// Copyright (c) 2013-2016 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package peer

import (
	"bytes"
	"container/list"
	"errors"
	"fmt"
	"io"
	"math/rand"
	"net"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/daglabs/btcd/util/random"
	"github.com/daglabs/btcd/util/subnetworkid"

	"github.com/btcsuite/go-socks/socks"
	"github.com/daglabs/btcd/blockdag"
	"github.com/daglabs/btcd/dagconfig"
	"github.com/daglabs/btcd/logger"
	"github.com/daglabs/btcd/util/daghash"
	"github.com/daglabs/btcd/wire"
	"github.com/davecgh/go-spew/spew"
)

const (
	// MaxProtocolVersion is the max protocol version the peer supports.
	MaxProtocolVersion = wire.ProtocolVersion

	// minAcceptableProtocolVersion is the lowest protocol version that a
	// connected peer may support.
	minAcceptableProtocolVersion = wire.ProtocolVersion

	// outputBufferSize is the number of elements the output channels use.
	outputBufferSize = 50

	// invTrickleSize is the maximum amount of inventory to send in a single
	// message when trickling inventory to remote peers.
	maxInvTrickleSize = 1000

	// maxKnownInventory is the maximum number of items to keep in the known
	// inventory cache.
	maxKnownInventory = 1000

	// pingInterval is the interval of time to wait in between sending ping
	// messages.
	pingInterval = 2 * time.Minute

	// negotiateTimeout is the duration of inactivity before we timeout a
	// peer that hasn't completed the initial version negotiation.
	negotiateTimeout = 30 * time.Second

	// idleTimeout is the duration of inactivity before we time out a peer.
	idleTimeout = 5 * time.Minute

	// stallTickInterval is the interval of time between each check for
	// stalled peers.
	stallTickInterval = 15 * time.Second

	// stallResponseTimeout is the base maximum amount of time messages that
	// expect a response will wait before disconnecting the peer for
	// stalling.  The deadlines are adjusted for callback running times and
	// only checked on each stall tick interval.
	stallResponseTimeout = 30 * time.Second

	// trickleTimeout is the duration of the ticker which trickles down the
	// inventory to a peer.
	trickleTimeout = 10 * time.Second
)

var (
	// nodeCount is the total number of peer connections made since startup
	// and is used to assign an id to a peer.
	nodeCount int32

	// sentNonces houses the unique nonces that are generated when pushing
	// version messages that are used to detect self connections.
	sentNonces = newMruNonceMap(50)

	// allowSelfConns is only used to allow the tests to bypass the self
	// connection detecting and disconnect logic since they intentionally
	// do so for testing purposes.
	allowSelfConns bool
)

// MessageListeners defines callback function pointers to invoke with message
// listeners for a peer. Any listener which is not set to a concrete callback
// during peer initialization is ignored. Execution of multiple message
// listeners occurs serially, so one callback blocks the execution of the next.
//
// NOTE: Unless otherwise documented, these listeners must NOT directly call any
// blocking calls (such as WaitForShutdown) on the peer instance since the input
// handler goroutine blocks until the callback has completed.  Doing so will
// result in a deadlock.
type MessageListeners struct {
	// OnGetAddr is invoked when a peer receives a getaddr bitcoin message.
	OnGetAddr func(p *Peer, msg *wire.MsgGetAddr)

	// OnAddr is invoked when a peer receives an addr bitcoin message.
	OnAddr func(p *Peer, msg *wire.MsgAddr)

	// OnPing is invoked when a peer receives a ping bitcoin message.
	OnPing func(p *Peer, msg *wire.MsgPing)

	// OnPong is invoked when a peer receives a pong bitcoin message.
	OnPong func(p *Peer, msg *wire.MsgPong)

	// OnAlert is invoked when a peer receives an alert bitcoin message.
	OnAlert func(p *Peer, msg *wire.MsgAlert)

	// OnMemPool is invoked when a peer receives a mempool bitcoin message.
	OnMemPool func(p *Peer, msg *wire.MsgMemPool)

	// OnTx is invoked when a peer receives a tx bitcoin message.
	OnTx func(p *Peer, msg *wire.MsgTx)

	// OnBlock is invoked when a peer receives a block bitcoin message.
	OnBlock func(p *Peer, msg *wire.MsgBlock, buf []byte)

	// OnCFilter is invoked when a peer receives a cfilter bitcoin message.
	OnCFilter func(p *Peer, msg *wire.MsgCFilter)

	// OnCFHeaders is invoked when a peer receives a cfheaders bitcoin
	// message.
	OnCFHeaders func(p *Peer, msg *wire.MsgCFHeaders)

	// OnCFCheckpt is invoked when a peer receives a cfcheckpt bitcoin
	// message.
	OnCFCheckpt func(p *Peer, msg *wire.MsgCFCheckpt)

	// OnInv is invoked when a peer receives an inv bitcoin message.
	OnInv func(p *Peer, msg *wire.MsgInv)

	// OnHeaders is invoked when a peer receives a headers bitcoin message.
	OnHeaders func(p *Peer, msg *wire.MsgHeaders)

	// OnNotFound is invoked when a peer receives a notfound bitcoin
	// message.
	OnNotFound func(p *Peer, msg *wire.MsgNotFound)

	// OnGetData is invoked when a peer receives a getdata bitcoin message.
	OnGetData func(p *Peer, msg *wire.MsgGetData)

	// OnGetBlocks is invoked when a peer receives a getblocks bitcoin
	// message.
	OnGetBlocks func(p *Peer, msg *wire.MsgGetBlocks)

	// OnGetHeaders is invoked when a peer receives a getheaders bitcoin
	// message.
	OnGetHeaders func(p *Peer, msg *wire.MsgGetHeaders)

	// OnGetCFilters is invoked when a peer receives a getcfilters bitcoin
	// message.
	OnGetCFilters func(p *Peer, msg *wire.MsgGetCFilters)

	// OnGetCFHeaders is invoked when a peer receives a getcfheaders
	// bitcoin message.
	OnGetCFHeaders func(p *Peer, msg *wire.MsgGetCFHeaders)

	// OnGetCFCheckpt is invoked when a peer receives a getcfcheckpt
	// bitcoin message.
	OnGetCFCheckpt func(p *Peer, msg *wire.MsgGetCFCheckpt)

	// OnFeeFilter is invoked when a peer receives a feefilter bitcoin message.
	OnFeeFilter func(p *Peer, msg *wire.MsgFeeFilter)

	// OnFilterAdd is invoked when a peer receives a filteradd bitcoin message.
	OnFilterAdd func(p *Peer, msg *wire.MsgFilterAdd)

	// OnFilterClear is invoked when a peer receives a filterclear bitcoin
	// message.
	OnFilterClear func(p *Peer, msg *wire.MsgFilterClear)

	// OnFilterLoad is invoked when a peer receives a filterload bitcoin
	// message.
	OnFilterLoad func(p *Peer, msg *wire.MsgFilterLoad)

	// OnMerkleBlock  is invoked when a peer receives a merkleblock bitcoin
	// message.
	OnMerkleBlock func(p *Peer, msg *wire.MsgMerkleBlock)

	// OnVersion is invoked when a peer receives a version bitcoin message.
	OnVersion func(p *Peer, msg *wire.MsgVersion)

	// OnVerAck is invoked when a peer receives a verack bitcoin message.
	OnVerAck func(p *Peer, msg *wire.MsgVerAck)

	// OnReject is invoked when a peer receives a reject bitcoin message.
	OnReject func(p *Peer, msg *wire.MsgReject)

	// OnSendHeaders is invoked when a peer receives a sendheaders bitcoin
	// message.
	OnSendHeaders func(p *Peer, msg *wire.MsgSendHeaders)

	// OnRead is invoked when a peer receives a bitcoin message.  It
	// consists of the number of bytes read, the message, and whether or not
	// an error in the read occurred.  Typically, callers will opt to use
	// the callbacks for the specific message types, however this can be
	// useful for circumstances such as keeping track of server-wide byte
	// counts or working with custom message types for which the peer does
	// not directly provide a callback.
	OnRead func(p *Peer, bytesRead int, msg wire.Message, err error)

	// OnWrite is invoked when we write a bitcoin message to a peer.  It
	// consists of the number of bytes written, the message, and whether or
	// not an error in the write occurred.  This can be useful for
	// circumstances such as keeping track of server-wide byte counts.
	OnWrite func(p *Peer, bytesWritten int, msg wire.Message, err error)
}

// Config is the struct to hold configuration options useful to Peer.
type Config struct {
	// SelectedTip specifies a callback which provides the selected tip
	// to the peer as needed.
	SelectedTip func() *daghash.Hash

	// SelectedTip specifies a callback which provides the selected tip
	// to the peer as needed.
	BlockExists func(*daghash.Hash) (bool, error)

