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package pex
import (
"context"
"fmt"
"runtime/debug"
"sync"
"time"
"github.com/tendermint/tendermint/internal/p2p"
"github.com/tendermint/tendermint/internal/p2p/conn"
"github.com/tendermint/tendermint/libs/log"
tmmath "github.com/tendermint/tendermint/libs/math"
"github.com/tendermint/tendermint/libs/service"
protop2p "github.com/tendermint/tendermint/proto/tendermint/p2p"
"github.com/tendermint/tendermint/types"
)
var (
_ service.Service = (*Reactor)(nil)
_ p2p.Wrapper = (*protop2p.PexMessage)(nil)
)
const (
// PexChannel is a channel for PEX messages
PexChannel = 0x00
// over-estimate of max NetAddress size
// hexID (40) + IP (16) + Port (2) + Name (100) ...
// NOTE: dont use massive DNS name ..
maxAddressSize = 256
// max addresses returned by GetSelection
// NOTE: this must match "maxMsgSize"
maxGetSelection = 250
// NOTE: amplification factor!
// small request results in up to maxMsgSize response
maxMsgSize = maxAddressSize * maxGetSelection
// the minimum time one peer can send another request to the same peer
minReceiveRequestInterval = 100 * time.Millisecond
// the maximum amount of addresses that can be included in a response
maxAddresses uint16 = 100
// How long to wait when there are no peers available before trying again
noAvailablePeersWaitPeriod = 1 * time.Second
// indicates the ping rate of the pex reactor when the peer store is full.
// The reactor should still look to add new peers in order to flush out low
// scoring peers that are still in the peer store
fullCapacityInterval = 10 * time.Minute
)
// TODO: We should decide whether we want channel descriptors to be housed
// within each reactor (as they are now) or, considering that the reactor doesn't
// really need to care about the channel descriptors, if they should be housed
// in the node module.
func ChannelDescriptor() *conn.ChannelDescriptor {
return &conn.ChannelDescriptor{
ID: PexChannel,
MessageType: new(protop2p.PexMessage),
Priority: 1,
SendQueueCapacity: 10,
RecvMessageCapacity: maxMsgSize,
RecvBufferCapacity: 128,
}
}
// The peer exchange or PEX reactor supports the peer manager by sending
// requests to other peers for addresses that can be given to the peer manager
// and at the same time advertises addresses to peers that need more.
//
// The reactor is able to tweak the intensity of it's search by decreasing or
// increasing the interval between each request. It tracks connected peers via
// a linked list, sending a request to the node at the front of the list and
// adding it to the back of the list once a response is received.
type Reactor struct {
service.BaseService
peerManager *p2p.PeerManager
pexCh *p2p.Channel
peerUpdates *p2p.PeerUpdates
closeCh chan struct{}
// list of available peers to loop through and send peer requests to
availablePeers map[types.NodeID]struct{}
mtx sync.RWMutex
// requestsSent keeps track of which peers the PEX reactor has sent requests
// to. This prevents the sending of spurious responses.
// NOTE: If a node never responds, they will remain in this map until a
// peer down status update is sent
requestsSent map[types.NodeID]struct{}
// lastReceivedRequests keeps track of when peers send a request to prevent
// peers from sending requests too often (as defined by
// minReceiveRequestInterval).
lastReceivedRequests map[types.NodeID]time.Time
// the time when another request will be sent
nextRequestTime time.Time
// keep track of how many new peers to existing peers we have received to
// extrapolate the size of the network
newPeers uint32
totalPeers uint32
// discoveryRatio is the inverse ratio of new peers to old peers squared.
// This is multiplied by the minimum duration to calculate how long to wait
// between each request.
discoveryRatio float32
}
// NewReactor returns a reference to a new reactor.
func NewReactor(
logger log.Logger,
peerManager *p2p.PeerManager,
pexCh *p2p.Channel,
peerUpdates *p2p.PeerUpdates,
) *Reactor {
r := &Reactor{
peerManager: peerManager,
pexCh: pexCh,
peerUpdates: peerUpdates,
closeCh: make(chan struct{}),
availablePeers: make(map[types.NodeID]struct{}),
requestsSent: make(map[types.NodeID]struct{}),
lastReceivedRequests: make(map[types.NodeID]time.Time),
}
r.BaseService = *service.NewBaseService(logger, "PEX", r)
return r
}
// OnStart starts separate go routines for each p2p Channel and listens for
// envelopes on each. In addition, it also listens for peer updates and handles
// messages on that p2p channel accordingly. The caller must be sure to execute
// OnStop to ensure the outbound p2p Channels are closed.
func (r *Reactor) OnStart(ctx context.Context) error {
go r.processPexCh(ctx)
go r.processPeerUpdates(ctx)
return nil
}
// OnStop stops the reactor by signaling to all spawned goroutines to exit and
// blocking until they all exit.
func (r *Reactor) OnStop() {
// Close closeCh to signal to all spawned goroutines to gracefully exit. All
// p2p Channels should execute Close().
close(r.closeCh)
// Wait for all p2p Channels to be closed before returning. This ensures we
// can easily reason about synchronization of all p2p Channels and ensure no
// panics will occur.
