server.go

// Copyright (c) 2013-2016 The btcsuite developers
// Copyright (c) 2015-2025 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package main

import (
	"context"
	"crypto/elliptic"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"math"
	"net"
	"net/netip"
	"os"
	"path"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/decred/dcrd/addrmgr/v3"
	"github.com/decred/dcrd/blockchain/stake/v5"
	"github.com/decred/dcrd/blockchain/standalone/v2"
	"github.com/decred/dcrd/certgen"
	"github.com/decred/dcrd/chaincfg/chainhash"
	"github.com/decred/dcrd/chaincfg/v3"
	"github.com/decred/dcrd/connmgr/v3"
	"github.com/decred/dcrd/container/apbf"
	"github.com/decred/dcrd/container/lru"
	"github.com/decred/dcrd/crypto/rand"
	"github.com/decred/dcrd/database/v3"
	"github.com/decred/dcrd/dcrutil/v4"
	"github.com/decred/dcrd/internal/blockchain"
	"github.com/decred/dcrd/internal/blockchain/indexers"
	"github.com/decred/dcrd/internal/fees"
	"github.com/decred/dcrd/internal/mempool"
	"github.com/decred/dcrd/internal/mining"
	"github.com/decred/dcrd/internal/mining/cpuminer"
	"github.com/decred/dcrd/internal/netsync"
	"github.com/decred/dcrd/internal/rpcserver"
	"github.com/decred/dcrd/internal/version"
	"github.com/decred/dcrd/math/uint256"
	"github.com/decred/dcrd/mixing"
	"github.com/decred/dcrd/mixing/mixpool"
	"github.com/decred/dcrd/peer/v3"
	"github.com/decred/dcrd/txscript/v4"
	"github.com/decred/dcrd/wire"
	"github.com/syndtr/goleveldb/leveldb"
)

const (
	// defaultServices describes the default services that are supported by
	// the server.
	defaultServices = wire.SFNodeNetwork

	// defaultRequiredServices describes the default services that are
	// required to be supported by outbound peers.
	defaultRequiredServices = wire.SFNodeNetwork

	// defaultTargetOutbound is the default number of outbound peers to
	// target.
	defaultTargetOutbound = 8

	// defaultMaximumVoteAge is the threshold of blocks before the tip
	// that can be voted on.
	defaultMaximumVoteAge = 1440

	// connectionRetryInterval is the base amount of time to wait in between
	// retries when connecting to persistent peers.  It is adjusted by the
	// number of retries such that there is a retry backoff.
	connectionRetryInterval = time.Second * 5

	// maxProtocolVersion is the max protocol version the server supports.
	maxProtocolVersion = wire.BatchedCFiltersV2Version

	// These fields are used to track known addresses on a per-peer basis.
	//
	// maxKnownAddrsPerPeer is the maximum number of items to track.
	//
	// knownAddrsFPRate is the false positive rate for the APBF used to track
	// them.  It is set to a rate of 1 per 1000 since addresses are not very
	// large and they only need to be filtered once per connection, so an extra
	// 10 of them being sent (on average) again even though they technically
	// wouldn't need to is a good tradeoff.
	//
	// These values result in about 40 KiB memory usage including overhead.
	maxKnownAddrsPerPeer = 10000
	knownAddrsFPRate     = 0.001

	// maxCachedNaSubmissions is the maximum number of network address
	// submissions cached.
	maxCachedNaSubmissions = 20

	// These constants control the maximum number of simultaneous pending
	// getdata messages and the individual data item requests they make without
	// being disconnected.
	//
	// Since each getdata message is comprised of several individual data item
	// requests, the limiting is applied on both dimensions to offer more
	// flexibility while still keeping memory usage bounded to reasonable
	// limits.
	//
	// maxConcurrentGetDataReqs is the maximum number of simultaneous pending
	// getdata message requests.
	//
	// maxPendingGetDataItemReqs is the maximum number of overall total
	// simultaneous pending individual data item requests.
	//
	// In other words, when combined, a peer may mix and match simultaneous
	// getdata requests for varying amounts of data items so long as it does not
	// exceed the maximum specified number of simultaneous pending getdata
	// messages or the maximum number of total overall pending individual data
	// item requests.
	maxConcurrentGetDataReqs  = 1000
	maxPendingGetDataItemReqs = 2 * wire.MaxInvPerMsg

	// maxReorgDepthNotify specifies the maximum reorganization depth for which
	// winning ticket notifications will be sent over RPC.  The reorg depth is
	// the number of blocks that would be reorganized out of the current best
	// chain if a side chain being considered for notifications were to
	// ultimately be extended to be longer than the current one.
	//
	// In effect, this helps to prevent large reorgs by refusing to send the
	// winning ticket information to RPC clients, such as voting wallets, which
	// depend on it to cast votes.
	//
	// This check also doubles to help reduce exhaustion attacks that could
	// otherwise arise from sending old orphan blocks and forcing nodes to do
	// expensive lottery data calculations for them.
	maxReorgDepthNotify = 6

	// These fields are used to track recently confirmed transactions.
	//
	// maxRecentlyConfirmedTxns specifies the maximum number to track and is set
	// to target tracking the maximum number transactions of the minimum
	// realistic size (~206 bytes) in approximately one hour of blocks on the
	// main network.
	//
	// recentlyConfirmedTxnsFPRate is the false positive rate for the APBF used
	// to track them and is set to a rate of 1 per 1 million which supports up
	// to ~11.5 transactions/s before a single false positive would be seen on
	// average and thus allows for plenty of future growth.
	//
	// These values result in about 183 KiB memory usage including overhead.
	maxRecentlyConfirmedTxns    = 23000
	recentlyConfirmedTxnsFPRate = 0.000001

	// These fields are used when caching recently advertised transactions.
	//
	// maxRecentlyAdvertisedTxns specifies the maximum number to cache and is
	// set to target tracking the maximum number transactions of the minimum
	// realistic size (~206 bytes) in approximately two blocks on the main
	// network plus an additional 20%.
	//
	// recentlyAdvertisedTxnsTTL is the time to keep recently advertised
	// transactions in the cache before they are expired.
	//
	// These values result in about 640 KiB memory usage including overhead.
	maxRecentlyAdvertisedTxns = 4500
	recentlyAdvertisedTxnsTTL = 45 * time.Second
)

var (
	// userAgentName is the user agent name and is used to help identify
	// ourselves to other Decred peers.
	userAgentName = "dcrd"

	// userAgentVersion is the user agent version and is used to help
	// identify ourselves to other peers.
	userAgentVersion = fmt.Sprintf("%d.%d.%d", version.Major, version.Minor,
		version.Patch)
)

// simpleAddr implements the net.Addr interface with two struct fields.
type simpleAddr struct {
	net, addr string
}

// String returns the address.
//
// This is part of the net.Addr interface.
func (a simpleAddr) String() string {
	return a.addr
}

// Network returns the network.
//
// This is part of the net.Addr interface.
func (a simpleAddr) Network() string {
	return a.net
}

// Ensure simpleAddr implements the net.Addr interface.
var _ net.Addr = simpleAddr{}

// broadcastMsg provides the ability to house a Decred message to be broadcast
// to all connected peers except specified excluded peers.
type broadcastMsg struct {
	message      wire.Message
	excludePeers []*serverPeer
}

// broadcastInventoryAdd is a type used to declare that the InvVect it contains
// needs to be added to the rebroadcast map.
type broadcastInventoryAdd relayMsg

// broadcastInventoryDel is a type used to declare that the InvVect it contains
// needs to be removed from the rebroadcast map.
type broadcastInventoryDel *wire.InvVect

// broadcastPruneInventory is a type used to declare that rebroadcast
// inventory entries need to be filtered and removed where necessary.
type broadcastPruneInventory struct{}

// relayMsg packages an inventory vector along with the newly discovered
// inventory and a flag that determines if the relay should happen immediately
// (it will be put into a trickle queue if false) so the relay has access to
// that information.
type relayMsg struct {
	invVect     *wire.InvVect
	data        interface{}
	immediate   bool
	reqServices wire.ServiceFlag
}

// naSubmission represents a network address submission from an outbound peer.
type naSubmission struct {
	na           *wire.NetAddress
	netType      addrmgr.NetAddressType
	reach        addrmgr.NetAddressReach
	score        uint32
	lastAccessed int64
}

// naSubmissionCache represents a bounded map for network address submisions.
type naSubmissionCache struct {
	cache map[string]*naSubmission
	limit int
	mtx   sync.Mutex
}

// add caches the provided address submission.
func (sc *naSubmissionCache) add(sub *naSubmission) error {
	if sub == nil {
		return fmt.Errorf("submission cannot be nil")
	}

	key := sub.na.IP.String()
	if key == "" {
		return fmt.Errorf("submission key cannot be an empty string")
	}

	sc.mtx.Lock()
	defer sc.mtx.Unlock()

	// Remove the oldest submission if cache limit has been reached.
	if len(sc.cache) == sc.limit {
		var oldestSub *naSubmission
		for _, sub := range sc.cache {
			if oldestSub == nil {
				oldestSub = sub
				continue
			}

			if sub.lastAccessed < oldestSub.lastAccessed {
				oldestSub = sub
			}
		}

		if oldestSub != nil {
			delete(sc.cache, oldestSub.na.IP.String())
		}
	}

	sub.score = 1
	sub.lastAccessed = time.Now().Unix()
	sc.cache[key] = sub
	return nil
}

// exists returns true if the provided key exist in the submissions cache.
func (sc *naSubmissionCache) exists(key string) bool {
	if key == "" {
		return false
	}

	sc.mtx.Lock()
	_, ok := sc.cache[key]
	sc.mtx.Unlock()
	return ok
}

// incrementScore increases the score of address submission referenced by
// the provided key by one.
func (sc *naSubmissionCache) incrementScore(key string) error {
	if key == "" {
		return fmt.Errorf("submission key cannot be an empty string")
	}

	sc.mtx.Lock()
	defer sc.mtx.Unlock()

	sub, ok := sc.cache[key]
	if !ok {
		return fmt.Errorf("submission key not found: %s", key)
	}

	sub.score++
	sub.lastAccessed = time.Now().Unix()
	sc.cache[key] = sub
	return nil
}

// bestSubmission fetches the best scoring submission of the provided
// network interface.
func (sc *naSubmissionCache) bestSubmission(net addrmgr.NetAddressType) *naSubmission {
	sc.mtx.Lock()
	defer sc.mtx.Unlock()

	var best *naSubmission
	for _, sub := range sc.cache {
		if sub.netType != net {
			continue
		}

		if best == nil {
			best = sub
			continue
		}

		if sub.score > best.score {
			best = sub
		}
	}

	return best
}

// peerState houses state of inbound, persistent, and outbound peers as well
// as banned peers and outbound groups.
type peerState struct {
	sync.Mutex

	// The following fields are protected by the embedded mutex.
	inboundPeers    map[int32]*serverPeer
	outboundPeers   map[int32]*serverPeer
	persistentPeers map[int32]*serverPeer
	banned          map[string]time.Time
	outboundGroups  map[string]int

	// subCache houses the network address submission cache and is protected
	// by its own mutex.
	subCache *naSubmissionCache
}

// makePeerState returns a peer state instance that is used to maintain the
// state of inbound, persistent, and outbound peers as well as banned peers and
// outbound groups.
func makePeerState() peerState {
	return peerState{
		inboundPeers:    make(map[int32]*serverPeer),
		persistentPeers: make(map[int32]*serverPeer),
		outboundPeers:   make(map[int32]*serverPeer),
		banned:          make(map[string]time.Time),
		outboundGroups:  make(map[string]int),
		subCache: &naSubmissionCache{
			cache: make(map[string]*naSubmission, maxCachedNaSubmissions),
			limit: maxCachedNaSubmissions,
		},
	}
}

// count returns the count of all known peers.
//
// This function MUST be called with the embedded mutex locked (for reads).
func (ps *peerState) count() int {
	return len(ps.inboundPeers) + len(ps.outboundPeers) +
		len(ps.persistentPeers)
}

// forAllOutboundPeers is a helper function that runs closure on all outbound
// peers known to peerState.
//
// This function MUST be called with the embedded mutex locked (for reads).
func (ps *peerState) forAllOutboundPeers(closure func(sp *serverPeer)) {
	for _, e := range ps.outboundPeers {
		closure(e)
	}
	for _, e := range ps.persistentPeers {
		closure(e)
	}
}

// forAllPeers is a helper function that runs closure on all peers known to
// peerState.
//
// This function MUST be called with the embedded mutex locked (for reads).
func (ps *peerState) forAllPeers(closure func(sp *serverPeer)) {
	for _, e := range ps.inboundPeers {
		closure(e)
	}
	ps.forAllOutboundPeers(closure)
}

// ForAllPeers is a helper function that runs closure on all peers known to
// peerState.
//
// This function is safe for concurrent access.
func (ps *peerState) ForAllPeers(closure func(sp *serverPeer)) {
	ps.Lock()
	ps.forAllPeers(closure)
	ps.Unlock()
}

// connectionsWithIP returns the number of connections with the given IP.
//
// This function MUST be called with the embedded mutex locked (for reads).
func (ps *peerState) connectionsWithIP(ip net.IP) int {
	var total int
	ps.forAllPeers(func(sp *serverPeer) {
		if ip.Equal(sp.NA().IP) {
			total++
		}

	})
	return total
}

type resolveIPFn func(string) ([]net.IP, error)

// hostToNetAddress parses and returns an address manager network address given
// a hostname in a supported format (IPv4, IPv6).  If the hostname cannot be
// immediately converted from a known address format, it will be resolved using
// the provided DNS resolver function.  If it cannot be resolved, an error is
// returned.
//
// This function is safe for concurrent access.
func hostToNetAddress(host string, port uint16, services wire.ServiceFlag, resolver resolveIPFn) (*addrmgr.NetAddress, error) {
	addrType, addrBytes := addrmgr.EncodeHost(host)
	if addrType != addrmgr.UnknownAddressType {
		// Since the host type has been successfully recognized and encoded,
		// there is no need to perform a DNS lookup.
		now := time.Unix(time.Now().Unix(), 0)
		return addrmgr.NewNetAddressFromParams(addrType, addrBytes, port, now, services)
	}
	// Cannot determine the host address type. Must use DNS.
	ips, err := resolver(host)
	if err != nil {
		return nil, err
	}
	if len(ips) == 0 {
		return nil, fmt.Errorf("no addresses found for %s", host)
	}
	na := addrmgr.NewNetAddressFromIPPort(ips[0], port, services)
	return na, nil
}

// ResolveLocalAddress picks the best suggested network address from available
// options, per the network interface key provided. The best suggestion, if
// found, is added as a local address.
//
// This function is safe for concurrent access.
func (ps *peerState) ResolveLocalAddress(netType addrmgr.NetAddressType, addrMgr *addrmgr.AddrManager, services wire.ServiceFlag) {
	best := ps.subCache.bestSubmission(netType)
	if best == nil {
		return
	}

	targetOutbound := defaultTargetOutbound
	if cfg.MaxPeers < targetOutbound {
		targetOutbound = cfg.MaxPeers
	}

	// A valid best address suggestion must have a majority
	// (60 percent majority) of outbound peers concluding on
	// the same result.
	if best.score < uint32(math.Ceil(float64(targetOutbound)*0.6)) {
		return
	}

	addLocalAddress := func(bestSuggestion string, port uint16, services wire.ServiceFlag) {
		na, err := hostToNetAddress(bestSuggestion, port, services, dcrdLookup)
		if err != nil {
			amgrLog.Errorf("unable to generate network address using host %v: "+
				"%v", bestSuggestion, err)
			return
		}

		if !addrMgr.HasLocalAddress(na) {
			err := addrMgr.AddLocalAddress(na, addrmgr.ManualPrio)
			if err != nil {
				amgrLog.Errorf("unable to add local address: %v", err)
				return
			}
		}
	}

	stripIPv6Zone := func(ip string) string {
		// Strip IPv6 zone id if present.
		zoneIndex := strings.LastIndex(ip, "%")
		if zoneIndex > 0 {
			return ip[:zoneIndex]
		}

		return ip
	}

	for _, listener := range cfg.Listeners {
		host, portStr, err := net.SplitHostPort(listener)
		if err != nil {
			amgrLog.Errorf("unable to split network address: %v", err)
			return
		}

		port, err := strconv.ParseUint(portStr, 10, 16)
		if err != nil {
			amgrLog.Errorf("unable to parse port: %v", err)
			return
		}

		host = stripIPv6Zone(host)

		// Add a local address if the best suggestion is referenced by a
		// listener.
		if best.na.IP.String() == host {
			addLocalAddress(best.na.IP.String(), uint16(port), services)
			continue
		}

		// Add a local address if the listener is generic (applies
		// for both IPv4 and IPv6).
		if host == "" || (host == "*" && runtime.GOOS == "plan9") {
			addLocalAddress(best.na.IP.String(), uint16(port), services)
			continue
		}

		listenerIP := net.ParseIP(host)
		if listenerIP == nil {
			amgrLog.Errorf("unable to parse listener: %v", host)
			return
		}

		// Add a local address if the network address is a probable external
		// endpoint of the listener.
		lNet := addrmgr.IPv4Address
		if listenerIP.To4() == nil {
			lNet = addrmgr.IPv6Address
		}

		validExternal := (lNet == addrmgr.IPv4Address &&
			best.reach == addrmgr.Ipv4) || lNet == addrmgr.IPv6Address &&
			(best.reach == addrmgr.Ipv6Weak || best.reach == addrmgr.Ipv6Strong ||
				best.reach == addrmgr.Teredo)

		if validExternal {
			addLocalAddress(best.na.IP.String(), uint16(port), services)
			continue
		}
	}
}

// server provides a Decred server for handling communications to and from
// Decred peers.
type server struct {
	bytesReceived atomic.Uint64 // Total bytes received from all peers since start.
	bytesSent     atomic.Uint64 // Total bytes sent by all peers since start.
	shutdown      atomic.Bool

	// targetOutbound is the calculated number of target outbound peers to
	// maintain.  It is set at creation time and never modified afterwards, so
	// it does not need to be protected for concurrent access.
	targetOutbound uint32

	// minKnownWork houses the minimum known work from the associated network
	// params converted to a uint256 so the conversion only needs to be
	// performed once when the server is initialized.  Ideally, the chain params
	// should be updated to use the new type, but that will be a major version
	// bump, so a one-time conversion is a good tradeoff in the mean time.
	minKnownWork uint256.Uint256

	chainParams          *chaincfg.Params
	addrManager          *addrmgr.AddrManager
	connManager          *connmgr.ConnManager
	sigCache             *txscript.SigCache
	subsidyCache         *standalone.SubsidyCache
	rpcServer            *rpcserver.Server
	syncManager          *netsync.SyncManager
	bg                   *mining.BgBlkTmplGenerator
	chain                *blockchain.BlockChain
	txMemPool            *mempool.TxPool
	feeEstimator         *fees.Estimator
	cpuMiner             *cpuminer.CPUMiner
	mixMsgPool           *mixpool.Pool
	modifyRebroadcastInv chan interface{}
	peerState            peerState
	relayInv             chan relayMsg
	broadcast            chan broadcastMsg
	nat                  *upnpNAT
	db                   database.DB
	timeSource           blockchain.MedianTimeSource
	services             wire.ServiceFlag
	quit                 chan struct{}

	// The following fields are used for optional indexes.  They will be nil
	// if the associated index is not enabled.  These fields are set during
	// initial creation of the server and never changed afterwards, so they
	// do not need to be protected for concurrent access.
	indexSubscriber *indexers.IndexSubscriber
	txIndex         *indexers.TxIndex
	existsAddrIndex *indexers.ExistsAddrIndex

	// These following fields are used to filter duplicate block lottery data
	// anouncements.
	lotteryDataBroadcastMtx sync.Mutex
	lotteryDataBroadcast    map[chainhash.Hash]struct{}

	// recentlyConfirmedTxns tracks transactions that have been confirmed in the
	// most recent blocks.
	recentlyConfirmedTxns *apbf.Filter

