Strip external use of mdns

go.mod

@@ -4,7 +4,6 @@ go 1.13
 
 require (
 	github.com/BurntSushi/toml v0.3.1
-	github.com/beevik/ntp v0.2.0
 	github.com/bitly/go-simplejson v0.5.0
 	github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869 // indirect
 	github.com/bwmarrin/discordgo v0.20.2
@@ -47,7 +46,6 @@ require (
 	github.com/lucas-clemente/quic-go v0.14.1
 	github.com/mholt/certmagic v0.9.3
 	github.com/micro/cli/v2 v2.1.2
-	github.com/micro/mdns v0.3.0
 	github.com/miekg/dns v1.1.27
 	github.com/mitchellh/hashstructure v1.0.0
 	github.com/nats-io/nats-server/v2 v2.1.6

go.sum

@@ -53,8 +53,6 @@ github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5 h1:0CwZNZbxp69SHPd
 github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5/go.mod h1:wHh0iHkYZB8zMSxRWpUBQtwG5a7fFgvEO+odwuTv2gs=
 github.com/aws/aws-sdk-go v1.23.0/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
 github.com/baiyubin/aliyun-sts-go-sdk v0.0.0-20180326062324-cfa1a18b161f/go.mod h1:AuiFmCCPBSrqvVMvuqFuk0qogytodnVFVSN5CeJB8Gc=
-github.com/beevik/ntp v0.2.0 h1:sGsd+kAXzT0bfVfzJfce04g+dSRfrs+tbQW8lweuYgw=
-github.com/beevik/ntp v0.2.0/go.mod h1:hIHWr+l3+/clUnF44zdK+CWW7fO8dR5cIylAQ76NRpg=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
@@ -290,9 +288,6 @@ github.com/mholt/certmagic v0.9.3 h1:RmzuNJ5mpFplDbyS41z+gGgE/py24IX6m0nHZ0yNTQU
 github.com/mholt/certmagic v0.9.3/go.mod h1:nu8jbsbtwK4205EDH/ZUMTKsfYpJA1Q7MKXHfgTihNw=
 github.com/micro/cli/v2 v2.1.2 h1:43J1lChg/rZCC1rvdqZNFSQDrGT7qfMrtp6/ztpIkEM=
 github.com/micro/cli/v2 v2.1.2/go.mod h1:EguNh6DAoWKm9nmk+k/Rg0H3lQnDxqzu5x5srOtGtYg=
-github.com/micro/mdns v0.3.0 h1:bYycYe+98AXR3s8Nq5qvt6C573uFTDPIYzJemWON0QE=
-github.com/micro/mdns v0.3.0/go.mod h1:KJ0dW7KmicXU2BV++qkLlmHYcVv7/hHnbtguSWt9Aoc=
-github.com/miekg/dns v1.1.3/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=
 github.com/miekg/dns v1.1.15/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=
 github.com/miekg/dns v1.1.27 h1:aEH/kqUzUxGJ/UHcEKdJY+ugH6WEzsEBBSPa8zuy1aM=
 github.com/miekg/dns v1.1.27/go.mod h1:KNUDUusw/aVsxyTYZM1oqvCicbwhgbNgztCETuNZ7xM=
@@ -314,7 +309,6 @@ github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRW
 github.com/namedotcom/go v0.0.0-20180403034216-08470befbe04/go.mod h1:5sN+Lt1CaY4wsPvgQH/jsuJi4XO2ssZbdsIizr4CVC8=
 github.com/nats-io/jwt v0.3.2 h1:+RB5hMpXUUA2dfxuhBTEkMOrYmM+gKIZYS1KjSostMI=
 github.com/nats-io/jwt v0.3.2/go.mod h1:/euKqTS1ZD+zzjYrY7pseZrTtWQSjujC7xjPc8wL6eU=
-github.com/nats-io/nats-server v1.4.1 h1:Ul1oSOGNV/L8kjr4v6l2f9Yet6WY+LevH1/7cRZ/qyA=
 github.com/nats-io/nats-server/v2 v2.1.6 h1:qAaHZaS8pRRNQLFaiBA1rq5WynyEGp9DFgmMfoaiXGY=
 github.com/nats-io/nats-server/v2 v2.1.6/go.mod h1:BL1NOtaBQ5/y97djERRVWNouMW7GT3gxnmbE/eC8u8A=
 github.com/nats-io/nats.go v1.9.2 h1:oDeERm3NcZVrPpdR/JpGdWHMv3oJ8yY30YwxKq+DU2s=
@@ -454,7 +448,6 @@ go.uber.org/zap v1.13.0/go.mod h1:zwrFLgMcdUuIBviXEYEH1YKNaOBnKXsx2IPda5bBwHM=
 golang.org/x/crypto v0.0.0-20180621125126-a49355c7e3f8/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20181030102418-4d3f4d9ffa16/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
-golang.org/x/crypto v0.0.0-20190130090550-b01c7a725664/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190219172222-a4c6cb3142f2/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
@@ -465,8 +458,6 @@ golang.org/x/crypto v0.0.0-20190701094942-4def268fd1a4/go.mod h1:yigFU9vqHzYiE8U
 golang.org/x/crypto v0.0.0-20190829043050-9756ffdc2472/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20190927123631-a832865fa7ad/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
-golang.org/x/crypto v0.0.0-20200221231518-2aa609cf4a9d h1:1ZiEyfaQIg3Qh0EoqpwAakHVhecoE5wlSg5GjnafJGw=
-golang.org/x/crypto v0.0.0-20200221231518-2aa609cf4a9d/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20200323165209-0ec3e9974c59 h1:3zb4D3T4G8jdExgVU/95+vQXfpEPiMdCaZgmGVxjNHM=
 golang.org/x/crypto v0.0.0-20200323165209-0ec3e9974c59/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
@@ -530,7 +521,6 @@ golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190129075346-302c3dd5f1cc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190209173611-3b5209105503/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190221075227-b4e8571b14e0/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