	// HostToNetAddress returns the netaddress for the given host. This can be
	// nil in  which case the host will be parsed as an IP address.
	HostToNetAddress HostToNetAddrFunc

	// Proxy indicates a proxy is being used for connections.  The only
	// effect this has is to prevent leaking the tor proxy address, so it
	// only needs to specified if using a tor proxy.
	Proxy string

	// UserAgentName specifies the user agent name to advertise.  It is
	// highly recommended to specify this value.
	UserAgentName string

	// UserAgentVersion specifies the user agent version to advertise.  It
	// is highly recommended to specify this value and that it follows the
	// form "major.minor.revision" e.g. "2.6.41".
	UserAgentVersion string

	// UserAgentComments specify the user agent comments to advertise.  These
	// values must not contain the illegal characters specified in BIP 14:
	// '/', ':', '(', ')'.
	UserAgentComments []string

	// DAGParams identifies which DAG parameters the peer is associated
	// with.  It is highly recommended to specify this field, however it can
	// be omitted in which case the test network will be used.
	DAGParams *dagconfig.Params

	// Services specifies which services to advertise as supported by the
	// local peer.  This field can be omitted in which case it will be 0
	// and therefore advertise no supported services.
	Services wire.ServiceFlag

	// ProtocolVersion specifies the maximum protocol version to use and
	// advertise.  This field can be omitted in which case
	// peer.MaxProtocolVersion will be used.
	ProtocolVersion uint32

	// DisableRelayTx specifies if the remote peer should be informed to
	// not send inv messages for transactions.
	DisableRelayTx bool

	// Listeners houses callback functions to be invoked on receiving peer
	// messages.
	Listeners MessageListeners

	// SubnetworkID specifies which subnetwork the peer is associated with.
	// It is nil in full nodes.
	SubnetworkID *subnetworkid.SubnetworkID
}

// minUint32 is a helper function to return the minimum of two uint32s.
// This avoids a math import and the need to cast to floats.
func minUint32(a, b uint32) uint32 {
	if a < b {
		return a
	}
	return b
}

// newNetAddress attempts to extract the IP address and port from the passed
// net.Addr interface and create a bitcoin NetAddress structure using that
// information.
func newNetAddress(addr net.Addr, services wire.ServiceFlag) (*wire.NetAddress, error) {
	// addr will be a net.TCPAddr when not using a proxy.
	if tcpAddr, ok := addr.(*net.TCPAddr); ok {
		ip := tcpAddr.IP
		port := uint16(tcpAddr.Port)
		na := wire.NewNetAddressIPPort(ip, port, services)
		return na, nil
	}

	// addr will be a socks.ProxiedAddr when using a proxy.
	if proxiedAddr, ok := addr.(*socks.ProxiedAddr); ok {
		ip := net.ParseIP(proxiedAddr.Host)
		if ip == nil {
			ip = net.ParseIP("0.0.0.0")
		}
		port := uint16(proxiedAddr.Port)
		na := wire.NewNetAddressIPPort(ip, port, services)
		return na, nil
	}

	// For the most part, addr should be one of the two above cases, but
	// to be safe, fall back to trying to parse the information from the
	// address string as a last resort.
	host, portStr, err := net.SplitHostPort(addr.String())
	if err != nil {
		return nil, err
	}
	ip := net.ParseIP(host)
	port, err := strconv.ParseUint(portStr, 10, 16)
	if err != nil {
		return nil, err
	}
	na := wire.NewNetAddressIPPort(ip, uint16(port), services)
	return na, nil
}

// outMsg is used to house a message to be sent along with a channel to signal
// when the message has been sent (or won't be sent due to things such as
// shutdown)
type outMsg struct {
	msg      wire.Message
	doneChan chan<- struct{}
}

// stallControlCmd represents the command of a stall control message.
type stallControlCmd uint8

// Constants for the command of a stall control message.
const (
	// sccSendMessage indicates a message is being sent to the remote peer.
	sccSendMessage stallControlCmd = iota

	// sccReceiveMessage indicates a message has been received from the
	// remote peer.
	sccReceiveMessage

	// sccHandlerStart indicates a callback handler is about to be invoked.
	sccHandlerStart

	// sccHandlerStart indicates a callback handler has completed.
	sccHandlerDone
)

// stallControlMsg is used to signal the stall handler about specific events
// so it can properly detect and handle stalled remote peers.
type stallControlMsg struct {
	command stallControlCmd
	message wire.Message
}

// StatsSnap is a snapshot of peer stats at a point in time.
type StatsSnap struct {
	ID             int32
	Addr           string
	Services       wire.ServiceFlag
	LastSend       time.Time
	LastRecv       time.Time
	BytesSent      uint64
	BytesRecv      uint64
	ConnTime       time.Time
	TimeOffset     int64
	Version        uint32
	UserAgent      string
	Inbound        bool
	SelectedTip    *daghash.Hash
	LastPingNonce  uint64
	LastPingTime   time.Time
	LastPingMicros int64
}

// HashFunc is a function which returns a block hash, height and error
// It is used as a callback to get newest block details.
type HashFunc func() (hash *daghash.Hash, height int32, err error)

// AddrFunc is a func which takes an address and returns a related address.
type AddrFunc func(remoteAddr *wire.NetAddress) *wire.NetAddress

// HostToNetAddrFunc is a func which takes a host, port, services and returns
// the netaddress.
type HostToNetAddrFunc func(host string, port uint16,
	services wire.ServiceFlag) (*wire.NetAddress, error)

// NOTE: The overall data flow of a peer is split into 3 goroutines.  Inbound
// messages are read via the inHandler goroutine and generally dispatched to
// their own handler.  For inbound data-related messages such as blocks,
// transactions, and inventory, the data is handled by the corresponding
// message handlers.  The data flow for outbound messages is split into 2
// goroutines, queueHandler and outHandler.  The first, queueHandler, is used
// as a way for external entities to queue messages, by way of the QueueMessage
// function, quickly regardless of whether the peer is currently sending or not.
// It acts as the traffic cop between the external world and the actual
// goroutine which writes to the network socket.

// Peer provides a basic concurrent safe bitcoin peer for handling bitcoin
// communications via the peer-to-peer protocol.  It provides full duplex
// reading and writing, automatic handling of the initial handshake process,
// querying of usage statistics and other information about the remote peer such
// as its address, user agent, and protocol version, output message queuing,
// inventory trickling, and the ability to dynamically register and unregister
// callbacks for handling bitcoin protocol messages.
//
// Outbound messages are typically queued via QueueMessage or QueueInventory.
// QueueMessage is intended for all messages, including responses to data such
// as blocks and transactions.  QueueInventory, on the other hand, is only
// intended for relaying inventory as it employs a trickling mechanism to batch
// the inventory together.  However, some helper functions for pushing messages
// of specific types that typically require common special handling are
// provided as a convenience.
type Peer struct {
	// The following variables must only be used atomically.
	bytesReceived uint64
	bytesSent     uint64
	lastRecv      int64
	lastSend      int64
	connected     int32
	disconnect    int32

	conn net.Conn

	// These fields are set at creation time and never modified, so they are
	// safe to read from concurrently without a mutex.
	addr    string
	cfg     Config
	inbound bool

	flagsMtx             sync.Mutex // protects the peer flags below
	na                   *wire.NetAddress
	id                   int32
	userAgent            string
	services             wire.ServiceFlag
	versionKnown         bool
	advertisedProtoVer   uint32 // protocol version advertised by remote
	protocolVersion      uint32 // negotiated protocol version
	sendHeadersPreferred bool   // peer sent a sendheaders message
	verAckReceived       bool

	knownInventory     *mruInventoryMap
	prevGetBlocksMtx   sync.Mutex
	prevGetBlocksBegin *daghash.Hash
	prevGetBlocksStop  *daghash.Hash
	prevGetHdrsMtx     sync.Mutex
	prevGetHdrsBegin   *daghash.Hash
	prevGetHdrsStop    *daghash.Hash

	// These fields keep track of statistics for the peer and are protected
	// by the statsMtx mutex.
	statsMtx       sync.RWMutex
	timeOffset     int64
	timeConnected  time.Time
	selectedTip    *daghash.Hash
	lastPingNonce  uint64    // Set to nonce if we have a pending ping.
	lastPingTime   time.Time // Time we sent last ping.
	lastPingMicros int64     // Time for last ping to return.

	stallControl  chan stallControlMsg
	outputQueue   chan outMsg
	sendQueue     chan outMsg
	sendDoneQueue chan struct{}
	outputInvChan chan *wire.InvVect
	inQuit        chan struct{}
	queueQuit     chan struct{}
	outQuit       chan struct{}
	quit          chan struct{}
}

// String returns the peer's address and directionality as a human-readable
// string.
//
// This function is safe for concurrent access.
func (p *Peer) String() string {
	return fmt.Sprintf("%s (%s)", p.addr, logger.DirectionString(p.inbound))
}