	// recentlyAdvertisedTxns caches transactions that have recently been
	// advertised to other peers.  The cache handles automatic expiration and
	// maximum entry limiting.
	//
	// It is considered misbehavior to advertise a transaction and then claim it
	// is not found when the corresponding request arrives.  Further, since the
	// mempool only contains the unconfirmed transactions as of the current best
	// chain tip, a transaction might be advertised when it is first added to
	// the mempool and then removed from the mempool prior to it being requested
	// in the case new blocks are connected in between the advertisement and
	// request.
	//
	// Thus, maintaining a separate cache of advertised transactions increases
	// the probability they are available to serve regardless of whether or not
	// they are still in the mempool when a request for the advertisement
	// arrives.
	//
	// Note that it might be tempting to keep track of the number of times a tx
	// has been advertised and requested so it can be removed from the cache as
	// soon as there are no longer any potential outstanding requests, however,
	// that is intentionally not done because it is exceedingly rare for
	// advertisements to result in a request from all peers, so the extra
	// overhead is not warranted.
	recentlyAdvertisedTxns *lru.Map[chainhash.Hash, *dcrutil.Tx]

	// The following fields are used to periodically log the total number
	// evicted recently advertised transactions.  They are only accessed from
	// a single long-running goroutine, so they are not protected for concurrent
	// access.
	//
	// totalAdvertisedTxnsEvicted is the total number of advertised transactions
	// that have been evicted from the cache since the previous report.
	//
	// lastAdvertisedTxnsEvictedLogged is the last time the total number of
	// advertised transactions that have been evicted from the cache was
	// reported.
	totalAdvertisedTxnsEvicted      uint64
	lastAdvertisedTxnsEvictedLogged time.Time
}

// serverPeer extends the peer to maintain state shared by the server.
type serverPeer struct {
	*peer.Peer

	// These fields are set at creation time and never modified afterwards, so
	// they do not need to be protected for concurrent access.
	server        *server
	persistent    bool
	isWhitelisted bool
	quit          chan struct{}

	// syncMgrPeer houses the network sync manager peer instance that wraps the
	// underlying peer similar to the way this server peer itself wraps it.
	syncMgrPeer *netsync.Peer

	// All fields below this point are either not set at creation time or are
	// otherwise modified during operation and thus need to consider whether or
	// not they need to be protected for concurrent access.

	connReq        atomic.Pointer[connmgr.ConnReq]
	continueHash   atomic.Pointer[chainhash.Hash]
	disableRelayTx atomic.Bool
	knownAddresses *apbf.Filter
	banScore       connmgr.DynamicBanScore

	// addrsSent, getMiningStateSent and initState track whether or not the peer
	// has already sent the respective request.  They are used to prevent more
	// than one response of each respective request per connection.
	//
	// They are only accessed directly in callbacks which all run in the same
	// peer input handler goroutine and thus do not need to be protected for
	// concurrent access.
	addrsSent          bool
	getMiningStateSent bool
	initStateSent      bool

	// peerNa is network address of the peer connected to.
	peerNa atomic.Pointer[wire.NetAddress]

	// announcedBlock tracks the most recent block announced to this peer and is
	// used to filter duplicates.
	//
	// It is only accessed in the goroutine that handles relaying inventory and
	// thus does not need to be protected for concurrent access.
	announcedBlock *chainhash.Hash

	// The following fields are used to serve getdata requests asynchronously as
	// opposed to directly in the peer input handler.
	//
	// getDataQueue is a buffered channel for queueing up concurrent getdata
	// requests.
	//
	// numPendingGetDataItemReqs tracks the total number of pending individual
	// data item requests that still need to be served.
	getDataQueue              chan []*wire.InvVect
	numPendingGetDataItemReqs atomic.Uint32
}

// newServerPeer returns a new serverPeer instance. The peer needs to be set by
// the caller.
func newServerPeer(s *server, isPersistent bool) *serverPeer {
	return &serverPeer{
		server:         s,
		persistent:     isPersistent,
		knownAddresses: apbf.NewFilter(maxKnownAddrsPerPeer, knownAddrsFPRate),
		quit:           make(chan struct{}),
		getDataQueue:   make(chan []*wire.InvVect, maxConcurrentGetDataReqs),
	}
}

// handleServeGetData is the primary logic for servicing queued getdata
// requests.
//
// It makes use of the given send done channel and semaphore to provide
// a little pipelining of database loads while keeping the memory usage bounded
// to reasonable limits.
//
// It is invoked from the serveGetData goroutine.
func (sp *serverPeer) handleServeGetData(invVects []*wire.InvVect,
	sendDoneChan chan struct{}, semaphore chan struct{}) {

	var notFoundMsg *wire.MsgNotFound
	for _, iv := range invVects {
		var sendInv bool
		var dataMsg wire.Message
		switch iv.Type {
		case wire.InvTypeTx:
			// Attempt to fetch the requested transaction.  Try the pool of
			// recently advertised transactions first and then fall back to the
			// mempool.
			//
			// Note that this does not allow peers to request transactions
			// already in a block over p2p unless they still happen to be in the
			// pool of advertised transactions, as that would require all nodes
			// to maintain a full transaction index which can be expensive.
			// That ability is restricted to authenticated RPC only and requires
			// the aforementioned full transaction index.
			txHash := &iv.Hash
			tx, ok := sp.server.recentlyAdvertisedTxns.Get(*txHash)
			if !ok {
				// Note that a call could be made to check for existence first,
				// but simply trying to fetch a missing transaction results in
				// the same behavior.
				var err error
				tx, err = sp.server.txMemPool.FetchTransaction(txHash)
				if err != nil {
					peerLog.Debugf("Unable to fetch tx %v from transaction "+
						"pool for peer %s: %v", txHash, sp, err)
					break
				}
			}
			dataMsg = tx.MsgTx()

		case wire.InvTypeBlock:
			blockHash := &iv.Hash
			block, err := sp.server.chain.BlockByHash(blockHash)
			if err != nil {
				peerLog.Debugf("Unable to fetch block hash %v for peer %s: %v",
					blockHash, sp, err)
				break
			}
			dataMsg = block.MsgBlock()

			// When the peer requests the final block that was advertised in
			// response to a getblocks message which requested more blocks than
			// would fit into a single message, it requires a new inventory
			// message to trigger it to issue another getblocks message for the
			// next batch of inventory.
			//
			// However, that inventory message should not be sent until after
			// the block itself is sent, so keep a flag for later use.
			//
			// Note that this is to support the legacy syncing model that is no
			// longer used in dcrd which is now based on a much more robust
			// headers-based syncing model.  Nevertheless, this behavior is
			// still a required part of the getblocks protocol semantics.  It
			// can be removed if a future protocol upgrade also removes the
			// getblocks message.
			continueHash := sp.continueHash.Load()
			sendInv = continueHash != nil && *continueHash == *blockHash

		case wire.InvTypeMix:
			mixHash := &iv.Hash
			msg, ok := sp.server.mixMsgPool.RecentMessage(mixHash)
			if !ok {
				peerLog.Debugf("Unable to fetch mix message %v from the mix "+
					"pool for peer %s", mixHash, sp)
				break
			}
			dataMsg = msg

		default:
			peerLog.Warnf("Unknown type '%d' in inventory request from %s",
				iv.Type, sp)
			continue
		}
		if dataMsg == nil {
			// Keep track of all items that were not found in order to send a
			// consolidated messsage once the entire batch is processed.
			//
			// The error when adding the inventory vector is ignored because the
			// only way it could fail would be by exceeding the max allowed
			// number of items which is impossible given the getdata message is
			// enforced to not exceed that same maximum limit.
			if notFoundMsg == nil {
				notFoundMsg = wire.NewMsgNotFound()
			}
			notFoundMsg.AddInvVect(iv)

			// There is no need to wait for the semaphore below when there is
			// not any data to send.
			sp.numPendingGetDataItemReqs.Add(^uint32(0))
			continue
		}

		// Limit the number of items that can be queued to prevent wasting a
		// bunch of memory by queuing far more data than can be sent in a
		// reasonable time.  The waiting occurs after the database fetch for the
		// next one to provide a little pipelining.
		//
		// This also monitors the channel that is notified when queued messages
		// are sent in order to release the semaphore without needing a separate
		// monitoring goroutine.
		for semAcquired := false; !semAcquired; {
			select {
			case <-sp.quit:
				return

			case semaphore <- struct{}{}:
				semAcquired = true

			case <-sendDoneChan:
				// Release semaphore.
				<-semaphore
			}
		}

		// Decrement the pending data item requests accordingly and queue the
		// data to be sent to the peer.
		sp.numPendingGetDataItemReqs.Add(^uint32(0))
		sp.QueueMessage(dataMsg, sendDoneChan)

		// Send a new inventory message to trigger the peer to issue another
		// getblocks message for the next batch of inventory if needed.
		if sendInv {
			best := sp.server.chain.BestSnapshot()
			invMsg := wire.NewMsgInvSizeHint(1)
			iv := wire.NewInvVect(wire.InvTypeBlock, &best.Hash)
			invMsg.AddInvVect(iv)
			sp.QueueMessage(invMsg, nil)
			sp.continueHash.Store(nil)
		}
	}
	if notFoundMsg != nil {
		sp.QueueMessage(notFoundMsg, nil)
	}
}

// serveGetData provides an asynchronous queue that services all data requested
// via getdata requests such that the peer may mix and match simultaneous
// getdata requests for varying amounts of data items so long as it does not
// exceed the maximum number of simultaneous pending getdata messages or the
// maximum number of total overall pending data item requests.
//
// It must be run in a goroutine.
func (sp *serverPeer) serveGetData() {
	// Allow a max number of items to be loaded from the database/mempool and
	// queued for send.
	const maxPendingSend = 3
	sendDoneChan := make(chan struct{}, maxPendingSend+1)
	semaphore := make(chan struct{}, maxPendingSend)

	for {
		select {
		case <-sp.quit:
			return

		case invVects := <-sp.getDataQueue:
			sp.handleServeGetData(invVects, sendDoneChan, semaphore)

		// Release the semaphore as queued messages are sent.
		case <-sendDoneChan:
			<-semaphore
		}
	}
}

// Run starts additional async processing for the peer and blocks until the peer
// disconnects at which point it notifies the server and net sync manager that
// the peer has disconnected and performs other associated cleanup such as
// evicting any remaining orphans sent by the peer and shutting down all
// goroutines.
func (sp *serverPeer) Run() {
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		sp.serveGetData()
		wg.Done()
	}()

	// Wait for the peer to disconnect and notify the net sync manager and
	// server accordingly.
	sp.WaitForDisconnect()
	srvr := sp.server
	srvr.DonePeer(sp)
	srvr.syncManager.OnPeerDisconnected(sp.syncMgrPeer)

	if sp.VersionKnown() {
		// Evict any remaining orphans that were sent by the peer.
		numEvicted := srvr.txMemPool.RemoveOrphansByTag(mempool.Tag(sp.ID()))
		if numEvicted > 0 {
			srvrLog.Debugf("Evicted %d %s from peer %v (id %d)", numEvicted,
				pickNoun(numEvicted, "orphan", "orphans"), sp, sp.ID())
		}
	}

	// Shutdown remaining peer goroutines.
	close(sp.quit)
	wg.Wait()
}

// newestBlock returns the current best block hash and height using the format
// required by the configuration for the peer package.
func (sp *serverPeer) newestBlock() (*chainhash.Hash, int64, error) {
	best := sp.server.chain.BestSnapshot()
	return &best.Hash, best.Height, nil
}

// addKnownAddress adds the given address to the set of known addresses to
// the peer to prevent sending duplicate addresses.
func (sp *serverPeer) addKnownAddress(na *addrmgr.NetAddress) {
	sp.knownAddresses.Add([]byte(na.Key()))
}

// addKnownAddresses adds the given addresses to the set of known addresses to
// the peer to prevent sending duplicate addresses.
func (sp *serverPeer) addKnownAddresses(addresses []*addrmgr.NetAddress) {
	for _, na := range addresses {
		sp.addKnownAddress(na)
	}
}

// addressKnown true if the given address is already known to the peer.
func (sp *serverPeer) addressKnown(na *addrmgr.NetAddress) bool {
	return sp.knownAddresses.Contains([]byte(na.Key()))
}

// wireToAddrmgrNetAddress converts a wire NetAddress to an address manager
// NetAddress.
func wireToAddrmgrNetAddress(netAddr *wire.NetAddress) *addrmgr.NetAddress {
	newNetAddr := addrmgr.NewNetAddressFromIPPort(netAddr.IP, netAddr.Port,
		netAddr.Services)
	newNetAddr.Timestamp = netAddr.Timestamp
	return newNetAddr
}

// wireToAddrmgrNetAddresses converts a collection of wire net addresses to a
// collection of address manager net addresses.
func wireToAddrmgrNetAddresses(netAddr []*wire.NetAddress) []*addrmgr.NetAddress {
	addrs := make([]*addrmgr.NetAddress, len(netAddr))
	for i, wireAddr := range netAddr {
		addrs[i] = wireToAddrmgrNetAddress(wireAddr)
	}
	return addrs
}

// addrmgrToWireNetAddress converts an address manager net address to a wire net
// address.
func addrmgrToWireNetAddress(netAddr *addrmgr.NetAddress) *wire.NetAddress {
	return wire.NewNetAddressTimestamp(netAddr.Timestamp, netAddr.Services,
		netAddr.IP, netAddr.Port)
}

// pushAddrMsg sends an addr message to the connected peer using the provided
// addresses.
func (sp *serverPeer) pushAddrMsg(addresses []*addrmgr.NetAddress) {
	// Filter addresses already known to the peer.
	addrs := make([]*wire.NetAddress, 0, len(addresses))
	for _, addr := range addresses {
		if !sp.addressKnown(addr) {
			wireNetAddr := addrmgrToWireNetAddress(addr)
			addrs = append(addrs, wireNetAddr)
		}
	}
	known, err := sp.PushAddrMsg(addrs)
	if err != nil {
		peerLog.Errorf("Can't push address message to %s: %v", sp, err)
		sp.Disconnect()
		return
	}

	knownNetAddrs := wireToAddrmgrNetAddresses(known)
	sp.addKnownAddresses(knownNetAddrs)
}

// addBanScore increases the persistent and decaying ban score fields by the
// values passed as parameters. If the resulting score exceeds half of the ban
// threshold, a warning is logged including the reason provided. Further, if
// the score is above the ban threshold, the peer will be banned and
// disconnected.
func (sp *serverPeer) addBanScore(persistent, transient uint32, reason string) bool {
	// No warning is logged and no score is calculated if banning is disabled.
	if cfg.DisableBanning {
		return false
	}
	if sp.isWhitelisted {
		srvrLog.Debugf("Misbehaving whitelisted peer %s: %s", sp, reason)
		return false
	}

	warnThreshold := cfg.BanThreshold >> 1
	if transient == 0 && persistent == 0 {
		// The score is not being increased, but a warning message is still
		// logged if the score is above the warn threshold.
		score := sp.banScore.Int()
		if score > warnThreshold {
			srvrLog.Warnf("Misbehaving peer %s: %s -- ban score is %d, "+
				"it was not increased this time", sp, reason, score)
		}
		return false
	}
	score := sp.banScore.Increase(persistent, transient)
	if score > warnThreshold {
		srvrLog.Warnf("Misbehaving peer %s: %s -- ban score increased to %d",
			sp, reason, score)
		if score > cfg.BanThreshold {
			const reason = "ban score exceeds threshold"
			sp.server.BanPeer(sp, reason)
			return true
		}
	}
	return false
}

// hasServices returns whether or not the provided advertised service flags have
// all of the provided desired service flags set.
func hasServices(advertised, desired wire.ServiceFlag) bool {
	return advertised&desired == desired
}

// isSupportedNetAddrTypeV1 is a filter which returns whether the provided
// network address type is supported by the addr wire message.
func isSupportedNetAddrTypeV1(addrType addrmgr.NetAddressType) bool {
	return addrType == addrmgr.IPv4Address || addrType == addrmgr.IPv6Address
}

// natfSupported returns a filter for the address types supported by the
// protocol version.
func natfSupported(pver uint32) addrmgr.NetAddressTypeFilter {
	return isSupportedNetAddrTypeV1
}

// OnVersion is invoked when a peer receives a version wire message and is used
// to negotiate the protocol version details as well as kick start the
// communications.
func (sp *serverPeer) OnVersion(_ *peer.Peer, msg *wire.MsgVersion) {
	// Update the address manager with the advertised services for outbound
	// connections in case they have changed.  This is not done for inbound
	// connections to help prevent malicious behavior and is skipped when
	// running on the simulation and regression test networks since they are
	// only intended to connect to specified peers and actively avoid
	// advertising and connecting to discovered peers.
	//
	// NOTE: This is done before rejecting peers that are too old to ensure
	// it is updated regardless in the case a new minimum protocol version is
	// enforced and the remote node has not upgraded yet.
	isInbound := sp.Inbound()
	remoteAddr := wireToAddrmgrNetAddress(sp.NA())
	addrManager := sp.server.addrManager
	if !cfg.SimNet && !cfg.RegNet && !isInbound {
		err := addrManager.SetServices(remoteAddr, msg.Services)
		if err != nil {
			srvrLog.Errorf("Setting services for address failed: %v", err)
		}
	}

	// Reject peers that have a protocol version that is too old.
	const reqProtocolVersion = int32(wire.RemoveRejectVersion)
	if msg.ProtocolVersion < reqProtocolVersion {
		srvrLog.Debugf("Rejecting peer %s with protocol version %d prior to "+
			"the required version %d", sp, msg.ProtocolVersion,
			reqProtocolVersion)
		sp.Disconnect()
		return
	}

	// Maintain a minimum desired number of outbound peers capable of supporting
	// p2p mixing.
	if !isInbound && msg.ProtocolVersion < int32(wire.MixVersion) {
		var numOutbound, numMixCapableOutbound uint32
		peerState := &sp.server.peerState
		peerState.Lock()
		peerState.forAllOutboundPeers(func(sp *serverPeer) {
			if sp.ProtocolVersion() >= wire.MixVersion {
				numMixCapableOutbound++
			}
			numOutbound++
		})
		peerState.Unlock()

		const defaultWantMixCapableOutbound uint32 = 3
		wantMixCapableOutbound := defaultWantMixCapableOutbound
		if sp.server.targetOutbound < wantMixCapableOutbound {
			wantMixCapableOutbound = sp.server.targetOutbound
		}
		hasMinMixCapableOuts := numMixCapableOutbound >= wantMixCapableOutbound
		needsMoreMixCapable := !hasMinMixCapableOuts &&
			numOutbound+wantMixCapableOutbound >= sp.server.targetOutbound
		if needsMoreMixCapable {
			srvrLog.Debugf("Rejecting outbound peer %s with protocol version "+
				"%d in favor of a peer with minimum version %d (have: %d, "+
				"target: %d)", sp, msg.ProtocolVersion, wire.MixVersion,
				numMixCapableOutbound, wantMixCapableOutbound)
			sp.Disconnect()
		}
	}

	// Reject outbound peers that are not full nodes.
	wantServices := wire.SFNodeNetwork
	if !isInbound && !hasServices(msg.Services, wantServices) {
		missingServices := wantServices & ^msg.Services
		srvrLog.Debugf("Rejecting peer %s with services %v due to not "+
			"providing desired services %v", sp, msg.Services, missingServices)
		sp.Disconnect()
		return
	}

	// Update the address manager and request known addresses from the
	// remote peer for outbound connections.  This is skipped when running
	// on the simulation and regression test networks since they are only
	// intended to connect to specified peers and actively avoid advertising
	// and connecting to discovered peers.
	if !cfg.SimNet && !cfg.RegNet && !isInbound {
		// Advertise the local address when the server accepts incoming
		// connections and it believes itself to be close to the best
		// known tip.
		if !cfg.DisableListen && sp.server.syncManager.IsCurrent() {
			// Get address that best matches.
			addrTypeFilter := natfSupported(uint32(msg.ProtocolVersion))
			lna := addrManager.GetBestLocalAddress(remoteAddr, addrTypeFilter)
			if lna.IsRoutable() {
				// Filter addresses the peer already knows about.
				addresses := []*addrmgr.NetAddress{lna}
				sp.pushAddrMsg(addresses)
			}
		}

		// Request known addresses if the server address manager needs
		// more.
		if addrManager.NeedMoreAddresses() {
			sp.QueueMessage(wire.NewMsgGetAddr(), nil)
		}