registry/mdns_registry.go

@@ -17,7 +17,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/micro/go-micro/v2/logger"
-	"github.com/micro/mdns"
+	"github.com/micro/go-micro/v2/util/mdns"
 )
 
 var (

registry/mdns_watcher.go

@@ -4,7 +4,7 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/micro/mdns"
+	"github.com/micro/go-micro/v2/util/mdns"
 )
 
 type mdnsWatcher struct {

util/mdns/.gitignore

@@ -0,0 +1,23 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test

util/mdns/client.go

@@ -0,0 +1,501 @@
+package mdns
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+// ServiceEntry is returned after we query for a service
+type ServiceEntry struct {
+	Name       string
+	Host       string
+	AddrV4     net.IP
+	AddrV6     net.IP
+	Port       int
+	Info       string
+	InfoFields []string
+	TTL        int
+	Type       uint16
+
+	Addr net.IP // @Deprecated
+
+	hasTXT bool
+	sent   bool
+}
+
+// complete is used to check if we have all the info we need
+func (s *ServiceEntry) complete() bool {
+	return (s.AddrV4 != nil || s.AddrV6 != nil || s.Addr != nil) && s.Port != 0 && s.hasTXT
+}
+
+// QueryParam is used to customize how a Lookup is performed
+type QueryParam struct {
+	Service             string               // Service to lookup
+	Domain              string               // Lookup domain, default "local"
+	Type                uint16               // Lookup type, defaults to dns.TypePTR
+	Context             context.Context      // Context
+	Timeout             time.Duration        // Lookup timeout, default 1 second. Ignored if Context is provided
+	Interface           *net.Interface       // Multicast interface to use
+	Entries             chan<- *ServiceEntry // Entries Channel
+	WantUnicastResponse bool                 // Unicast response desired, as per 5.4 in RFC
+}
+
+// DefaultParams is used to return a default set of QueryParam's
+func DefaultParams(service string) *QueryParam {
+	return &QueryParam{
+		Service:             service,
+		Domain:              "local",
+		Timeout:             time.Second,
+		Entries:             make(chan *ServiceEntry),
+		WantUnicastResponse: false, // TODO(reddaly): Change this default.
+	}
+}
+
+// Query looks up a given service, in a domain, waiting at most
+// for a timeout before finishing the query. The results are streamed
+// to a channel. Sends will not block, so clients should make sure to
+// either read or buffer.
+func Query(params *QueryParam) error {
+	// Create a new client
+	client, err := newClient()
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	// Set the multicast interface
+	if params.Interface != nil {
+		if err := client.setInterface(params.Interface, false); err != nil {
+			return err
+		}
+	}
+
+	// Ensure defaults are set
+	if params.Domain == "" {
+		params.Domain = "local"
+	}
+
+	if params.Context == nil {
+		if params.Timeout == 0 {
+			params.Timeout = time.Second
+		}
+		params.Context, _ = context.WithTimeout(context.Background(), params.Timeout)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Run the query
+	return client.query(params)
+}
+
+// Listen listens indefinitely for multicast updates
+func Listen(entries chan<- *ServiceEntry, exit chan struct{}) error {
+	// Create a new client
+	client, err := newClient()
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	client.setInterface(nil, true)
+
+	// Start listening for response packets
+	msgCh := make(chan *dns.Msg, 32)
+
+	go client.recv(client.ipv4UnicastConn, msgCh)
+	go client.recv(client.ipv6UnicastConn, msgCh)
+	go client.recv(client.ipv4MulticastConn, msgCh)
+	go client.recv(client.ipv6MulticastConn, msgCh)
+
+	ip := make(map[string]*ServiceEntry)
+
+	for {
+		select {
+		case <-exit:
+			return nil
+		case <-client.closedCh:
+			return nil
+		case m := <-msgCh:
+			e := messageToEntry(m, ip)
+			if e == nil {
+				continue
+			}
+
+			// Check if this entry is complete
+			if e.complete() {
+				if e.sent {
+					continue
+				}
+				e.sent = true
+				entries <- e
+				ip = make(map[string]*ServiceEntry)
+			} else {
+				// Fire off a node specific query
+				m := new(dns.Msg)
+				m.SetQuestion(e.Name, dns.TypePTR)
+				m.RecursionDesired = false
+				if err := client.sendQuery(m); err != nil {
+					log.Printf("[ERR] mdns: Failed to query instance %s: %v", e.Name, err)
