ceremonyclient/go-libp2p/p2p/discovery/backoff/backoffcache.go

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2023-08-21 03:50:38 +00:00
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()
}
// withClock lets you override the default time.Now() call. Useful for tests.
func withClock(c clock) BackoffDiscoveryOption {
return func(b *BackoffDiscovery) error {
b.clock = c
return nil
}
}
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
}