package pex import ( "fmt" "reflect" "sort" "sync" "time" "github.com/pkg/errors" amino "github.com/tendermint/go-amino" cmn "github.com/tendermint/tendermint/libs/common" "github.com/tendermint/tendermint/p2p" "github.com/tendermint/tendermint/p2p/conn" ) type Peer = p2p.Peer const ( // PexChannel is a channel for PEX messages PexChannel = byte(0x00) // over-estimate of max NetAddress size // hexID (40) + IP (16) + Port (2) + Name (100) ... // NOTE: dont use massive DNS name .. maxAddressSize = 256 // NOTE: amplificaiton factor! // small request results in up to maxMsgSize response maxMsgSize = maxAddressSize * maxGetSelection // ensure we have enough peers defaultEnsurePeersPeriod = 30 * time.Second // Seed/Crawler constants // We want seeds to only advertise good peers. Therefore they should wait at // least as long as we expect it to take for a peer to become good before // disconnecting. // see consensus/reactor.go: blocksToContributeToBecomeGoodPeer // 10000 blocks assuming 1s blocks ~ 2.7 hours. defaultSeedDisconnectWaitPeriod = 3 * time.Hour defaultCrawlPeerInterval = 2 * time.Minute // don't redial for this. TODO: back-off. what for? defaultCrawlPeersPeriod = 30 * time.Second // check some peers every this maxAttemptsToDial = 16 // ~ 35h in total (last attempt - 18h) // if node connects to seed, it does not have any trusted peers. // Especially in the beginning, node should have more trusted peers than // untrusted. biasToSelectNewPeers = 30 // 70 to select good peers ) // PEXReactor handles PEX (peer exchange) and ensures that an // adequate number of peers are connected to the switch. // // It uses `AddrBook` (address book) to store `NetAddress`es of the peers. // // ## Preventing abuse // // Only accept pexAddrsMsg from peers we sent a corresponding pexRequestMsg too. // Only accept one pexRequestMsg every ~defaultEnsurePeersPeriod. type PEXReactor struct { p2p.BaseReactor book AddrBook config *PEXReactorConfig ensurePeersPeriod time.Duration // TODO: should go in the config // maps to prevent abuse requestsSent *cmn.CMap // ID->struct{}: unanswered send requests lastReceivedRequests *cmn.CMap // ID->time.Time: last time peer requested from us seedAddrs []*p2p.NetAddress attemptsToDial sync.Map // address (string) -> {number of attempts (int), last time dialed (time.Time)} } func (r *PEXReactor) minReceiveRequestInterval() time.Duration { // NOTE: must be less than ensurePeersPeriod, otherwise we'll request // peers too quickly from others and they'll think we're bad! return r.ensurePeersPeriod / 3 } // PEXReactorConfig holds reactor specific configuration data. type PEXReactorConfig struct { // Seed/Crawler mode SeedMode bool // Seeds is a list of addresses reactor may use // if it can't connect to peers in the addrbook. Seeds []string } type _attemptsToDial struct { number int lastDialed time.Time } // NewPEXReactor creates new PEX reactor. func NewPEXReactor(b AddrBook, config *PEXReactorConfig) *PEXReactor { r := &PEXReactor{ book: b, config: config, ensurePeersPeriod: defaultEnsurePeersPeriod, requestsSent: cmn.NewCMap(), lastReceivedRequests: cmn.NewCMap(), } r.BaseReactor = *p2p.NewBaseReactor("PEXReactor", r) return r } // OnStart implements BaseService func (r *PEXReactor) OnStart() error { err := r.book.Start() if err != nil && err != cmn.ErrAlreadyStarted { return err } numOnline, seedAddrs, err := r.checkSeeds() if err != nil { return err } else if numOnline == 0 && r.book.Empty() { return errors.New("Address book is empty, and could not connect to any seed nodes") } r.seedAddrs = seedAddrs // Check if this node should run // in seed/crawler mode if r.config.SeedMode { go r.crawlPeersRoutine() } else { go r.ensurePeersRoutine() } return nil } // OnStop implements BaseService