package pex import ( "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() error { go r.processPexCh() go r.processPeerUpdates() 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() { defer r.pexCh.Close() for { select { case <-r.closeCh: r.Logger.Debug("stopped listening on PEX channel; closing...") return // outbound requests for new peers case <-r.waitUntilNextRequest(): 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() { defer r.peerUpdates.Close() for { select { 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: } } func (r *Reactor) waitUntilNextRequest() <-chan time.Time { return time.After(time.Until(r.nextRequestTime)) } // 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 }