package backoff import ( "context" "fmt" "sync" "time" "github.com/libp2p/go-libp2p/core/discovery" "github.com/libp2p/go-libp2p/core/peer" ma "github.com/multiformats/go-multiaddr" ) // BackoffDiscovery is an implementation of discovery that caches peer data and attenuates repeated queries type BackoffDiscovery struct { disc discovery.Discovery stratFactory BackoffFactory peerCache map[string]*backoffCache peerCacheMux sync.RWMutex parallelBufSz int returnedBufSz int clock clock } type BackoffDiscoveryOption func(*BackoffDiscovery) error func NewBackoffDiscovery(disc discovery.Discovery, stratFactory BackoffFactory, opts ...BackoffDiscoveryOption) (discovery.Discovery, error) { b := &BackoffDiscovery{ disc: disc, stratFactory: stratFactory, peerCache: make(map[string]*backoffCache), parallelBufSz: 32, returnedBufSz: 32, clock: realClock{}, } for _, opt := range opts { if err := opt(b); err != nil { return nil, err } } return b, nil } // WithBackoffDiscoverySimultaneousQueryBufferSize sets the buffer size for the channels between the main FindPeers query // for a given namespace and all simultaneous FindPeers queries for the namespace func WithBackoffDiscoverySimultaneousQueryBufferSize(size int) BackoffDiscoveryOption { return func(b *BackoffDiscovery) error { if size < 0 { return fmt.Errorf("cannot set size to be smaller than 0") } b.parallelBufSz = size return nil } } // WithBackoffDiscoveryReturnedChannelSize sets the size of the buffer to be used during a FindPeer query. // Note: This does not apply if the query occurs during the backoff time func WithBackoffDiscoveryReturnedChannelSize(size int) BackoffDiscoveryOption { return func(b *BackoffDiscovery) error { if size < 0 { return fmt.Errorf("cannot set size to be smaller than 0") } b.returnedBufSz = size return nil } } type clock interface { Now() time.Time } type realClock struct{} func (c realClock) Now() time.Time { return time.Now() } type backoffCache struct { // strat is assigned on creation and not written to strat BackoffStrategy mux sync.Mutex // guards writes to all following fields nextDiscover time.Time prevPeers map[peer.ID]peer.AddrInfo peers map[peer.ID]peer.AddrInfo sendingChs map[chan peer.AddrInfo]int ongoing bool clock clock } func (d *BackoffDiscovery) Advertise(ctx context.Context, ns string, opts ...discovery.Option) (time.Duration, error) { return d.disc.Advertise(ctx, ns, opts...) } func (d *BackoffDiscovery) FindPeers(ctx context.Context, ns string, opts ...discovery.Option) (<-chan peer.AddrInfo, error) { // Get options var options discovery.Options err := options.Apply(opts...) if err != nil { return nil, err } // Get cached peers d.peerCacheMux.RLock() c, ok := d.peerCache[ns] d.peerCacheMux.RUnlock() /* Overall plan: If it's time to look for peers, look for peers, then return them If it's not time then return cache If it's time to look for peers, but we have already started looking. Get up to speed with ongoing request */ // Setup cache if we don't have one yet if !ok { pc := &backoffCache{ nextDiscover: time.Time{}, prevPeers: make(map[peer.ID]peer.AddrInfo), peers: make(map[peer.ID]peer.AddrInfo), sendingChs: make(map[chan peer.AddrInfo]int), strat: d.stratFactory(), clock: d.clock, } d.peerCacheMux.Lock() c, ok = d.peerCache[ns] if !ok { d.peerCache[ns] = pc c = pc } d.peerCacheMux.Unlock() } c.mux.Lock() defer c.mux.Unlock() timeExpired := d.clock.Now().After(c.nextDiscover) // If it's not yet time to search again and no searches are in progress then return cached peers if !