		// Mark the address as a known good address.
		err := addrManager.Good(remoteAddr)
		if err != nil {
			srvrLog.Errorf("Marking address as good failed: %v", err)
		}
	}

	sp.peerNa.Store(&msg.AddrYou)

	// Choose whether or not to relay transactions.
	sp.disableRelayTx.Store(msg.DisableRelayTx)

	// Add the remote peer time as a sample for creating an offset against
	// the local clock to keep the network time in sync.
	sp.server.timeSource.AddTimeSample(sp.Addr(), msg.Timestamp)

	// Add valid peer to the server.
	sp.server.AddPeer(sp)
}

// OnVerAck is invoked when a peer receives a verack wire message.  It creates
// and sends a sendheaders message to request all block annoucements are made
// via full headers instead of the inv message.
func (sp *serverPeer) OnVerAck(_ *peer.Peer, msg *wire.MsgVerAck) {
	sp.QueueMessage(wire.NewMsgSendHeaders(), nil)
}

// OnMemPool is invoked when a peer receives a mempool wire message.  It creates
// and sends an inventory message with the contents of the memory pool up to the
// maximum inventory allowed per message.
func (sp *serverPeer) OnMemPool(_ *peer.Peer, msg *wire.MsgMemPool) {
	// A decaying ban score increase is applied to prevent flooding.
	// The ban score accumulates and passes the ban threshold if a burst of
	// mempool messages comes from a peer. The score decays each minute to
	// half of its value.
	if sp.addBanScore(0, 33, "mempool") {
		return
	}

	// Generate inventory message with the available transactions in the
	// transaction memory pool.  Limit it to the max allowed inventory
	// per message.  The NewMsgInvSizeHint function automatically limits
	// the passed hint to the maximum allowed, so it's safe to pass it
	// without double checking it here.
	txMemPool := sp.server.txMemPool
	txDescs := txMemPool.TxDescs()

	// Send the inventory message if there is anything to send.
	for _, txDesc := range txDescs {
		iv := wire.NewInvVect(wire.InvTypeTx, txDesc.Tx.Hash())
		sp.QueueInventory(iv)
	}
}

// pushMiningStateMsg pushes a mining state message to the queue for a
// requesting peer.
func (sp *serverPeer) pushMiningStateMsg(height uint32, blockHashes []chainhash.Hash, voteHashes []chainhash.Hash) error {
	// Nothing to send, abort.
	if len(blockHashes) == 0 {
		return nil
	}

	// Construct the mining state request and queue it to be sent.
	msg := wire.NewMsgMiningState()
	msg.Height = height
	for i := range blockHashes {
		err := msg.AddBlockHash(&blockHashes[i])
		if err != nil {
			return err
		}
	}
	for i := range voteHashes {
		err := msg.AddVoteHash(&voteHashes[i])
		if err != nil {
			return err
		}
		if i+1 >= wire.MaxMSBlocksAtHeadPerMsg {
			break
		}
	}

	sp.QueueMessage(msg, nil)

	return nil
}

// OnGetMiningState is invoked when a peer receives a getminings wire message.
// It constructs a list of the current best blocks and votes that should be
// mined on and pushes a miningstate wire message back to the requesting peer.
func (sp *serverPeer) OnGetMiningState(_ *peer.Peer, msg *wire.MsgGetMiningState) {
	if sp.getMiningStateSent {
		peerLog.Tracef("Ignoring getminingstate from %v - already sent", sp)
		return
	}
	sp.getMiningStateSent = true

	// Send out blank mining states if it's early in the blockchain.
	best := sp.server.chain.BestSnapshot()
	if best.Height < sp.server.chainParams.StakeValidationHeight-1 {
		err := sp.pushMiningStateMsg(0, nil, nil)
		if err != nil {
			peerLog.Warnf("unexpected error while pushing data for mining "+
				"state request: %v", err)
		}

		return
	}

	// Obtain the entire generation of blocks stemming from the parent of the
	// current tip.
	children := sp.server.chain.TipGeneration()

	// Get the list of blocks that are eligible to build on and limit the
	// list to the maximum number of allowed eligible block hashes per
	// mining state message.  There is nothing to send when there are no
	// eligible blocks.
	mp := sp.server.txMemPool
	blockHashes := mining.SortParentsByVotes(mp, best.Hash, children,
		sp.server.chainParams)
	numBlocks := len(blockHashes)
	if numBlocks == 0 {
		return
	}
	if numBlocks > wire.MaxMSBlocksAtHeadPerMsg {
		blockHashes = blockHashes[:wire.MaxMSBlocksAtHeadPerMsg]
	}

	// Construct the set of votes to send.
	voteHashes := make([]chainhash.Hash, 0, wire.MaxMSVotesAtHeadPerMsg)
	for i := range blockHashes {
		// Fetch the vote hashes themselves and append them.
		bh := &blockHashes[i]
		vhsForBlock := mp.VoteHashesForBlock(bh)
		if len(vhsForBlock) == 0 {
			peerLog.Warnf("unexpected error while fetching vote hashes "+
				"for block %v for a mining state request: no vote "+
				"metadata for block", bh)
			return
		}
		voteHashes = append(voteHashes, vhsForBlock...)
	}

	err := sp.pushMiningStateMsg(uint32(best.Height), blockHashes, voteHashes)
	if err != nil {
		peerLog.Warnf("unexpected error while pushing data for mining state "+
			"request: %v", err)
	}
}

// OnMiningState is invoked when a peer receives a miningstate wire message.  It
// requests the data advertised in the message from the peer.
func (sp *serverPeer) OnMiningState(_ *peer.Peer, msg *wire.MsgMiningState) {
	var blockHashes, voteHashes []chainhash.Hash
	if len(msg.BlockHashes) > 0 {
		blockHashes = make([]chainhash.Hash, 0, len(msg.BlockHashes))
		for _, hash := range msg.BlockHashes {
			blockHashes = append(blockHashes, *hash)
		}
	}
	if len(msg.VoteHashes) > 0 {
		voteHashes = make([]chainhash.Hash, 0, len(msg.VoteHashes))
		for _, hash := range msg.VoteHashes {
			voteHashes = append(voteHashes, *hash)
		}
	}

	sp.server.syncManager.RequestFromPeer(sp.syncMgrPeer, blockHashes,
		voteHashes, nil)
}

// OnGetInitState is invoked when a peer receives a getinitstate wire message.
// It sends the available requested info to the remote peer.
func (sp *serverPeer) OnGetInitState(_ *peer.Peer, msg *wire.MsgGetInitState) {
	if sp.initStateSent {
		peerLog.Tracef("Ignoring getinitstate from %v - already sent", sp)
		return
	}
	sp.initStateSent = true

	// Send out blank mining states if it's early in the blockchain.
	best := sp.server.chain.BestSnapshot()
	if best.Height < sp.server.chainParams.StakeValidationHeight-1 {
		sp.QueueMessage(wire.NewMsgInitState(), nil)
		return
	}

	// Response data.
	var blockHashes, voteHashes, tspendHashes []chainhash.Hash

	// Map from the types slice into a map for easier checking.
	types := make(map[string]struct{}, len(msg.Types))
	for _, typ := range msg.Types {
		types[typ] = struct{}{}
	}
	_, wantBlocks := types[wire.InitStateHeadBlocks]
	_, wantVotes := types[wire.InitStateHeadBlockVotes]
	_, wantTSpends := types[wire.InitStateTSpends]

	// Fetch head block hashes if we need to send either them or their
	// votes.
	mp := sp.server.txMemPool
	if wantBlocks || wantVotes {
		// Obtain the entire generation of blocks stemming from the parent of
		// the current tip.
		children := sp.server.chain.TipGeneration()

		// Get the list of blocks that are eligible to build on and
		// limit the list to the maximum number of allowed eligible
		// block hashes per init state message.  There is nothing to
		// send when there are no eligible blocks.
		blockHashes = mining.SortParentsByVotes(mp, best.Hash, children,
			sp.server.chainParams)
		if len(blockHashes) > wire.MaxISBlocksAtHeadPerMsg {
			blockHashes = blockHashes[:wire.MaxISBlocksAtHeadPerMsg]
		}
	}

	// Construct the set of votes to send.
	if wantVotes {
		for i := range blockHashes {
			// Fetch the vote hashes themselves and append them.
			bh := &blockHashes[i]
			vhsForBlock := mp.VoteHashesForBlock(bh)
			voteHashes = append(voteHashes, vhsForBlock...)
		}
	}

	// Construct tspends to send.
	if wantTSpends {
		tspendHashes = mp.TSpendHashes()
	}

	// Clear out block hashes to be sent if they weren't requested.
	if !wantBlocks {
		blockHashes = nil
	}

	// Build and push the response.
	initMsg, err := wire.NewMsgInitStateFilled(blockHashes, voteHashes, tspendHashes)
	if err != nil {
		peerLog.Warnf("Unexpected error while building initstate msg: %v", err)
		return
	}
	sp.QueueMessage(initMsg, nil)
}

// OnInitState is invoked when a peer receives a initstate wire message.  It
// requests the data advertised in the message from the peer.
func (sp *serverPeer) OnInitState(_ *peer.Peer, msg *wire.MsgInitState) {
	sp.server.syncManager.RequestFromPeer(sp.syncMgrPeer, msg.BlockHashes,
		msg.VoteHashes, msg.TSpendHashes)
}

// OnTx is invoked when a peer receives a tx wire message.  It blocks until the
// transaction has been fully processed.  Unlock the block handler this does not
// serialize all transactions through a single thread transactions don't rely on
// the previous one in a linear fashion like blocks.
func (sp *serverPeer) OnTx(_ *peer.Peer, msg *wire.MsgTx) {
	if cfg.BlocksOnly {
		peerLog.Tracef("Ignoring tx %v from %v - blocksonly enabled",
			msg.TxHash(), sp)
		return
	}

	// Add the transaction to the known inventory for the peer.
	// Convert the raw MsgTx to a dcrutil.Tx which provides some convenience
	// methods and things such as hash caching.
	tx := dcrutil.NewTx(msg)
	iv := wire.NewInvVect(wire.InvTypeTx, tx.Hash())
	sp.AddKnownInventory(iv)

	// Handle the transaction with the net sync manager.  Notice that this
	// intentionally blocks further receives until the transaction is fully
	// processed and known good or bad.  This helps prevent a malicious peer
	// from queuing up a bunch of bad transactions before disconnecting (or
	// being disconnected) and wasting memory.
	//
	// Also, announce any accepted transactions to the network and websocket
	// clients.
	acceptedTxns := sp.server.syncManager.OnTx(sp.syncMgrPeer, tx)
	if len(acceptedTxns) > 0 {
		sp.server.AnnounceNewTransactions(acceptedTxns)
	}
}

// OnBlock is invoked when a peer receives a block wire message.  It blocks
// until the network block has been fully processed.
func (sp *serverPeer) OnBlock(_ *peer.Peer, msg *wire.MsgBlock, buf []byte) {
	// Convert the raw MsgBlock to a dcrutil.Block which provides some
	// convenience methods and things such as hash caching.
	block := dcrutil.NewBlockFromBlockAndBytes(msg, buf)

	// Add the block to the known inventory for the peer.
	iv := wire.NewInvVect(wire.InvTypeBlock, block.Hash())
	sp.AddKnownInventory(iv)

	// Handle the block with the net sync manager.  Notice that this
	// intentionally blocks further receives until the block is fully processed
	// and known good or bad.  This helps prevent a malicious peer from queuing
	// up a bunch of bad blocks before disconnecting (or being disconnected) and
	// wasting memory.
	sp.server.syncManager.OnBlock(sp.syncMgrPeer, block)
}

// OnInv is invoked when a peer receives an inv wire message and is used to
// examine the inventory being advertised by the remote peer and react
// accordingly.  We pass the message down to the net sync manager which will
// call QueueMessage with any appropriate responses.
func (sp *serverPeer) OnInv(_ *peer.Peer, msg *wire.MsgInv) {
	// Ban peers sending empty inventory announcements.
	if len(msg.InvList) == 0 {
		const reason = "sent empty inventory announcement"
		sp.server.BanPeer(sp, reason)
		return
	}

	if !cfg.BlocksOnly {
		sp.server.syncManager.OnInv(sp.syncMgrPeer, msg)
		return
	}

	for _, invVect := range msg.InvList {
		var typ string
		switch invVect.Type {
		case wire.InvTypeTx:
			typ = "transactions"
		case wire.InvTypeMix:
			typ = "mix messages"
		default:
			continue
		}
		peerLog.Infof("Peer %v is announcing %s -- disconnecting", sp, typ)
		sp.Disconnect()
		return
	}

	sp.server.syncManager.OnInv(sp.syncMgrPeer, msg)
}

// OnHeaders is invoked when a peer receives a headers wire message.  The
// message is passed down to the net sync manager.
func (sp *serverPeer) OnHeaders(_ *peer.Peer, msg *wire.MsgHeaders) {
	sp.server.syncManager.OnHeaders(sp.syncMgrPeer, msg)
}

// OnGetData is invoked when a peer receives a getdata wire message and is used
// to deliver block and transaction information.
func (sp *serverPeer) OnGetData(_ *peer.Peer, msg *wire.MsgGetData) {
	// Ban peers sending empty getdata requests.
	if len(msg.InvList) == 0 {
		const reason = "sent an empty getdata request"
		sp.server.BanPeer(sp, reason)
		return
	}

	// A decaying ban score increase is applied to prevent exhausting resources
	// with unusually large inventory queries.
	//
	// Requesting more than the maximum inventory vector length within a short
	// period of time yields a score above the default ban threshold.  Sustained
	// bursts of small requests are not penalized as that would potentially ban
	// peers performing the inintial chain sync.
	//
	// This incremental score decays each minute to half of its value.
	numNewReqs := uint32(len(msg.InvList))
	if sp.addBanScore(0, numNewReqs*99/wire.MaxInvPerMsg, "getdata") {
		return
	}

	// Prevent too many outstanding requests while still allowing the
	// flexibility to send multiple simultaneous getdata requests that are
	// served asynchronously.
	numPendingGetDataReqs := len(sp.getDataQueue)
	if numPendingGetDataReqs+1 > maxConcurrentGetDataReqs {
		peerLog.Debugf("%s exceeded max allowed concurrent pending getdata "+
			"requests (max %d) -- disconnecting", sp, maxConcurrentGetDataReqs)
		sp.Disconnect()
		return
	}
	numPendingDataItemReqs := sp.numPendingGetDataItemReqs.Load()
	if numPendingDataItemReqs+numNewReqs > maxPendingGetDataItemReqs {
		peerLog.Debugf("%s exceeded max allowed pending data item requests "+
			"(new %d, pending %d, max %d) -- disconnecting", sp, numNewReqs,
			numPendingDataItemReqs, maxPendingGetDataItemReqs)
		sp.Disconnect()
		return
	}

	// Queue the data requests to be served asynchronously.  Note that this will
	// not block due to the use of a buffered channel and the checks above that
	// disconnect the peer when the new request would otherwise exceed the
	// capacity.
	sp.numPendingGetDataItemReqs.Add(numNewReqs)
	select {
	case <-sp.quit:
	case sp.getDataQueue <- msg.InvList:
	}
}

// OnGetBlocks is invoked when a peer receives a getblocks wire message.
func (sp *serverPeer) OnGetBlocks(_ *peer.Peer, msg *wire.MsgGetBlocks) {
	// Find the most recent known block in the best chain based on the block
	// locator and fetch all of the block hashes after it until either
	// wire.MaxBlocksPerMsg have been fetched or the provided stop hash is
	// encountered.
	//
	// Use the block after the genesis block if no other blocks in the
	// provided locator are known.  This does mean the client will start
	// over with the genesis block if unknown block locators are provided.
	chain := sp.server.chain
	hashList := chain.LocateBlocks(msg.BlockLocatorHashes, &msg.HashStop,
		wire.MaxBlocksPerMsg)

	// Generate inventory message.
	invMsg := wire.NewMsgInv()
	for i := range hashList {
		iv := wire.NewInvVect(wire.InvTypeBlock, &hashList[i])
		if sp.IsKnownInventory(iv) {
			// TODO: Increase ban score
			continue
		}
		invMsg.AddInvVect(iv)
	}

	// Send the inventory message if there is anything to send.
	if len(invMsg.InvList) > 0 {
		invListLen := len(invMsg.InvList)
		if invListLen == wire.MaxBlocksPerMsg {
			// Intentionally use a copy of the final hash so there
			// is not a reference into the inventory slice which
			// would prevent the entire slice from being eligible
			// for GC as soon as it's sent.
			continueHash := invMsg.InvList[invListLen-1].Hash
			sp.continueHash.Store(&continueHash)
		}
		sp.QueueMessage(invMsg, nil)
	}
}

// OnGetHeaders is invoked when a peer receives a getheaders wire message.
func (sp *serverPeer) OnGetHeaders(_ *peer.Peer, msg *wire.MsgGetHeaders) {
	// Send an empty headers message in the case the local best known chain does
	// not have the minimum cumulative work value already known to have been
	// achieved on the network.  This signals to the remote peer that there are
	// no interesting headers available without appearing unresponsive.
	chain := sp.server.chain
	tipHash := chain.BestSnapshot().Hash
	workSum, err := chain.ChainWork(&tipHash)
	if err == nil && workSum.Lt(&sp.server.minKnownWork) {
		srvrLog.Debugf("Sending empty headers to peer %s in response to "+
			"getheaders due to local best known tip having too little work", sp)
		sp.QueueMessage(&wire.MsgHeaders{}, nil)
		return
	}

	// Find the most recent known block in the best chain based on the block
	// locator and fetch all of the headers after it until either
	// wire.MaxBlockHeadersPerMsg have been fetched or the provided stop
	// hash is encountered.
	//
	// Use the block after the genesis block if no other blocks in the
	// provided locator are known.  This does mean the client will start
	// over with the genesis block if unknown block locators are provided.
	locatorHashes := msg.BlockLocatorHashes
	headers := chain.LocateHeaders(locatorHashes, &msg.HashStop)

	// Send found headers to the requesting peer.
	blockHeaders := make([]*wire.BlockHeader, len(headers))
	for i := range headers {
		blockHeaders[i] = &headers[i]
	}
	sp.QueueMessage(&wire.MsgHeaders{Headers: blockHeaders}, nil)
}

// enforceNodeCFFlag bans the peer if it has negotiated to a protocol version
// that is high enough to observe the committed filter service support bit since
// it is intentionally violating the protocol by requesting one from when the
// server does not advertise support for it.
//
// It disconnects the peer when it has negotiated to a protocol version prior to
// being able to understand the service bit.
func (sp *serverPeer) enforceNodeCFFlag(cmd string) {
	// Ban the peer if the protocol version is high enough that the peer is
	// knowingly violating the protocol and banning is enabled.
	//
	// NOTE: Even though the addBanScore function already examines whether
	// or not banning is enabled, it is checked here as well to ensure the
	// violation is logged and the peer is disconnected regardless.
	if sp.ProtocolVersion() >= wire.NodeCFVersion && !cfg.DisableBanning {
		// Disconnect the peer regardless of whether it was banned.
		sp.addBanScore(100, 0, cmd)
		sp.Disconnect()
		return
	}

	// Disconnect the peer regardless of protocol version or banning state.
	peerLog.Debugf("%s sent an unsupported %s request -- disconnecting", sp,
		cmd)
	sp.Disconnect()
}

// OnGetCFilter is invoked when a peer receives a getcfilter wire message.
func (sp *serverPeer) OnGetCFilter(_ *peer.Peer, msg *wire.MsgGetCFilter) {
	// Disconnect and/or ban depending on the node cf services flag and
	// negotiated protocol version.
	sp.enforceNodeCFFlag(msg.Command())
}

// OnGetCFilterV2 is invoked when a peer receives a getcfilterv2 wire message.
func (sp *serverPeer) OnGetCFilterV2(_ *peer.Peer, msg *wire.MsgGetCFilterV2) {
	// Attempt to obtain the requested filter.
	//
	// Ignore request for unknown block or otherwise missing filters.
	chain := sp.server.chain
	filter, proof, err := chain.FilterByBlockHash(&msg.BlockHash)
	if err != nil {
		return
	}

	filterMsg := wire.NewMsgCFilterV2(&msg.BlockHash, filter.Bytes(),
		proof.ProofIndex, proof.ProofHashes)
	sp.QueueMessage(filterMsg, nil)
}

