125 lines
2.5 KiB
Go
125 lines
2.5 KiB
Go
package multicast
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import (
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"context"
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"net"
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"time"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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"github.com/google/gopacket/pcap"
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)
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type JoinLeaveHandler func(sourceIP, groupIP net.IP, join bool)
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type Listener struct {
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iface *net.Interface
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handle *pcap.Handle
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joinHandler JoinLeaveHandler
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}
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func NewListener(iface *net.Interface, joinHandler JoinLeaveHandler) (*Listener, error) {
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handle, err := pcap.OpenLive(iface.Name, 65536, true, 5*time.Second)
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if err != nil {
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return nil, err
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}
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if err := handle.SetBPFFilter("igmp"); err != nil {
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handle.Close()
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return nil, err
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}
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return &Listener{
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iface: iface,
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handle: handle,
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joinHandler: joinHandler,
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}, nil
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}
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func (l *Listener) Run(ctx context.Context) {
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defer l.handle.Close()
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packetSource := gopacket.NewPacketSource(l.handle, l.handle.LinkType())
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packets := packetSource.Packets()
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for {
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select {
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case <-ctx.Done():
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return
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case packet, ok := <-packets:
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if !ok {
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return
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}
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l.handlePacket(packet)
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}
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}
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}
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func (l *Listener) Close() {
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l.handle.Close()
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}
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func (l *Listener) handlePacket(packet gopacket.Packet) {
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ipLayer := packet.Layer(layers.LayerTypeIPv4)
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if ipLayer == nil {
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return
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}
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ip := ipLayer.(*layers.IPv4)
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sourceIP := ip.SrcIP
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igmpLayer := packet.Layer(layers.LayerTypeIGMP)
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if igmpLayer == nil {
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return
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}
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switch igmp := igmpLayer.(type) {
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case *layers.IGMPv1or2:
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l.handleIGMPv1or2(sourceIP, igmp)
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case *layers.IGMP:
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l.handleIGMPv3(sourceIP, igmp)
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}
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}
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func (l *Listener) handleIGMPv1or2(sourceIP net.IP, igmp *layers.IGMPv1or2) {
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switch igmp.Type {
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case layers.IGMPMembershipReportV1, layers.IGMPMembershipReportV2:
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groupIP := igmp.GroupAddress
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if !groupIP.IsMulticast() || groupIP.IsLinkLocalMulticast() {
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return
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}
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if l.joinHandler != nil {
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l.joinHandler(sourceIP, groupIP, true)
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}
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case layers.IGMPLeaveGroup:
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groupIP := igmp.GroupAddress
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if l.joinHandler != nil {
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l.joinHandler(sourceIP, groupIP, false)
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}
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}
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}
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func (l *Listener) handleIGMPv3(sourceIP net.IP, igmp *layers.IGMP) {
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if igmp.Type != layers.IGMPMembershipReportV3 {
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return
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}
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for _, record := range igmp.GroupRecords {
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groupIP := record.MulticastAddress
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if !groupIP.IsMulticast() || groupIP.IsLinkLocalMulticast() {
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continue
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}
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switch record.Type {
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case layers.IGMPIsEx, layers.IGMPToEx, layers.IGMPIsIn, layers.IGMPToIn:
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if l.joinHandler != nil {
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l.joinHandler(sourceIP, groupIP, true)
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}
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case layers.IGMPBlock:
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if l.joinHandler != nil {
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l.joinHandler(sourceIP, groupIP, false)
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}
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}
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}
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}
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