Result<(), NetworkError> {
		let nonce = self.info.write().next_nonce();
		let mut sessions = self.sessions.write();

		let token = sessions.insert_with_opt(|token| {
			match Session::new(io, socket, token, id, &nonce, self.stats.clone(), &self.info.read()) {
				Ok(s) => Some(Arc::new(Mutex::new(s))),
				Err(e) => {
					debug!(target: "network", "Session create error: {:?}", e);
					None
				}
			}
		});

		match token {
			Some(t) => io.register_stream(t).map(|_| ()).map_err(Into::into),
			None => {
				debug!(target: "network", "Max sessions reached");
				Ok(())
			}
		}
	}

	fn accept(&self, io: &IoContext<NetworkIoMessage>) {
		trace!(target: "network", "Accepting incoming connection");
		loop {
			let socket = match self.tcp_listener.lock().accept() {
				Ok((sock, _addr)) => sock,
				Err(e) => {
					if e.kind() != ErrorKind::WouldBlock {
						debug!(target: "network", "Error accepting connection: {:?}", e);
					}
					break
				},
			};
			if let Err(e) = self.create_connection(socket, None, io) {
				debug!(target: "network", "Can't accept connection: {:?}", e);
			}
		}
	}

	fn session_writable(&self, token: StreamToken, io: &IoContext<NetworkIoMessage>) {
		let session = { self.sessions.read().get(token).cloned() };

		if let Some(session) = session {
			let mut s = session.lock();
			if let Err(e) = s.writable(io, &self.info.read()) {
				trace!(target: "network", "Session write error: {}: {:?}", token, e);
			}
			if s.done() {
				io.deregister_stream(token).unwrap_or_else(|e| debug!("Error deregistering stream: {:?}", e));
			}
		}
	}

	fn connection_closed(&self, token: TimerToken, io: &IoContext<NetworkIoMessage>) {
		trace!(target: "network", "Connection closed: {}", token);
		self.kill_connection(token, io, true);
	}

	#[cfg_attr(feature="dev", allow(collapsible_if))]
	fn session_readable(&self, token: StreamToken, io: &IoContext<NetworkIoMessage>) {
		let mut ready_data: Vec<ProtocolId> = Vec::new();
		let mut packet_data: Vec<(ProtocolId, PacketId, Vec<u8>)> = Vec::new();
		let mut kill = false;
		let session = { self.sessions.read().get(token).cloned() };
		let mut ready_id = None;
		if let Some(session) = session.clone() {
			{
				let mut s = session.lock();
				loop {
					let session_result = s.readable(io, &self.info.read());
					match session_result {
						Err(e) => {
							trace!(target: "network", "Session read error: {}:{:?} ({:?}) {:?}", token, s.id(), s.remote_addr(), e);
							if let NetworkError::Disconnect(DisconnectReason::IncompatibleProtocol) = e {
								if let Some(id) = s.id() {
									if !self.reserved_nodes.read().contains(id) {
										self.nodes.write().mark_as_useless(id);
									}
								}
							}
							kill = true;
							break;
						},
						Ok(SessionData::Ready) => {
							self.num_sessions.fetch_add(1, AtomicOrdering::SeqCst);
							let session_count = self.session_count();
							let (min_peers, max_peers, reserved_only) = {
								let info = self.info.read();
								let mut max_peers = info.config.max_peers;
								for cap in s.info.capabilities.iter() {
									if let Some(num) = info.config.reserved_protocols.get(&cap.protocol) {
										max_peers += *num;
										break;
									}
								}
								(info.config.min_peers as usize, max_peers as usize, info.config.non_reserved_mode == NonReservedPeerMode::Deny)
							};

							let id = s.id().expect("Ready session always has id").clone();

							// Check for the session limit. session_counts accounts for the new session.
							if reserved_only ||
								(s.info.originated && session_count > min_peers) ||
								(!s.info.originated && session_count > max_peers) {
								// only proceed if the connecting peer is reserved.
								if !self.reserved_nodes.read().contains(&id) {
									s.disconnect(io, DisconnectReason::TooManyPeers);
									kill = true;
									break;
								}
							}
							ready_id = Some(id);