// OnGetCFiltersV2 is invoked when a peer receives a getcfsv2 wire message.
func (sp *serverPeer) OnGetCFiltersV2(_ *peer.Peer, msg *wire.MsgGetCFsV2) {
	filtersMsg, err := sp.server.chain.LocateCFiltersV2(&msg.StartHash, &msg.EndHash)
	if err != nil {
		return
	}

	sp.QueueMessage(filtersMsg, nil)
}

// OnGetCFHeaders is invoked when a peer receives a getcfheader wire message.
func (sp *serverPeer) OnGetCFHeaders(_ *peer.Peer, msg *wire.MsgGetCFHeaders) {
	// Disconnect and/or ban depending on the node cf services flag and
	// negotiated protocol version.
	sp.enforceNodeCFFlag(msg.Command())
}

// OnGetCFTypes is invoked when a peer receives a getcftypes wire message.
func (sp *serverPeer) OnGetCFTypes(_ *peer.Peer, msg *wire.MsgGetCFTypes) {
	// Disconnect and/or ban depending on the node cf services flag and
	// negotiated protocol version.
	sp.enforceNodeCFFlag(msg.Command())
}

// OnGetAddr is invoked when a peer receives a getaddr wire message and is used
// to provide the peer with known addresses from the address manager.
func (sp *serverPeer) OnGetAddr(_ *peer.Peer, msg *wire.MsgGetAddr) {
	// Don't return any addresses when running on the simulation and regression
	// test networks.  This helps prevent the networks from becoming another
	// public test network since they will not be able to learn about other
	// peers that have not specifically been provided.
	if cfg.SimNet || cfg.RegNet {
		return
	}

	// Do not accept getaddr requests from outbound peers.  This reduces
	// fingerprinting attacks.
	if !sp.Inbound() {
		return
	}

	// Only respond with addresses once per connection.  This helps reduce
	// traffic and further reduces fingerprinting attacks.
	if sp.addrsSent {
		peerLog.Tracef("Ignoring getaddr from %v - already sent", sp)
		return
	}
	sp.addrsSent = true

	// Get a randomized subset of the current known addresses from the address
	// manager which are supported by the negotiated protocol version.
	pver := sp.ProtocolVersion()
	addrTypeFilter := natfSupported(pver)
	addrCache := sp.server.addrManager.AddressCache(addrTypeFilter)

	// Push the addresses.
	sp.pushAddrMsg(addrCache)
}

// OnAddr is invoked when a peer receives an addr wire message and is used to
// notify the server about advertised addresses.
func (sp *serverPeer) OnAddr(_ *peer.Peer, msg *wire.MsgAddr) {
	// Ignore addresses when running on the simulation and regression test
	// networks.  This helps prevent the networks from becoming another public
	// test network since they will not be able to learn about other peers that
	// have not specifically been provided.
	if cfg.SimNet || cfg.RegNet {
		return
	}

	// A message that has no addresses is invalid.
	if len(msg.AddrList) == 0 {
		// Ban peers sending empty address requests.
		const reason = "sent an empty address list"
		sp.server.BanPeer(sp, reason)
		return
	}

	now := time.Now()
	addrList := wireToAddrmgrNetAddresses(msg.AddrList)
	for _, na := range addrList {
		// Don't add more address if we're disconnecting.
		if !sp.Connected() {
			return
		}

		// Set the timestamp to 5 days ago if it's more than 24 hours
		// in the future so this address is one of the first to be
		// removed when space is needed.
		if na.Timestamp.After(now.Add(time.Minute * 10)) {
			na.Timestamp = now.Add(-1 * time.Hour * 24 * 5)
		}

		// Add address to known addresses for this peer.
		sp.addKnownAddress(na)
	}

	// Add addresses to server address manager.  The address manager handles
	// the details of things such as preventing duplicate addresses, max
	// addresses, and last seen updates.
	remoteAddr := wireToAddrmgrNetAddress(sp.NA())
	sp.server.addrManager.AddAddresses(addrList, remoteAddr)
}

// onMixMessage is the generic handler for all mix messages handler callbacks.
func (sp *serverPeer) onMixMessage(msg mixing.Message) {
	if cfg.BlocksOnly {
		peerLog.Tracef("Ignoring mix message %v from %v - blocksonly "+
			"enabled", msg.Hash(), sp)
		return
	}

	// Add the message to the known inventory for the peer.
	hash := msg.Hash()
	iv := wire.NewInvVect(wire.InvTypeMix, &hash)
	sp.AddKnownInventory(iv)

	// Handle the message with the net sync manager.  Notice that this
	// intentionally blocks further receives until the message is fully
	// processed and known good or bad.  This helps prevent a malicious peer
	// from queuing up a bunch of bad mix messages before disconnecting (or
	// being disconnected) and wasting memory.
	//
	// Also, announce any accepted messages to the network and websocket
	// clients.
	//
	// The accepted slice is intentionally used when non-empty before checking
	// the error because accepting a message can cause a cascade of other
	// messages that were previously orphans to be considered too and it is
	// possible that one or more of those previous orphans are rejected which
	// results in a mix of accepted messages and rejected messages.  The
	// accepted slice contains the ones that were successfully accepted and thus
	// they still need to be announced.
	//
	// Finally, when the error is the result of an orphan KE with unknown PR,
	// request the PR from the peer submitting the KE.  This is a normal
	// occurrence.
	//
	// XXX: add ban score increases for non-instaban errors?
	accepted, err := sp.server.syncManager.OnMixMsg(sp.syncMgrPeer, msg)
	if len(accepted) > 0 {
		sp.server.AnnounceMixMessages(accepted)
	}
	var missingOwnPRErr *mixpool.MissingOwnPRError
	if errors.As(err, &missingOwnPRErr) {
		mixHash := &missingOwnPRErr.MissingPR
		sp.server.syncManager.RequestMixMsgFromPeer(sp.syncMgrPeer, mixHash)
		return
	}
	if mixpool.IsBannable(err, sp.Services()) {
		reason := fmt.Sprintf("sent malformed mix message: %s", err)
		sp.server.BanPeer(sp, reason)
	}
}

// OnMixPairReq submits a received mixing pair request message to the mixpool.
func (sp *serverPeer) OnMixPairReq(_ *peer.Peer, msg *wire.MsgMixPairReq) {
	sp.onMixMessage(msg)
}

// OnMixKeyExchange submits a received mixing key exchange message to the
// mixpool.
func (sp *serverPeer) OnMixKeyExchange(_ *peer.Peer, msg *wire.MsgMixKeyExchange) {
	sp.onMixMessage(msg)
}

// OnMixCiphertexts submits a received mixing ciphertext exchange message to
// the mixpool.
func (sp *serverPeer) OnMixCiphertexts(_ *peer.Peer, msg *wire.MsgMixCiphertexts) {
	sp.onMixMessage(msg)
}

// OnMixSlotReserve submits a received mixing slot reservation message to the
// mixpool.
func (sp *serverPeer) OnMixSlotReserve(_ *peer.Peer, msg *wire.MsgMixSlotReserve) {
	sp.onMixMessage(msg)
}

// OnMixDCNet submits a received mixing XOR DC-net message to the mixpool.
func (sp *serverPeer) OnMixDCNet(_ *peer.Peer, msg *wire.MsgMixDCNet) {
	sp.onMixMessage(msg)
}

// OnMixConfirm submits a received mixing confirmation message to the mixpool.
func (sp *serverPeer) OnMixConfirm(_ *peer.Peer, msg *wire.MsgMixConfirm) {
	sp.onMixMessage(msg)
}

// OnMixFactoredPoly submits a received factored polynomial message to the
// mixpool.
func (sp *serverPeer) OnMixFactoredPoly(_ *peer.Peer, msg *wire.MsgMixFactoredPoly) {
	sp.onMixMessage(msg)
}

// OnMixSecrets submits a received mixing reveal secrets message to the
// mixpool.
func (sp *serverPeer) OnMixSecrets(_ *peer.Peer, msg *wire.MsgMixSecrets) {
	sp.onMixMessage(msg)
}

// OnRead is invoked when a peer receives a message and it is used to update
// the bytes received by the server.
func (sp *serverPeer) OnRead(_ *peer.Peer, bytesRead int, msg wire.Message, err error) {
	// Ban peers sending messages that do not conform to the wire protocol.
	var errCode wire.ErrorCode
	if errors.As(err, &errCode) {
		reason := fmt.Sprintf("sent malformed wire message: %s", err)
		sp.server.BanPeer(sp, reason)
	}

	sp.server.AddBytesReceived(uint64(bytesRead))
}

// OnWrite is invoked when a peer sends a message and it is used to update
// the bytes sent by the server.
func (sp *serverPeer) OnWrite(_ *peer.Peer, bytesWritten int, msg wire.Message, err error) {
	sp.server.AddBytesSent(uint64(bytesWritten))
}

// OnNotFound is invoked when a peer sends a notfound message.
func (sp *serverPeer) OnNotFound(_ *peer.Peer, msg *wire.MsgNotFound) {
	if !sp.Connected() {
		return
	}

	var numBlocks, numTxns, numMixMsgs uint32
	for _, inv := range msg.InvList {
		switch inv.Type {
		case wire.InvTypeBlock:
			numBlocks++
		case wire.InvTypeTx:
			numTxns++
		case wire.InvTypeMix:
			numMixMsgs++
		default:
			peerLog.Debugf("Invalid inv type '%d' in notfound message from %s",
				inv.Type, sp)
			sp.Disconnect()
			return
		}
	}
	if numBlocks > 0 {
		blockStr := pickNoun(uint64(numBlocks), "block", "blocks")
		reason := fmt.Sprintf("%d %v not found", numBlocks, blockStr)
		if sp.addBanScore(20*numBlocks, 0, reason) {
			return
		}
	}
	if numTxns > 0 {
		txStr := pickNoun(uint64(numTxns), "transaction", "transactions")
		reason := fmt.Sprintf("%d %v not found", numTxns, txStr)
		if sp.addBanScore(0, 10*numTxns, reason) {
			return
		}
	}
	if numMixMsgs > 0 {
		mixStr := pickNoun(uint64(numMixMsgs), "mix message", "mix messages")
		reason := fmt.Sprintf("%d %v not found", numMixMsgs, mixStr)
		if sp.addBanScore(0, 10*numMixMsgs, reason) {
			return
		}
	}
	sp.server.syncManager.OnNotFound(sp.syncMgrPeer, msg)
}

// attemptDcrdDial is a wrapper function around dcrdDial which adds and marks
// the remote peer as attempted in the address manager.
func (s *server) attemptDcrdDial(ctx context.Context, network, addr string) (net.Conn, error) {
	if !cfg.SimNet && !cfg.RegNet {
		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
		}
		remoteAddr, err := hostToNetAddress(host, uint16(port), 0, dcrdLookup)
		if err != nil {
			return nil, err
		}
		// Be sure the address exists in the address manager.
		s.addrManager.AddAddresses([]*addrmgr.NetAddress{remoteAddr},
			remoteAddr)

		err = s.addrManager.Attempt(remoteAddr)
		if err != nil {
			srvrLog.Errorf("Marking address as attempted failed: %v", err)
		}
	}

	return dcrdDial(ctx, network, addr)
}

// AddRebroadcastInventory adds 'iv' to the list of inventories to be
// rebroadcasted at random intervals until they show up in a block.
func (s *server) AddRebroadcastInventory(iv *wire.InvVect, data interface{}) {
	select {
	case <-s.quit:
	case s.modifyRebroadcastInv <- broadcastInventoryAdd{invVect: iv, data: data}:
	}
}

// RemoveRebroadcastInventory removes 'iv' from the list of items to be
// rebroadcasted if present.
func (s *server) RemoveRebroadcastInventory(iv *wire.InvVect) {
	select {
	case <-s.quit:
	case s.modifyRebroadcastInv <- broadcastInventoryDel(iv):
	}
}

// PruneRebroadcastInventory filters and removes rebroadcast inventory entries
// where necessary.
func (s *server) PruneRebroadcastInventory() {
	select {
	case <-s.quit:
	case s.modifyRebroadcastInv <- broadcastPruneInventory{}:
	}
}

// relayTransactions generates and relays inventory vectors for all of the
// passed transactions to all connected peers.
func (s *server) relayTransactions(txns []*dcrutil.Tx) {
	for _, tx := range txns {
		iv := wire.NewInvVect(wire.InvTypeTx, tx.Hash())
		s.RelayInventory(iv, tx, false)
	}
}

// relayMixMessages generates and relays inventory vectors for all of the
// passed mixing messages to all connected peers.
func (s *server) relayMixMessages(msgs []mixing.Message) {
	for _, m := range msgs {
		hash := m.Hash()
		iv := wire.NewInvVect(wire.InvTypeMix, &hash)
		s.RelayInventory(iv, m, false)
	}
}

// AnnounceNewTransactions generates and relays inventory vectors and notifies
// websocket clients of the passed transactions.  This function should be
// called whenever new transactions are added to the mempool.
func (s *server) AnnounceNewTransactions(txns []*dcrutil.Tx) {
	// Generate and relay inventory vectors for all newly accepted
	// transactions.
	s.relayTransactions(txns)

	// Notify websocket clients of all newly accepted transactions.
	if s.rpcServer != nil {
		s.rpcServer.NotifyNewTransactions(txns)
	}
}

// AnnounceMixMessages generates and relays inventory vectors of the passed
// mixing messages.  This function should be called whenever new messages are
// accepted to the mixpool.
func (s *server) AnnounceMixMessages(msgs []mixing.Message) {
	// Generate and relay inventory vectors for all newly accepted mixing
	// messages.
	s.relayMixMessages(msgs)

	if s.rpcServer != nil {
		s.rpcServer.NotifyMixMessages(msgs)
	}
}

// TransactionConfirmed marks the provided single confirmation transaction as
// no longer needing rebroadcasting and keeps track of it for use when avoiding
// requests for recently confirmed transactions.
func (s *server) TransactionConfirmed(tx *dcrutil.Tx) {
	txHash := tx.Hash()
	s.recentlyConfirmedTxns.Add(txHash[:])

	// Rebroadcasting is only necessary when the RPC server is active.
	if s.rpcServer != nil {
		iv := wire.NewInvVect(wire.InvTypeTx, txHash)
		s.RemoveRebroadcastInventory(iv)
	}
}

// maybeLogRecentlyAdvertisedNumEvicted periodically logs the total number of
// evicted advertised transactions.
//
// It is NOT safe for concurrent access.
func (s *server) maybeLogRecentlyAdvertisedNumEvicted() {
	// Do not log anything when there haven't been any evicted transactions.
	totalEvicted := s.totalAdvertisedTxnsEvicted
	if totalEvicted == 0 {
		return
	}

	// Only log a maximum of once per day.
	const logInterval = 24 * time.Hour
	sinceLastLogged := time.Since(s.lastAdvertisedTxnsEvictedLogged)
	if sinceLastLogged < logInterval {
		return
	}

	srvrLog.Debugf("Evicted %d advertised %s in the last %v (%d remaining, "+
		"%.2f%% hit ratio)", totalEvicted, pickNoun(totalEvicted, "tx", "txns"),
		sinceLastLogged.Truncate(time.Second), s.recentlyAdvertisedTxns.Len(),
		s.recentlyAdvertisedTxns.HitRatio())

	s.totalAdvertisedTxnsEvicted = 0
	s.lastAdvertisedTxnsEvictedLogged = time.Now()
}

// handleRelayPeerInvMsg handles the relay of a message to a specific
// serverPeer.
func (s *server) handleRelayPeerInvMsg(msg relayMsg, sp *serverPeer) {
	if !sp.Connected() {
		return
	}

	// Ignore peers that do not have the required service flags.
	if !hasServices(sp.Services(), msg.reqServices) {
		return
	}

	// Filter duplicate block announcements.
	iv := msg.invVect
	isBlockAnnouncement := iv.Type == wire.InvTypeBlock
	if isBlockAnnouncement {
		if sp.announcedBlock != nil && *sp.announcedBlock == iv.Hash {
			sp.announcedBlock = nil
			return
		}
		sp.announcedBlock = &iv.Hash
	}

	// Generate and send a headers message instead of an inventory message
	// for block announcements when the peer prefers headers.
	if isBlockAnnouncement && sp.WantsHeaders() {
		blockHeader, ok := msg.data.(wire.BlockHeader)
		if !ok {
			peerLog.Warn("Underlying data for headers is not a block header")
			return
		}
		msgHeaders := wire.NewMsgHeaders()
		if err := msgHeaders.AddBlockHeader(&blockHeader); err != nil {
			peerLog.Errorf("Failed to add block header: %v", err)
			return
		}
		sp.QueueMessage(msgHeaders, nil)
		return
	}

	if iv.Type == wire.InvTypeTx {
		// Don't relay the transaction to the peer when it has transaction
		// relaying disabled.
		if sp.disableRelayTx.Load() {
			return
		}

		// Track advertised transactions for a period of time in order to
		// increase the probability they are available to serve regardless
		// of whether or not they are still in the mempool when a request
		// for the advertisement arrives.  Note that it is still possible
		// for the advertised transaction to not be available in the case it
		// is later removed from the advertised transactions pool due to
		// expiration and/or exceeding the maximum limits prior to the
		// request for it arriving.  However, not only is that case
		// extremely rare in practice, the transaction is also likely still
		// in the mempool in that case and will be served from there given
		// peers generally do not request transactions that have been
		// recently confirmed.
		tx, ok := msg.data.(*dcrutil.Tx)
		if !ok {
			peerLog.Warn("Underlying data for inventory vector is not a " +
				"transaction")
			return
		}
		numEvicted := s.recentlyAdvertisedTxns.Put(iv.Hash, tx)
		s.totalAdvertisedTxnsEvicted += uint64(numEvicted)
		s.maybeLogRecentlyAdvertisedNumEvicted()
	}

	if iv.Type == wire.InvTypeMix {
		// Don't relay the mixing message to the peer when it has transaction
		// relaying disabled.
		if sp.disableRelayTx.Load() {
			return
		}

		// Don't relay mix message inventory when unsupported
		// by the negotiated protocol version.
		if sp.ProtocolVersion() < wire.MixVersion {
			return
		}
	}

	// Either queue the inventory to be relayed immediately or with
	// the next batch depending on the immediate flag.
	//
	// It will be ignored in either case if the peer is already
	// known to have the inventory.
	if msg.immediate {
		sp.QueueInventoryImmediate(iv)
	} else {
		sp.QueueInventory(iv)
	}
}

// handleRelayInvMsg deals with relaying inventory to peers that are not already
// known to have it.  It is invoked from the peerHandler goroutine.
func (s *server) handleRelayInvMsg(state *peerState, msg relayMsg) {
	state.ForAllPeers(func(sp *serverPeer) {
		s.handleRelayPeerInvMsg(msg, sp)
	})
}

// handleBroadcastMsg deals with broadcasting messages to peers.  It is invoked
// from the peerHandler goroutine.
func (s *server) handleBroadcastMsg(state *peerState, bmsg *broadcastMsg) {
	state.ForAllPeers(func(sp *serverPeer) {
		if !sp.Connected() {
			return
		}

		for _, ep := range bmsg.excludePeers {
			if sp == ep {
				return
			}
		}

		sp.QueueMessage(bmsg.message, nil)
	})
}

// disconnectPeer attempts to drop the connection of a targeted peer in the
// passed peer list. Targets are identified via usage of the passed
// `compareFunc`, which should return `true` if the passed peer is the target
// peer. This function returns true on success and false if the peer is unable
// to be located. If the peer is found, and the passed callback: `whenFound'
// isn't nil, we call it with the peer as the argument before it is removed
// from the peerList, and is disconnected from the server.
func disconnectPeer(peerList map[int32]*serverPeer, compareFunc func(*serverPeer) bool, whenFound func(*serverPeer)) bool {
	for addr, peer := range peerList {
		if compareFunc(peer) {
			if whenFound != nil {
				whenFound(peer)
			}

			// This is ok because we are not continuing
			// to iterate so won't corrupt the loop.
			delete(peerList, addr)
			peer.Disconnect()
			return true
		}
	}
	return false
}