func (r *PEXReactor) OnStop() { r.book.Stop() } // GetChannels implements Reactor func (r *PEXReactor) GetChannels() []*conn.ChannelDescriptor { return []*conn.ChannelDescriptor{ { ID: PexChannel, Priority: 1, SendQueueCapacity: 10, }, } } // AddPeer implements Reactor by adding peer to the address book (if inbound) // or by requesting more addresses (if outbound). func (r *PEXReactor) AddPeer(p Peer) { if p.IsOutbound() { // For outbound peers, the address is already in the books - // either via DialPeersAsync or r.Receive. // Ask it for more peers if we need. if r.book.NeedMoreAddrs() { r.RequestAddrs(p) } } else { // inbound peer is its own source addr := p.NodeInfo().NetAddress() src := addr // add to book. dont RequestAddrs right away because // we don't trust inbound as much - let ensurePeersRoutine handle it. err := r.book.AddAddress(addr, src) r.logErrAddrBook(err) } } func (r *PEXReactor) logErrAddrBook(err error) { if err != nil { switch err.(type) { case ErrAddrBookNilAddr: r.Logger.Error("Failed to add new address", "err", err) default: // non-routable, self, full book, private, etc. r.Logger.Debug("Failed to add new address", "err", err) } } } // RemovePeer implements Reactor. func (r *PEXReactor) RemovePeer(p Peer, reason interface{}) { id := string(p.ID()) r.requestsSent.Delete(id) r.lastReceivedRequests.Delete(id) } // Receive implements Reactor by handling incoming PEX messages. func (r *PEXReactor) Receive(chID byte, src Peer, msgBytes []byte) { msg, err := decodeMsg(msgBytes) if err != nil { r.Logger.Error("Error decoding message", "src", src, "chId", chID, "msg", msg, "err", err, "bytes", msgBytes) r.Switch.StopPeerForError(src, err) return } r.Logger.Debug("Received message", "src", src, "chId", chID, "msg", msg) switch msg := msg.(type) { case *pexRequestMessage: // Check we're not receiving too many requests if err := r.receiveRequest(src); err != nil { r.Switch.StopPeerForError(src, err) return } // Seeds disconnect after sending a batch of addrs // NOTE: this is a prime candidate for amplification attacks // so it's important we // 1) restrict how frequently peers can request // 2) limit the output size if r.config.SeedMode { r.SendAddrs(src, r.book.GetSelectionWithBias(biasToSelectNewPeers)) r.Switch.StopPeerGracefully(src) } else { r.SendAddrs(src, r.book.GetSelection()) } case *pexAddrsMessage: // If we asked for addresses, add them to the book if err := r.ReceiveAddrs(msg.Addrs, src); err != nil { r.Switch.StopPeerForError(src, err) return } default: r.Logger.Error(fmt.Sprintf("Unknown message type %v", reflect.TypeOf(msg))) } } // enforces a minimum amount of time between requests func (r *PEXReactor) receiveRequest(src Peer) error { id := string(src.ID()) v := r.lastReceivedRequests.Get(id) if v == nil { // initialize with empty time lastReceived := time.Time{} r.lastReceivedRequests.Set(id, lastReceived) return nil } lastReceived := v.(time.Time) if lastReceived.Equal(time.Time{}) { // first time gets a free pass. then we start tracking the time lastReceived = time.Now() r.lastReceivedRequests.Set(id, lastReceived) return nil } now := time.Now() minInterval := r.minReceiveRequestInterval() if now.Sub(lastReceived) < minInterval { return fmt.Errorf("Peer (%v) sent next PEX request too soon. lastReceived: %v, now: %v, minInterval: %v. Disconnecting", src.ID(), lastReceived, now, minInterval, ) } r.lastReceivedRequests.Set(id, now) return nil } // RequestAddrs asks peer for more addresses if we do not already // have a request out for this peer. func (r *PEXReactor) RequestAddrs(p Peer) { r.Logger.Debug("Request addrs", "from", p) id := string(p.ID()) if r.requestsSent.Has(id) { return } r.requestsSent.Set(id, struct{}{}) p.Send(PexChannel, cdc.MustMarshalBinaryBare(&pexRequestMessage{})) } // ReceiveAddrs