135 lines
2.8 KiB
Go
135 lines
2.8 KiB
Go
package weavedns
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import (
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"github.com/miekg/dns"
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"log"
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"net"
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"sync"
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)
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// Portions of this code taken from github.com/armon/mdns
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const (
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ipv4mdns = "224.0.0.251" // link-local multicast address
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mdnsPort = 5353 // mDNS assigned port
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)
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var (
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ipv4Addr = &net.UDPAddr{
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IP: net.ParseIP(ipv4mdns),
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Port: mdnsPort,
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}
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)
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type ResponseA struct {
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Name string
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Addr net.IP
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}
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type responseInfo struct {
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ch chan<- *ResponseA
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}
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// Represents one query that we have sent for one name.
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// If we, internally, get several requests for the same name while we have
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// a query in flight, then we don't want to send more queries out.
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type inflightQuery struct {
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name string
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Id uint16 // the DNS message ID
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responseInfos []*responseInfo
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// add timeout here ?
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}
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type MDNSClient struct {
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sync.RWMutex
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conn *net.UDPConn
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addr *net.UDPAddr
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inflight map[string]*inflightQuery
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}
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func NewMDNSClient() (*MDNSClient, error) {
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conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
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if err != nil {
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log.Println(err)
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return nil, err
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}
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retval := &MDNSClient{
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conn: conn,
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addr: ipv4Addr,
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inflight: make(map[string]*inflightQuery)}
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return retval, nil
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}
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func LinkLocalMulticastListener() (net.PacketConn, error) {
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conn, err := net.ListenMulticastUDP("udp", nil, ipv4Addr)
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return conn, err
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}
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func (c *MDNSClient) SendQuery(name string, querytype uint16, responseCh chan<- *ResponseA) error {
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m := new(dns.Msg)
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m.SetQuestion(name, querytype)
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m.RecursionDesired = false
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c.Lock()
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query, found := c.inflight[name]
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if !found {
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query = &inflightQuery{name: name, Id: m.Id}
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c.inflight[name] = query
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}
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info := &responseInfo{ch: responseCh}
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query.responseInfos = append(query.responseInfos, info)
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c.Unlock()
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buf, err := m.Pack()
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if err != nil {
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return err
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}
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_, err = c.conn.WriteTo(buf, c.addr)
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return err
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}
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func (c *MDNSClient) SendResponse(m *dns.Msg) error {
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buf, err := m.Pack()
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if err != nil {
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return err
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}
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_, err = c.conn.WriteTo(buf, c.addr)
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return err
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}
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func (c *MDNSClient) IsInflightQuery(m *dns.Msg) bool {
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if len(m.Question) == 1 {
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q := m.Question[0]
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if q.Qtype == dns.TypeA {
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c.Lock()
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defer c.Unlock()
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if query, found := c.inflight[q.Name]; found {
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if query.Id == m.Id {
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return true
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}
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}
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}
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}
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return false
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}
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func (c *MDNSClient) HandleResponse(r *dns.Msg) {
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for _, answer := range r.Answer {
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switch rr := answer.(type) {
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case *dns.A:
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c.Lock()
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if query, found := c.inflight[rr.Hdr.Name]; found {
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for _, resp := range query.responseInfos {
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resp.ch <- &ResponseA{Name: rr.Hdr.Name, Addr: rr.A}
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}
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// To be simple for now, assume this is the only response coming
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delete(c.inflight, rr.Hdr.Name)
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} else {
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// We've received a response that didn't match a query
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// Do we want to cache it?
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}
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c.Unlock()
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}
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}
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}
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