// newPeerConfig returns the configuration for the given serverPeer.
func newPeerConfig(sp *serverPeer) *peer.Config {
	var userAgentComments []string
	if version.PreRelease != "" {
		userAgentComments = append(userAgentComments, version.PreRelease)
	}

	return &peer.Config{
		Listeners: peer.MessageListeners{
			OnVersion:         sp.OnVersion,
			OnVerAck:          sp.OnVerAck,
			OnMemPool:         sp.OnMemPool,
			OnGetMiningState:  sp.OnGetMiningState,
			OnMiningState:     sp.OnMiningState,
			OnGetInitState:    sp.OnGetInitState,
			OnInitState:       sp.OnInitState,
			OnTx:              sp.OnTx,
			OnBlock:           sp.OnBlock,
			OnMixPairReq:      sp.OnMixPairReq,
			OnMixKeyExchange:  sp.OnMixKeyExchange,
			OnMixCiphertexts:  sp.OnMixCiphertexts,
			OnMixSlotReserve:  sp.OnMixSlotReserve,
			OnMixDCNet:        sp.OnMixDCNet,
			OnMixConfirm:      sp.OnMixConfirm,
			OnMixFactoredPoly: sp.OnMixFactoredPoly,
			OnMixSecrets:      sp.OnMixSecrets,
			OnInv:             sp.OnInv,
			OnHeaders:         sp.OnHeaders,
			OnGetData:         sp.OnGetData,
			OnGetBlocks:       sp.OnGetBlocks,
			OnGetHeaders:      sp.OnGetHeaders,
			OnGetCFilter:      sp.OnGetCFilter,
			OnGetCFilterV2:    sp.OnGetCFilterV2,
			OnGetCFiltersV2:   sp.OnGetCFiltersV2,
			OnGetCFHeaders:    sp.OnGetCFHeaders,
			OnGetCFTypes:      sp.OnGetCFTypes,
			OnGetAddr:         sp.OnGetAddr,
			OnAddr:            sp.OnAddr,
			OnRead:            sp.OnRead,
			OnWrite:           sp.OnWrite,
			OnNotFound:        sp.OnNotFound,
		},
		NewestBlock: sp.newestBlock,
		HostToNetAddress: func(host string, port uint16, services wire.ServiceFlag) (*wire.NetAddress, error) {
			address, err := hostToNetAddress(host, port, services, dcrdLookup)
			if err != nil {
				return nil, err
			}
			return addrmgrToWireNetAddress(address), nil
		},
		Proxy:             cfg.Proxy,
		UserAgentName:     userAgentName,
		UserAgentVersion:  userAgentVersion,
		UserAgentComments: userAgentComments,
		Net:               sp.server.chainParams.Net,
		Services:          sp.server.services,
		DisableRelayTx:    cfg.BlocksOnly,
		ProtocolVersion:   maxProtocolVersion,
		IdleTimeout:       cfg.PeerIdleTimeout,
	}
}

// inboundPeerConnected is invoked by the connection manager when a new inbound
// connection is established.  It initializes a new inbound server peer
// instance, associates it with the connection, and starts all additional server
// peer processing goroutines.
func (s *server) inboundPeerConnected(conn net.Conn) {
	sp := newServerPeer(s, false)
	sp.isWhitelisted = isWhitelisted(conn.RemoteAddr())
	sp.Peer = peer.NewInboundPeer(newPeerConfig(sp))
	sp.syncMgrPeer = netsync.NewPeer(sp.Peer)
	sp.AssociateConnection(conn)
	go sp.Run()
}

// outboundPeerConnected is invoked by the connection manager when a new
// outbound connection is established.  It initializes a new outbound server
// peer instance, associates it with the relevant state such as the connection
// request instance and the connection itself, and start all additional server
// peer processing goroutines.
func (s *server) outboundPeerConnected(c *connmgr.ConnReq, conn net.Conn) {
	sp := newServerPeer(s, c.Permanent)
	p, err := peer.NewOutboundPeer(newPeerConfig(sp), c.Addr.String())
	if err != nil {
		srvrLog.Debugf("Cannot create outbound peer %s: %v", c.Addr, err)
		s.connManager.Disconnect(c.ID())
		return
	}
	sp.Peer = p
	sp.syncMgrPeer = netsync.NewPeer(sp.Peer)
	sp.connReq.Store(c)
	sp.isWhitelisted = isWhitelisted(conn.RemoteAddr())
	sp.AssociateConnection(conn)
	go sp.Run()
}

// peerHandler is used to handle peer operations such as inventory relay and
// broadcasting messages to peers.
//
// It must be run in a goroutine.
func (s *server) peerHandler(ctx context.Context) {
	// Start the address manager which is needed by peers.  This is done here
	// since its lifecycle is closely tied to this handler and rather than
	// adding more channels to synchronize things, it's easier and slightly
	// faster to simply start and stop it in this handler.
	s.addrManager.Start()

	srvrLog.Tracef("Starting peer handler")

out:
	for {
		select {
		// New inventory to potentially be relayed to other peers.
		case invMsg := <-s.relayInv:
			s.handleRelayInvMsg(&s.peerState, invMsg)

		// Message to broadcast to all connected peers except those
		// which are excluded by the message.
		case bmsg := <-s.broadcast:
			s.handleBroadcastMsg(&s.peerState, &bmsg)

		case <-ctx.Done():
			close(s.quit)

			// Disconnect all peers on server shutdown.
			s.peerState.ForAllPeers(func(sp *serverPeer) {
				srvrLog.Tracef("Shutdown peer %s", sp)
				sp.Disconnect()
			})
			break out
		}
	}

	s.addrManager.Stop()
	srvrLog.Tracef("Peer handler done")
}

// handleAddPeer deals with adding new peers and includes logic such as
// categorizing the type of peer, limiting the maximum allowed number of peers,
// and local external address resolution.
//
// It returns whether or not the peer was accepted by the server.
//
// This function is safe for concurrent access.
func (s *server) handleAddPeer(sp *serverPeer) bool {
	// Ignore new peers when shutting down.
	if s.shutdown.Load() {
		srvrLog.Infof("New peer %s ignored - server is shutting down", sp)
		sp.Disconnect()
		return false
	}

	state := &s.peerState
	defer state.Unlock()
	state.Lock()

	// Disconnect banned peers.
	host, _, err := net.SplitHostPort(sp.Addr())
	if err != nil {
		srvrLog.Debugf("can't split hostport %v", err)
		sp.Disconnect()
		return false
	}
	if banEnd, ok := state.banned[host]; ok {
		if time.Now().Before(banEnd) {
			srvrLog.Debugf("Peer %s is banned for another %v - disconnecting",
				host, time.Until(banEnd))
			sp.Disconnect()
			return false
		}

		srvrLog.Infof("Peer %s is no longer banned", host)
		delete(state.banned, host)
	}

	// Limit max number of connections from a single IP.  However, allow
	// whitelisted inbound peers and localhost connections regardless.
	isInboundWhitelisted := sp.isWhitelisted && sp.Inbound()
	peerIP := sp.NA().IP
	if cfg.MaxSameIP > 0 && !isInboundWhitelisted && !peerIP.IsLoopback() &&
		state.connectionsWithIP(peerIP)+1 > cfg.MaxSameIP {

		srvrLog.Infof("Max connections with %s reached [%d] - disconnecting "+
			"peer", sp, cfg.MaxSameIP)
		sp.Disconnect()
		return false
	}

	// Limit max number of total peers.  However, allow whitelisted inbound
	// peers regardless.
	if state.count()+1 > cfg.MaxPeers && !isInboundWhitelisted {
		srvrLog.Infof("Max peers reached [%d] - disconnecting peer %s",
			cfg.MaxPeers, sp)
		sp.Disconnect()
		// TODO: how to handle permanent peers here?
		// they should be rescheduled.
		return false
	}

	na := sp.peerNa.Load()

	// Add the new peer.
	srvrLog.Debugf("New peer %s", sp)
	if sp.Inbound() {
		state.inboundPeers[sp.ID()] = sp

		if na != nil {
			id := na.IP.String()

			// Inbound peers can only corroborate existing address submissions.
			if state.subCache.exists(id) {
				err := state.subCache.incrementScore(id)
				if err != nil {
					srvrLog.Errorf("unable to increment submission score: %v", err)
					return true
				}
			}
		}

		return true
	}

	// The peer is an outbound peer at this point.
	remoteAddr := wireToAddrmgrNetAddress(sp.NA())
	state.outboundGroups[remoteAddr.GroupKey()]++
	if sp.persistent {
		state.persistentPeers[sp.ID()] = sp
	} else {
		state.outboundPeers[sp.ID()] = sp
	}

	// Fetch the suggested public IP from the outbound peer if there are no
	// prevailing conditions to disable automatic network address discovery.
	//
	// The conditions to disable automatic network address discovery are:
	//  - There is a proxy set (--proxy, --onion)
	//  - Automatic network address discovery is explicitly disabled
	//    (--nodiscoverip)
	//  - There is an external IP explicitly set (--externalip)
	//  - Listening has been disabled (--nolisten, listen disabled because of
	//    --connect, etc)
	//  - Universal Plug and Play is enabled (--upnp)
	//  - The active network is simnet or regnet
	if (cfg.Proxy != "" || cfg.OnionProxy != "") ||
		cfg.NoDiscoverIP ||
		len(cfg.ExternalIPs) > 0 ||
		(cfg.DisableListen || len(cfg.Listeners) == 0) || cfg.Upnp ||
		s.chainParams.Name == simNetParams.Name ||
		s.chainParams.Name == regNetParams.Name {

		return true
	}

	if na != nil {
		net := addrmgr.IPv4Address
		if na.IP.To4() == nil {
			net = addrmgr.IPv6Address
		}

		localAddr := wireToAddrmgrNetAddress(na)
		good, reach := s.addrManager.IsExternalAddrCandidate(localAddr,
			remoteAddr)
		if !good {
			return true
		}

		id := na.IP.String()
		if state.subCache.exists(id) {
			// Increment the submission score if it already exists.
			err := state.subCache.incrementScore(id)
			if err != nil {
				srvrLog.Errorf("unable to increment submission score: %v", err)
				return true
			}
		} else {
			// Create a cache entry for a new submission.
			sub := &naSubmission{
				na:      na,
				netType: net,
				reach:   reach,
			}

			err := state.subCache.add(sub)
			if err != nil {
				srvrLog.Errorf("unable to add submission: %v", err)
				return true
			}
		}

		// Pick the local address for the provided network based on
		// submission scores.
		state.ResolveLocalAddress(net, s.addrManager, s.services)
	}

	return true
}

// AddPeer adds a new peer that has already been connected to the server.
//
// This function is safe for concurrent access.
func (s *server) AddPeer(sp *serverPeer) {
	s.handleAddPeer(sp)

	// Signal the net sync manager this peer is a new sync candidate unless it
	// was disconnected above.
	if sp.Connected() {
		srvrLog.Infof("New valid peer %s (%s)", sp, sp.UserAgent())
		s.syncManager.OnPeerConnected(sp.syncMgrPeer)
	}
}

// DonePeer removes a disconnected peer from the server.  It includes logic such
// as updating the peer tracking state and the last time the peer was seen.
//
// This function is safe for concurrent access.
func (s *server) DonePeer(sp *serverPeer) {
	state := &s.peerState
	defer state.Unlock()
	state.Lock()

	var list map[int32]*serverPeer
	if sp.persistent {
		list = state.persistentPeers
	} else if sp.Inbound() {
		list = state.inboundPeers
	} else {
		list = state.outboundPeers
	}
	if _, ok := list[sp.ID()]; ok {
		if !sp.Inbound() && sp.VersionKnown() {
			remoteAddr := wireToAddrmgrNetAddress(sp.NA())
			state.outboundGroups[remoteAddr.GroupKey()]--
		}
		if !sp.Inbound() {
			connReq := sp.connReq.Load()
			if connReq != nil {
				s.connManager.Disconnect(connReq.ID())
			}
		}
		delete(list, sp.ID())
		srvrLog.Debugf("Removed peer %s", sp)
		return
	}

	connReq := sp.connReq.Load()
	if connReq != nil {
		s.connManager.Disconnect(connReq.ID())
	}

	// Update the address manager with the last seen time when the peer has
	// acknowledged our version and has sent us its version as well.  This is
	// skipped when running on the simulation and regression test networks since
	// they are only intended to connect to specified peers and actively avoid
	// advertising and connecting to discovered peers.
	if !cfg.SimNet && !cfg.RegNet && sp.VerAckReceived() && sp.VersionKnown() &&
		sp.NA() != nil {

		remoteAddr := wireToAddrmgrNetAddress(sp.NA())
		err := s.addrManager.Connected(remoteAddr)
		if err != nil {
			srvrLog.Errorf("Marking address as connected failed: %v", err)
		}
	}
}

// BanPeer bans and disconnects a peer that has already been connected to the
// server by ip unless banning is disabled or the peer has been whitelisted.
func (s *server) BanPeer(sp *serverPeer, reason string) {
	// No warning is logged when banning is disabled.
	if cfg.DisableBanning {
		return
	}
	if sp.isWhitelisted {
		srvrLog.Debugf("Misbehaving whitelisted peer %s: %s", sp, reason)
		return
	}

	host, _, err := net.SplitHostPort(sp.Addr())
	if err != nil {
		srvrLog.Debugf("can't split ban peer %s: %v", sp, err)
		srvrLog.Warnf("Misbehaving peer %s: %s -- disconnecting", sp, reason)
		sp.Disconnect()
		return
	}

	direction := directionString(sp.Inbound())
	srvrLog.Warnf("Misbehaving peer %s (%s): %s -- banned for %v", host,
		direction, reason, cfg.BanDuration)
	bannedUntil := time.Now().Add(cfg.BanDuration)
	s.peerState.Lock()
	s.peerState.banned[host] = bannedUntil
	s.peerState.Unlock()
	sp.Disconnect()
}

// RelayInventory relays the passed inventory vector to all connected peers
// that are not already known to have it.
func (s *server) RelayInventory(invVect *wire.InvVect, data interface{}, immediate bool) {
	select {
	case <-s.quit:
	case s.relayInv <- relayMsg{invVect: invVect, data: data, immediate: immediate}:
	}
}

// RelayBlockAnnouncement creates a block announcement for the passed block and
// relays that announcement immediately to all connected peers that advertise
// the given required services and are not already known to have it.
func (s *server) RelayBlockAnnouncement(block *dcrutil.Block, reqServices wire.ServiceFlag) {
	invVect := wire.NewInvVect(wire.InvTypeBlock, block.Hash())
	select {
	case <-s.quit:
	case s.relayInv <- relayMsg{
		invVect:     invVect,
		data:        block.MsgBlock().Header,
		immediate:   true,
		reqServices: reqServices,
	}:
	}
}

// BroadcastMessage sends msg to all peers currently connected to the server
// except those in the passed peers to exclude.
func (s *server) BroadcastMessage(msg wire.Message, exclPeers ...*serverPeer) {
	select {
	case <-s.quit:
	case s.broadcast <- broadcastMsg{message: msg, excludePeers: exclPeers}:
	}
}

// ConnectedCount returns the number of currently connected peers.
func (s *server) ConnectedCount() int32 {
	var numConnected int32
	s.peerState.ForAllPeers(func(sp *serverPeer) {
		if sp.Connected() {
			numConnected++
		}
	})
	return numConnected
}

// OutboundGroupCount returns the number of peers connected to the given
// outbound group key.
func (s *server) OutboundGroupCount(key string) int {
	s.peerState.Lock()
	count := s.peerState.outboundGroups[key]
	s.peerState.Unlock()
	return count
}

// AddBytesSent adds the passed number of bytes to the total bytes sent counter
// for the server.  It is safe for concurrent access.
func (s *server) AddBytesSent(bytesSent uint64) {
	s.bytesSent.Add(bytesSent)
}

// AddBytesReceived adds the passed number of bytes to the total bytes received
// counter for the server.  It is safe for concurrent access.
func (s *server) AddBytesReceived(bytesReceived uint64) {
	s.bytesReceived.Add(bytesReceived)
}

// NetTotals returns the sum of all bytes received and sent across the network
// for all peers.  It is safe for concurrent access.
func (s *server) NetTotals() (uint64, uint64) {
	return s.bytesReceived.Load(), s.bytesSent.Load()
}

// notifiedWinningTickets returns whether or not the winning tickets
// notification for the specified block hash has already been sent.
func (s *server) notifiedWinningTickets(hash *chainhash.Hash) bool {
	s.lotteryDataBroadcastMtx.Lock()
	_, beenNotified := s.lotteryDataBroadcast[*hash]
	s.lotteryDataBroadcastMtx.Unlock()
	return beenNotified
}

// headerApprovesParent returns whether or not the vote bits in the passed
// header indicate the regular transaction tree of the parent block should be
// considered valid.
func headerApprovesParent(header *wire.BlockHeader) bool {
	return dcrutil.IsFlagSet16(header.VoteBits, dcrutil.BlockValid)
}

// proactivelyEvictSigCacheEntries fetches the block that is
// txscript.ProactiveEvictionDepth levels deep from bestHeight and passes it to
// SigCache to evict the entries associated with the transactions in that block.
func (s *server) proactivelyEvictSigCacheEntries(bestHeight int64) {
	// Nothing to do before the eviction depth is reached.
	if bestHeight <= txscript.ProactiveEvictionDepth {
		return
	}

	evictHeight := bestHeight - txscript.ProactiveEvictionDepth
	block, err := s.chain.BlockByHeight(evictHeight)
	if err != nil {
		srvrLog.Warnf("Failed to retrieve the block at height %d: %v",
			evictHeight, err)
		return
	}

	s.sigCache.EvictEntries(block.MsgBlock())
}

// handleBlockchainNotification handles notifications from blockchain.  It does
// things such as request orphan block parents and relay accepted blocks to
// connected peers.
func (s *server) handleBlockchainNotification(notification *blockchain.Notification) {
	switch notification.Type {
	// A block that intends to extend the main chain has passed all sanity and
	// contextual checks and the chain is believed to be current.  Relay it to
	// other peers.
	case blockchain.NTNewTipBlockChecked:
		// WARNING: The chain lock is not released before sending this
		// notification, so care must be taken to avoid calling chain functions
		// which could result in a deadlock.
		block, ok := notification.Data.(*dcrutil.Block)
		if !ok {
			syncLog.Warnf("New tip block checked notification is not a block.")
			break
		}

		// Relay the block announcement immediately to full nodes.
		s.RelayBlockAnnouncement(block, wire.SFNodeNetwork)

	// A block has been accepted into the block chain.  Relay it to other peers
	// (will be ignored if already relayed via NTNewTipBlockChecked) and
	// possibly notify RPC clients with the winning tickets.
	case blockchain.NTBlockAccepted:
		// Don't relay or notify RPC clients with winning tickets if we are not
		// current and unsynced mining is not allowed.  Other peers that are
		// current should already know about it and clients, such as wallets,
		// shouldn't be voting on old blocks.
		if !cfg.AllowUnsyncedMining && !s.syncManager.IsCurrent() {
			return
		}

		band, ok := notification.Data.(*blockchain.BlockAcceptedNtfnsData)
		if !ok {
			syncLog.Warnf("Chain accepted notification is not " +
				"BlockAcceptedNtfnsData.")
			break
		}
		block := band.Block

		// Send a winning tickets notification as needed.  The notification will
		// only be sent when the following conditions hold:
		//
		// - The RPC server is running
		// - The block that would build on this one is at or after the height
		//   voting begins
		// - The block that would build on this one would not cause a reorg
		//   larger than the max reorg notify depth
		// - A notification for this block has not already been sent
		//
		// To help visualize the math here, consider the following two competing
		// branches:
		//
		// 100 -> 101  -> 102  -> 103 -> 104 -> 105 -> 106
		//    \-> 101' -> 102'
		//
		// Further, assume that this is a notification for block 103', or in
		// other words, it is extending the shorter side chain.  The reorg depth
		// would be 106 - (103 - 3) = 6.  This should intuitively make sense,
		// because if the side chain were to be extended enough to become the
		// best chain, it would result in a reorg that would remove 6 blocks,
		// namely blocks 101, 102, 103, 104, 105, and 106.
		//
		// Additionally, a notification will NOT be sent for mainnet once block
		// height 777240 has been reached and the block version is prior to 10.
		// The intent is for future code to perform this type of check more
		// dynamically so it happens for all upgrades after a certain time frame
		// is provided for upgrades to occur, but it is hard coded for now in
		// the interest of time to allow PoS to force PoW to upgrade.
		blockHash := block.Hash()
		bestHeight := band.BestHeight
		blockHeader := &block.MsgBlock().Header
		blockHeight := int64(blockHeader.Height)
		reorgDepth := bestHeight - (blockHeight - band.ForkLen)
		isOldMainnetBlock := s.chainParams.Net == wire.MainNet &&
			blockHeight >= 777240 && blockHeader.Version < 10
		if s.rpcServer != nil &&
			blockHeight >= s.chainParams.StakeValidationHeight-1 &&
			reorgDepth < maxReorgDepthNotify &&
			!isOldMainnetBlock &&
			!s.notifiedWinningTickets(blockHash) {