							// Add it to the node table
							if !s.info.originated {
								if let Ok(address) = s.remote_addr() {
									let entry = NodeEntry { id: id, endpoint: NodeEndpoint { address: address, udp_port: address.port() } };
									self.nodes.write().add_node(Node::new(entry.id.clone(), entry.endpoint.clone()));
									let mut discovery = self.discovery.lock();
									if let Some(ref mut discovery) = *discovery {
										discovery.add_node(entry);
									}
								}
							}
							for (p, _) in self.handlers.read().iter() {
								if s.have_capability(*p) {
									ready_data.push(*p);
								}
							}
						},
						Ok(SessionData::Packet {
							data,
							protocol,
							packet_id,
						}) => {
							match self.handlers.read().get(&protocol) {
								None => { warn!(target: "network", "No handler found for protocol: {:?}", protocol) },
								Some(_) => packet_data.push((protocol, packet_id, data)),
							}
						},
						Ok(SessionData::Continue) => (),
						Ok(SessionData::None) => break,
					}
				}
			}

			if kill {
				self.kill_connection(token, io, true);
			}

			let handlers = self.handlers.read();
			if !ready_data.is_empty() {
				let duplicate = self.sessions.read().iter().any(|e| {
					let session = e.lock();
					session.token() != token && session.info.id == ready_id
				});
				if duplicate {
					trace!(target: "network", "Rejected duplicate connection: {}", token);
					session.lock().disconnect(io, DisconnectReason::DuplicatePeer);
					self.kill_connection(token, io, false);
					return;
				}
				for p in ready_data {
					self.stats.inc_sessions();
					let reserved = self.reserved_nodes.read();
					if let Some(h) = handlers.get(&p).clone() {
						h.connected(&NetworkContext::new(io, p, Some(session.clone()), self.sessions.clone(), &reserved), &token);
						// accumulate pending packets.
						let mut session = session.lock();
						packet_data.extend(session.mark_connected(p));
					}
				}
			}

			for (p, packet_id, data) in packet_data {
				let reserved = self.reserved_nodes.read();
				if let Some(h) = handlers.get(&p).clone() {
					h.read(&NetworkContext::new(io, p, Some(session.clone()), self.sessions.clone(), &reserved), &token, packet_id, &data[1..]);
				}
			}
		}
	}

	fn connection_timeout(&self, token: StreamToken, io: &IoContext<NetworkIoMessage>) {
		trace!(target: "network", "Connection timeout: {}", token);
		self.kill_connection(token, io, true)
	}

	fn kill_connection(&self, token: StreamToken, io: &IoContext<NetworkIoMessage>, remote: bool) {
		let mut to_disconnect: Vec<ProtocolId> = Vec::new();
		let mut failure_id = None;
		let mut deregister = false;
		let mut expired_session = None;
		if let FIRST_SESSION ... LAST_SESSION = token {
			let sessions = self.sessions.write();
			if let Some(session) = sessions.get(token).cloned() {
				expired_session = Some(session.clone());
				let mut s = session.lock();
				if !s.expired() {
					if s.is_ready() {
						self.num_sessions.fetch_sub(1, AtomicOrdering::SeqCst);
						for (p, _) in self.handlers.read().iter() {
							if s.have_capability(*p)  {
								to_disconnect.push(*p);
							}
						}
					}
					s.set_expired();
					failure_id = s.id().cloned();
				}
				deregister = remote || s.done();
			}
		}
		if let Some(id) = failure_id {
			if remote {
				self.nodes.write().note_failure(&id);
			}
		}
		for p in to_disconnect {
			let reserved = self.reserved_nodes.read();
			if let Some(h) = self.handlers.read().get(&p).clone() {
				h.disconnected(&NetworkContext::new(io, p, expired_session.clone(), self.sessions.clone(), &reserved), &token);
			}
		}
		if deregister {
			io.deregister_stream(token).unwrap_or_else(|e| debug!("Error deregistering stream: {:?}", e));
		}
	}