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+// Lookup is the same as Query, however it uses all the default parameters
+func Lookup(service string, entries chan<- *ServiceEntry) error {
+	params := DefaultParams(service)
+	params.Entries = entries
+	return Query(params)
+}
+
+// Client provides a query interface that can be used to
+// search for service providers using mDNS
+type client struct {
+	ipv4UnicastConn *net.UDPConn
+	ipv6UnicastConn *net.UDPConn
+
+	ipv4MulticastConn *net.UDPConn
+	ipv6MulticastConn *net.UDPConn
+
+	closed    bool
+	closedCh  chan struct{} // TODO(reddaly): This doesn't appear to be used.
+	closeLock sync.Mutex
+}
+
+// NewClient creates a new mdns Client that can be used to query
+// for records
+func newClient() (*client, error) {
+	// TODO(reddaly): At least attempt to bind to the port required in the spec.
+	// Create a IPv4 listener
+	uconn4, err4 := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	uconn6, err6 := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err4 != nil && err6 != nil {
+		log.Printf("[ERR] mdns: Failed to bind to udp port: %v %v", err4, err6)
+	}
+
+	if uconn4 == nil && uconn6 == nil {
+		return nil, fmt.Errorf("failed to bind to any unicast udp port")
+	}
+
+	if uconn4 == nil {
+		uconn4 = &net.UDPConn{}
+	}
+
+	if uconn6 == nil {
+		uconn6 = &net.UDPConn{}
+	}
+
+	mconn4, err4 := net.ListenUDP("udp4", mdnsWildcardAddrIPv4)
+	mconn6, err6 := net.ListenUDP("udp6", mdnsWildcardAddrIPv6)
+	if err4 != nil && err6 != nil {
+		log.Printf("[ERR] mdns: Failed to bind to udp port: %v %v", err4, err6)
+	}
+
+	if mconn4 == nil && mconn6 == nil {
+		return nil, fmt.Errorf("failed to bind to any multicast udp port")
+	}
+
+	if mconn4 == nil {
+		mconn4 = &net.UDPConn{}
+	}
+
+	if mconn6 == nil {
+		mconn6 = &net.UDPConn{}
+	}
+
+	p1 := ipv4.NewPacketConn(mconn4)
+	p2 := ipv6.NewPacketConn(mconn6)
+	p1.SetMulticastLoopback(true)
+	p2.SetMulticastLoopback(true)
+
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	var errCount1, errCount2 int
+
+	for _, iface := range ifaces {
+		if err := p1.JoinGroup(&iface, &net.UDPAddr{IP: mdnsGroupIPv4}); err != nil {
+			errCount1++
+		}
+		if err := p2.JoinGroup(&iface, &net.UDPAddr{IP: mdnsGroupIPv6}); err != nil {
+			errCount2++
+		}
+	}
+
+	if len(ifaces) == errCount1 && len(ifaces) == errCount2 {
+		return nil, fmt.Errorf("Failed to join multicast group on all interfaces!")
+	}
+
+	c := &client{
+		ipv4MulticastConn: mconn4,
+		ipv6MulticastConn: mconn6,
+		ipv4UnicastConn:   uconn4,
+		ipv6UnicastConn:   uconn6,
+		closedCh:          make(chan struct{}),
+	}
+	return c, nil
+}
+
+// Close is used to cleanup the client
+func (c *client) Close() error {
+	c.closeLock.Lock()
+	defer c.closeLock.Unlock()
+
+	if c.closed {
+		return nil
+	}
+	c.closed = true
+
+	close(c.closedCh)
+
+	if c.ipv4UnicastConn != nil {
+		c.ipv4UnicastConn.Close()
+	}
+	if c.ipv6UnicastConn != nil {
+		c.ipv6UnicastConn.Close()
+	}
+	if c.ipv4MulticastConn != nil {
+		c.ipv4MulticastConn.Close()
+	}
+	if c.ipv6MulticastConn != nil {
+		c.ipv6MulticastConn.Close()
+	}
+
+	return nil
+}
+
+// setInterface is used to set the query interface, uses sytem
+// default if not provided
+func (c *client) setInterface(iface *net.Interface, loopback bool) error {
+	p := ipv4.NewPacketConn(c.ipv4UnicastConn)
+	if err := p.JoinGroup(iface, &net.UDPAddr{IP: mdnsGroupIPv4}); err != nil {
+		return err
+	}
+	p2 := ipv6.NewPacketConn(c.ipv6UnicastConn)
+	if err := p2.JoinGroup(iface, &net.UDPAddr{IP: mdnsGroupIPv6}); err != nil {
+		return err
+	}
+	p = ipv4.NewPacketConn(c.ipv4MulticastConn)
+	if err := p.JoinGroup(iface, &net.UDPAddr{IP: mdnsGroupIPv4}); err != nil {
+		return err
+	}
+	p2 = ipv6.NewPacketConn(c.ipv6MulticastConn)
+	if err := p2.JoinGroup(iface, &net.UDPAddr{IP: mdnsGroupIPv6}); err != nil {
+		return err
+	}
+
+	if loopback {
+		p.SetMulticastLoopback(true)
+		p2.SetMulticastLoopback(true)
+	}
+
+	return nil
+}
+
+// query is used to perform a lookup and stream results
+func (c *client) query(params *QueryParam) error {
+	// Create the service name
+	serviceAddr := fmt.Sprintf("%s.%s.", trimDot(params.Service), trimDot(params.Domain))
+
+	// Start listening for response packets
+	msgCh := make(chan *dns.Msg, 32)
+	go c.recv(c.ipv4UnicastConn, msgCh)
+	go c.recv(c.ipv6UnicastConn, msgCh)
+	go c.recv(c.ipv4MulticastConn, msgCh)