			// Obtain the winning tickets for this block.  handleNotifyMsg
			// should be safe for concurrent access of things contained within
			// blockchain.
			wt, _, _, err := s.chain.LotteryDataForBlock(blockHash)
			if err != nil {
				syncLog.Errorf("Couldn't calculate winning tickets for "+
					"accepted block %v: %v", blockHash, err)
			} else {
				// Notify registered websocket clients of newly eligible tickets
				// to vote on.
				s.rpcServer.NotifyWinningTickets(&rpcserver.WinningTicketsNtfnData{
					BlockHash:   *blockHash,
					BlockHeight: blockHeight,
					Tickets:     wt,
				})

				s.lotteryDataBroadcastMtx.Lock()
				s.lotteryDataBroadcast[*blockHash] = struct{}{}
				s.lotteryDataBroadcastMtx.Unlock()
			}
		}

		// Relay the block announcement immediately to all peers that were not
		// already notified via NTNewTipBlockChecked.
		const noRequiredServices = 0
		s.RelayBlockAnnouncement(block, noRequiredServices)

		// Inform the background block template generator about the accepted
		// block.
		if s.bg != nil {
			s.bg.BlockAccepted(block)
		}

		if !s.feeEstimator.IsEnabled() {
			// fee estimation can only start after we have performed an initial
			// sync, otherwise we'll start adding mempool transactions at the
			// wrong height.
			s.feeEstimator.Enable(block.Height())
		}

	// A block has been connected to the main block chain.
	case blockchain.NTBlockConnected:
		ntfn, ok := notification.Data.(*blockchain.BlockConnectedNtfnsData)
		if !ok {
			syncLog.Warnf("Block connected notification is not " +
				"BlockConnectedNtfnsData")
			break
		}
		block := ntfn.Block
		parentBlock := ntfn.ParentBlock

		// Determine active agendas based on flags.
		isTreasuryEnabled := ntfn.CheckTxFlags.IsTreasuryEnabled()

		// Account for transactions mined in the newly connected block for fee
		// estimation. This must be done before attempting to remove
		// transactions from the mempool because the mempool will alert the
		// estimator of the txs that are leaving
		s.feeEstimator.ProcessBlock(block)

		// TODO: In the case the new tip disapproves the previous block, any
		// transactions the previous block contains in its regular tree which
		// double spend the same inputs as transactions in either tree of the
		// current tip should ideally be tracked in the pool as eligible for
		// inclusion in an alternative tip (side chain block) in case the
		// current tip block does not get enough votes.  However, the
		// transaction pool currently does not provide any way to distinguish
		// this condition and thus only provides tracking based on the current
		// tip.  In order to handle this condition, the pool would have to
		// provide a way to track and independently query which txns are
		// eligible based on the current tip both approving and disapproving the
		// previous block as well as the previous block itself.

		// Remove all of the regular and stake transactions in the connected
		// block from the transaction pool.  Also, remove any transactions which
		// are now double spends as a result of these new transactions.
		// Finally, remove any transaction that is no longer an orphan.
		// Transactions which depend on a confirmed transaction are NOT removed
		// recursively because they are still valid.  Also, the coinbase of the
		// regular tx tree is skipped because the transaction pool doesn't (and
		// can't) have regular tree coinbase transactions in it.
		//
		// Also, in the case the RPC server is enabled, stop rebroadcasting any
		// transactions in the block that were setup to be rebroadcast.
		txMemPool := s.txMemPool
		handleConnectedBlockTxns := func(txns []*dcrutil.Tx) {
			for _, tx := range txns {
				txMemPool.RemoveTransaction(tx, false)
				txMemPool.MaybeAcceptDependents(tx, isTreasuryEnabled)
				txMemPool.RemoveDoubleSpends(tx)
				txMemPool.RemoveOrphan(tx)
				acceptedTxs := txMemPool.ProcessOrphans(tx, ntfn.CheckTxFlags)
				s.AnnounceNewTransactions(acceptedTxs)

				// Now that this block is in the blockchain, mark the
				// transaction (except the coinbase) as no longer needing
				// rebroadcasting and keep track of it for use when avoiding
				// requests for recently confirmed transactions.
				s.TransactionConfirmed(tx)
			}
		}

		// Add regular transactions back to the mempool, excluding the coinbase
		// since it does not belong in the mempool.
		handleConnectedBlockTxns(block.Transactions()[1:])
		if isTreasuryEnabled {
			// Skip treasurybase
			handleConnectedBlockTxns(block.STransactions()[1:])
		} else {
			handleConnectedBlockTxns(block.STransactions())
		}

		// In the case the regular tree of the previous block was disapproved,
		// add all of the its transactions, with the exception of the coinbase,
		// back to the transaction pool to be mined in a future block.
		//
		// Notice that some of those transactions might have been included in
		// the current block and others might also be spending some of the same
		// outputs that transactions in the previous originally block spent.
		// This is the expected behavior because disapproval of the regular tree
		// of the previous block essentially makes it as if those transactions
		// never happened.
		//
		// Finally, if transactions fail to add to the pool for some reason
		// other than the pool already having it (a duplicate) or now being a
		// double spend, remove all transactions that depend on it as well.
		// The dependents are not removed for double spends because the only
		// way a transaction which was not a double spend in the previous block
		// to now be one is due to some transaction in the current block
		// (probably the same one) also spending those outputs, and, in that
		// case, anything that happens to be in the pool which depends on the
		// transaction is still valid.
		if !headerApprovesParent(&block.MsgBlock().Header) {
			txns := parentBlock.Transactions()[1:]
			txMemPool.MaybeAcceptTransactions(txns)
		}
		if r := s.rpcServer; r != nil {
			// Filter and update the rebroadcast inventory.
			s.PruneRebroadcastInventory()

			// Notify registered websocket clients of incoming block.
			r.NotifyBlockConnected(block)
		}

		if s.bg != nil {
			s.bg.BlockConnected(block)
		}

		if s.cpuMiner != nil {
			s.cpuMiner.BlockConnected(block)
		}

		// Notify subscribed indexes of connected block.
		if s.indexSubscriber != nil {
			s.indexSubscriber.Notify(&indexers.IndexNtfn{
				NtfnType:          indexers.ConnectNtfn,
				Block:             block,
				Parent:            parentBlock,
				IsTreasuryEnabled: isTreasuryEnabled,
			})
		}

		// Proactively evict signature cache entries that are virtually
		// guaranteed to no longer be useful.
		s.proactivelyEvictSigCacheEntries(block.Height())

	// Stake tickets are matured from the most recently connected block.
	case blockchain.NTNewTickets:
		// WARNING: The chain lock is not released before sending this
		// notification, so care must be taken to avoid calling chain functions
		// which could result in a deadlock.
		tnd, ok := notification.Data.(*blockchain.TicketNotificationsData)
		if !ok {
			syncLog.Warnf("Tickets connected notification is not " +
				"TicketNotificationsData")
			break
		}

		if r := s.rpcServer; r != nil {
			r.NotifyNewTickets(tnd)
		}

	// A block has been disconnected from the main block chain.
	case blockchain.NTBlockDisconnected:
		// NOTE: The chain lock is released for this notification.
		ntfn, ok := notification.Data.(*blockchain.BlockDisconnectedNtfnsData)
		if !ok {
			syncLog.Warnf("Block disconnected notification is not " +
				"BlockDisconnectedNtfnsData.")
			break
		}
		block := ntfn.Block
		parentBlock := ntfn.ParentBlock

		// Determine active agendas based on flags.
		isTreasuryEnabled := ntfn.CheckTxFlags.IsTreasuryEnabled()

		// In the case the regular tree of the previous block was disapproved,
		// disconnecting the current block makes all of those transactions valid
		// again.  Thus, with the exception of the coinbase, remove all of those
		// transactions and any that are now double spends from the transaction
		// pool.  Transactions which depend on a confirmed transaction are NOT
		// removed recursively because they are still valid.
		txMemPool := s.txMemPool
		if !headerApprovesParent(&block.MsgBlock().Header) {
			for _, tx := range parentBlock.Transactions()[1:] {
				txMemPool.RemoveTransaction(tx, false)
				txMemPool.MaybeAcceptDependents(tx, isTreasuryEnabled)
				txMemPool.RemoveDoubleSpends(tx)
				txMemPool.RemoveOrphan(tx)
				txMemPool.ProcessOrphans(tx, ntfn.CheckTxFlags)
			}
		}

		// Add all of the regular and stake transactions in the disconnected
		// block, with the exception of the regular tree coinbase, back to the
		// transaction pool to be mined in a future block.
		//
		// Notice that, in the case the previous block was disapproved, some of
		// the transactions in the block being disconnected might have been
		// included in the previous block and others might also have been
		// spending some of the same outputs.  This is the expected behavior
		// because disapproval of the regular tree of the previous block
		// essentially makes it as if those transactions never happened, so
		// disconnecting the block that disapproved those transactions
		// effectively revives them.
		//
		// Finally, if transactions fail to add to the pool for some reason
		// other than the pool already having it (a duplicate) or now being a
		// double spend, remove all transactions that depend on it as well.
		// The dependents are not removed for double spends because the only
		// way a transaction which was not a double spend in the block being
		// disconnected to now be one is due to some transaction in the previous
		// block (probably the same one), which was disapproved, also spending
		// those outputs, and, in that case, anything that happens to be in the
		// pool which depends on the transaction is still valid.
		handleDisconnectedBlockTxns := func(txns []*dcrutil.Tx) {
			txMemPool.MaybeAcceptTransactions(txns)
		}
		handleDisconnectedBlockTxns(block.Transactions()[1:])

		if isTreasuryEnabled {
			// Skip treasurybase
			handleDisconnectedBlockTxns(block.STransactions()[1:])
		} else {
			handleDisconnectedBlockTxns(block.STransactions())
		}

		if s.bg != nil {
			s.bg.BlockDisconnected(block)
		}

		// Notify subscribed indexes of disconnected block.
		if s.indexSubscriber != nil {
			s.indexSubscriber.Notify(&indexers.IndexNtfn{
				NtfnType:          indexers.DisconnectNtfn,
				Block:             block,
				Parent:            parentBlock,
				IsTreasuryEnabled: isTreasuryEnabled,
			})
		}

		// Notify registered websocket clients.
		if r := s.rpcServer; r != nil {
			// Filter and update the rebroadcast inventory.
			s.PruneRebroadcastInventory()

			// Notify registered websocket clients.
			r.NotifyBlockDisconnected(block)
		}

	// Chain reorganization has commenced.
	case blockchain.NTChainReorgStarted:
		// WARNING: The chain lock is not released before sending this
		// notification, so care must be taken to avoid calling chain functions
		// which could result in a deadlock.
		if s.bg != nil {
			s.bg.ChainReorgStarted()
		}

	// Chain reorganization has concluded.
	case blockchain.NTChainReorgDone:
		// WARNING: The chain lock is not released before sending this
		// notification, so care must be taken to avoid calling chain functions
		// which could result in a deadlock.
		if s.bg != nil {
			s.bg.ChainReorgDone()
		}

	// The blockchain is reorganizing.
	case blockchain.NTReorganization:
		// WARNING: The chain lock is not released before sending this
		// notification, so care must be taken to avoid calling chain functions
		// which could result in a deadlock.
		rd, ok := notification.Data.(*blockchain.ReorganizationNtfnsData)
		if !ok {
			syncLog.Warnf("Chain reorganization notification is malformed")
			break
		}

		// Notify registered websocket clients.
		if r := s.rpcServer; r != nil {
			r.NotifyReorganization(rd)
		}
	}
}

// rebroadcastHandler keeps track of user submitted inventories that we have
// sent out but have not yet made it into a block. We periodically rebroadcast
// them in case our peers restarted or otherwise lost track of them.
func (s *server) rebroadcastHandler(ctx context.Context) {
	// Wait 5 min before first tx rebroadcast.
	timer := time.NewTimer(5 * time.Minute)
	pendingInvs := make(map[wire.InvVect]interface{})

	for {
		select {
		case riv := <-s.modifyRebroadcastInv:
			switch msg := riv.(type) {

			// Incoming InvVects are added to our map of RPC txs.
			case broadcastInventoryAdd:
				pendingInvs[*msg.invVect] = msg.data

			// When an InvVect has been added to a block, we can
			// now remove it, if it was present.
			case broadcastInventoryDel:
				delete(pendingInvs, *msg)

			case broadcastPruneInventory:
				best := s.chain.BestSnapshot()
				for iv, data := range pendingInvs {
					tx, ok := data.(*dcrutil.Tx)
					if !ok {
						continue
					}

					txType := stake.DetermineTxType(tx.MsgTx())

					// Remove the ticket rebroadcast if the amount not equal to
					// the current stake difficulty.
					if txType == stake.TxTypeSStx &&
						tx.MsgTx().TxOut[0].Value != best.NextStakeDiff {
						delete(pendingInvs, iv)
						srvrLog.Debugf("Pending ticket purchase broadcast "+
							"inventory for tx %v removed. Ticket value not "+
							"equal to stake difficulty.", tx.Hash())
						continue
					}

					// Remove the ticket rebroadcast if it has already expired.
					if txType == stake.TxTypeSStx &&
						blockchain.IsExpired(tx, best.Height) {
						delete(pendingInvs, iv)
						srvrLog.Debugf("Pending ticket purchase broadcast "+
							"inventory for tx %v removed. Transaction "+
							"expired.", tx.Hash())
						continue
					}

					// Remove the revocation rebroadcast if the associated
					// ticket has been revived.
					if txType == stake.TxTypeSSRtx {
						refSStxHash := tx.MsgTx().TxIn[0].PreviousOutPoint.Hash
						if !s.chain.CheckLiveTicket(refSStxHash) {
							delete(pendingInvs, iv)
							srvrLog.Debugf("Pending revocation broadcast "+
								"inventory for tx %v removed. "+
								"Associated ticket was revived.", tx.Hash())
							continue
						}
					}
				}
			}

		case <-timer.C:
			// Any inventory we have has not made it into a block
			// yet. We periodically resubmit them until they have.
			for iv, data := range pendingInvs {
				ivCopy := iv
				s.RelayInventory(&ivCopy, data, false)
			}

			// Process at a random time up to 30mins in the future.
			timer.Reset(rand.Duration(30 * time.Minute))

		case <-ctx.Done():
			timer.Stop()
			return
		}
	}
}

// querySeeders queries the configured seeders to discover peers that supported
// the required services and adds the discovered peers to the address manager.
// Each seeder is contacted in a separate goroutine.
func (s *server) querySeeders(ctx context.Context) {
	// Add peers discovered through DNS to the address manager.
	seeders := s.chainParams.Seeders()
	errs := make(chan error, len(seeders))
	seed := func(seeder string) {
		ctx, cancel := context.WithTimeout(ctx, time.Minute)
		defer cancel()

		addrs, err := connmgr.SeedAddrs(ctx, seeder, dcrdDial,
			connmgr.SeedFilterServices(defaultRequiredServices))
		if err != nil {
			srvrLog.Infof("seeder '%s' error: %v", seeder, err)
			errs <- err
			return
		}

		// Nothing to do if the seeder didn't return any addresses.
		if len(addrs) == 0 {
			errs <- nil
			return
		}

		// Lookup the IP of the https seeder to use as the source of the
		// seeded addresses.  In the incredibly rare event that the lookup
		// fails after it just succeeded, fall back to using the first
		// returned address as the source.
		srcAddr := wireToAddrmgrNetAddress(addrs[0])
		srcIPs, err := dcrdLookup(seeder)
		if err == nil && len(srcIPs) > 0 {
			const httpsPort = 443
			srcAddr = addrmgr.NewNetAddressFromIPPort(srcIPs[0], httpsPort, 0)
		}
		addresses := wireToAddrmgrNetAddresses(addrs)
		s.addrManager.AddAddresses(addresses, srcAddr)
		errs <- nil
	}

	backoff := time.Second
	for {
		for _, seeder := range seeders {
			go seed(seeder)
		}
		var errCount int
		for range seeders {
			if err := <-errs; err != nil {
				errCount++
			}
		}
		if errCount < len(seeders) || !s.addrManager.NeedMoreAddresses() {
			return
		}

		select {
		case <-time.After(backoff):
		case <-ctx.Done():
			return
		}
		if backoff < 10*time.Second {
			backoff += time.Second
		}
	}
}

// Run starts the server and blocks until the provided context is cancelled.
// This entails accepting connections from peers.
func (s *server) Run(ctx context.Context) {
	srvrLog.Trace("Starting server")

	// Start the peer handler which in turn starts the address manager.
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		s.peerHandler(ctx)
		wg.Done()
	}()

	// Start the sync manager.
	wg.Add(1)
	go func() {
		s.syncManager.Run(ctx)
		wg.Done()
	}()

	// Query the seeders and start the connection manager.
	wg.Add(1)
	go func() {
		if !cfg.DisableSeeders {
			go s.querySeeders(ctx)
		}
		s.connManager.Run(ctx)
		wg.Done()
	}()

	if s.nat != nil {
		wg.Add(1)
		go func() {
			s.upnpUpdateThread(ctx)
			wg.Done()
		}()
	}

	if !cfg.DisableRPC {
		// Start the RPC server and rebroadcast handler which ensures
		// transactions submitted to the RPC server are rebroadcast until being
		// included in a block.
		wg.Add(2)
		go func() {
			s.rebroadcastHandler(ctx)
			wg.Done()
		}()
		go func() {
			s.rpcServer.Run(ctx)
			wg.Done()
		}()
	}

	// Start the background block template generator and CPU miner if the config
	// provides a mining address.
	if len(cfg.miningAddrs) > 0 {
		wg.Add(2)
		go func() {
			s.bg.Run(ctx)
			wg.Done()
		}()
		go func() {
			s.cpuMiner.Run(ctx)
			wg.Done()
		}()

		// The CPU miner is started without any workers which means it is idle.
		// Start mining by setting the default number of workers when requested.
		if cfg.Generate {
			s.cpuMiner.SetNumWorkers(-1)
		}
	}

	// Start the chain's index subscriber.
	wg.Add(1)
	go func() {
		s.indexSubscriber.Run(ctx)
		wg.Done()
	}()

	// Shutdown the server when the context is cancelled.
	<-ctx.Done()
	s.shutdown.Store(true)

	srvrLog.Warnf("Server shutting down")
	s.feeEstimator.Close()
	s.chain.ShutdownUtxoCache()
	wg.Wait()
	srvrLog.Trace("Server stopped")
}

// parseListeners determines whether each listen address is IPv4 and IPv6 and
// returns a slice of appropriate net.Addrs to listen on with TCP. It also
// properly detects addresses which apply to "all interfaces" and adds the
// address as both IPv4 and IPv6.
func parseListeners(addrs []string) ([]net.Addr, error) {
	netAddrs := make([]net.Addr, 0, len(addrs)*2)
	for _, addr := range addrs {
		host, _, err := net.SplitHostPort(addr)
		if err != nil {
			// Shouldn't happen due to already being normalized.
			return nil, err
		}

		// Empty host or host of * on plan9 is both IPv4 and IPv6.
		if host == "" || (host == "*" && runtime.GOOS == "plan9") {
			netAddrs = append(netAddrs, simpleAddr{net: "tcp4", addr: addr})
			netAddrs = append(netAddrs, simpleAddr{net: "tcp6", addr: addr})
			continue
		}