	fn update_nodes(&self, _io: &IoContext<NetworkIoMessage>, node_changes: TableUpdates) {
		let mut to_remove: Vec<PeerId> = Vec::new();
		{
			let sessions = self.sessions.write();
			for c in sessions.iter() {
				let s = c.lock();
				if let Some(id) = s.id() {
					if node_changes.removed.contains(id) {
						to_remove.push(s.token());
					}
				}
			}
		}
		for i in to_remove {
			trace!(target: "network", "Removed from node table: {}", i);
		}
		self.nodes.write().update(node_changes, &*self.reserved_nodes.read());
	}

	pub fn with_context<F>(&self, protocol: ProtocolId, io: &IoContext<NetworkIoMessage>, action: F) where F: FnOnce(&NetworkContext) {
		let reserved = { self.reserved_nodes.read() };

		let context = NetworkContext::new(io, protocol, None, self.sessions.clone(), &reserved);
		action(&context);
	}

	pub fn with_context_eval<F, T>(&self, protocol: ProtocolId, io: &IoContext<NetworkIoMessage>, action: F) -> T where F: FnOnce(&NetworkContext) -> T {
		let reserved = { self.reserved_nodes.read() };

		let context = NetworkContext::new(io, protocol, None, self.sessions.clone(), &reserved);
		action(&context)
	}
}

impl IoHandler<NetworkIoMessage> for Host {
	/// Initialize networking
	fn initialize(&self, io: &IoContext<NetworkIoMessage>) {
		io.register_timer(IDLE, MAINTENANCE_TIMEOUT).expect("Error registering Network idle timer");
		io.message(NetworkIoMessage::InitPublicInterface).unwrap_or_else(|e| warn!("Error sending IO notification: {:?}", e));
		self.maintain_network(io)
	}

	fn stream_hup(&self, io: &IoContext<NetworkIoMessage>, stream: StreamToken) {
		trace!(target: "network", "Hup: {}", stream);
		match stream {
			FIRST_SESSION ... LAST_SESSION => self.connection_closed(stream, io),
			_ => warn!(target: "network", "Unexpected hup"),
		};
	}

	fn stream_readable(&self, io: &IoContext<NetworkIoMessage>, stream: StreamToken) {
		if self.stopping.load(AtomicOrdering::Acquire) {
			return;
		}
		match stream {
			FIRST_SESSION ... LAST_SESSION => self.session_readable(stream, io),
			DISCOVERY => {
				let node_changes = { self.discovery.lock().as_mut().map_or(None, |d| d.readable(io)) };
				if let Some(node_changes) = node_changes {
					self.update_nodes(io, node_changes);
				}
			},
			TCP_ACCEPT => self.accept(io),
			_ => panic!("Received unknown readable token"),
		}
	}

	fn stream_writable(&self, io: &IoContext<NetworkIoMessage>, stream: StreamToken) {
		if self.stopping.load(AtomicOrdering::Acquire) {
			return;
		}
		match stream {
			FIRST_SESSION ... LAST_SESSION => self.session_writable(stream, io),
			DISCOVERY => {
				self.discovery.lock().as_mut().map(|d| d.writable(io));
			}
			_ => panic!("Received unknown writable token"),
		}
	}