+	go c.recv(c.ipv6MulticastConn, msgCh)
+
+	// Send the query
+	m := new(dns.Msg)
+	if params.Type == dns.TypeNone {
+		m.SetQuestion(serviceAddr, dns.TypePTR)
+	} else {
+		m.SetQuestion(serviceAddr, params.Type)
+	}
+	// RFC 6762, section 18.12.  Repurposing of Top Bit of qclass in Question
+	// Section
+	//
+	// In the Question Section of a Multicast DNS query, the top bit of the qclass
+	// field is used to indicate that unicast responses are preferred for this
+	// particular question.  (See Section 5.4.)
+	if params.WantUnicastResponse {
+		m.Question[0].Qclass |= 1 << 15
+	}
+	m.RecursionDesired = false
+	if err := c.sendQuery(m); err != nil {
+		return err
+	}
+
+	// Map the in-progress responses
+	inprogress := make(map[string]*ServiceEntry)
+
+	for {
+		select {
+		case resp := <-msgCh:
+			inp := messageToEntry(resp, inprogress)
+			if inp == nil {
+				continue
+			}
+
+			// Check if this entry is complete
+			if inp.complete() {
+				if inp.sent {
+					continue
+				}
+				inp.sent = true
+				select {
+				case params.Entries <- inp:
+				case <-params.Context.Done():
+					return nil
+				}
+			} else {
+				// Fire off a node specific query
+				m := new(dns.Msg)
+				m.SetQuestion(inp.Name, inp.Type)
+				m.RecursionDesired = false
+				if err := c.sendQuery(m); err != nil {
+					log.Printf("[ERR] mdns: Failed to query instance %s: %v", inp.Name, err)
+				}
+			}
+		case <-params.Context.Done():
+			return nil
+		}
+	}
+}
+
+// sendQuery is used to multicast a query out
+func (c *client) sendQuery(q *dns.Msg) error {
+	buf, err := q.Pack()
+	if err != nil {
+		return err
+	}
+	if c.ipv4UnicastConn != nil {
+		c.ipv4UnicastConn.WriteToUDP(buf, ipv4Addr)
+	}
+	if c.ipv6UnicastConn != nil {
+		c.ipv6UnicastConn.WriteToUDP(buf, ipv6Addr)
+	}
+	return nil
+}
+
+// recv is used to receive until we get a shutdown
+func (c *client) recv(l *net.UDPConn, msgCh chan *dns.Msg) {
+	if l == nil {
+		return
+	}
+	buf := make([]byte, 65536)
+	for {
+		c.closeLock.Lock()
+		if c.closed {
+			c.closeLock.Unlock()
+			return
+		}
+		c.closeLock.Unlock()
+		n, err := l.Read(buf)
+		if err != nil {
+			continue
+		}
+		msg := new(dns.Msg)
+		if err := msg.Unpack(buf[:n]); err != nil {
+			continue
+		}
+		select {
+		case msgCh <- msg:
+		case <-c.closedCh:
+			return
+		}
+	}
+}
+
+// ensureName is used to ensure the named node is in progress
+func ensureName(inprogress map[string]*ServiceEntry, name string, typ uint16) *ServiceEntry {
+	if inp, ok := inprogress[name]; ok {
+		return inp
+	}
+	inp := &ServiceEntry{
+		Name: name,
+		Type: typ,
+	}
+	inprogress[name] = inp
+	return inp
+}
+
+// alias is used to setup an alias between two entries
+func alias(inprogress map[string]*ServiceEntry, src, dst string, typ uint16) {
+	srcEntry := ensureName(inprogress, src, typ)
+	inprogress[dst] = srcEntry
+}
+
+func messageToEntry(m *dns.Msg, inprogress map[string]*ServiceEntry) *ServiceEntry {
+	var inp *ServiceEntry
+
+	for _, answer := range append(m.Answer, m.Extra...) {
+		// TODO(reddaly): Check that response corresponds to serviceAddr?
+		switch rr := answer.(type) {
+		case *dns.PTR:
+			// Create new entry for this
+			inp = ensureName(inprogress, rr.Ptr, rr.Hdr.Rrtype)
+			if inp.complete() {
+				continue
+			}
+		case *dns.SRV:
+			// Check for a target mismatch
+			if rr.Target != rr.Hdr.Name {
+				alias(inprogress, rr.Hdr.Name, rr.Target, rr.Hdr.Rrtype)
+			}
+
+			// Get the port
+			inp = ensureName(inprogress, rr.Hdr.Name, rr.Hdr.Rrtype)
+			if inp.complete() {
+				continue
+			}
+			inp.Host = rr.Target
+			inp.Port = int(rr.Port)
+		case *dns.TXT:
+			// Pull out the txt
+			inp = ensureName(inprogress, rr.Hdr.Name, rr.Hdr.Rrtype)
+			if inp.complete() {
+				continue
+			}
+			inp.Info = strings.Join(rr.Txt, "|")
+			inp.InfoFields = rr.Txt
+			inp.hasTXT = true
+		case *dns.A:
+			// Pull out the IP
+			inp = ensureName(inprogress, rr.Hdr.Name, rr.Hdr.Rrtype)
+			if inp.complete() {
+				continue
+			}
+			inp.Addr = rr.A // @Deprecated
+			inp.AddrV4 = rr.A
+		case *dns.AAAA:
+			// Pull out the IP
+			inp = ensureName(inprogress, rr.Hdr.Name, rr.Hdr.Rrtype)
+			if inp.complete() {
+				continue
+			}
+			inp.Addr = rr.AAAA // @Deprecated
+			inp.AddrV6 = rr.AAAA
+		}
+
+		if inp != nil {
+			inp.TTL = int(answer.Header().Ttl)
+		}
+	}
+
+	return inp
+}