		// Parse the IP.
		ip, err := netip.ParseAddr(host)
		if err != nil {
			return nil, fmt.Errorf("'%s' is not a valid IP address", host)
		}

		// Determine the address type.
		if ip.Unmap().Is6() {
			netAddrs = append(netAddrs, simpleAddr{net: "tcp6", addr: addr})
		} else {
			netAddrs = append(netAddrs, simpleAddr{net: "tcp4", addr: addr})
		}
	}
	return netAddrs, nil
}

func (s *server) upnpUpdateThread(ctx context.Context) {
	// Go off immediately to prevent code duplication, thereafter we renew
	// lease every 15 minutes.
	timer := time.NewTimer(0 * time.Second)
	lport, _ := strconv.ParseInt(s.chainParams.DefaultPort, 10, 16)

	first := true
out:
	for {
		select {
		case <-timer.C:
			// TODO: pick external port more cleverly
			// TODO: know which ports we are listening to on an external net.
			// TODO: if specific listen port doesn't work then ask for wildcard
			// listen port?
			// XXX this assumes timeout is in seconds.
			listenPort, err := s.nat.AddPortMapping("tcp", int(lport), int(lport),
				"dcrd listen port", 20*60)
			if err != nil {
				srvrLog.Warnf("can't add UPnP port mapping: %v", err)
			}
			if first && err == nil {
				// TODO: look this up periodically to see if upnp domain changed
				// and so did ip.
				externalip, err := s.nat.GetExternalAddress()
				if err != nil {
					srvrLog.Warnf("UPnP can't get external address: %v", err)
					continue out
				}
				localAddr := addrmgr.NewNetAddressFromIPPort(externalip,
					uint16(listenPort), s.services)
				err = s.addrManager.AddLocalAddress(localAddr, addrmgr.UpnpPrio)
				if err != nil {
					srvrLog.Warnf("Failed to add UPnP local address %s: %v",
						localAddr, err)
				} else {
					srvrLog.Warnf("Successfully bound via UPnP to %s",
						localAddr)
					first = false
				}
			}
			timer.Reset(time.Minute * 15)

		case <-ctx.Done():
			break out
		}
	}

	timer.Stop()

	err := s.nat.DeletePortMapping("tcp", int(lport), int(lport))
	if err != nil {
		srvrLog.Warnf("unable to remove UPnP port mapping: %v", err)
	} else {
		srvrLog.Debugf("successfully disestablished UPnP port mapping")
	}
}

// standardScriptVerifyFlags returns the script flags that should be used when
// executing transaction scripts to enforce additional checks which are required
// for the script to be considered standard.  Note these flags are different
// than what is required for the consensus rules in that they are more strict.
func standardScriptVerifyFlags(chain *blockchain.BlockChain) (txscript.ScriptFlags, error) {
	scriptFlags := mempool.BaseStandardVerifyFlags

	// Enable validation of OP_SHA256 when the associated agenda is active.
	tipHash := &chain.BestSnapshot().Hash
	isActive, err := chain.IsLNFeaturesAgendaActive(tipHash)
	if err != nil {
		return 0, err
	}
	if isActive {
		scriptFlags |= txscript.ScriptVerifySHA256
	}

	// Enable validation of treasury-related opcodes when the associated agenda
	// is active.
	isActive, err = chain.IsTreasuryAgendaActive(tipHash)
	if err != nil {
		return 0, err
	}
	if isActive {
		scriptFlags |= txscript.ScriptVerifyTreasury
	}

	return scriptFlags, nil
}

// genCertPair generates a key/cert pair to the paths provided.
func genCertPair(certFile, keyFile string, altDNSNames []string, tlsCurve elliptic.Curve) error {
	rpcsLog.Infof("Generating TLS certificates...")

	org := "dcrd autogenerated cert"
	validUntil := time.Now().Add(10 * 365 * 24 * time.Hour)
	cert, key, err := certgen.NewTLSCertPair(tlsCurve, org,
		validUntil, altDNSNames)
	if err != nil {
		return err
	}

	// Write cert and key files.
	if err = os.WriteFile(certFile, cert, 0644); err != nil {
		return err
	}
	if err = os.WriteFile(keyFile, key, 0600); err != nil {
		os.Remove(certFile)
		return err
	}

	rpcsLog.Infof("Done generating TLS certificates")
	return nil
}

// watchedFile houses details about a file that is being watched for updates.
type watchedFile struct {
	path    string
	curTime time.Time
	curSize int64
}

// updated returns whether or not the file has been updated since the last time
// it was checked and updates the file info details used to make that
// determination accordingly.
//
// It returns true for files that no longer exist.
//
// It returns false when any unexpected errors are encountered while attempting
// to get the file details or the provided watched file does not have a path
// associated with it.
func (f *watchedFile) updated() bool {
	// Ignore watched files that don't have a path associated with them.
	if f.path == "" {
		return false
	}

	// Attempt to get file info about the watched file.  Note that errors aside
	// from files that no longer exist are intentionally ignored here so
	// unexpected errors do not result in the file being reported as changed
	// when it very likely was not.
	fi, err := os.Stat(f.path)
	if err != nil {
		return os.IsNotExist(err)
	}
	changed := fi.Size() != f.curSize || fi.ModTime() != f.curTime
	if changed {
		f.curSize = fi.Size()
		f.curTime = fi.ModTime()
	}
	return changed
}

// reloadableTLSConfig houses information for a TLS configuration that will
// dynamically reload the server certificate, server key, and client CAs when
// the associated files are updated.
type reloadableTLSConfig struct {
	mtx                 sync.Mutex
	minReloadCheckDelay time.Duration
	nextReloadCheck     time.Time
	cert                watchedFile
	key                 watchedFile
	clientCAs           watchedFile
	cachedConfig        *tls.Config
	prevAttemptErr      error
}

// needsReload determines whether or the not the watched certificate files (and
// hence the TLS config that houses them) need to be reloaded.
//
// The conditions for reload are as follows:
//   - Enough time has passed since the last time the files were checked
//   - Either the modified time or file of any of the watched cert files have
//     changed.
//
// This function MUST be called with the embedded mutex locked (for writes).
func (c *reloadableTLSConfig) needsReload() bool {
	// Avoid checking for cert updates when not enough time has passed.
	now := time.Now()
	if now.Before(c.nextReloadCheck) {
		return false
	}
	c.nextReloadCheck = now.Add(c.minReloadCheckDelay)

	return c.cert.updated() || c.key.updated() || c.clientCAs.updated()
}

// newTLSConfig loads the provided server certificate and key pair along with
// the provided client CAs and returns a new tls.Config instance populated with
// the parsed values.
//
// The clientCAsPath may be an empty string when client authentication is not
// required.
func newTLSConfig(certPath, keyPath, clientCAsPath string, minVersion uint16) (*tls.Config, error) {
	serverCert, err := tls.LoadX509KeyPair(certPath, keyPath)
	if err != nil {
		return nil, err
	}

	tlsConfig := tls.Config{
		Certificates: []tls.Certificate{serverCert},
		MinVersion:   minVersion,
	}
	if clientCAsPath != "" {
		clientCAs, err := os.ReadFile(clientCAsPath)
		if err != nil {
			return nil, err
		}
		tlsConfig.ClientAuth = tls.RequireAndVerifyClientCert
		tlsConfig.ClientCAs = x509.NewCertPool()
		if !tlsConfig.ClientCAs.AppendCertsFromPEM(clientCAs) {
			return nil, fmt.Errorf("no certificates found in %q", clientCAsPath)
		}
	}
	return &tlsConfig, nil
}

// configFileClient is intended to be set as the GetConfigForClient callback in
// the initial TLS configuration passed to the listener in order to enable
// automatically detecting and reloading certificate changes.
//
// This function is safe for concurrent access.
func (c *reloadableTLSConfig) configFileClient(_ *tls.ClientHelloInfo) (*tls.Config, error) {
	defer c.mtx.Unlock()
	c.mtx.Lock()

	if !c.needsReload() {
		return c.cachedConfig, nil
	}

	// Attempt to reload the certs and generate a new TLS config for them.
	//
	// Only update the cached config when there was no error in order to
	// preserve the current working config.
	tlsConfig, err := newTLSConfig(c.cert.path, c.key.path, c.clientCAs.path,
		c.cachedConfig.MinVersion)
	if err != nil {
		if c.prevAttemptErr == nil || err.Error() != c.prevAttemptErr.Error() {
			rpcsLog.Warnf("RPC certificates modification detected, but existing "+
				"configuration preserved because the certificates failed to "+
				"reload: %v\n", err)
		}
		c.prevAttemptErr = err
		return c.cachedConfig, nil
	}
	c.prevAttemptErr = nil

	rpcsLog.Info("Reloaded modified RPC certificates")
	c.cachedConfig = tlsConfig
	return c.cachedConfig, nil
}

// mixpoolChain adapts the internal blockchain type with a FetchUtxoEntry
// method that is compatible with the mixpool package.
type mixpoolChain struct {
	blockchain *blockchain.BlockChain
	mempool    *mempool.TxPool
}

var _ mixpool.BlockChain = (*mixpoolChain)(nil)
var _ mixpool.UtxoEntry = (*blockchain.UtxoEntry)(nil)

func (m *mixpoolChain) ChainParams() *chaincfg.Params {
	return m.blockchain.ChainParams()
}

func (m *mixpoolChain) FetchUtxoEntry(op wire.OutPoint) (mixpool.UtxoEntry, error) {
	if m.mempool.IsSpent(op) {
		return nil, nil
	}

	entry, err := m.blockchain.FetchUtxoEntry(op)
	if err != nil {
		return nil, err
	}
	if entry == nil {
		return nil, err
	}
	return entry, nil
}

func (m *mixpoolChain) CurrentTip() (chainhash.Hash, int64) {
	snap := m.blockchain.BestSnapshot()
	return snap.Hash, snap.Height
}

// makeReloadableTLSConfig returns a TLS configuration that will dynamically
// reload the server certificate, server key, and client CAs from the configured
// paths when the files are updated.
//
// The client CAs path may be an empty string when client authentication is not
// required.
//
// This works by hooking up the GetConfigForClient callback which is invoked
// when a client connects.  It makes use of caching and lazy loading (as opposed
// to polling) for better efficiency.
//
// An overview of the behavior is as follows:
//
//   - All connections used a cached TLS config
//   - When an underlying file is updated, as determined by its modification
//     time being newer or its size changing, the certificates are reloaded and
//     cached
//   - Files are not checked for updates more than once every several seconds
//   - Files are only checked for updates when a connection is made and are not
//     checked more than once every several seconds
//   - The existing cached config will be retained if any errors that would
//     result in an invalid config are encountered (for example, removing the
//     files, replacing the files with malformed or empty data, or replacing the
//     key with one that is not valid for the cert)
func makeReloadableTLSConfig(certPath, keyPath, clientCAsPath string) (*tls.Config, error) {
	const minVer = tls.VersionTLS12
	cachedConfig, err := newTLSConfig(certPath, keyPath, clientCAsPath, minVer)
	if err != nil {
		return nil, err
	}

	minReloadCheckDelay := 5 * time.Second
	c := &reloadableTLSConfig{
		minReloadCheckDelay: minReloadCheckDelay,
		nextReloadCheck:     time.Now().Add(minReloadCheckDelay),
		cert:                watchedFile{path: certPath},
		key:                 watchedFile{path: keyPath},
		clientCAs:           watchedFile{path: clientCAsPath},
		cachedConfig:        cachedConfig,
	}

	// Populate the initial file info for all watched files.
	c.cert.updated()
	c.key.updated()
	c.clientCAs.updated()

	return &tls.Config{
		GetConfigForClient: c.configFileClient,
		MinVersion:         minVer,
	}, nil
}

// setupRPCListeners returns a slice of listeners that are configured for use
// with the RPC server depending on the configuration settings for listen
// addresses and TLS.
func setupRPCListeners() ([]net.Listener, error) {
	var notifyAddrServer boundAddrEventServer
	if cfg.BoundAddrEvents {
		notifyAddrServer = newBoundAddrEventServer(outgoingPipeMessages)
	}

	// Setup TLS if not disabled.
	listenFunc := net.Listen
	if !cfg.DisableRPC && !cfg.DisableTLS {
		// Generate the TLS cert and key file if both don't already exist.
		keyFileExists := fileExists(cfg.RPCKey)
		certFileExists := fileExists(cfg.RPCCert)
		if len(cfg.AltDNSNames) != 0 && (keyFileExists || certFileExists) {
			rpcsLog.Warn("Additional DNS names specified when TLS " +
				"certificates already exist will NOT be included:")
			rpcsLog.Warnf("- In order to create TLS certs that include the "+
				"additional DNS names, delete %q and %q and restart the server",
				cfg.RPCKey, cfg.RPCCert)
		}
		if !keyFileExists && !certFileExists {
			curve, err := tlsCurve(cfg.TLSCurve)
			if err != nil {
				return nil, err
			}
			err = genCertPair(cfg.RPCCert, cfg.RPCKey, cfg.AltDNSNames, curve)
			if err != nil {
				return nil, err
			}
		}
		var clientCACerts string
		if cfg.RPCAuthType == authTypeClientCert {
			clientCACerts = cfg.RPCClientCAs
		}
		tlsConfig, err := makeReloadableTLSConfig(cfg.RPCCert, cfg.RPCKey,
			clientCACerts)
		if err != nil {
			return nil, err
		}

		// Change the standard net.Listen function to the tls one.
		listenFunc = func(net string, laddr string) (net.Listener, error) {
			return tls.Listen(net, laddr, tlsConfig)
		}
	}

	netAddrs, err := parseListeners(cfg.RPCListeners)
	if err != nil {
		return nil, err
	}

	listeners := make([]net.Listener, 0, len(netAddrs))
	for _, addr := range netAddrs {
		listener, err := listenFunc(addr.Network(), addr.String())
		if err != nil {
			rpcsLog.Warnf("Can't listen on %s: %v", addr, err)
			continue
		}
		listeners = append(listeners, listener)
		notifyAddrServer.notifyRPCAddress(listener.Addr().String())
	}

	return listeners, nil
}

// newServer returns a new dcrd server configured to listen on addr for the
// decred network type specified by chainParams.  Use start to begin accepting
// connections from peers.
func newServer(ctx context.Context, profiler *profileServer,
	listenAddrs []string, db database.DB, utxoDb *leveldb.DB,
	chainParams *chaincfg.Params, dataDir string) (*server, error) {

	amgr := addrmgr.New(cfg.DataDir)
	services := defaultServices

	var listeners []net.Listener
	var nat *upnpNAT
	if !cfg.DisableListen {
		var err error
		listeners, nat, err = initListeners(ctx, chainParams, amgr, listenAddrs,
			services)
		if err != nil {
			return nil, err
		}
		if len(listeners) == 0 {
			return nil, errors.New("no valid listen address")
		}
	}

	// Create a SigCache instance.
	sigCache, err := txscript.NewSigCache(cfg.SigCacheMaxSize)
	if err != nil {
		return nil, err
	}

	s := server{
		targetOutbound:       defaultTargetOutbound,
		chainParams:          chainParams,
		addrManager:          amgr,
		peerState:            makePeerState(),
		relayInv:             make(chan relayMsg, cfg.MaxPeers),
		broadcast:            make(chan broadcastMsg, cfg.MaxPeers),
		modifyRebroadcastInv: make(chan interface{}),
		nat:                  nat,
		db:                   db,
		timeSource:           blockchain.NewMedianTime(),
		services:             services,
		sigCache:             sigCache,
		subsidyCache:         standalone.NewSubsidyCache(chainParams),
		lotteryDataBroadcast: make(map[chainhash.Hash]struct{}),
		recentlyConfirmedTxns: apbf.NewFilter(maxRecentlyConfirmedTxns,
			recentlyConfirmedTxnsFPRate),
		indexSubscriber: indexers.NewIndexSubscriber(ctx),
		quit:            make(chan struct{}),
		recentlyAdvertisedTxns: lru.NewMapWithDefaultTTL[chainhash.Hash,
			*dcrutil.Tx](maxRecentlyAdvertisedTxns, recentlyAdvertisedTxnsTTL),
		lastAdvertisedTxnsEvictedLogged: time.Now(),
	}

	// Convert the minimum known work to a uint256 when it exists.  Ideally, the
	// chain params should be updated to use the new type, but that will be a
	// major version bump, so a one-time conversion is a good tradeoff in the
	// mean time.
	minKnownWorkBig := chainParams.MinKnownChainWork
	if minKnownWorkBig != nil {
		s.minKnownWork.SetBig(minKnownWorkBig)
	}

	feC := fees.EstimatorConfig{
		MinBucketFee: cfg.minRelayTxFee,
		MaxBucketFee: dcrutil.Amount(fees.DefaultMaxBucketFeeMultiplier) * cfg.minRelayTxFee,
		MaxConfirms:  fees.DefaultMaxConfirmations,
		FeeRateStep:  fees.DefaultFeeRateStep,
		DatabaseFile: path.Join(dataDir, "feesdb"),

		// 1e5 is the previous (up to 1.1.0) mempool.DefaultMinRelayTxFee that
		// un-upgraded wallets will be using, so track this particular rate
		// explicitly. Note that bumping this value will cause the existing fees
		// database to become invalid and will force nodes to explicitly delete
		// it.
		ExtraBucketFee: 1e5,
	}
	fe, err := fees.NewEstimator(&feC)
	if err != nil {
		return nil, err
	}
	s.feeEstimator = fe

	if cfg.AllowOldForks {
		srvrLog.Info("Processing forks deep in history is enabled")
	}

	// Set assume valid when enabled.
	var assumeValid chainhash.Hash
	if cfg.AssumeValid != "0" {
		// Default assume valid to the value specified by chain params.
		assumeValid = s.chainParams.AssumeValid

		// Override assume valid if specified by the config option.
		if cfg.AssumeValid != "" {
			hash, err := chainhash.NewHashFromStr(cfg.AssumeValid)
			if err != nil {
				err = fmt.Errorf("invalid hex for --assumevalid: %w", err)
				return nil, err
			}
			assumeValid = *hash
			srvrLog.Infof("Assume valid set to %v", assumeValid)
		}
	} else {
		srvrLog.Info("Assume valid is disabled")
	}