	fn timeout(&self, io: &IoContext<NetworkIoMessage>, token: TimerToken) {
		if self.stopping.load(AtomicOrdering::Acquire) {
			return;
		}
		match token {
			IDLE => self.maintain_network(io),
			FIRST_SESSION ... LAST_SESSION => self.connection_timeout(token, io),
			DISCOVERY_REFRESH => {
				self.discovery.lock().as_mut().map(|d| d.refresh());
				io.update_registration(DISCOVERY).unwrap_or_else(|e| debug!("Error updating discovery registration: {:?}", e));
			},
			DISCOVERY_ROUND => {
				let node_changes = { self.discovery.lock().as_mut().map_or(None, |d| d.round()) };
				if let Some(node_changes) = node_changes {
					self.update_nodes(io, node_changes);
				}
				io.update_registration(DISCOVERY).unwrap_or_else(|e| debug!("Error updating discovery registration: {:?}", e));
			},
			NODE_TABLE => {
				trace!(target: "network", "Refreshing node table");
				self.nodes.write().clear_useless();
				self.nodes.write().save();
			},
			_ => match self.timers.read().get(&token).cloned() {
				Some(timer) => match self.handlers.read().get(&timer.protocol).cloned() {
					None => { warn!(target: "network", "No handler found for protocol: {:?}", timer.protocol) },
					Some(h) => {
						let reserved = self.reserved_nodes.read();
						h.timeout(&NetworkContext::new(io, timer.protocol, None, self.sessions.clone(), &reserved), timer.token);
					}
				},
				None => { warn!("Unknown timer token: {}", token); } // timer is not registerd through us
			}
		}
	}

	fn message(&self, io: &IoContext<NetworkIoMessage>, message: &NetworkIoMessage) {
		if self.stopping.load(AtomicOrdering::Acquire) {
			return;
		}
		match *message {
			NetworkIoMessage::AddHandler {
				ref handler,
				ref protocol,
				ref versions,
				ref packet_count,
			} => {
				let h = handler.clone();
				let reserved = self.reserved_nodes.read();
				h.initialize(&NetworkContext::new(io, *protocol, None, self.sessions.clone(), &reserved));
				self.handlers.write().insert(*protocol, h);
				let mut info = self.info.write();
				for v in versions {
					info.capabilities.push(CapabilityInfo { protocol: *protocol, version: *v, packet_count: *packet_count });
				}
			},
			NetworkIoMessage::AddTimer {
				ref protocol,
				ref delay,
				ref token,
			} => {
				let handler_token = {
					let mut timer_counter = self.timer_counter.write();
					let counter = &mut *timer_counter;
					let handler_token = *counter;
					*counter += 1;
					handler_token
				};
				self.timers.write().insert(handler_token, ProtocolTimer { protocol: *protocol, token: *token });
				io.register_timer(handler_token, *delay).unwrap_or_else(|e| debug!("Error registering timer {}: {:?}", token, e));
			},
			NetworkIoMessage::Disconnect(ref peer) => {
				let session = { self.sessions.read().get(*peer).cloned() };
				if let Some(session) = session {
					session.lock().disconnect(io, DisconnectReason::DisconnectRequested);
				}
				trace!(target: "network", "Disconnect requested {}", peer);
				self.kill_connection(*peer, io, false);
			},
			NetworkIoMessage::DisablePeer(ref peer) => {
				let session = { self.sessions.read().get(*peer).cloned() };
				if let Some(session) = session {
					session.lock().disconnect(io, DisconnectReason::DisconnectRequested);
					if let Some(id) = session.lock().id() {
						self.nodes.write().mark_as_useless(id)
					}
				}
				trace!(target: "network", "Disabling peer {}", peer);
				self.kill_connection(*peer, io, false);
			},
			NetworkIoMessage::InitPublicInterface =>
				self.init_public_interface(io).unwrap_or_else(|e| warn!("Error initializing public interface: {:?}", e)),
			_ => {}	// ignore others.
		}
	}

	fn register_stream(&self, stream: StreamToken, reg: Token, event_loop: &mut EventLoop<IoManager<NetworkIoMessage>>) {
		match stream {
			FIRST_SESSION ... LAST_SESSION => {
				let session = { self.sessions.read().get(stream).cloned() };
				if let Some(session) = session {
					session.lock().register_socket(reg, event_loop).expect("Error registering socket");
				}
			}
			DISCOVERY => self.discovery.lock().as_ref().and_then(|d| d.register_socket(event_loop).ok()).expect("Error registering discovery socket"),
			TCP_ACCEPT => event_loop.register(&*self.tcp_listener.lock(), Token(TCP_ACCEPT), Ready::all(), PollOpt::edge()).expect("Error registering stream"),
			_ => warn!("Unexpected stream registration")
		}
	}