adds the given addrs to the addrbook if theres an open // request for this peer and deletes the open request. // If there's no open request for the src peer, it returns an error. func (r *PEXReactor) ReceiveAddrs(addrs []*p2p.NetAddress, src Peer) error { id := string(src.ID()) if !r.requestsSent.Has(id) { return cmn.NewError("Received unsolicited pexAddrsMessage") } r.requestsSent.Delete(id) srcAddr := src.NodeInfo().NetAddress() for _, netAddr := range addrs { // NOTE: GetSelection methods should never return nil addrs if netAddr == nil { return cmn.NewError("received nil addr") } err := r.book.AddAddress(netAddr, srcAddr) r.logErrAddrBook(err) // If this address came from a seed node, try to connect to it without waiting. for _, seedAddr := range r.seedAddrs { if seedAddr.Equals(srcAddr) { r.ensurePeers() } } } return nil } // SendAddrs sends addrs to the peer. func (r *PEXReactor) SendAddrs(p Peer, netAddrs []*p2p.NetAddress) { p.Send(PexChannel, cdc.MustMarshalBinaryBare(&pexAddrsMessage{Addrs: netAddrs})) } // SetEnsurePeersPeriod sets period to ensure peers connected. func (r *PEXReactor) SetEnsurePeersPeriod(d time.Duration) { r.ensurePeersPeriod = d } // Ensures that sufficient peers are connected. (continuous) func (r *PEXReactor) ensurePeersRoutine() { var ( seed = cmn.NewRand() jitter = seed.Int63n(r.ensurePeersPeriod.Nanoseconds()) ) // Randomize first round of communication to avoid thundering herd. // If no potential peers are present directly start connecting so we guarantee // swift setup with the help of configured seeds. if r.hasPotentialPeers() { time.Sleep(time.Duration(jitter)) } // fire once immediately. // ensures we dial the seeds right away if the book is empty r.ensurePeers() // fire periodically ticker := time.NewTicker(r.ensurePeersPeriod) for { select { case <-ticker.C: r.ensurePeers() case <-r.Quit(): ticker.Stop() return } } } // ensurePeers ensures that sufficient peers are connected. (once) // // heuristic that we haven't perfected yet, or, perhaps is manually edited by // the node operator. It should not be used to compute what addresses are // already connected or not. func (r *PEXReactor) ensurePeers() { var ( out, in, dial = r.Switch.NumPeers() numToDial = r.Switch.MaxNumOutboundPeers() - (out + dial) ) r.Logger.Info( "Ensure peers", "numOutPeers", out, "numInPeers", in, "numDialing", dial, "numToDial", numToDial, ) if numToDial <= 0 { return } // bias to prefer more vetted peers when we have fewer connections. // not perfect, but somewhate ensures that we prioritize connecting to more-vetted // NOTE: range here is [10, 90]. Too high ? newBias := cmn.MinInt(out, 8)*10 + 10 toDial := make(map[p2p.ID]*p2p.NetAddress) // Try maxAttempts times to pick numToDial addresses to dial maxAttempts := numToDial * 3 for i := 0; i < maxAttempts && len(toDial) < numToDial; i++ { try := r.book.PickAddress(newBias) if try == nil { continue } if _, selected := toDial[try.ID]; selected { continue } if r.Switch.IsDialingOrExistingAddress(try) { continue } // TODO: consider moving some checks from toDial into here // so we don't even consider dialing peers that we want to wait // before dialling again, or have dialed too many times already r.Logger.Info("Will dial address", "addr", try) toDial[try.ID] = try } // Dial picked addresses for _, addr := range toDial { go r.dialPeer(addr) } // If we need more addresses, pick a random peer and ask for more. if r.book.NeedMoreAddrs() { peers := r.Switch.Peers().List() peersCount := len(peers) if peersCount > 0 { peer := peers[cmn.RandInt()%peersCount] // nolint: gas r.Logger.Info("We need more addresses. Sending pexRequest to random peer", "peer", peer) r.RequestAddrs(peer) } } // If we are not connected to nor dialing anybody, fallback to dialing a seed. if out+in+dial+len(toDial) == 0 { r.Logger.Info("No addresses to dial nor connected peers. Falling back to seeds") r.dialSeeds() } } func (r *PEXReactor) dialAttemptsInfo(addr *p2p.NetAddress) (attempts int, lastDialed time.Time) { _attempts, ok := r.attemptsToDial.Load(addr.DialString()) if !ok { return } atd := _attempts.