291 lines
6.8 KiB
Go
291 lines
6.8 KiB
Go
package nameserver
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import (
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"bytes"
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"fmt"
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"math"
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"net"
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"time"
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"github.com/miekg/dns"
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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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// We wait this long to hear a response from other mDNS servers on
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// the network.
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mDNSTimeout = 500 * time.Millisecond
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MaxDuration = time.Duration(math.MaxInt64)
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MailboxSize = 16
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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 Response struct {
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name string
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addr net.IP
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ttl int
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err error
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}
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func (r Response) Name() string { return r.name }
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func (r Response) IP() net.IP { return r.addr }
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func (r Response) Priority() int { return 0 }
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func (r Response) Weight() int { return 0 }
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func (r Response) TTL() int { return r.ttl }
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func (r Response) Equal(r2 *Response) bool {
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if r.name != r2.name {
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return false
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}
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if !r.addr.Equal(r2.addr) {
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return false
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}
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if r.err != r2.err {
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return false
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}
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return true
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}
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func (r Response) String() string {
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var buf bytes.Buffer
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if r.err != nil {
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fmt.Fprintf(&buf, "%s", r.err)
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} else {
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if len(r.Name()) > 0 {
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fmt.Fprintf(&buf, "%s", r.Name())
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}
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if !r.IP().IsUnspecified() {
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fmt.Fprintf(&buf, "[%s]", r.IP())
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}
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if r.ttl > 0 {
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fmt.Fprintf(&buf, "(TTL:%d)", r.TTL())
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}
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}
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return buf.String()
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}
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type responseInfo struct {
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timeout time.Time // if no answer by this time, give up
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insistent bool // insistent queries are not removed on the first reply
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ch chan<- *Response
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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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// Invariant on responseInfos: they are in ascending order of timeout.
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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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}
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type MDNSClient struct {
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// note unorthodox use of 'Server' class in client logic - using it to
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// listen on a multicast socket and call callback whenever a message comes in.
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listener *dns.Server
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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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actionChan chan<- MDNSAction
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}
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type mDNSQueryInfo struct {
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name string
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querytype uint16
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responseCh chan<- *Response
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}
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func NewMDNSClient() (*MDNSClient, error) {
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return &MDNSClient{
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addr: ipv4Addr,
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inflight: make(map[string]*inflightQuery)}, nil
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}
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func (c *MDNSClient) Start(ifi *net.Interface) (err error) {
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if c.conn, err = net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0}); err != nil {
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return err
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}
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multicast, err := LinkLocalMulticastListener(ifi)
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if err != nil {
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return err
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}
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handleMDNS := func(w dns.ResponseWriter, r *dns.Msg) {
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// Don't want to handle queries here, so filter anything out that isn't a response
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if len(r.Answer) > 0 {
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c.ResponseCallback(r)
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}
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}
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actionChan := make(chan MDNSAction, MailboxSize)
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c.actionChan = actionChan
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go c.actorLoop(actionChan)
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c.listener = &dns.Server{Unsafe: true, PacketConn: multicast, Handler: dns.HandlerFunc(handleMDNS)}
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go c.listener.ActivateAndServe()
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return nil
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}
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func (c *MDNSClient) Stop() error {
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c.actionChan <- nil
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return nil
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}
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func LinkLocalMulticastListener(ifi *net.Interface) (net.PacketConn, error) {
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return net.ListenMulticastUDP("udp", ifi, ipv4Addr)
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}
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// ACTOR client API
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type MDNSAction func()
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// Async
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func (c *MDNSClient) SendQuery(name string, querytype uint16, insistent bool, responseCh chan<- *Response) {
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c.actionChan <- func() {
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query, found := c.inflight[name]
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if !found {
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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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buf, err := m.Pack()
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if err != nil {
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responseCh <- &Response{err: err}
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close(responseCh)
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return
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}
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query = &inflightQuery{
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name: name,
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id: m.Id,
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}
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if _, err = c.conn.WriteTo(buf, c.addr); err != nil {
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responseCh <- &Response{err: err}
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close(responseCh)
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return
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}
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c.inflight[name] = query
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}
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info := &responseInfo{
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ch: responseCh,
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timeout: time.Now().Add(mDNSTimeout),
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insistent: insistent,
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}
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// Invariant on responseInfos: they are in ascending order of
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// timeout. Since we use a fixed interval from Now(), this
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// must be after all existing timeouts.
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query.responseInfos = append(query.responseInfos, info)
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}
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}
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// Async - called from dns library multiplexer
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func (c *MDNSClient) ResponseCallback(r *dns.Msg) {
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c.actionChan <- func() {
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for _, answer := range r.Answer {
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var name string
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var res *Response
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switch rr := answer.(type) {
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case *dns.A:
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name = rr.Hdr.Name
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res = &Response{name: name, addr: rr.A, ttl: int(rr.Hdr.Ttl)}
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case *dns.PTR:
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name = rr.Hdr.Name
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raddr, _ := raddrToIP(name)
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res = &Response{name: rr.Ptr, addr: raddr, ttl: int(rr.Hdr.Ttl)}
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default:
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return
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}
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if query, found := c.inflight[name]; found {
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var newResponseInfos []*responseInfo
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for _, resp := range query.responseInfos {
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resp.ch <- res
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// insistent queries are not removed on the first reply, but on the timeout
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if resp.insistent {
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newResponseInfos = append(newResponseInfos, resp)
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} else {
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close(resp.ch)
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}
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}
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if len(newResponseInfos) == 0 {
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delete(c.inflight, name)
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} else {
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query.responseInfos = newResponseInfos
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}
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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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}
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}
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}
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// ACTOR server
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// Check all in-flight queries, close all that have already timed out,
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// and return the duration until the next timeout
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func (c *MDNSClient) checkInFlightQueries() time.Duration {
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now := time.Now()
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after := MaxDuration
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for name, query := range c.inflight {
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// Invariant on responseInfos: they are in ascending order of timeout.
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numClosed := 0
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for _, item := range query.responseInfos {
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duration := item.timeout.Sub(now)
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if duration <= 0 { // timed out
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close(item.ch)
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numClosed++
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} else {
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if duration < after {
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after = duration
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}
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break // don't need to look at any more for this query
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}
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}
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// Remove timed-out items from the slice
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query.responseInfos = query.responseInfos[numClosed:]
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if len(query.responseInfos) == 0 {
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delete(c.inflight, name)
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}
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}
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return after
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}
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func (c *MDNSClient) actorLoop(actionChan <-chan MDNSAction) {
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timer := time.NewTimer(MaxDuration)
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run := func() { timer.Reset(c.checkInFlightQueries()) }
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loop:
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for {
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select {
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case action := <-actionChan:
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if action == nil {
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c.listener.Shutdown()
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break loop
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} else {
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action()
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run()
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}
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case <-timer.C:
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run()
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}
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}
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// Close all response channels at termination
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for _, query := range c.inflight {
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for _, item := range query.responseInfos {
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close(item.ch)
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}
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}
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}
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