<-r.pexCh.Done()
<-r.peerUpdates.Done()
}
// processPexCh implements a blocking event loop where we listen for p2p
// Envelope messages from the pexCh.
func (r *Reactor) processPexCh(ctx context.Context) {
defer r.pexCh.Close()
timer := time.NewTimer(0)
defer timer.Stop()
for {
timer.Reset(time.Until(r.nextRequestTime))
select {
case <-ctx.Done():
return
case <-r.closeCh:
r.Logger.Debug("stopped listening on PEX channel; closing...")
return
// outbound requests for new peers
case <-timer.C:
r.sendRequestForPeers()
// inbound requests for new peers or responses to requests sent by this
// reactor
case envelope := <-r.pexCh.In:
if err := r.handleMessage(r.pexCh.ID, envelope); err != nil {
r.Logger.Error("failed to process message", "ch_id", r.pexCh.ID, "envelope", envelope, "err", err)
r.pexCh.Error <- p2p.PeerError{
NodeID: envelope.From,
Err: err,
}
}
}
}
}
// processPeerUpdates initiates a blocking process where we listen for and handle
// PeerUpdate messages. When the reactor is stopped, we will catch the signal and
// close the p2p PeerUpdatesCh gracefully.
func (r *Reactor) processPeerUpdates(ctx context.Context) {
defer r.peerUpdates.Close()
for {
select {
case <-ctx.Done():
return
case peerUpdate := <-r.peerUpdates.Updates():
r.processPeerUpdate(peerUpdate)
case <-r.closeCh:
r.Logger.Debug("stopped listening on peer updates channel; closing...")
return
}
}
}
// handlePexMessage handles envelopes sent from peers on the PexChannel.
func (r *Reactor) handlePexMessage(envelope p2p.Envelope) error {
logger := r.Logger.With("peer", envelope.From)
switch msg := envelope.Message.(type) {
case *protop2p.PexRequest:
// check if the peer hasn't sent a prior request too close to this one
// in time
if err := r.markPeerRequest(envelope.From); err != nil {
return err
}
// request peers from the peer manager and parse the NodeAddresses into
// URL strings
nodeAddresses := r.peerManager.Advertise(envelope.From, maxAddresses)
pexAddresses := make([]protop2p.PexAddress, len(nodeAddresses))
for idx, addr := range nodeAddresses {
pexAddresses[idx] = protop2p.PexAddress{
URL: addr.String(),
}
}
r.pexCh.Out <- p2p.Envelope{
To: envelope.From,
Message: &protop2p.PexResponse{Addresses: pexAddresses},
}
case *protop2p.PexResponse:
// check if the response matches a request that was made to that peer
if err := r.markPeerResponse(envelope.From); err != nil {
return err
}
// check the size of the response
if len(msg.Addresses) > int(maxAddresses) {
return fmt.Errorf("peer sent too many addresses (max: %d, got: %d)",
maxAddresses,
len(msg.Addresses),
)
}
for _, pexAddress := range msg.Addresses {
peerAddress, err := p2p.ParseNodeAddress(pexAddress.URL)
if err != nil {
continue
}
added, err := r.peerManager.Add(peerAddress)
if err != nil {
logger.Error("failed to add PEX address", "address", peerAddress, "err", err)
}
if added {
r.newPeers++
logger.Debug("added PEX address", "address", peerAddress)
}
r.totalPeers++
}
default:
return fmt.Errorf("received unknown message: %T", msg)
}
return nil
}
// handleMessage handles an Envelope sent from a peer on a specific p2p Channel.
// It will handle errors and any possible panics gracefully. A caller can handle
// any error returned by sending a PeerError on the respective channel.
func (r *Reactor) handleMessage(chID p2p.ChannelID, envelope p2p.Envelope) (err error) {
defer func() {
if e := recover(); e != nil {
err = fmt.Errorf("panic in processing message: %v", e)
r.Logger.Error(
"recovering from processing message panic",
"err", err,
"stack", string(debug.Stack()),
)
}
}()
r.Logger.Debug("received PEX message", "peer", envelope.From)
switch chID {
case p2p.ChannelID(PexChannel):
err = r.handlePexMessage(envelope)
default:
err = fmt.Errorf("unknown channel ID (%d) for envelope (%v)", chID, envelope)
}
return err
}
// processPeerUpdate processes a PeerUpdate. For added peers, PeerStatusUp, we
// send a request for addresses.