util/mdns/dns_sd.go

@@ -0,0 +1,84 @@
+package mdns
+
+import "github.com/miekg/dns"
+
+// DNSSDService is a service that complies with the DNS-SD (RFC 6762) and MDNS
+// (RFC 6762) specs for local, multicast-DNS-based discovery.
+//
+// DNSSDService implements the Zone interface and wraps an MDNSService instance.
+// To deploy an mDNS service that is compliant with DNS-SD, it's recommended to
+// register only the wrapped instance with the server.
+//
+// Example usage:
+//     service := &mdns.DNSSDService{
+//       MDNSService: &mdns.MDNSService{
+// 	       Instance: "My Foobar Service",
+// 	       Service: "_foobar._tcp",
+// 	       Port:    8000,
+//        }
+//      }
+//      server, err := mdns.NewServer(&mdns.Config{Zone: service})
+//      if err != nil {
+//        log.Fatalf("Error creating server: %v", err)
+//      }
+//      defer server.Shutdown()
+type DNSSDService struct {
+	MDNSService *MDNSService
+}
+
+// Records returns DNS records in response to a DNS question.
+//
+// This function returns the DNS response of the underlying MDNSService
+// instance.  It also returns a PTR record for a request for "
+// _services._dns-sd._udp.<Domain>", as described in section 9 of RFC 6763
+// ("Service Type Enumeration"), to allow browsing of the underlying MDNSService
+// instance.
+func (s *DNSSDService) Records(q dns.Question) []dns.RR {
+	var recs []dns.RR
+	if q.Name == "_services._dns-sd._udp."+s.MDNSService.Domain+"." {
+		recs = s.dnssdMetaQueryRecords(q)
+	}
+	return append(recs, s.MDNSService.Records(q)...)
+}
+
+// dnssdMetaQueryRecords returns the DNS records in response to a "meta-query"
+// issued to browse for DNS-SD services, as per section 9. of RFC6763.
+//
+// A meta-query has a name of the form "_services._dns-sd._udp.<Domain>" where
+// Domain is a fully-qualified domain, such as "local."
+func (s *DNSSDService) dnssdMetaQueryRecords(q dns.Question) []dns.RR {
+	// Intended behavior, as described in the RFC:
+	//     ...it may be useful for network administrators to find the list of
+	//     advertised service types on the network, even if those Service Names
+	//     are just opaque identifiers and not particularly informative in
+	//     isolation.
+	//
+	//     For this purpose, a special meta-query is defined.  A DNS query for PTR
+	//     records with the name "_services._dns-sd._udp.<Domain>" yields a set of
+	//     PTR records, where the rdata of each PTR record is the two-abel
+	//     <Service> name, plus the same domain, e.g., "_http._tcp.<Domain>".
+	//     Including the domain in the PTR rdata allows for slightly better name
+	//     compression in Unicast DNS responses, but only the first two labels are
+	//     relevant for the purposes of service type enumeration.  These two-label
+	//     service types can then be used to construct subsequent Service Instance
+	//     Enumeration PTR queries, in this <Domain> or others, to discover
+	//     instances of that service type.
+	return []dns.RR{
+		&dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    defaultTTL,
+			},
+			Ptr: s.MDNSService.serviceAddr,
+		},
+	}
+}
+
+// Announcement returns DNS records that should be broadcast during the initial
+// availability of the service, as described in section 8.3 of RFC 6762.
+// TODO(reddaly): Add this when Announcement is added to the mdns.Zone interface.
+//func (s *DNSSDService) Announcement() []dns.RR {
+//	return s.MDNSService.Announcement()
+//}