	fn deregister_stream(&self, stream: StreamToken, event_loop: &mut EventLoop<IoManager<NetworkIoMessage>>) {
		match stream {
			FIRST_SESSION ... LAST_SESSION => {
				let mut connections = self.sessions.write();
				if let Some(connection) = connections.get(stream).cloned() {
					let c = connection.lock();
					if c.expired() { // make sure it is the same connection that the event was generated for
						c.deregister_socket(event_loop).expect("Error deregistering socket");
						connections.remove(stream);
					}
				}
			}
			DISCOVERY => (),
			_ => warn!("Unexpected stream deregistration")
		}
	}

	fn update_stream(&self, stream: StreamToken, reg: Token, event_loop: &mut EventLoop<IoManager<NetworkIoMessage>>) {
		match stream {
			FIRST_SESSION ... LAST_SESSION => {
				let connection = { self.sessions.read().get(stream).cloned() };
				if let Some(connection) = connection {
					connection.lock().update_socket(reg, event_loop).expect("Error updating socket");
				}
			}
			DISCOVERY => self.discovery.lock().as_ref().and_then(|d| d.update_registration(event_loop).ok()).expect("Error reregistering discovery socket"),
			TCP_ACCEPT => event_loop.reregister(&*self.tcp_listener.lock(), Token(TCP_ACCEPT), Ready::all(), PollOpt::edge()).expect("Error reregistering stream"),
			_ => warn!("Unexpected stream update")
		}
	}
}

fn save_key(path: &Path, key: &Secret) {
	let mut path_buf = PathBuf::from(path);
	if let Err(e) = fs::create_dir_all(path_buf.as_path()) {
		warn!("Error creating key directory: {:?}", e);
		return;
	};
	path_buf.push("key");
	let path = path_buf.as_path();
	let mut file = match fs::File::create(&path) {
		Ok(file) => file,
		Err(e) => {
			warn!("Error creating key file: {:?}", e);
			return;
		}
	};
	if let Err(e) = restrict_permissions_owner(path, true, false) {
		warn!(target: "network", "Failed to modify permissions of the file ({})", e);
	}
	if let Err(e) = file.write(&key.hex().into_bytes()) {
		warn!("Error writing key file: {:?}", e);
	}
}

fn load_key(path: &Path) -> Option<Secret> {
	let mut path_buf = PathBuf::from(path);
	path_buf.push("key");
	let mut file = match fs::File::open(path_buf.as_path()) {
		Ok(file) => file,
		Err(e) => {
			debug!("Error opening key file: {:?}", e);
			return None;
		}
	};
	let mut buf = String::new();
	match file.read_to_string(&mut buf) {
		Ok(_) => {},
		Err(e) => {
			warn!("Error reading key file: {:?}", e);
			return None;
		}
	}
	match Secret::from_str(&buf) {
		Ok(key) => Some(key),
		Err(e) => {
			warn!("Error parsing key file: {:?}", e);
			None
		}
	}
}

#[test]
fn key_save_load() {
	use ::devtools::RandomTempPath;
	let temp_path = RandomTempPath::create_dir();
	let key = Secret::from_slice(&H256::random()).unwrap();
	save_key(temp_path.as_path(), &key);
	let r = load_key(temp_path.as_path());
	assert_eq!(key, r.unwrap());
}


#[test]
fn host_client_url() {
	let mut config = NetworkConfiguration::new_local();
	let key = "6f7b0d801bc7b5ce7bbd930b84fd0369b3eb25d09be58d64ba811091046f3aa2".parse().unwrap();
	config.use_secret = Some(key);
	let host: Host = Host::new(config, Arc::new(NetworkStats::new())).unwrap();
	assert!(host.local_url().starts_with("enode://101b3ef5a4ea7a1c7928e24c4c75fd053c235d7b80c22ae5c03d145d0ac7396e2a4ffff9adee3133a7b05044a5cee08115fd65145e5165d646bde371010d803c@"));
}