// AddKnownInventory adds the passed inventory to the cache of known inventory
// for the peer.
//
// This function is safe for concurrent access.
func (p *Peer) AddKnownInventory(invVect *wire.InvVect) {
	p.knownInventory.Add(invVect)
}

// StatsSnapshot returns a snapshot of the current peer flags and statistics.
//
// This function is safe for concurrent access.
func (p *Peer) StatsSnapshot() *StatsSnap {
	p.statsMtx.RLock()

	p.flagsMtx.Lock()
	id := p.id
	addr := p.addr
	userAgent := p.userAgent
	services := p.services
	protocolVersion := p.advertisedProtoVer
	p.flagsMtx.Unlock()

	// Get a copy of all relevant flags and stats.
	statsSnap := &StatsSnap{
		ID:             id,
		Addr:           addr,
		UserAgent:      userAgent,
		Services:       services,
		LastSend:       p.LastSend(),
		LastRecv:       p.LastRecv(),
		BytesSent:      p.BytesSent(),
		BytesRecv:      p.BytesReceived(),
		ConnTime:       p.timeConnected,
		TimeOffset:     p.timeOffset,
		Version:        protocolVersion,
		Inbound:        p.inbound,
		SelectedTip:    p.selectedTip,
		LastPingNonce:  p.lastPingNonce,
		LastPingMicros: p.lastPingMicros,
		LastPingTime:   p.lastPingTime,
	}

	p.statsMtx.RUnlock()
	return statsSnap
}

// ID returns the peer id.
//
// This function is safe for concurrent access.
func (p *Peer) ID() int32 {
	p.flagsMtx.Lock()
	id := p.id
	p.flagsMtx.Unlock()

	return id
}

// NA returns the peer network address.
//
// This function is safe for concurrent access.
func (p *Peer) NA() *wire.NetAddress {
	p.flagsMtx.Lock()
	na := p.na
	p.flagsMtx.Unlock()

	return na
}

// Addr returns the peer address.
//
// This function is safe for concurrent access.
func (p *Peer) Addr() string {
	// The address doesn't change after initialization, therefore it is not
	// protected by a mutex.
	return p.addr
}

// Inbound returns whether the peer is inbound.
//
// This function is safe for concurrent access.
func (p *Peer) Inbound() bool {
	return p.inbound
}

// Services returns the services flag of the remote peer.
//
// This function is safe for concurrent access.
func (p *Peer) Services() wire.ServiceFlag {
	p.flagsMtx.Lock()
	services := p.services
	p.flagsMtx.Unlock()

	return services
}

// UserAgent returns the user agent of the remote peer.
//
// This function is safe for concurrent access.
func (p *Peer) UserAgent() string {
	p.flagsMtx.Lock()
	userAgent := p.userAgent
	p.flagsMtx.Unlock()

	return userAgent
}

// SubnetworkID returns peer subnetwork ID
func (p *Peer) SubnetworkID() *subnetworkid.SubnetworkID {
	p.flagsMtx.Lock()
	subnetworkID := p.cfg.SubnetworkID
	p.flagsMtx.Unlock()

	return subnetworkID
}

// LastPingNonce returns the last ping nonce of the remote peer.
//
// This function is safe for concurrent access.
func (p *Peer) LastPingNonce() uint64 {
	p.statsMtx.RLock()
	lastPingNonce := p.lastPingNonce
	p.statsMtx.RUnlock()

	return lastPingNonce
}

// LastPingTime returns the last ping time of the remote peer.
//
// This function is safe for concurrent access.
func (p *Peer) LastPingTime() time.Time {
	p.statsMtx.RLock()
	lastPingTime := p.lastPingTime
	p.statsMtx.RUnlock()

	return lastPingTime
}

// LastPingMicros returns the last ping micros of the remote peer.
//
// This function is safe for concurrent access.
func (p *Peer) LastPingMicros() int64 {
	p.statsMtx.RLock()
	lastPingMicros := p.lastPingMicros
	p.statsMtx.RUnlock()

	return lastPingMicros
}

// VersionKnown returns the whether or not the version of a peer is known
// locally.
//
// This function is safe for concurrent access.
func (p *Peer) VersionKnown() bool {
	p.flagsMtx.Lock()
	versionKnown := p.versionKnown
	p.flagsMtx.Unlock()

	return versionKnown
}

// VerAckReceived returns whether or not a verack message was received by the
// peer.
//
// This function is safe for concurrent access.
func (p *Peer) VerAckReceived() bool {
	p.flagsMtx.Lock()
	verAckReceived := p.verAckReceived
	p.flagsMtx.Unlock()

	return verAckReceived
}

// ProtocolVersion returns the negotiated peer protocol version.
//
// This function is safe for concurrent access.
func (p *Peer) ProtocolVersion() uint32 {
	p.flagsMtx.Lock()
	protocolVersion := p.protocolVersion
	p.flagsMtx.Unlock()

	return protocolVersion
}

// SelectedTip returns the selected tip of the peer.
//
// This function is safe for concurrent access.
func (p *Peer) SelectedTip() *daghash.Hash {
	p.statsMtx.RLock()
	selectedTip := p.selectedTip
	p.statsMtx.RUnlock()

	return selectedTip
}

// IsSyncCandidate returns whether or not this peer is a sync candidate.
//
// This function is safe for concurrent access.
func (p *Peer) IsSyncCandidate() (bool, error) {
	exists, err := p.cfg.BlockExists(p.selectedTip)
	if err != nil {
		return false, err
	}
	return !exists, nil
}

// LastSend returns the last send time of the peer.
//
// This function is safe for concurrent access.
func (p *Peer) LastSend() time.Time {
	return time.Unix(atomic.LoadInt64(&p.lastSend), 0)
}

// LastRecv returns the last recv time of the peer.
//
// This function is safe for concurrent access.
func (p *Peer) LastRecv() time.Time {
	return time.Unix(atomic.LoadInt64(&p.lastRecv), 0)
}

// BytesSent returns the total number of bytes sent by the peer.
//
// This function is safe for concurrent access.
func (p *Peer) BytesSent() uint64 {
	return atomic.LoadUint64(&p.bytesSent)
}

// BytesReceived returns the total number of bytes received by the peer.
//
// This function is safe for concurrent access.
func (p *Peer) BytesReceived() uint64 {
	return atomic.LoadUint64(&p.bytesReceived)
}

// TimeConnected returns the time at which the peer connected.
//
// This function is safe for concurrent access.
func (p *Peer) TimeConnected() time.Time {
	p.statsMtx.RLock()
	timeConnected := p.timeConnected
	p.statsMtx.RUnlock()

	return timeConnected
}

// TimeOffset returns the number of seconds the local time was offset from the
// time the peer reported during the initial negotiation phase.  Negative values
// indicate the remote peer's time is before the local time.
//
// This function is safe for concurrent access.
func (p *Peer) TimeOffset() int64 {
	p.statsMtx.RLock()
	timeOffset := p.timeOffset
	p.statsMtx.RUnlock()

	return timeOffset
}

// WantsHeaders returns if the peer wants header messages instead of
// inventory vectors for blocks.
//
// This function is safe for concurrent access.
func (p *Peer) WantsHeaders() bool {
	p.flagsMtx.Lock()
	sendHeadersPreferred := p.sendHeadersPreferred
	p.flagsMtx.Unlock()

	return sendHeadersPreferred
}

// localVersionMsg creates a version message that can be used to send to the
// remote peer.
func (p *Peer) localVersionMsg() (*wire.MsgVersion, error) {
	selectedTip := p.cfg.SelectedTip()
	theirNA := p.na

	// If we are behind a proxy and the connection comes from the proxy then
	// we return an unroutable address as their address. This is to prevent
	// leaking the tor proxy address.
	if p.cfg.Proxy != "" {
		proxyaddress, _, err := net.SplitHostPort(p.cfg.Proxy)
		// invalid proxy means poorly configured, be on the safe side.
		if err != nil || p.na.IP.String() == proxyaddress {
			theirNA = wire.NewNetAddressIPPort(net.IP([]byte{0, 0, 0, 0}), 0, 0)
		}
	}

	// Create a wire.NetAddress with only the services set to use as the
	// "addrme" in the version message.
	//
	// Older nodes previously added the IP and port information to the
	// address manager which proved to be unreliable as an inbound
	// connection from a peer didn't necessarily mean the peer itself
	// accepted inbound connections.
	//
	// Also, the timestamp is unused in the version message.
	ourNA := &wire.NetAddress{
		Services: p.cfg.Services,
	}

	// Generate a unique nonce for this peer so self connections can be
	// detected.  This is accomplished by adding it to a size-limited map of
	// recently seen nonces.
	nonce := uint64(rand.Int63())
	sentNonces.Add(nonce)

	subnetworkID := p.cfg.SubnetworkID

	// Version message.
	msg := wire.NewMsgVersion(ourNA, theirNA, nonce, selectedTip, subnetworkID)
	msg.AddUserAgent(p.cfg.UserAgentName, p.cfg.UserAgentVersion,
		p.cfg.UserAgentComments...)