util/mdns/dns_sd_test.go

@@ -0,0 +1,68 @@
+package mdns
+
+import (
+	"reflect"
+	"testing"
+)
+import "github.com/miekg/dns"
+
+type mockMDNSService struct{}
+
+func (s *mockMDNSService) Records(q dns.Question) []dns.RR {
+	return []dns.RR{
+		&dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   "fakerecord",
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    42,
+			},
+			Ptr: "fake.local.",
+		},
+	}
+}
+
+func (s *mockMDNSService) Announcement() []dns.RR {
+	return []dns.RR{
+		&dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   "fakeannounce",
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    42,
+			},
+			Ptr: "fake.local.",
+		},
+	}
+}
+
+func TestDNSSDServiceRecords(t *testing.T) {
+	s := &DNSSDService{
+		MDNSService: &MDNSService{
+			serviceAddr: "_foobar._tcp.local.",
+			Domain:      "local",
+		},
+	}
+	q := dns.Question{
+		Name:   "_services._dns-sd._udp.local.",
+		Qtype:  dns.TypePTR,
+		Qclass: dns.ClassINET,
+	}
+	recs := s.Records(q)
+	if got, want := len(recs), 1; got != want {
+		t.Fatalf("s.Records(%v) returned %v records, want %v", q, got, want)
+	}
+
+	want := dns.RR(&dns.PTR{
+		Hdr: dns.RR_Header{
+			Name:   "_services._dns-sd._udp.local.",
+			Rrtype: dns.TypePTR,
+			Class:  dns.ClassINET,
+			Ttl:    defaultTTL,
+		},
+		Ptr: "_foobar._tcp.local.",
+	})
+	if got := recs[0]; !reflect.DeepEqual(got, want) {
+		t.Errorf("s.Records()[0] = %v, want %v", got, want)
+	}
+}