	// Create a new block chain instance with the appropriate configuration.
	utxoBackend := blockchain.NewLevelDbUtxoBackend(utxoDb)
	utxoCache := blockchain.NewUtxoCache(&blockchain.UtxoCacheConfig{
		Backend:      utxoBackend,
		FlushBlockDB: s.db.Flush,
		MaxSize:      uint64(cfg.UtxoCacheMaxSize) * 1024 * 1024,
	})
	s.chain, err = blockchain.New(ctx,
		&blockchain.Config{
			DB:              s.db,
			UtxoBackend:     utxoBackend,
			ChainParams:     s.chainParams,
			AssumeValid:     assumeValid,
			TimeSource:      s.timeSource,
			Notifications:   s.handleBlockchainNotification,
			SigCache:        s.sigCache,
			SubsidyCache:    s.subsidyCache,
			IndexSubscriber: s.indexSubscriber,
			UtxoCache:       utxoCache,
		})
	if err != nil {
		return nil, err
	}

	queryer := &blockchain.ChainQueryerAdapter{BlockChain: s.chain}
	if cfg.TxIndex {
		indxLog.Info("Transaction index is enabled")
		s.txIndex, err = indexers.NewTxIndex(s.indexSubscriber, db, queryer)
		if err != nil {
			return nil, err
		}
	}
	if !cfg.NoExistsAddrIndex {
		indxLog.Info("Exists address index is enabled")
		s.existsAddrIndex, err = indexers.NewExistsAddrIndex(s.indexSubscriber,
			db, queryer)
		if err != nil {
			return nil, err
		}
	}
	err = s.indexSubscriber.CatchUp(ctx, s.db, queryer)
	if err != nil {
		return nil, err
	}

	txC := mempool.Config{
		Policy: mempool.Policy{
			EnableAncestorTracking: len(cfg.miningAddrs) > 0,
			AcceptNonStd:           cfg.AcceptNonStd,
			MaxOrphanTxs:           cfg.MaxOrphanTxs,
			MaxOrphanTxSize:        mempool.MaxStandardTxSize,
			MaxSigOpsPerTx:         blockchain.MaxSigOpsPerBlock / 5,
			MinRelayTxFee:          cfg.minRelayTxFee,
			AllowOldVotes:          cfg.AllowOldVotes,
			MaxVoteAge: func() uint16 {
				switch chainParams.Net {
				case wire.MainNet, wire.SimNet, wire.RegNet:
					return chainParams.CoinbaseMaturity

				case wire.TestNet3:
					return defaultMaximumVoteAge

				default:
					return chainParams.CoinbaseMaturity
				}
			}(),
			StandardVerifyFlags: func() (txscript.ScriptFlags, error) {
				return standardScriptVerifyFlags(s.chain)
			},
		},
		ChainParams: chainParams,
		NextStakeDifficulty: func() (int64, error) {
			return s.chain.BestSnapshot().NextStakeDiff, nil
		},
		FetchUtxoView:    s.chain.FetchUtxoView,
		BlockByHash:      s.chain.BlockByHash,
		BestHash:         func() *chainhash.Hash { return &s.chain.BestSnapshot().Hash },
		BestHeight:       func() int64 { return s.chain.BestSnapshot().Height },
		HeaderByHash:     s.chain.HeaderByHash,
		CalcSequenceLock: s.chain.CalcSequenceLock,
		SubsidyCache:     s.subsidyCache,
		SigCache:         s.sigCache,
		PastMedianTime: func() time.Time {
			return s.chain.BestSnapshot().MedianTime
		},
		ExistsAddrIndex:           s.existsAddrIndex,
		AddTxToFeeEstimation:      s.feeEstimator.AddMemPoolTransaction,
		RemoveTxFromFeeEstimation: s.feeEstimator.RemoveMemPoolTransaction,
		OnVoteReceived: func(voteTx *dcrutil.Tx) {
			if s.bg != nil {
				s.bg.VoteReceived(voteTx)
			}
		},
		OnTSpendReceived: func(tx *dcrutil.Tx) {
			if s.rpcServer != nil {
				s.rpcServer.NotifyTSpend(tx)
			}
		},
		IsTreasuryAgendaActive: func() (bool, error) {
			tipHash := &s.chain.BestSnapshot().Hash
			return s.chain.IsTreasuryAgendaActive(tipHash)
		},
		IsAutoRevocationsAgendaActive: func() (bool, error) {
			tipHash := &s.chain.BestSnapshot().Hash
			return s.chain.IsAutoRevocationsAgendaActive(tipHash)
		},
		IsSubsidySplitAgendaActive: func() (bool, error) {
			tipHash := &s.chain.BestSnapshot().Hash
			return s.chain.IsSubsidySplitAgendaActive(tipHash)
		},
		IsSubsidySplitR2AgendaActive: func() (bool, error) {
			tipHash := &s.chain.BestSnapshot().Hash
			return s.chain.IsSubsidySplitR2AgendaActive(tipHash)
		},
		TSpendMinedOnAncestor: func(tspend chainhash.Hash) error {
			tipHash := s.chain.BestSnapshot().Hash
			return s.chain.CheckTSpendExists(tipHash, tspend)
		},
	}
	s.txMemPool = mempool.New(&txC)

	mixchain := &mixpoolChain{s.chain, s.txMemPool}
	s.mixMsgPool = mixpool.NewPool(mixchain)

	targetOutbound := defaultTargetOutbound
	if cfg.MaxPeers < targetOutbound {
		targetOutbound = cfg.MaxPeers
	}
	s.syncManager = netsync.New(&netsync.Config{
		Chain:                 s.chain,
		ChainParams:           s.chainParams,
		TimeSource:            s.timeSource,
		TxMemPool:             s.txMemPool,
		NoMiningStateSync:     cfg.NoMiningStateSync,
		MaxOutboundPeers:      uint64(targetOutbound),
		MaxPeers:              cfg.MaxPeers,
		MaxOrphanTxs:          cfg.MaxOrphanTxs,
		RecentlyConfirmedTxns: s.recentlyConfirmedTxns,
		MixPool:               s.mixMsgPool,
	})

	// Dump the blockchain and quit if requested.
	if cfg.DumpBlockchain != "" {
		err := dumpBlockChain(s.chainParams, s.chain)
		if err != nil {
			return nil, err
		}

		return nil, fmt.Errorf("closing after dumping blockchain")
	}

	// Create the background block template generator and CPU miner if the
	// config has a mining address.
	if len(cfg.miningAddrs) > 0 {
		// Create the mining policy and block template generator based on the
		// configuration options.
		//
		// NOTE: The CPU miner relies on the mempool, so the mempool has to be
		// created before calling the function to create the CPU miner.
		policy := mining.Policy{
			BlockMaxSize:     cfg.BlockMaxSize,
			TxMinFreeFee:     cfg.minRelayTxFee,
			AggressiveMining: !cfg.NonAggressive,
			StandardVerifyFlags: func() (txscript.ScriptFlags, error) {
				return standardScriptVerifyFlags(s.chain)
			},
		}
		tg := mining.NewBlkTmplGenerator(&mining.Config{
			Policy:                     &policy,
			TxSource:                   s.txMemPool,
			TimeSource:                 s.timeSource,
			SubsidyCache:               s.subsidyCache,
			ChainParams:                s.chainParams,
			MiningTimeOffset:           cfg.MiningTimeOffset,
			BestSnapshot:               s.chain.BestSnapshot,
			BlockByHash:                s.chain.BlockByHash,
			CalcNextRequiredDifficulty: s.chain.CalcNextRequiredDifficulty,
			CalcStakeVersionByHash:     s.chain.CalcStakeVersionByHash,
			CheckConnectBlockTemplate:  s.chain.CheckConnectBlockTemplate,
			CheckTicketExhaustion:      s.chain.CheckTicketExhaustion,
			CheckTransactionInputs: func(tx *dcrutil.Tx, txHeight int64,
				view *blockchain.UtxoViewpoint, checkFraudProof bool,
				prevHeader *wire.BlockHeader, isTreasuryEnabled,
				isAutoRevocationsEnabled bool,
				subsidySplitVariant standalone.SubsidySplitVariant) (int64, error) {

				return blockchain.CheckTransactionInputs(s.subsidyCache, tx, txHeight,
					view, checkFraudProof, s.chainParams, prevHeader, isTreasuryEnabled,
					isAutoRevocationsEnabled, subsidySplitVariant)
			},
			CheckTSpendHasVotes:             s.chain.CheckTSpendHasVotes,
			CountSigOps:                     blockchain.CountSigOps,
			FetchUtxoEntry:                  s.chain.FetchUtxoEntry,
			FetchUtxoView:                   s.chain.FetchUtxoView,
			FetchUtxoViewParentTemplate:     s.chain.FetchUtxoViewParentTemplate,
			ForceHeadReorganization:         s.chain.ForceHeadReorganization,
			HeaderByHash:                    s.chain.HeaderByHash,
			IsFinalizedTransaction:          blockchain.IsFinalizedTransaction,
			IsHeaderCommitmentsAgendaActive: s.chain.IsHeaderCommitmentsAgendaActive,
			IsTreasuryAgendaActive:          s.chain.IsTreasuryAgendaActive,
			IsAutoRevocationsAgendaActive:   s.chain.IsAutoRevocationsAgendaActive,
			IsSubsidySplitAgendaActive:      s.chain.IsSubsidySplitAgendaActive,
			IsSubsidySplitR2AgendaActive:    s.chain.IsSubsidySplitR2AgendaActive,
			MaxTreasuryExpenditure:          s.chain.MaxTreasuryExpenditure,
			NewUtxoViewpoint: func() *blockchain.UtxoViewpoint {
				return blockchain.NewUtxoViewpoint(utxoCache)
			},
			TipGeneration: s.chain.TipGeneration,
			ValidateTransactionScripts: func(tx *dcrutil.Tx,
				utxoView *blockchain.UtxoViewpoint, flags txscript.ScriptFlags,
				isAutoRevocationsEnabled bool) error {

				return blockchain.ValidateTransactionScripts(tx, utxoView, flags,
					s.sigCache, isAutoRevocationsEnabled)
			},
		})

		s.bg = mining.NewBgBlkTmplGenerator(&mining.BgBlkTmplConfig{
			TemplateGenerator:   tg,
			MiningAddrs:         cfg.miningAddrs,
			AllowUnsyncedMining: cfg.AllowUnsyncedMining,
			IsCurrent:           s.syncManager.IsCurrent,
		})

		s.cpuMiner = cpuminer.New(&cpuminer.Config{
			ChainParams:                s.chainParams,
			PermitConnectionlessMining: cfg.SimNet || cfg.RegNet,
			BgBlkTmplGenerator:         s.bg,
			BestSnapshot:               s.chain.BestSnapshot,
			BlockHashByHeight:          s.chain.BlockHashByHeight,
			ProcessBlock:               s.syncManager.ProcessBlock,
			ConnectedCount:             s.ConnectedCount,
			IsCurrent:                  s.syncManager.IsCurrent,
			IsBlake3PowAgendaActive:    s.chain.IsBlake3PowAgendaActive,
		})
	}

	// Only setup a function to return new addresses to connect to when
	// not running in connect-only mode.  The simulation and regression networks
	// are always in connect-only mode since they are only intended to connect
	// to specified peers and actively avoid advertising and connecting to
	// discovered peers in order to prevent it from becoming a public test
	// network.
	var newAddressFunc func() (net.Addr, error)
	if !cfg.SimNet && !cfg.RegNet && len(cfg.ConnectPeers) == 0 {
		newAddressFunc = func() (net.Addr, error) {
			for tries := 0; tries < 100; tries++ {
				// Note that this does not filter by address type.  Unsupported
				// network address types should be pruned from the address
				// manager's internal storage prior to calling this function.
				addr := s.addrManager.GetAddress()
				if addr == nil {
					break
				}

				// Address will not be invalid, local or unroutable
				// because addrmanager rejects those on addition.
				// Just check that we don't already have an address
				// in the same group so that we are not connecting
				// to the same network segment at the expense of
				// others.
				netAddr := addr.NetAddress()
				if s.OutboundGroupCount(netAddr.GroupKey()) != 0 {
					continue
				}

				// Skip recently attempted nodes until we have
				// tried 30 times.
				if tries < 30 {
					lastAttempt := addr.LastAttempt()
					if !lastAttempt.IsZero() &&
						time.Since(lastAttempt) < 10*time.Minute {
						continue
					}
				}

				// allow nondefault ports after 50 failed tries.
				if fmt.Sprintf("%d", netAddr.Port) !=
					s.chainParams.DefaultPort && tries < 50 {
					continue
				}

				return addrStringToNetAddr(netAddr.Key())
			}

			return nil, errors.New("no valid connect address")
		}
	}

	// Create a connection manager.
	if uint32(cfg.MaxPeers) < s.targetOutbound {
		s.targetOutbound = uint32(cfg.MaxPeers)
	}
	cmgr, err := connmgr.New(&connmgr.Config{
		Listeners:      listeners,
		OnAccept:       s.inboundPeerConnected,
		RetryDuration:  connectionRetryInterval,
		TargetOutbound: s.targetOutbound,
		Dial:           s.attemptDcrdDial,
		Timeout:        cfg.DialTimeout,
		OnConnection:   s.outboundPeerConnected,
		GetNewAddress:  newAddressFunc,
	})
	if err != nil {
		return nil, err
	}
	s.connManager = cmgr

	// Start up persistent peers.
	permanentPeers := cfg.ConnectPeers
	if len(permanentPeers) == 0 {
		permanentPeers = cfg.AddPeers
	}
	for _, addr := range permanentPeers {
		tcpAddr, err := addrStringToNetAddr(addr)
		if err != nil {
			return nil, err
		}

		go s.connManager.Connect(ctx,
			&connmgr.ConnReq{
				Addr:      tcpAddr,
				Permanent: true,
			})
	}

	if !cfg.DisableRPC {
		// Setup listeners for the configured RPC listen addresses and
		// TLS settings.
		rpcListeners, err := setupRPCListeners()
		if err != nil {
			return nil, err
		}

		if len(rpcListeners) == 0 {
			return nil, errors.New("no usable rpc listen addresses")
		}

		rpcsConfig := rpcserver.Config{
			Listeners:    rpcListeners,
			ProfilerMgr:  profiler,
			ConnMgr:      &rpcConnManager{&s},
			SyncMgr:      &rpcSyncMgr{server: &s, syncMgr: s.syncManager},
			FeeEstimator: s.feeEstimator,
			TimeSource:   s.timeSource,
			Services:     s.services,
			AddrManager:  s.addrManager,
			Clock:        &rpcClock{},
			SubsidyCache: s.subsidyCache,
			Chain:        &rpcChain{s.chain},
			ChainParams:  chainParams,
			SanityChecker: &rpcSanityChecker{
				chain:       s.chain,
				timeSource:  s.timeSource,
				chainParams: chainParams,
			},
			DB:                   db,
			TxMempooler:          s.txMemPool,
			CPUMiner:             &rpcCPUMiner{s.cpuMiner},
			NetInfo:              cfg.generateNetworkInfo(),
			MinRelayTxFee:        cfg.minRelayTxFee,
			Proxy:                cfg.Proxy,
			RPCUser:              cfg.RPCUser,
			RPCPass:              cfg.RPCPass,
			RPCLimitUser:         cfg.RPCLimitUser,
			RPCLimitPass:         cfg.RPCLimitPass,
			RPCMaxClients:        cfg.RPCMaxClients,
			RPCMaxConcurrentReqs: cfg.RPCMaxConcurrentReqs,
			RPCMaxWebsockets:     cfg.RPCMaxWebsockets,
			TestNet:              cfg.TestNet,
			MiningAddrs:          cfg.miningAddrs,
			AllowUnsyncedMining:  cfg.AllowUnsyncedMining,
			MaxProtocolVersion:   maxProtocolVersion,
			UserAgentVersion:     userAgentVersion,
			LogManager:           &rpcLogManager{},
			FiltererV2:           s.chain,
			MixPooler:            s.mixMsgPool,
		}
		if s.existsAddrIndex != nil {
			rpcsConfig.ExistsAddresser = s.existsAddrIndex
		}
		if s.bg != nil {
			rpcsConfig.BlockTemplater = &rpcBlockTemplater{s.bg}
		}
		if s.txIndex != nil {
			rpcsConfig.TxIndexer = s.txIndex
		}

		s.rpcServer, err = rpcserver.New(&rpcsConfig)
		if err != nil {
			return nil, err
		}

		// Signal process shutdown when the RPC server requests it.
		go func() {
			<-s.rpcServer.RequestedProcessShutdown()
			shutdownRequestChannel <- struct{}{}
		}()
	}

	return &s, nil
}

// initListeners initializes the configured net listeners and adds any bound
// addresses to the address manager. Returns the listeners and a NAT interface,
// which is non-nil if UPnP is in use.
func initListeners(ctx context.Context, params *chaincfg.Params, amgr *addrmgr.AddrManager, listenAddrs []string, services wire.ServiceFlag) ([]net.Listener, *upnpNAT, error) {
	// Listen for TCP connections at the configured addresses
	netAddrs, err := parseListeners(listenAddrs)
	if err != nil {
		return nil, nil, err
	}

	var notifyAddrServer boundAddrEventServer
	if cfg.BoundAddrEvents {
		notifyAddrServer = newBoundAddrEventServer(outgoingPipeMessages)
	}

	listeners := make([]net.Listener, 0, len(netAddrs))
	for _, addr := range netAddrs {
		var listenConfig net.ListenConfig
		listener, err := listenConfig.Listen(ctx, addr.Network(), addr.String())
		if err != nil {
			srvrLog.Warnf("Can't listen on %s: %v", addr, err)
			continue
		}
		listeners = append(listeners, listener)
		notifyAddrServer.notifyP2PAddress(listener.Addr().String())
	}

	var nat *upnpNAT
	if len(cfg.ExternalIPs) != 0 {
		defaultPort, err := strconv.ParseUint(params.DefaultPort, 10, 16)
		if err != nil {
			srvrLog.Errorf("Can not parse default port %s for active chain: %v",
				params.DefaultPort, err)
			return nil, nil, err
		}

		for _, sip := range cfg.ExternalIPs {
			eport := uint16(defaultPort)
			host, portstr, err := net.SplitHostPort(sip)
			if err != nil {
				// no port, use default.
				host = sip
			} else {
				port, err := strconv.ParseUint(portstr, 10, 16)
				if err != nil {
					srvrLog.Warnf("Can not parse port from %s for "+
						"externalip: %v", sip, err)
					continue
				}
				eport = uint16(port)
			}

			na, err := hostToNetAddress(host, eport, services, dcrdLookup)
			if err != nil {
				srvrLog.Warnf("Not adding %s as externalip: %v", sip, err)
				continue
			}

			err = amgr.AddLocalAddress(na, addrmgr.ManualPrio)
			if err != nil {
				amgrLog.Warnf("Skipping specified external IP: %v", err)
			}
		}
	} else {
		if cfg.Upnp {
			var err error
			nat, err = discover(ctx)
			if err != nil {
				srvrLog.Warnf("Can't discover upnp: %v", err)
			}
			// nil nat here is fine, just means no upnp on network.
		}

		// Add bound addresses to address manager to be advertised to peers.
		for _, listener := range listeners {
			addr := listener.Addr().String()
			err := addLocalAddress(amgr, addr, services)
			if err != nil {
				amgrLog.Warnf("Skipping bound address %s: %v", addr, err)
			}
		}
	}

	return listeners, nat, nil
}

// addrStringToNetAddr takes an address in the form of 'host:port' and returns
// a net.Addr which maps to the original address with any host names resolved
// to IP addresses.
func addrStringToNetAddr(addr string) (net.Addr, error) {
	host, strPort, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	// Attempt to look up an IP address associated with the parsed host.
	// The dcrdLookup function will transparently handle performing the
	// lookup over Tor if necessary.
	ips, err := dcrdLookup(host)
	if err != nil {
		return nil, err
	}
	if len(ips) == 0 {
		return nil, fmt.Errorf("no addresses found for %s", host)
	}

	port, err := strconv.Atoi(strPort)
	if err != nil {
		return nil, err
	}

	return &net.TCPAddr{
		IP:   ips[0],
		Port: port,
	}, nil
}

// addLocalAddress adds an address that this node is listening on to the
// address manager so that it may be relayed to peers.
func addLocalAddress(addrMgr *addrmgr.AddrManager, addr string, services wire.ServiceFlag) error {
	host, portStr, err := net.SplitHostPort(addr)
	if err != nil {
		return err
	}
	port, err := strconv.ParseUint(portStr, 10, 16)
	if err != nil {
		return err
	}

	if ip := net.ParseIP(host); ip != nil && ip.IsUnspecified() {
		// If bound to unspecified address, advertise all local interfaces
		addrs, err := net.InterfaceAddrs()
		if err != nil {
			return err
		}

		for _, addr := range addrs {
			ifaceIP, _, err := net.ParseCIDR(addr.String())
			if err != nil {
				continue
			}

			// If bound to 0.0.0.0, do not add IPv6 interfaces and if bound to
			// ::, do not add IPv4 interfaces.
			if (ip.To4() == nil) != (ifaceIP.To4() == nil) {
				continue
			}

			netAddr := addrmgr.NewNetAddressFromIPPort(ifaceIP, uint16(port),
				services)
			addrMgr.AddLocalAddress(netAddr, addrmgr.BoundPrio)
		}
	} else {
		netAddr, err := hostToNetAddress(host, uint16(port), services,
			dcrdLookup)
		if err != nil {
			return err
		}

		addrMgr.AddLocalAddress(netAddr, addrmgr.BoundPrio)
	}

	return nil
}

// isWhitelisted returns whether the IP address is included in the whitelisted
// networks and IPs.
func isWhitelisted(addr net.Addr) bool {
	if len(cfg.whitelists) == 0 {
		return false
	}

	host, _, err := net.SplitHostPort(addr.String())
	if err != nil {
		srvrLog.Warnf("Unable to SplitHostPort on '%s': %v", addr, err)
		return false
	}
	ip := net.ParseIP(host)
	if ip == nil {
		srvrLog.Warnf("Unable to parse IP '%s'", addr)
		return false
	}

	for _, ipnet := range cfg.whitelists {
		if ipnet.Contains(ip) {
			return true
		}
	}
	return false
}