	// XXX: bitcoind appears to always enable the full node services flag
	// of the remote peer netaddress field in the version message regardless
	// of whether it knows it supports it or not.  Also, bitcoind sets
	// the services field of the local peer to 0 regardless of support.
	//
	// Realistically, this should be set as follows:
	// - For outgoing connections:
	//    - Set the local netaddress services to what the local peer
	//      actually supports
	//    - Set the remote netaddress services to 0 to indicate no services
	//      as they are still unknown
	// - For incoming connections:
	//    - Set the local netaddress services to what the local peer
	//      actually supports
	//    - Set the remote netaddress services to the what was advertised by
	//      by the remote peer in its version message
	msg.AddrYou.Services = wire.SFNodeNetwork

	// Advertise the services flag
	msg.Services = p.cfg.Services

	// Advertise our max supported protocol version.
	msg.ProtocolVersion = int32(p.cfg.ProtocolVersion)

	// Advertise if inv messages for transactions are desired.
	msg.DisableRelayTx = p.cfg.DisableRelayTx

	return msg, nil
}

// PushAddrMsg sends an addr message to the connected peer using the provided
// addresses.  This function is useful over manually sending the message via
// QueueMessage since it automatically limits the addresses to the maximum
// number allowed by the message and randomizes the chosen addresses when there
// are too many.  It returns the addresses that were actually sent and no
// message will be sent if there are no entries in the provided addresses slice.
//
// This function is safe for concurrent access.
func (p *Peer) PushAddrMsg(addresses []*wire.NetAddress, subnetworkID *subnetworkid.SubnetworkID) ([]*wire.NetAddress, error) {
	addressCount := len(addresses)

	// Nothing to send.
	if addressCount == 0 {
		return nil, nil
	}

	msg := wire.NewMsgAddr(false, subnetworkID)
	msg.AddrList = make([]*wire.NetAddress, addressCount)
	copy(msg.AddrList, addresses)

	// Randomize the addresses sent if there are more than the maximum allowed.
	if addressCount > wire.MaxAddrPerMsg {
		// Shuffle the address list.
		for i := 0; i < wire.MaxAddrPerMsg; i++ {
			j := i + rand.Intn(addressCount-i)
			msg.AddrList[i], msg.AddrList[j] = msg.AddrList[j], msg.AddrList[i]
		}

		// Truncate it to the maximum size.
		msg.AddrList = msg.AddrList[:wire.MaxAddrPerMsg]
	}

	p.QueueMessage(msg, nil)
	return msg.AddrList, nil
}

// PushGetBlocksMsg sends a getblocks message for the provided block locator
// and stop hash.  It will ignore back-to-back duplicate requests.
//
// This function is safe for concurrent access.
func (p *Peer) PushGetBlocksMsg(locator blockdag.BlockLocator, stopHash *daghash.Hash) error {
	// Extract the begin hash from the block locator, if one was specified,
	// to use for filtering duplicate getblocks requests.
	var beginHash *daghash.Hash
	if len(locator) > 0 {
		beginHash = locator[0]
	}

	// Filter duplicate getblocks requests.
	p.prevGetBlocksMtx.Lock()
	isDuplicate := p.prevGetBlocksStop != nil && p.prevGetBlocksBegin != nil &&
		beginHash != nil && stopHash.IsEqual(p.prevGetBlocksStop) &&
		beginHash.IsEqual(p.prevGetBlocksBegin)
	p.prevGetBlocksMtx.Unlock()

	if isDuplicate {
		log.Tracef("Filtering duplicate [getblocks] with begin "+
			"hash %s, stop hash %s", beginHash, stopHash)
		return nil
	}

	// Construct the getblocks request and queue it to be sent.
	msg := wire.NewMsgGetBlocks(stopHash)
	for _, hash := range locator {
		err := msg.AddBlockLocatorHash(hash)
		if err != nil {
			return err
		}
	}
	p.QueueMessage(msg, nil)

	// Update the previous getblocks request information for filtering
	// duplicates.
	p.prevGetBlocksMtx.Lock()
	p.prevGetBlocksBegin = beginHash
	p.prevGetBlocksStop = stopHash
	p.prevGetBlocksMtx.Unlock()
	return nil
}

// PushGetHeadersMsg sends a getblocks message for the provided block locator
// and stop hash.  It will ignore back-to-back duplicate requests.
//
// This function is safe for concurrent access.
func (p *Peer) PushGetHeadersMsg(locator blockdag.BlockLocator, stopHash *daghash.Hash) error {
	// Extract the begin hash from the block locator, if one was specified,
	// to use for filtering duplicate getheaders requests.
	var beginHash *daghash.Hash
	if len(locator) > 0 {
		beginHash = locator[0]
	}

	// Filter duplicate getheaders requests.
	p.prevGetHdrsMtx.Lock()
	isDuplicate := p.prevGetHdrsStop != nil && p.prevGetHdrsBegin != nil &&
		beginHash != nil && stopHash.IsEqual(p.prevGetHdrsStop) &&
		beginHash.IsEqual(p.prevGetHdrsBegin)
	p.prevGetHdrsMtx.Unlock()

	if isDuplicate {
		log.Tracef("Filtering duplicate [getheaders] with begin hash %s",
			beginHash)
		return nil
	}

	// Construct the getheaders request and queue it to be sent.
	msg := wire.NewMsgGetHeaders()
	msg.HashStop = stopHash
	for _, hash := range locator {
		err := msg.AddBlockLocatorHash(hash)
		if err != nil {
			return err
		}
	}
	p.QueueMessage(msg, nil)

	// Update the previous getheaders request information for filtering
	// duplicates.
	p.prevGetHdrsMtx.Lock()
	p.prevGetHdrsBegin = beginHash
	p.prevGetHdrsStop = stopHash
	p.prevGetHdrsMtx.Unlock()
	return nil
}

// PushRejectMsg sends a reject message for the provided command, reject code,
// reject reason, and hash.  The hash will only be used when the command is a tx
// or block and should be nil in other cases.  The wait parameter will cause the
// function to block until the reject message has actually been sent.
//
// This function is safe for concurrent access.
func (p *Peer) PushRejectMsg(command string, code wire.RejectCode, reason string, hash *daghash.Hash, wait bool) {
	msg := wire.NewMsgReject(command, code, reason)
	if command == wire.CmdTx || command == wire.CmdBlock {
		if hash == nil {
			log.Warnf("Sending a reject message for command "+
				"type %s which should have specified a hash "+
				"but does not", command)
			hash = &daghash.ZeroHash
		}
		msg.Hash = hash
	}

	// Send the message without waiting if the caller has not requested it.
	if !wait {
		p.QueueMessage(msg, nil)
		return
	}

	// Send the message and block until it has been sent before returning.
	doneChan := make(chan struct{}, 1)
	p.QueueMessage(msg, doneChan)
	<-doneChan
}

// handleRemoteVersionMsg is invoked when a version bitcoin message is received
// from the remote peer.  It will return an error if the remote peer's version
// is not compatible with ours.
func (p *Peer) handleRemoteVersionMsg(msg *wire.MsgVersion) error {
	// Detect self connections.
	if !allowSelfConns && sentNonces.Exists(msg.Nonce) {
		return errors.New("disconnecting peer connected to self")
	}

	// Notify and disconnect clients that have a protocol version that is
	// too old.
	//
	// NOTE: If minAcceptableProtocolVersion is raised to be higher than
	// wire.RejectVersion, this should send a reject packet before
	// disconnecting.
	if uint32(msg.ProtocolVersion) < minAcceptableProtocolVersion {
		reason := fmt.Sprintf("protocol version must be %d or greater",
			minAcceptableProtocolVersion)
		return errors.New(reason)
	}

	// Disconnect if:
	// - we are a full node and the outbound connection we've initiated is a partial node
	// - the remote node is partial and our subnetwork doesn't match their subnetwork
	isLocalNodeFull := p.cfg.SubnetworkID == nil
	isRemoteNodeFull := msg.SubnetworkID == nil
	if (isLocalNodeFull && !isRemoteNodeFull && !p.inbound) ||
		(!isLocalNodeFull && !isRemoteNodeFull && !msg.SubnetworkID.IsEqual(p.cfg.SubnetworkID)) {

		return errors.New("incompatible subnetworks")
	}

	// Updating a bunch of stats including block based stats, and the
	// peer's time offset.
	p.statsMtx.Lock()
	p.selectedTip = msg.SelectedTip
	p.timeOffset = msg.Timestamp.Unix() - time.Now().Unix()
	p.statsMtx.Unlock()