util/mdns/server.go

@@ -0,0 +1,476 @@
+package mdns
+
+import (
+	"fmt"
+	"log"
+	"math/rand"
+	"net"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+var (
+	mdnsGroupIPv4 = net.ParseIP("224.0.0.251")
+	mdnsGroupIPv6 = net.ParseIP("ff02::fb")
+
+	// mDNS wildcard addresses
+	mdnsWildcardAddrIPv4 = &net.UDPAddr{
+		IP:   net.ParseIP("224.0.0.0"),
+		Port: 5353,
+	}
+	mdnsWildcardAddrIPv6 = &net.UDPAddr{
+		IP:   net.ParseIP("ff02::"),
+		Port: 5353,
+	}
+
+	// mDNS endpoint addresses
+	ipv4Addr = &net.UDPAddr{
+		IP:   mdnsGroupIPv4,
+		Port: 5353,
+	}
+	ipv6Addr = &net.UDPAddr{
+		IP:   mdnsGroupIPv6,
+		Port: 5353,
+	}
+)
+
+// Config is used to configure the mDNS server
+type Config struct {
+	// Zone must be provided to support responding to queries
+	Zone Zone
+
+	// Iface if provided binds the multicast listener to the given
+	// interface. If not provided, the system default multicase interface
+	// is used.
+	Iface *net.Interface
+
+	// Port If it is not 0, replace the port 5353 with this port number.
+	Port int
+}
+
+// mDNS server is used to listen for mDNS queries and respond if we
+// have a matching local record
+type Server struct {
+	config *Config
+
+	ipv4List *net.UDPConn
+	ipv6List *net.UDPConn
+
+	shutdown     bool
+	shutdownCh   chan struct{}
+	shutdownLock sync.Mutex
+	wg           sync.WaitGroup
+}
+
+// NewServer is used to create a new mDNS server from a config
+func NewServer(config *Config) (*Server, error) {
+	setCustomPort(config.Port)
+
+	// Create the listeners
+	// Create wildcard connections (because :5353 can be already taken by other apps)
+	ipv4List, _ := net.ListenUDP("udp4", mdnsWildcardAddrIPv4)
+	ipv6List, _ := net.ListenUDP("udp6", mdnsWildcardAddrIPv6)
+	if ipv4List == nil && ipv6List == nil {
+		return nil, fmt.Errorf("[ERR] mdns: Failed to bind to any udp port!")
+	}
+
+	if ipv4List == nil {
+		ipv4List = &net.UDPConn{}
+	}
+	if ipv6List == nil {
+		ipv6List = &net.UDPConn{}
+	}
+
+	// Join multicast groups to receive announcements
+	p1 := ipv4.NewPacketConn(ipv4List)
+	p2 := ipv6.NewPacketConn(ipv6List)
+	p1.SetMulticastLoopback(true)
+	p2.SetMulticastLoopback(true)
+
+	if config.Iface != nil {
+		if err := p1.JoinGroup(config.Iface, &net.UDPAddr{IP: mdnsGroupIPv4}); err != nil {
+			return nil, err
+		}
+		if err := p2.JoinGroup(config.Iface, &net.UDPAddr{IP: mdnsGroupIPv6}); err != nil {
+			return nil, err
+		}
+	} else {
+		ifaces, err := net.Interfaces()
+		if err != nil {
+			return nil, err
+		}
+		errCount1, errCount2 := 0, 0
+		for _, iface := range ifaces {
+			if err := p1.JoinGroup(&iface, &net.UDPAddr{IP: mdnsGroupIPv4}); err != nil {
+				errCount1++
+			}
+			if err := p2.JoinGroup(&iface, &net.UDPAddr{IP: mdnsGroupIPv6}); err != nil {
+				errCount2++
+			}
+		}
+		if len(ifaces) == errCount1 && len(ifaces) == errCount2 {
+			return nil, fmt.Errorf("Failed to join multicast group on all interfaces!")
+		}
+	}
+
+	s := &Server{
+		config:     config,
+		ipv4List:   ipv4List,
+		ipv6List:   ipv6List,
+		shutdownCh: make(chan struct{}),
+	}
+
+	go s.recv(s.ipv4List)
+	go s.recv(s.ipv6List)
+
+	s.wg.Add(1)
+	go s.probe()
+
+	return s, nil
+}
+
+// Shutdown is used to shutdown the listener
+func (s *Server) Shutdown() error {
+	s.shutdownLock.Lock()
+	defer s.shutdownLock.Unlock()
+
+	if s.shutdown {
+		return nil
+	}
+
+	s.shutdown = true
+	close(s.shutdownCh)
+	s.unregister()
+
+	if s.ipv4List != nil {
+		s.ipv4List.Close()
+	}
+	if s.ipv6List != nil {
+		s.ipv6List.Close()
+	}
+
+	s.wg.Wait()
+	return nil
+}
+
+// recv is a long running routine to receive packets from an interface
+func (s *Server) recv(c *net.UDPConn) {
+	if c == nil {
+		return
+	}
+	buf := make([]byte, 65536)
+	for {
+		s.shutdownLock.Lock()
+		if s.shutdown {
+			s.shutdownLock.Unlock()
+			return
+		}
+		s.shutdownLock.Unlock()
+		n, from, err := c.ReadFrom(buf)
+		if err != nil {
+			continue
+		}
+		if err := s.parsePacket(buf[:n], from); err != nil {
+			log.Printf("[ERR] mdns: Failed to handle query: %v", err)
+		}
+	}
+}
+
+// parsePacket is used to parse an incoming packet
+func (s *Server) parsePacket(packet []byte, from net.Addr) error {
+	var msg dns.Msg
+	if err := msg.Unpack(packet); err != nil {
+		log.Printf("[ERR] mdns: Failed to unpack packet: %v", err)
+		return err
+	}
+	// TODO: This is a bit of a hack
+	// We decided to ignore some mDNS answers for the time being
+	// See: https://tools.ietf.org/html/rfc6762#section-7.2
+	msg.Truncated = false
+	return s.handleQuery(&msg, from)
+}
+
+// handleQuery is used to handle an incoming query
+func (s *Server) handleQuery(query *dns.Msg, from net.Addr) error {
+	if query.Opcode != dns.OpcodeQuery {
+		// "In both multicast query and multicast response messages, the OPCODE MUST
+		// be zero on transmission (only standard queries are currently supported
+		// over multicast).  Multicast DNS messages received with an OPCODE other
+		// than zero MUST be silently ignored."  Note: OpcodeQuery == 0
+		return fmt.Errorf("mdns: received query with non-zero Opcode %v: %v", query.Opcode, *query)
+	}
+	if query.Rcode != 0 {
+		// "In both multicast query and multicast response messages, the Response
+		// Code MUST be zero on transmission.  Multicast DNS messages received with
+		// non-zero Response Codes MUST be silently ignored."
+		return fmt.Errorf("mdns: received query with non-zero Rcode %v: %v", query.Rcode, *query)
+	}
+
+	// TODO(reddaly): Handle "TC (Truncated) Bit":
+	//    In query messages, if the TC bit is set, it means that additional
+	//    Known-Answer records may be following shortly.  A responder SHOULD
+	//    record this fact, and wait for those additional Known-Answer records,
+	//    before deciding whether to respond.  If the TC bit is clear, it means
+	//    that the querying host has no additional Known Answers.
+	if query.Truncated {
+		return fmt.Errorf("[ERR] mdns: support for DNS requests with high truncated bit not implemented: %v", *query)
