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|
package peerdiscovery
import (
"net"
"sync"
"time"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
)
const (
// https://en.wikipedia.org/wiki/User_Datagram_Protocol#Packet_structure
maxDatagramSize = 66507
)
// PeerState is the state of a peer that has been discovered.
// It contains the address of the peer, the last time it was seen,
// the last payload it sent, and the metadata associated with it.
// To update the metadata, assign your own metadata to the Metadata.Data field.
// The metadata is not protected by a mutex, so you must do this yourself.
type PeerState struct {
Address string
lastSeen time.Time
lastPayload []byte
metadata *Metadata
}
type LostPeer struct {
Address string
LastSeen time.Time
LastPayload []byte
Metadata *Metadata
}
func (p *PeerDiscovery) gc() {
ticker := time.NewTicker(p.settings.Delay * 2)
defer ticker.Stop()
for range ticker.C {
p.Lock()
for ip, peerState := range p.received {
if time.Since(peerState.lastSeen) > p.settings.Delay*4 {
if p.settings.NotifyLost != nil {
p.settings.NotifyLost(LostPeer{
Address: ip,
LastSeen: peerState.lastSeen,
LastPayload: peerState.lastPayload,
Metadata: peerState.metadata,
})
}
delete(p.received, ip)
}
}
p.Unlock()
}
}
// PeerDiscovery is the object that can do the discovery for finding LAN peers.
type PeerDiscovery struct {
settings Settings
received map[string]*PeerState
sync.RWMutex
exit bool
}
func (p *PeerDiscovery) Shutdown() {
p.exit = true
}
func (p *PeerDiscovery) ActivePeers() (peers []*PeerState) {
p.RLock()
defer p.RUnlock()
for _, peerState := range p.received {
peers = append(peers, peerState)
}
return
}
// Listen binds to the UDP address and port given and writes packets received
// from that address to a buffer which is passed to a hander
func (p *PeerDiscovery) listen(c net.PacketConn) (recievedBytes []byte, err error) {
p.RLock()
portNum := p.settings.portNum
allowSelf := p.settings.AllowSelf
timeLimit := p.settings.TimeLimit
notify := p.settings.Notify
p.RUnlock()
localIPs := getLocalIPs()
// get interfaces
ifaces, err := net.Interfaces()
if err != nil {
return nil, err
}
// log.Println(ifaces)
group := p.settings.multicastAddressNumbers
var p2 NetPacketConn
if p.settings.IPVersion == IPv4 {
p2 = PacketConn4{ipv4.NewPacketConn(c)}
} else {
p2 = PacketConn6{ipv6.NewPacketConn(c)}
}
for i := range ifaces {
p2.JoinGroup(&ifaces[i], &net.UDPAddr{IP: group, Port: portNum})
}
start := time.Now()
// Loop forever reading from the socket
for {
buffer := make([]byte, maxDatagramSize)
var (
n int
src net.Addr
errRead error
)
n, src, errRead = p2.ReadFrom(buffer)
if errRead != nil {
err = errRead
return
}
srcHost, _, _ := net.SplitHostPort(src.String())
if _, ok := localIPs[srcHost]; ok && !allowSelf {
continue
}
// log.Println(src, hex.Dump(buffer[:n]))
p.Lock()
if peer, ok := p.received[srcHost]; ok {
peer.lastSeen = time.Now()
peer.lastPayload = buffer[:n]
} else {
p.received[srcHost] = &PeerState{
Address: srcHost,
lastPayload: buffer[:n],
lastSeen: time.Now(),
metadata: &Metadata{},
}
}
p.Unlock()
if notify != nil {
notify(Discovered{
Address: srcHost,
Payload: buffer[:n],
})
}
p.RLock()
if len(p.received) >= p.settings.Limit && p.settings.Limit > 0 {
p.RUnlock()
break
}
if p.exit || timeLimit > 0 && time.Since(start) > timeLimit {
p.RUnlock()
break
}
p.RUnlock()
}
return
}
|