	// Negotiate the protocol version.
	p.flagsMtx.Lock()
	p.advertisedProtoVer = uint32(msg.ProtocolVersion)
	p.protocolVersion = minUint32(p.protocolVersion, p.advertisedProtoVer)
	p.versionKnown = true
	log.Debugf("Negotiated protocol version %d for peer %s",
		p.protocolVersion, p)

	// Set the peer's ID.
	p.id = atomic.AddInt32(&nodeCount, 1)

	// Set the supported services for the peer to what the remote peer
	// advertised.
	p.services = msg.Services

	// Set the remote peer's user agent.
	p.userAgent = msg.UserAgent

	p.flagsMtx.Unlock()

	return nil
}

// handlePingMsg is invoked when a peer receives a ping bitcoin message.  For
// recent clients (protocol version > BIP0031Version), it replies with a pong
// message.  For older clients, it does nothing and anything other than failure
// is considered a successful ping.
func (p *Peer) handlePingMsg(msg *wire.MsgPing) {
	// Include nonce from ping so pong can be identified.
	p.QueueMessage(wire.NewMsgPong(msg.Nonce), nil)
}

// handlePongMsg is invoked when a peer receives a pong bitcoin message.  It
// updates the ping statistics as required for recent clients.
func (p *Peer) handlePongMsg(msg *wire.MsgPong) {
	// Arguably we could use a buffered channel here sending data
	// in a fifo manner whenever we send a ping, or a list keeping track of
	// the times of each ping. For now we just make a best effort and
	// only record stats if it was for the last ping sent. Any preceding
	// and overlapping pings will be ignored. It is unlikely to occur
	// without large usage of the ping rpc call since we ping infrequently
	// enough that if they overlap we would have timed out the peer.
	p.statsMtx.Lock()
	if p.lastPingNonce != 0 && msg.Nonce == p.lastPingNonce {
		p.lastPingMicros = time.Since(p.lastPingTime).Nanoseconds()
		p.lastPingMicros /= 1000 // convert to usec.
		p.lastPingNonce = 0
	}
	p.statsMtx.Unlock()
}

// readMessage reads the next bitcoin message from the peer with logging.
func (p *Peer) readMessage() (wire.Message, []byte, error) {
	n, msg, buf, err := wire.ReadMessageN(p.conn,
		p.ProtocolVersion(), p.cfg.DAGParams.Net)
	atomic.AddUint64(&p.bytesReceived, uint64(n))
	if p.cfg.Listeners.OnRead != nil {
		p.cfg.Listeners.OnRead(p, n, msg, err)
	}
	if err != nil {
		return nil, nil, err
	}

	// Use closures to log expensive operations so they are only run when
	// the logging level requires it.
	log.Debugf("%s", newLogClosure(func() string {
		// Debug summary of message.
		summary := messageSummary(msg)
		if len(summary) > 0 {
			summary = " (" + summary + ")"
		}
		return fmt.Sprintf("Received %s%s from %s",
			msg.Command(), summary, p)
	}))
	log.Tracef("%s", newLogClosure(func() string {
		return spew.Sdump(msg)
	}))
	log.Tracef("%s", newLogClosure(func() string {
		return spew.Sdump(buf)
	}))

	return msg, buf, nil
}

// writeMessage sends a bitcoin message to the peer with logging.
func (p *Peer) writeMessage(msg wire.Message) error {
	// Don't do anything if we're disconnecting.
	if atomic.LoadInt32(&p.disconnect) != 0 {
		return nil
	}

	// Use closures to log expensive operations so they are only run when
	// the logging level requires it.
	log.Debugf("%s", newLogClosure(func() string {
		// Debug summary of message.
		summary := messageSummary(msg)
		if len(summary) > 0 {
			summary = " (" + summary + ")"
		}
		return fmt.Sprintf("Sending %s%s to %s", msg.Command(),
			summary, p)
	}))
	log.Tracef("%s", newLogClosure(func() string {
		return spew.Sdump(msg)
	}))
	log.Tracef("%s", newLogClosure(func() string {
		var buf bytes.Buffer
		_, err := wire.WriteMessageN(&buf, msg, p.ProtocolVersion(),
			p.cfg.DAGParams.Net)
		if err != nil {
			return err.Error()
		}
		return spew.Sdump(buf.Bytes())
	}))

	// Write the message to the peer.
	n, err := wire.WriteMessageN(p.conn, msg,
		p.ProtocolVersion(), p.cfg.DAGParams.Net)
	atomic.AddUint64(&p.bytesSent, uint64(n))
	if p.cfg.Listeners.OnWrite != nil {
		p.cfg.Listeners.OnWrite(p, n, msg, err)
	}
	return err
}

// isAllowedReadError returns whether or not the passed error is allowed without
// disconnecting the peer.  In particular, regression tests need to be allowed
// to send malformed messages without the peer being disconnected.
func (p *Peer) isAllowedReadError(err error) bool {
	// Only allow read errors in regression test mode.
	if p.cfg.DAGParams.Net != wire.TestNet {
		return false
	}

	// Don't allow the error if it's not specifically a malformed message error.
	if _, ok := err.(*wire.MessageError); !ok {
		return false
	}

	// Don't allow the error if it's not coming from localhost or the
	// hostname can't be determined for some reason.
	host, _, err := net.SplitHostPort(p.addr)
	if err != nil {
		return false
	}

	if host != "127.0.0.1" && host != "localhost" {
		return false
	}

	// Allowed if all checks passed.
	return true
}

// shouldHandleReadError returns whether or not the passed error, which is
// expected to have come from reading from the remote peer in the inHandler,
// should be logged and responded to with a reject message.
func (p *Peer) shouldHandleReadError(err error) bool {
	// No logging or reject message when the peer is being forcibly
	// disconnected.
	if atomic.LoadInt32(&p.disconnect) != 0 {
		return false
	}

	// No logging or reject message when the remote peer has been
	// disconnected.
	if err == io.EOF {
		return false
	}
	if opErr, ok := err.(*net.OpError); ok && !opErr.Temporary() {
		return false
	}

	return true
}

// maybeAddDeadline potentially adds a deadline for the appropriate expected
// response for the passed wire protocol command to the pending responses map.
func (p *Peer) maybeAddDeadline(pendingResponses map[string]time.Time, msgCmd string) {
	// Setup a deadline for each message being sent that expects a response.
	//
	// NOTE: Pings are intentionally ignored here since they are typically
	// sent asynchronously and as a result of a long backlock of messages,
	// such as is typical in the case of initial block download, the
	// response won't be received in time.
	deadline := time.Now().Add(stallResponseTimeout)
	switch msgCmd {
	case wire.CmdVersion:
		// Expects a verack message.
		pendingResponses[wire.CmdVerAck] = deadline

	case wire.CmdMemPool:
		// Expects an inv message.
		pendingResponses[wire.CmdInv] = deadline

	case wire.CmdGetBlocks:
		// Expects an inv message.
		pendingResponses[wire.CmdInv] = deadline

	case wire.CmdGetData:
		// Expects a block, merkleblock, tx, or notfound message.
		pendingResponses[wire.CmdBlock] = deadline
		pendingResponses[wire.CmdMerkleBlock] = deadline
		pendingResponses[wire.CmdTx] = deadline
		pendingResponses[wire.CmdNotFound] = deadline

	case wire.CmdGetHeaders:
		// Expects a headers message.  Use a longer deadline since it
		// can take a while for the remote peer to load all of the
		// headers.
		deadline = time.Now().Add(stallResponseTimeout * 3)
		pendingResponses[wire.CmdHeaders] = deadline
	}
}

// stallHandler handles stall detection for the peer.  This entails keeping
// track of expected responses and assigning them deadlines while accounting for
// the time spent in callbacks.  It must be run as a goroutine.
func (p *Peer) stallHandler() {
	// These variables are used to adjust the deadline times forward by the
	// time it takes callbacks to execute.  This is done because new
	// messages aren't read until the previous one is finished processing
	// (which includes callbacks), so the deadline for receiving a response
	// for a given message must account for the processing time as well.
	var handlerActive bool
	var handlersStartTime time.Time
	var deadlineOffset time.Duration

	// pendingResponses tracks the expected response deadline times.
	pendingResponses := make(map[string]time.Time)

	// stallTicker is used to periodically check pending responses that have
	// exceeded the expected deadline and disconnect the peer due to
	// stalling.
	stallTicker := time.NewTicker(stallTickInterval)
	defer stallTicker.Stop()