(timeExpired || c.ongoing) { chLen := options.Limit if chLen == 0 { chLen = len(c.prevPeers) } else if chLen > len(c.prevPeers) { chLen = len(c.prevPeers) } pch := make(chan peer.AddrInfo, chLen) for _, ai := range c.prevPeers { select { case pch <- ai: default: // skip if we have asked for a lower limit than the number of peers known } } close(pch) return pch, nil } // If a request is not already in progress setup a dispatcher channel for dispatching incoming peers if !c.ongoing { pch, err := d.disc.FindPeers(ctx, ns, opts...) if err != nil { return nil, err } c.ongoing = true go findPeerDispatcher(ctx, c, pch) } // Setup receiver channel for receiving peers from ongoing requests evtCh := make(chan peer.AddrInfo, d.parallelBufSz) pch := make(chan peer.AddrInfo, d.returnedBufSz) rcvPeers := make([]peer.AddrInfo, 0, 32) for _, ai := range c.peers { rcvPeers = append(rcvPeers, ai) } c.sendingChs[evtCh] = options.Limit go findPeerReceiver(ctx, pch, evtCh, rcvPeers) return pch, nil } func findPeerDispatcher(ctx context.Context, c *backoffCache, pch <-chan peer.AddrInfo) { defer func() { c.mux.Lock() // If the peer addresses have changed reset the backoff if checkUpdates(c.prevPeers, c.peers) { c.strat.Reset() c.prevPeers = c.peers } c.nextDiscover = c.clock.Now().Add(c.strat.Delay()) c.ongoing = false c.peers = make(map[peer.ID]peer.AddrInfo) for ch := range c.sendingChs { close(ch) } c.sendingChs = make(map[chan peer.AddrInfo]int) c.mux.Unlock() }() for { select { case ai, ok := <-pch: if !ok { return } c.mux.Lock() // If we receive the same peer multiple times return the address union var sendAi peer.AddrInfo if prevAi, ok := c.peers[ai.ID]; ok { if combinedAi := mergeAddrInfos(prevAi, ai); combinedAi != nil { sendAi = *combinedAi } else { c.mux.Unlock() continue } } else { sendAi = ai } c.peers[ai.ID] = sendAi for ch, rem := range c.sendingChs { if rem > 0 { ch <- sendAi c.sendingChs[ch] = rem - 1 } } c.mux.Unlock() case <-ctx.Done(): return } } } func findPeerReceiver(ctx context.Context, pch, evtCh chan peer.AddrInfo, rcvPeers []peer.AddrInfo) { defer close(pch) for { select { case ai, ok := <-evtCh: if ok { rcvPeers = append(rcvPeers, ai) sentAll := true sendPeers: for i, p := range rcvPeers { select { case pch <- p: default: rcvPeers = rcvPeers[i:] sentAll = false break sendPeers } } if sentAll { rcvPeers = []peer.AddrInfo{} } } else { for _, p := range rcvPeers { select { case pch <- p: case <-ctx.Done(): return } } return } case <-ctx.Done(): return } } } func mergeAddrInfos(prevAi, newAi peer.AddrInfo) *peer.AddrInfo { seen := make(map[string]struct{}, len(prevAi.Addrs)) combinedAddrs := make([]ma.Multiaddr, 0, len(prevAi.Addrs)) addAddrs := func(addrs []ma.Multiaddr) { for _, addr := range addrs { if _, ok := seen[addr.String()]; ok { continue } seen[addr.String()] = struct{}{} combinedAddrs = append(combinedAddrs, addr) } } addAddrs(prevAi.Addrs) addAddrs(newAi.Addrs) if len(combinedAddrs) > len(prevAi.Addrs) { combinedAi := &peer.AddrInfo{ID: prevAi.ID, Addrs: combinedAddrs} return combinedAi } return nil } func checkUpdates(orig, update map[peer.ID]peer.AddrInfo) bool { if len(orig) != len(update) { return true } for p, ai := range update { if prevAi, ok := orig[p]; ok { if combinedAi := mergeAddrInfos(prevAi, ai); combinedAi != nil { return true } } else { return true } } return false }