(_attemptsToDial) return atd.number, atd.lastDialed } func (r *PEXReactor) dialPeer(addr *p2p.NetAddress) { attempts, lastDialed := r.dialAttemptsInfo(addr) if attempts > maxAttemptsToDial { r.Logger.Error("Reached max attempts to dial", "addr", addr, "attempts", attempts) r.book.MarkBad(addr) return } // exponential backoff if it's not our first attempt to dial given address if attempts > 0 { jitterSeconds := time.Duration(cmn.RandFloat64() * float64(time.Second)) // 1s == (1e9 ns) backoffDuration := jitterSeconds + ((1 << uint(attempts)) * time.Second) sinceLastDialed := time.Since(lastDialed) if sinceLastDialed < backoffDuration { r.Logger.Debug("Too early to dial", "addr", addr, "backoff_duration", backoffDuration, "last_dialed", lastDialed, "time_since", sinceLastDialed) return } } err := r.Switch.DialPeerWithAddress(addr, false) if err != nil { r.Logger.Error("Dialing failed", "addr", addr, "err", err, "attempts", attempts) // TODO: detect more "bad peer" scenarios if _, ok := err.(p2p.ErrSwitchAuthenticationFailure); ok { r.book.MarkBad(addr) r.attemptsToDial.Delete(addr.DialString()) } else { r.book.MarkAttempt(addr) // FIXME: if the addr is going to be removed from the addrbook (hard to // tell at this point), we need to Delete it from attemptsToDial, not // record another attempt. // record attempt r.attemptsToDial.Store(addr.DialString(), _attemptsToDial{attempts + 1, time.Now()}) } } else { // cleanup any history r.attemptsToDial.Delete(addr.DialString()) } } // checkSeeds checks that addresses are well formed. // Returns number of seeds we can connect to, along with all seeds addrs. // return err if user provided any badly formatted seed addresses. // Doesn't error if the seed node can't be reached. // numOnline returns -1 if no seed nodes were in the initial configuration. func (r *PEXReactor) checkSeeds() (numOnline int, netAddrs []*p2p.NetAddress, err error) { lSeeds := len(r.config.Seeds) if lSeeds == 0 { return -1, nil, nil } netAddrs, errs := p2p.NewNetAddressStrings(r.config.Seeds) numOnline = lSeeds - len(errs) for _, err := range errs { switch e := err.(type) { case p2p.ErrNetAddressLookup: r.Logger.Error("Connecting to seed failed", "err", e) default: return 0, nil, errors.Wrap(e, "seed node configuration has error") } } return } // randomly dial seeds until we connect to one or exhaust them func (r *PEXReactor) dialSeeds() { perm := cmn.RandPerm(len(r.seedAddrs)) // perm := r.Switch.rng.Perm(lSeeds) for _, i := range perm { // dial a random seed seedAddr := r.seedAddrs[i] err := r.Switch.DialPeerWithAddress(seedAddr, false) if err == nil { return } r.Switch.Logger.Error("Error dialing seed", "err", err, "seed", seedAddr) } r.Switch.Logger.Error("Couldn't connect to any seeds") } // AttemptsToDial returns the number of attempts to dial specific address. It // returns 0 if never attempted or successfully connected. func (r *PEXReactor) AttemptsToDial(addr *p2p.NetAddress) int { lAttempts, attempted := r.attemptsToDial.Load(addr.DialString()) if attempted { return lAttempts.