	// ioStopped is used to detect when both the input and output handler
	// goroutines are done.
	var ioStopped bool
out:
	for {
		select {
		case msg := <-p.stallControl:
			switch msg.command {
			case sccSendMessage:
				// Add a deadline for the expected response
				// message if needed.
				p.maybeAddDeadline(pendingResponses,
					msg.message.Command())

			case sccReceiveMessage:
				// Remove received messages from the expected
				// response map.  Since certain commands expect
				// one of a group of responses, remove
				// everything in the expected group accordingly.
				switch msgCmd := msg.message.Command(); msgCmd {
				case wire.CmdBlock:
					fallthrough
				case wire.CmdMerkleBlock:
					fallthrough
				case wire.CmdTx:
					fallthrough
				case wire.CmdNotFound:
					delete(pendingResponses, wire.CmdBlock)
					delete(pendingResponses, wire.CmdMerkleBlock)
					delete(pendingResponses, wire.CmdTx)
					delete(pendingResponses, wire.CmdNotFound)

				default:
					delete(pendingResponses, msgCmd)
				}

			case sccHandlerStart:
				// Warn on unbalanced callback signalling.
				if handlerActive {
					log.Warn("Received handler start " +
						"control command while a " +
						"handler is already active")
					continue
				}

				handlerActive = true
				handlersStartTime = time.Now()

			case sccHandlerDone:
				// Warn on unbalanced callback signalling.
				if !handlerActive {
					log.Warn("Received handler done " +
						"control command when a " +
						"handler is not already active")
					continue
				}

				// Extend active deadlines by the time it took
				// to execute the callback.
				duration := time.Since(handlersStartTime)
				deadlineOffset += duration
				handlerActive = false

			default:
				log.Warnf("Unsupported message command %s",
					msg.command)
			}

		case <-stallTicker.C:
			// Calculate the offset to apply to the deadline based
			// on how long the handlers have taken to execute since
			// the last tick.
			now := time.Now()
			offset := deadlineOffset
			if handlerActive {
				offset += now.Sub(handlersStartTime)
			}

			// Disconnect the peer if any of the pending responses
			// don't arrive by their adjusted deadline.
			for command, deadline := range pendingResponses {
				if now.Before(deadline.Add(offset)) {
					continue
				}

				log.Debugf("Peer %s appears to be stalled or "+
					"misbehaving, %s timeout -- "+
					"disconnecting", p, command)
				p.Disconnect()
				break
			}

			// Reset the deadline offset for the next tick.
			deadlineOffset = 0

		case <-p.inQuit:
			// The stall handler can exit once both the input and
			// output handler goroutines are done.
			if ioStopped {
				break out
			}
			ioStopped = true

		case <-p.outQuit:
			// The stall handler can exit once both the input and
			// output handler goroutines are done.
			if ioStopped {
				break out
			}
			ioStopped = true
		}
	}

	// Drain any wait channels before going away so there is nothing left
	// waiting on this goroutine.
cleanup:
	for {
		select {
		case <-p.stallControl:
		default:
			break cleanup
		}
	}
	log.Tracef("Peer stall handler done for %s", p)
}

// inHandler handles all incoming messages for the peer.  It must be run as a
// goroutine.
func (p *Peer) inHandler() {
	// The timer is stopped when a new message is received and reset after it
	// is processed.
	idleTimer := time.AfterFunc(idleTimeout, func() {
		log.Warnf("Peer %s no answer for %s -- disconnecting", p, idleTimeout)
		p.Disconnect()
	})

out:
	for atomic.LoadInt32(&p.disconnect) == 0 {
		// Read a message and stop the idle timer as soon as the read
		// is done.  The timer is reset below for the next iteration if
		// needed.
		rmsg, buf, err := p.readMessage()
		idleTimer.Stop()
		if err != nil {
			// In order to allow regression tests with malformed messages, don't
			// disconnect the peer when we're in regression test mode and the
			// error is one of the allowed errors.
			if p.isAllowedReadError(err) {
				log.Errorf("Allowed test error from %s: %s", p, err)
				idleTimer.Reset(idleTimeout)
				continue
			}

			// Only log the error and send reject message if the
			// local peer is not forcibly disconnecting and the
			// remote peer has not disconnected.
			if p.shouldHandleReadError(err) {
				errMsg := fmt.Sprintf("Can't read message from %s: %s", p, err)
				if err != io.ErrUnexpectedEOF {
					log.Errorf(errMsg)
				}

				// Push a reject message for the malformed message and wait for
				// the message to be sent before disconnecting.
				//
				// NOTE: Ideally this would include the command in the header if
				// at least that much of the message was valid, but that is not
				// currently exposed by wire, so just used malformed for the
				// command.
				p.PushRejectMsg("malformed", wire.RejectMalformed, errMsg, nil,
					true)
			}
			break out
		}
		atomic.StoreInt64(&p.lastRecv, time.Now().Unix())
		p.stallControl <- stallControlMsg{sccReceiveMessage, rmsg}

		// Handle each supported message type.
		p.stallControl <- stallControlMsg{sccHandlerStart, rmsg}
		switch msg := rmsg.(type) {
		case *wire.MsgVersion:

			p.PushRejectMsg(msg.Command(), wire.RejectDuplicate,
				"duplicate version message", nil, true)
			break out

		case *wire.MsgVerAck:

			// No read lock is necessary because verAckReceived is not written
			// to in any other goroutine.
			if p.verAckReceived {
				log.Infof("Already received 'verack' from peer %s -- "+
					"disconnecting", p)
				break out
			}
			p.flagsMtx.Lock()
			p.verAckReceived = true
			p.flagsMtx.Unlock()
			if p.cfg.Listeners.OnVerAck != nil {
				p.cfg.Listeners.OnVerAck(p, msg)
			}

		case *wire.MsgGetAddr:
			if p.cfg.Listeners.OnGetAddr != nil {
				p.cfg.Listeners.OnGetAddr(p, msg)
			}

		case *wire.MsgAddr:
			if p.cfg.Listeners.OnAddr != nil {
				p.cfg.Listeners.OnAddr(p, msg)
			}

		case *wire.MsgPing:
			p.handlePingMsg(msg)
			if p.cfg.Listeners.OnPing != nil {
				p.cfg.Listeners.OnPing(p, msg)
			}

		case *wire.MsgPong:
			p.handlePongMsg(msg)
			if p.cfg.Listeners.OnPong != nil {
				p.cfg.Listeners.OnPong(p, msg)
			}

		case *wire.MsgAlert:
			if p.cfg.Listeners.OnAlert != nil {
				p.cfg.Listeners.OnAlert(p, msg)
			}

		case *wire.MsgMemPool:
			if p.cfg.Listeners.OnMemPool != nil {
				p.cfg.Listeners.OnMemPool(p, msg)
			}

		case *wire.MsgTx:
			if p.cfg.Listeners.OnTx != nil {
				p.cfg.Listeners.OnTx(p, msg)
			}

		case *wire.MsgBlock:
			if p.cfg.Listeners.OnBlock != nil {
				p.cfg.Listeners.OnBlock(p, msg, buf)
			}

		case *wire.MsgInv:
			if p.cfg.Listeners.OnInv != nil {
				p.cfg.Listeners.OnInv(p, msg)
			}

		case *wire.MsgHeaders:
			if p.cfg.Listeners.OnHeaders != nil {
				p.cfg.Listeners.OnHeaders(p, msg)
			}

		case *wire.MsgNotFound:
			if p.cfg.Listeners.OnNotFound != nil {
				p.cfg.Listeners.OnNotFound(p, msg)
			}

		case *wire.MsgGetData:
			if p.cfg.Listeners.OnGetData != nil {
				p.cfg.Listeners.OnGetData(p, msg)
			}

		case *wire.MsgGetBlocks:
			if p.cfg.Listeners.OnGetBlocks != nil {
				p.cfg.Listeners.OnGetBlocks(p, msg)
			}

		case *wire.MsgGetHeaders:
			if p.cfg.Listeners.OnGetHeaders != nil {
				p.cfg.Listeners.OnGetHeaders(p, msg)
			}

		case *wire.MsgGetCFilters:
			if p.cfg.Listeners.OnGetCFilters != nil {
				p.cfg.Listeners.OnGetCFilters(p, msg)
			}

		case *wire.MsgGetCFHeaders:
			if p.cfg.Listeners.OnGetCFHeaders != nil {
				p.cfg.Listeners.OnGetCFHeaders(p, msg)
			}

		case *wire.MsgGetCFCheckpt:
			if p.cfg.Listeners.OnGetCFCheckpt != nil {
				p.cfg.Listeners.OnGetCFCheckpt(p, msg)
			}

		case *wire.MsgCFilter:
			if p.cfg.Listeners.OnCFilter != nil {
				p.cfg.Listeners.OnCFilter(p, msg)
			}

		case *wire.MsgCFHeaders:
			if p.cfg.Listeners.OnCFHeaders != nil {
				p.cfg.Listeners.OnCFHeaders(p, msg)
			}

