Alexey Khit
142 lines
2.5 KiB
Go
142 lines
2.5 KiB
Go
package mdns
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import (
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"fmt"
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"github.com/miekg/dns"
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"net"
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"strings"
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"time"
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)
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const ServiceHAP = "_hap._tcp.local." // HomeKit Accessory Protocol
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const requestTimeout = time.Millisecond * 505
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const responseTimeout = time.Second * 2
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type ServiceEntry struct {
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Name string
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IP net.IP
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Port uint16
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Info map[string]string
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}
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func (e *ServiceEntry) Complete() bool {
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return e.IP != nil && e.Port > 0 && e.Info != nil
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}
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func (e *ServiceEntry) Addr() string {
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return fmt.Sprintf("%s:%d", e.IP, e.Port)
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}
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func Discovery(service string, onentry func(*ServiceEntry) bool) error {
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addr := &net.UDPAddr{
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IP: net.IP{224, 0, 0, 251},
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Port: 5353,
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}
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conn, err := net.ListenMulticastUDP("udp4", nil, addr)
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if err != nil {
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return err
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}
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defer conn.Close()
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if err = conn.SetDeadline(time.Now().Add(responseTimeout)); err != nil {
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return err
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}
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msg := &dns.Msg{
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Question: []dns.Question{
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{service, dns.TypePTR, dns.ClassINET},
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},
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}
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b1, err := msg.Pack()
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if err != nil {
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return err
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}
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go func() {
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for {
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if _, err := conn.WriteToUDP(b1, addr); err != nil {
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return
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}
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time.Sleep(requestTimeout)
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}
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}()
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var skipPTR []string
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b2 := make([]byte, 1500)
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loop:
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for {
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// in the Hass docker network can receive same msg from different address
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n, _, err := conn.ReadFromUDP(b2)
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if err != nil {
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break
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}
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if err = msg.Unpack(b2[:n]); err != nil {
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continue
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}
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ptr := GetPTR(msg)
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if !strings.HasSuffix(ptr, service) {
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continue
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}
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for _, s := range skipPTR {
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if s == ptr {
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continue loop
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}
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}
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if entry := NewServiceEntry(msg); onentry(entry) {
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break
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}
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skipPTR = append(skipPTR, ptr)
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}
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return nil
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}
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func GetPTR(msg *dns.Msg) string {
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for _, rr := range msg.Answer {
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if rr, ok := rr.(*dns.PTR); ok {
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return rr.Ptr
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}
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}
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return ""
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}
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func NewServiceEntry(msg *dns.Msg) *ServiceEntry {
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entry := &ServiceEntry{}
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records := make([]dns.RR, 0, len(msg.Answer)+len(msg.Ns)+len(msg.Extra))
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records = append(records, msg.Answer...)
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records = append(records, msg.Ns...)
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records = append(records, msg.Extra...)
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for _, record := range records {
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switch record := record.(type) {
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case *dns.PTR:
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if i := strings.IndexByte(record.Ptr, '.'); i > 0 {
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entry.Name = record.Ptr[:i]
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}
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case *dns.A:
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entry.IP = record.A
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case *dns.SRV:
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entry.Port = record.Port
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case *dns.TXT:
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entry.Info = make(map[string]string, len(record.Txt))
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for _, txt := range record.Txt {
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k, v, _ := strings.Cut(txt, "=")
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entry.Info[k] = v
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}
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}
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}
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return entry
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}
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