(_attemptsToDial).number } return 0 } //---------------------------------------------------------- // Explores the network searching for more peers. (continuous) // Seed/Crawler Mode causes this node to quickly disconnect // from peers, except other seed nodes. func (r *PEXReactor) crawlPeersRoutine() { // Do an initial crawl r.crawlPeers() // Fire periodically ticker := time.NewTicker(defaultCrawlPeersPeriod) for { select { case <-ticker.C: r.attemptDisconnects() r.crawlPeers() case <-r.Quit(): return } } } // hasPotentialPeers indicates if there is a potential peer to connect to, by // consulting the Switch as well as the AddrBook. func (r *PEXReactor) hasPotentialPeers() bool { out, in, dial := r.Switch.NumPeers() return out+in+dial > 0 && len(r.book.ListOfKnownAddresses()) > 0 } // crawlPeerInfo handles temporary data needed for the // network crawling performed during seed/crawler mode. type crawlPeerInfo struct { // The listening address of a potential peer we learned about Addr *p2p.NetAddress // The last time we attempt to reach this address LastAttempt time.Time // The last time we successfully reached this address LastSuccess time.Time } // oldestFirst implements sort.Interface for []crawlPeerInfo // based on the LastAttempt field. type oldestFirst []crawlPeerInfo func (of oldestFirst) Len() int { return len(of) } func (of oldestFirst) Swap(i, j int) { of[i], of[j] = of[j], of[i] } func (of oldestFirst) Less(i, j int) bool { return of[i].LastAttempt.Before(of[j].LastAttempt) } // getPeersToCrawl returns addresses of potential peers that we wish to validate. // NOTE: The status information is ordered as described above. func (r *PEXReactor) getPeersToCrawl() []crawlPeerInfo { var of oldestFirst // TODO: be more selective addrs := r.book.ListOfKnownAddresses() for _, addr := range addrs { if len(addr.ID()) == 0 { continue // dont use peers without id } of = append(of, crawlPeerInfo{ Addr: addr.Addr, LastAttempt: addr.LastAttempt, LastSuccess: addr.LastSuccess, }) } sort.Sort(of) return of } // crawlPeers will crawl the network looking for new peer addresses. (once) func (r *PEXReactor) crawlPeers() { peerInfos := r.getPeersToCrawl() now := time.Now() // Use addresses we know of to reach additional peers for _, pi := range peerInfos { // Do not attempt to connect with peers we recently dialed if now.Sub(pi.LastAttempt) < defaultCrawlPeerInterval { continue } // Otherwise, attempt to connect with the known address err := r.Switch.DialPeerWithAddress(pi.Addr, false) if err != nil { r.book.MarkAttempt(pi.Addr) continue } // Ask for more addresses peer := r.Switch.Peers().Get(pi.Addr.ID) if peer != nil { r.RequestAddrs(peer) } } } // attemptDisconnects checks if we've been with each peer long enough to disconnect func (r *PEXReactor) attemptDisconnects() { for _, peer := range r.Switch.Peers().List() { if peer.Status().Duration < defaultSeedDisconnectWaitPeriod { continue } if peer.IsPersistent() { continue } r.Switch.StopPeerGracefully(peer) } } //----------------------------------------------------------------------------- // Messages // PexMessage is a primary type for PEX messages. Underneath, it could contain // either pexRequestMessage, or pexAddrsMessage messages. type PexMessage interface{} func RegisterPexMessage(cdc *amino.Codec) { cdc.RegisterInterface((*PexMessage)(nil), nil) cdc.RegisterConcrete(&pexRequestMessage{}, "tendermint/p2p/PexRequestMessage", nil) cdc.RegisterConcrete(&pexAddrsMessage{}, "tendermint/p2p/PexAddrsMessage", nil) } func decodeMsg(bz []byte) (msg PexMessage, err error) { if len(bz) > maxMsgSize { return msg, fmt.Errorf("Msg exceeds max size (%d > %d)", len(bz), maxMsgSize) } err = cdc.UnmarshalBinaryBare(bz, &msg) return } /* A pexRequestMessage requests additional peer addresses. */ type pexRequestMessage struct { } func (m *pexRequestMessage) String() string { return "[pexRequest]" } /* A message with announced peer addresses. */ type pexAddrsMessage struct { Addrs []*p2p.NetAddress } func (m *pexAddrsMessage) String() string { return fmt.Sprintf("[pexAddrs %v]", m.Addrs) }