func (r *Reactor) processPeerUpdate(peerUpdate p2p.PeerUpdate) {
r.Logger.Debug("received PEX peer update", "peer", peerUpdate.NodeID, "status", peerUpdate.Status)
r.mtx.Lock()
defer r.mtx.Unlock()
switch peerUpdate.Status {
case p2p.PeerStatusUp:
r.availablePeers[peerUpdate.NodeID] = struct{}{}
case p2p.PeerStatusDown:
delete(r.availablePeers, peerUpdate.NodeID)
delete(r.requestsSent, peerUpdate.NodeID)
delete(r.lastReceivedRequests, peerUpdate.NodeID)
default:
}
}
// sendRequestForPeers pops the first peerID off the list and sends the
// peer a request for more peer addresses. The function then moves the
// peer into the requestsSent bucket and calculates when the next request
// time should be
func (r *Reactor) sendRequestForPeers() {
r.mtx.Lock()
defer r.mtx.Unlock()
if len(r.availablePeers) == 0 {
// no peers are available
r.Logger.Debug("no available peers to send request to, waiting...")
r.nextRequestTime = time.Now().Add(noAvailablePeersWaitPeriod)
return
}
var peerID types.NodeID
// use range to get a random peer.
for peerID = range r.availablePeers {
break
}
// send out the pex request
r.pexCh.Out <- p2p.Envelope{
To: peerID,
Message: &protop2p.PexRequest{},
}
// remove the peer from the abvailable peers list and mark it in the requestsSent map
delete(r.availablePeers, peerID)
r.requestsSent[peerID] = struct{}{}
r.calculateNextRequestTime()
r.Logger.Debug("peer request sent", "next_request_time", r.nextRequestTime)
}
// calculateNextRequestTime implements something of a proportional controller
// to estimate how often the reactor should be requesting new peer addresses.
// The dependent variable in this calculation is the ratio of new peers to
// all peers that the reactor receives. The interval is thus calculated as the
// inverse squared. In the beginning, all peers should be new peers.
// We expect this ratio to be near 1 and thus the interval to be as short
// as possible. As the node becomes more familiar with the network the ratio of
// new nodes will plummet to a very small number, meaning the interval expands
// to its upper bound.
// CONTRACT: Must use a write lock as nextRequestTime is updated
func (r *Reactor) calculateNextRequestTime() {
// check if the peer store is full. If so then there is no need
// to send peer requests too often
if ratio := r.peerManager.PeerRatio(); ratio >= 0.95 {
r.Logger.Debug("peer manager near full ratio, sleeping...",
"sleep_period", fullCapacityInterval, "ratio", ratio)
r.nextRequestTime = time.Now().Add(fullCapacityInterval)
return
}
// baseTime represents the shortest interval that we can send peer requests
// in. For example if we have 10 peers and we can't send a message to the
// same peer every 500ms, then we can send a request every 50ms. In practice
// we use a safety margin of 2, ergo 100ms
peers := tmmath.MinInt(len(r.availablePeers), 50)
baseTime := minReceiveRequestInterval
if peers > 0 {
baseTime = minReceiveRequestInterval * 2 / time.Duration(peers)
}
if r.totalPeers > 0 || r.discoveryRatio == 0 {
// find the ratio of new peers. NOTE: We add 1 to both sides to avoid
// divide by zero problems
ratio := float32(r.totalPeers+1) / float32(r.newPeers+1)
// square the ratio in order to get non linear time intervals
// NOTE: The longest possible interval for a network with 100 or more peers
// where a node is connected to 50 of them is 2 minutes.
r.discoveryRatio = ratio * ratio
r.newPeers = 0
r.totalPeers = 0
}
// NOTE: As ratio is always >= 1, discovery ratio is >= 1. Therefore we don't need to worry
// about the next request time being less than the minimum time
r.nextRequestTime = time.Now().Add(baseTime * time.Duration(r.discoveryRatio))
}
func (r *Reactor) markPeerRequest(peer types.NodeID) error {
r.mtx.Lock()
defer r.mtx.Unlock()
if lastRequestTime, ok := r.lastReceivedRequests[peer]; ok {
if time.Now().Before(lastRequestTime.Add(minReceiveRequestInterval)) {
return fmt.Errorf("peer sent a request too close after a prior one. Minimum interval: %v",
minReceiveRequestInterval)
}
}
r.lastReceivedRequests[peer] = time.Now()
return nil
}
func (r *Reactor) markPeerResponse(peer types.NodeID) error {
r.mtx.Lock()
defer r.mtx.Unlock()
// check if a request to this peer was sent
if _, ok := r.requestsSent[peer]; !ok {
return fmt.Errorf("peer sent a PEX response when none was requested (%v)", peer)
}
delete(r.requestsSent, peer)
// attach to the back of the list so that the peer can be used again for
// future requests
r.availablePeers[peer] = struct{}{}
return nil
}