		case *wire.MsgFeeFilter:
			if p.cfg.Listeners.OnFeeFilter != nil {
				p.cfg.Listeners.OnFeeFilter(p, msg)
			}

		case *wire.MsgFilterAdd:
			if p.cfg.Listeners.OnFilterAdd != nil {
				p.cfg.Listeners.OnFilterAdd(p, msg)
			}

		case *wire.MsgFilterClear:
			if p.cfg.Listeners.OnFilterClear != nil {
				p.cfg.Listeners.OnFilterClear(p, msg)
			}

		case *wire.MsgFilterLoad:
			if p.cfg.Listeners.OnFilterLoad != nil {
				p.cfg.Listeners.OnFilterLoad(p, msg)
			}

		case *wire.MsgMerkleBlock:
			if p.cfg.Listeners.OnMerkleBlock != nil {
				p.cfg.Listeners.OnMerkleBlock(p, msg)
			}

		case *wire.MsgReject:
			if p.cfg.Listeners.OnReject != nil {
				p.cfg.Listeners.OnReject(p, msg)
			}

		case *wire.MsgSendHeaders:
			p.flagsMtx.Lock()
			p.sendHeadersPreferred = true
			p.flagsMtx.Unlock()

			if p.cfg.Listeners.OnSendHeaders != nil {
				p.cfg.Listeners.OnSendHeaders(p, msg)
			}

		default:
			log.Debugf("Received unhandled message of type %s "+
				"from %s", rmsg.Command(), p)
		}
		p.stallControl <- stallControlMsg{sccHandlerDone, rmsg}

		// A message was received so reset the idle timer.
		idleTimer.Reset(idleTimeout)
	}

	// Ensure the idle timer is stopped to avoid leaking the resource.
	idleTimer.Stop()

	// Ensure connection is closed.
	p.Disconnect()

	close(p.inQuit)
	log.Tracef("Peer input handler done for %s", p)
}

// queueHandler handles the queuing of outgoing data for the peer. This runs as
// a muxer for various sources of input so we can ensure that server and peer
// handlers will not block on us sending a message.  That data is then passed on
// to outHandler to be actually written.
func (p *Peer) queueHandler() {
	pendingMsgs := list.New()
	invSendQueue := list.New()
	trickleTicker := time.NewTicker(trickleTimeout)
	defer trickleTicker.Stop()

	// We keep the waiting flag so that we know if we have a message queued
	// to the outHandler or not.  We could use the presence of a head of
	// the list for this but then we have rather racy concerns about whether
	// it has gotten it at cleanup time - and thus who sends on the
	// message's done channel.  To avoid such confusion we keep a different
	// flag and pendingMsgs only contains messages that we have not yet
	// passed to outHandler.
	waiting := false

	// To avoid duplication below.
	queuePacket := func(msg outMsg, list *list.List, waiting bool) bool {
		if !waiting {
			p.sendQueue <- msg
		} else {
			list.PushBack(msg)
		}
		// we are always waiting now.
		return true
	}
out:
	for {
		select {
		case msg := <-p.outputQueue:
			waiting = queuePacket(msg, pendingMsgs, waiting)

		// This channel is notified when a message has been sent across
		// the network socket.
		case <-p.sendDoneQueue:
			// No longer waiting if there are no more messages
			// in the pending messages queue.
			next := pendingMsgs.Front()
			if next == nil {
				waiting = false
				continue
			}

			// Notify the outHandler about the next item to
			// asynchronously send.
			val := pendingMsgs.Remove(next)
			p.sendQueue <- val.(outMsg)

		case iv := <-p.outputInvChan:
			// No handshake?  They'll find out soon enough.
			if p.VersionKnown() {
				// If this is a new block, then we'll blast it
				// out immediately, sipping the inv trickle
				// queue.
				if iv.Type == wire.InvTypeBlock {
					invMsg := wire.NewMsgInvSizeHint(1)
					invMsg.AddInvVect(iv)
					waiting = queuePacket(outMsg{msg: invMsg},
						pendingMsgs, waiting)
				} else {
					invSendQueue.PushBack(iv)
				}
			}

		case <-trickleTicker.C:
			// Don't send anything if we're disconnecting or there
			// is no queued inventory.
			// version is known if send queue has any entries.
			if atomic.LoadInt32(&p.disconnect) != 0 ||
				invSendQueue.Len() == 0 {
				continue
			}

			// Create and send as many inv messages as needed to
			// drain the inventory send queue.
			invMsg := wire.NewMsgInvSizeHint(uint(invSendQueue.Len()))
			for e := invSendQueue.Front(); e != nil; e = invSendQueue.Front() {
				iv := invSendQueue.Remove(e).(*wire.InvVect)

				// Don't send inventory that became known after
				// the initial check.
				if p.knownInventory.Exists(iv) {
					continue
				}

				invMsg.AddInvVect(iv)
				if len(invMsg.InvList) >= maxInvTrickleSize {
					waiting = queuePacket(
						outMsg{msg: invMsg},
						pendingMsgs, waiting)
					invMsg = wire.NewMsgInvSizeHint(uint(invSendQueue.Len()))
				}

				// Add the inventory that is being relayed to
				// the known inventory for the peer.
				p.AddKnownInventory(iv)
			}
			if len(invMsg.InvList) > 0 {
				waiting = queuePacket(outMsg{msg: invMsg},
					pendingMsgs, waiting)
			}

		case <-p.quit:
			break out
		}
	}

	// Drain any wait channels before we go away so we don't leave something
	// waiting for us.
	for e := pendingMsgs.Front(); e != nil; e = pendingMsgs.Front() {
		val := pendingMsgs.Remove(e)
		msg := val.(outMsg)
		if msg.doneChan != nil {
			msg.doneChan <- struct{}{}
		}
	}
cleanup:
	for {
		select {
		case msg := <-p.outputQueue:
			if msg.doneChan != nil {
				msg.doneChan <- struct{}{}
			}
		case <-p.outputInvChan:
			// Just drain channel
		// sendDoneQueue is buffered so doesn't need draining.
		default:
			break cleanup
		}
	}
	close(p.queueQuit)
	log.Tracef("Peer queue handler done for %s", p)
}

// shouldLogWriteError returns whether or not the passed error, which is
// expected to have come from writing to the remote peer in the outHandler,
// should be logged.
func (p *Peer) shouldLogWriteError(err error) bool {
	// No logging when the peer is being forcibly disconnected.
	if atomic.LoadInt32(&p.disconnect) != 0 {
		return false
	}

	// No logging when the remote peer has been disconnected.
	if err == io.EOF {
		return false
	}
	if opErr, ok := err.(*net.OpError); ok && !opErr.Temporary() {
		return false
	}

	return true
}

// outHandler handles all outgoing messages for the peer.  It must be run as a
// goroutine.  It uses a buffered channel to serialize output messages while
// allowing the sender to continue running asynchronously.
func (p *Peer) outHandler() {
out:
	for {
		select {
		case msg := <-p.sendQueue:
			switch m := msg.msg.(type) {
			case *wire.MsgPing:
				p.statsMtx.Lock()
				p.lastPingNonce = m.Nonce
				p.lastPingTime = time.Now()
				p.statsMtx.Unlock()
			}

			p.stallControl <- stallControlMsg{sccSendMessage, msg.msg}

			err := p.writeMessage(msg.msg)
			if err != nil {
				p.Disconnect()
				if p.shouldLogWriteError(err) {
					log.Errorf("Failed to send message to "+
						"%s: %s", p, err)
				}
				if msg.doneChan != nil {
					msg.doneChan <- struct{}{}
				}
				continue
			}

			// At this point, the message was successfully sent, so
			// update the last send time, signal the sender of the
			// message that it has been sent (if requested), and
			// signal the send queue to the deliver the next queued
			// message.
			atomic.StoreInt64(&p.lastSend, time.Now().Unix())
			if msg.doneChan != nil {
				msg.doneChan <- struct{}{}
			}
			p.sendDoneQueue <- struct{}{}

		case <-p.quit:
			break out
		}
	}

	<-p.queueQuit

	// Drain any wait channels before we go away so we don't leave something
	// waiting for us. We have waited on queueQuit and thus we can be sure
	// that we will not miss anything sent on sendQueue.
cleanup:
	for {
		select {
		case msg := <-p.sendQueue:
			if msg.doneChan != nil {
				msg.doneChan <- struct{}{}
			}
			// no need to send on sendDoneQueue since queueHandler
			// has been waited on and already exited.
		default:
			break cleanup
		}
	}
	close(p.outQuit)
	log.Tracef("Peer output handler done for %s", p)
}

// pingHandler periodically pings the peer.  It must be run as a goroutine.
func (p *Peer) pingHandler() {
	pingTicker := time.NewTicker(pingInterval)
	defer pingTicker.Stop()

out:
	for {
		select {
		case <-pingTicker.C:
			nonce, err := random.Uint64()
			if err != nil {
				log.Errorf("Not sending ping to %s: %s", p, err)
				continue
			}
			p.QueueMessage(wire.NewMsgPing(nonce), nil)

		case <-p.quit:
			break out
		}
	}
}

// QueueMessage adds the passed bitcoin message to the peer send queue.
//
// This function is safe for concurrent access.
func (p *Peer) QueueMessage(msg wire.Message, doneChan chan<- struct{}) {
	// Avoid risk of deadlock if goroutine already exited.  The goroutine
	// we will be sending to hangs around until it knows for a fact that
	// it is marked as disconnected and *then* it drains the channels.
	if !p.Connected() {
		if doneChan != nil {
			spawn(func() {
				doneChan <- struct{}{}
			})
		}
		return
	}
	p.outputQueue <- outMsg{msg: msg, doneChan: doneChan}
}

// QueueInventory adds the passed inventory to the inventory send queue which
// might not be sent right away, rather it is trickled to the peer in batches.
// Inventory that the peer is already known to have is ignored.
//
// This function is safe for concurrent access.
func (p *Peer) QueueInventory(invVect *wire.InvVect) {
	// Don't add the inventory to the send queue if the peer is already
	// known to have it.
	if p.knownInventory.Exists(invVect) {
		return
	}

	// Avoid risk of deadlock if goroutine already exited.  The goroutine
	// we will be sending to hangs around until it knows for a fact that
	// it is marked as disconnected and *then* it drains the channels.
	if !p.Connected() {
		return
	}

	p.outputInvChan <- invVect
}

// AssociateConnection associates the given conn to the peer.   Calling this
// function when the peer is already connected will have no effect.
func (p *Peer) AssociateConnection(conn net.Conn) {
	// Already connected?
	if !atomic.CompareAndSwapInt32(&p.connected, 0, 1) {
		return
	}

	p.conn = conn
	p.timeConnected = time.Now()

	if p.inbound {
		p.addr = p.conn.RemoteAddr().String()

		// Set up a NetAddress for the peer to be used with AddrManager.  We
		// only do this inbound because outbound set this up at connection time
		// and no point recomputing.
		na, err := newNetAddress(p.conn.RemoteAddr(), p.services)
		if err != nil {
			log.Errorf("Cannot create remote net address: %s", err)
			p.Disconnect()
			return
		}
		p.na = na
	}

	spawn(func() {
		if err := p.start(); err != nil {
			log.Debugf("Cannot start peer %s: %s", p, err)
			p.Disconnect()
		}
	})
}

// Connected returns whether or not the peer is currently connected.
//
// This function is safe for concurrent access.
func (p *Peer) Connected() bool {
	return atomic.LoadInt32(&p.connected) != 0 &&
		atomic.LoadInt32(&p.disconnect) == 0
}

// Disconnect disconnects the peer by closing the connection.  Calling this
// function when the peer is already disconnected or in the process of
// disconnecting will have no effect.
func (p *Peer) Disconnect() {
	if atomic.AddInt32(&p.disconnect, 1) != 1 {
		return
	}

	log.Tracef("Disconnecting %s", p)
	if atomic.LoadInt32(&p.connected) != 0 {
		p.conn.Close()
	}
	close(p.quit)
}

// start begins processing input and output messages.
func (p *Peer) start() error {
	log.Tracef("Starting peer %s", p)

	negotiateErr := make(chan error, 1)
	spawn(func() {
		if p.inbound {
			negotiateErr <- p.negotiateInboundProtocol()
		} else {
			negotiateErr <- p.negotiateOutboundProtocol()
		}
	})

	// Negotiate the protocol within the specified negotiateTimeout.
	select {
	case err := <-negotiateErr:
		if err != nil {
			return err
		}
	case <-time.After(negotiateTimeout):
		return errors.New("protocol negotiation timeout")
	}
	log.Debugf("Connected to %s", p.Addr())

	// The protocol has been negotiated successfully so start processing input
	// and output messages.
	spawn(p.stallHandler)
	spawn(p.inHandler)
	spawn(p.queueHandler)
	spawn(p.outHandler)
	spawn(p.pingHandler)

	// Send our verack message now that the IO processing machinery has started.
	p.QueueMessage(wire.NewMsgVerAck(), nil)
	return nil
}

// WaitForDisconnect waits until the peer has completely disconnected and all
// resources are cleaned up.  This will happen if either the local or remote
// side has been disconnected or the peer is forcibly disconnected via
// Disconnect.
func (p *Peer) WaitForDisconnect() {
	<-p.quit
}

// readRemoteVersionMsg waits for the next message to arrive from the remote
// peer.  If the next message is not a version message or the version is not
// acceptable then return an error.
func (p *Peer) readRemoteVersionMsg() error {
	// Read their version message.
	msg, _, err := p.readMessage()
	if err != nil {
		return err
	}

	remoteVerMsg, ok := msg.(*wire.MsgVersion)
	if !ok {
		errStr := "A version message must precede all others"
		log.Errorf(errStr)

		rejectMsg := wire.NewMsgReject(msg.Command(), wire.RejectMalformed,
			errStr)
		return p.writeMessage(rejectMsg)
	}

	if err := p.handleRemoteVersionMsg(remoteVerMsg); err != nil {
		return err
	}

	if p.cfg.Listeners.OnVersion != nil {
		p.cfg.Listeners.OnVersion(p, remoteVerMsg)
	}
	return nil
}

// writeLocalVersionMsg writes our version message to the remote peer.
func (p *Peer) writeLocalVersionMsg() error {
	localVerMsg, err := p.localVersionMsg()
	if err != nil {
		return err
	}

	return p.writeMessage(localVerMsg)
}

// negotiateInboundProtocol waits to receive a version message from the peer
// then sends our version message. If the events do not occur in that order then
// it returns an error.
func (p *Peer) negotiateInboundProtocol() error {
	if err := p.readRemoteVersionMsg(); err != nil {
		return err
	}

	return p.writeLocalVersionMsg()
}

// negotiateOutboundProtocol sends our version message then waits to receive a
// version message from the peer.  If the events do not occur in that order then
// it returns an error.
func (p *Peer) negotiateOutboundProtocol() error {
	if err := p.writeLocalVersionMsg(); err != nil {
		return err
	}

	return p.readRemoteVersionMsg()
}

// newPeerBase returns a new base bitcoin peer based on the inbound flag.  This
// is used by the NewInboundPeer and NewOutboundPeer functions to perform base
// setup needed by both types of peers.
func newPeerBase(origCfg *Config, inbound bool) *Peer {
	// Default to the max supported protocol version if not specified by the
	// caller.
	cfg := *origCfg // Copy to avoid mutating caller.
	if cfg.ProtocolVersion == 0 {
		cfg.ProtocolVersion = MaxProtocolVersion
	}

	// Set the DAG parameters to testnet if the caller did not specify any.
	if cfg.DAGParams == nil {
		cfg.DAGParams = &dagconfig.TestNet3Params
	}

	p := Peer{
		inbound:         inbound,
		knownInventory:  newMruInventoryMap(maxKnownInventory),
		stallControl:    make(chan stallControlMsg, 1), // nonblocking sync
		outputQueue:     make(chan outMsg, outputBufferSize),
		sendQueue:       make(chan outMsg, 1),   // nonblocking sync
		sendDoneQueue:   make(chan struct{}, 1), // nonblocking sync
		outputInvChan:   make(chan *wire.InvVect, outputBufferSize),
		inQuit:          make(chan struct{}),
		queueQuit:       make(chan struct{}),
		outQuit:         make(chan struct{}),
		quit:            make(chan struct{}),
		cfg:             cfg, // Copy so caller can't mutate.
		services:        cfg.Services,
		protocolVersion: cfg.ProtocolVersion,
	}
	return &p
}

// NewInboundPeer returns a new inbound bitcoin peer. Use Start to begin
// processing incoming and outgoing messages.
func NewInboundPeer(cfg *Config) *Peer {
	return newPeerBase(cfg, true)
}

// NewOutboundPeer returns a new outbound bitcoin peer.
func NewOutboundPeer(cfg *Config, addr string) (*Peer, error) {
	p := newPeerBase(cfg, false)
	p.addr = addr

	host, portStr, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	port, err := strconv.ParseUint(portStr, 10, 16)
	if err != nil {
		return nil, err
	}

	if cfg.HostToNetAddress != nil {
		na, err := cfg.HostToNetAddress(host, uint16(port), cfg.Services)
		if err != nil {
			return nil, err
		}
		p.na = na
	} else {
		p.na = wire.NewNetAddressIPPort(net.ParseIP(host), uint16(port),
			cfg.Services)
	}

	return p, nil
}

func init() {
	rand.Seed(time.Now().UnixNano())
}