+	}
+
+	var unicastAnswer, multicastAnswer []dns.RR
+
+	// Handle each question
+	for _, q := range query.Question {
+		mrecs, urecs := s.handleQuestion(q)
+		multicastAnswer = append(multicastAnswer, mrecs...)
+		unicastAnswer = append(unicastAnswer, urecs...)
+	}
+
+	// See section 18 of RFC 6762 for rules about DNS headers.
+	resp := func(unicast bool) *dns.Msg {
+		// 18.1: ID (Query Identifier)
+		// 0 for multicast response, query.Id for unicast response
+		id := uint16(0)
+		if unicast {
+			id = query.Id
+		}
+
+		var answer []dns.RR
+		if unicast {
+			answer = unicastAnswer
+		} else {
+			answer = multicastAnswer
+		}
+		if len(answer) == 0 {
+			return nil
+		}
+
+		return &dns.Msg{
+			MsgHdr: dns.MsgHdr{
+				Id: id,
+
+				// 18.2: QR (Query/Response) Bit - must be set to 1 in response.
+				Response: true,
+
+				// 18.3: OPCODE - must be zero in response (OpcodeQuery == 0)
+				Opcode: dns.OpcodeQuery,
+
+				// 18.4: AA (Authoritative Answer) Bit - must be set to 1
+				Authoritative: true,
+
+				// The following fields must all be set to 0:
+				// 18.5: TC (TRUNCATED) Bit
+				// 18.6: RD (Recursion Desired) Bit
+				// 18.7: RA (Recursion Available) Bit
+				// 18.8: Z (Zero) Bit
+				// 18.9: AD (Authentic Data) Bit
+				// 18.10: CD (Checking Disabled) Bit
+				// 18.11: RCODE (Response Code)
+			},
+			// 18.12 pertains to questions (handled by handleQuestion)
+			// 18.13 pertains to resource records (handled by handleQuestion)
+
+			// 18.14: Name Compression - responses should be compressed (though see
+			// caveats in the RFC), so set the Compress bit (part of the dns library
+			// API, not part of the DNS packet) to true.
+			Compress: true,
+
+			Answer: answer,
+		}
+	}
+
+	if mresp := resp(false); mresp != nil {
+		if err := s.sendResponse(mresp, from); err != nil {
+			return fmt.Errorf("mdns: error sending multicast response: %v", err)
+		}
+	}
+	if uresp := resp(true); uresp != nil {
+		if err := s.sendResponse(uresp, from); err != nil {
+			return fmt.Errorf("mdns: error sending unicast response: %v", err)
+		}
+	}
+	return nil
+}
+
+// handleQuestion is used to handle an incoming question
+//
+// The response to a question may be transmitted over multicast, unicast, or
+// both.  The return values are DNS records for each transmission type.
+func (s *Server) handleQuestion(q dns.Question) (multicastRecs, unicastRecs []dns.RR) {
+	records := s.config.Zone.Records(q)
+
+	if len(records) == 0 {
+		return nil, nil
+	}
+
+	// Handle unicast and multicast responses.
+	// TODO(reddaly): The decision about sending over unicast vs. multicast is not
+	// yet fully compliant with RFC 6762.  For example, the unicast bit should be
+	// ignored if the records in question are close to TTL expiration.  For now,
+	// we just use the unicast bit to make the decision, as per the spec:
+	//     RFC 6762, section 18.12.  Repurposing of Top Bit of qclass in Question
+	//     Section
+	//
+	//     In the Question Section of a Multicast DNS query, the top bit of the
+	//     qclass field is used to indicate that unicast responses are preferred
+	//     for this particular question.  (See Section 5.4.)
+	if q.Qclass&(1<<15) != 0 {
+		return nil, records
+	}
+	return records, nil
+}
+
+func (s *Server) probe() {
+	defer s.wg.Done()
+
+	sd, ok := s.config.Zone.(*MDNSService)
+	if !ok {
+		return
+	}
+
+	name := fmt.Sprintf("%s.%s.%s.", sd.Instance, trimDot(sd.Service), trimDot(sd.Domain))
+
+	q := new(dns.Msg)
+	q.SetQuestion(name, dns.TypePTR)
+	q.RecursionDesired = false
+
+	srv := &dns.SRV{
+		Hdr: dns.RR_Header{
+			Name:   name,
+			Rrtype: dns.TypeSRV,
+			Class:  dns.ClassINET,
+			Ttl:    defaultTTL,
+		},
+		Priority: 0,
+		Weight:   0,
+		Port:     uint16(sd.Port),
+		Target:   sd.HostName,
+	}
+	txt := &dns.TXT{
+		Hdr: dns.RR_Header{
+			Name:   name,
+			Rrtype: dns.TypeTXT,
+			Class:  dns.ClassINET,
+			Ttl:    defaultTTL,
+		},
+		Txt: sd.TXT,
+	}
+	q.Ns = []dns.RR{srv, txt}
+
+	randomizer := rand.New(rand.NewSource(time.Now().UnixNano()))
+
+	for i := 0; i < 3; i++ {
+		if err := s.SendMulticast(q); err != nil {
+			log.Println("[ERR] mdns: failed to send probe:", err.Error())
+		}
+		time.Sleep(time.Duration(randomizer.Intn(250)) * time.Millisecond)
+	}
+
+	resp := new(dns.Msg)
+	resp.MsgHdr.Response = true
+
+	// set for query
+	q.SetQuestion(name, dns.TypeANY)
+
+	resp.Answer = append(resp.Answer, s.config.Zone.Records(q.Question[0])...)
+
+	// reset
+	q.SetQuestion(name, dns.TypePTR)
+
+	// From RFC6762
+	//    The Multicast DNS responder MUST send at least two unsolicited
+	//    responses, one second apart. To provide increased robustness against
+	//    packet loss, a responder MAY send up to eight unsolicited responses,
+	//    provided that the interval between unsolicited responses increases by
+	//    at least a factor of two with every response sent.
+	timeout := 1 * time.Second
+	timer := time.NewTimer(timeout)
+	for i := 0; i < 3; i++ {
+		if err := s.SendMulticast(resp); err != nil {
+			log.Println("[ERR] mdns: failed to send announcement:", err.Error())
+		}
+		select {
+		case <-timer.C:
+			timeout *= 2
+			timer.Reset(timeout)
+		case <-s.shutdownCh:
+			timer.Stop()
+			return
+		}
+	}
+}
+
+// multicastResponse us used to send a multicast response packet
+func (s *Server) SendMulticast(msg *dns.Msg) error {
+	buf, err := msg.Pack()
+	if err != nil {
+		return err
+	}
+	if s.ipv4List != nil {
+		s.ipv4List.WriteToUDP(buf, ipv4Addr)
+	}
+	if s.ipv6List != nil {
+		s.ipv6List.WriteToUDP(buf, ipv6Addr)
+	}
+	return nil
+}
+
+// sendResponse is used to send a response packet
+func (s *Server) sendResponse(resp *dns.Msg, from net.Addr) error {
+	// TODO(reddaly): Respect the unicast argument, and allow sending responses
+	// over multicast.
+	buf, err := resp.Pack()
+	if err != nil {
+		return err
+	}
+
+	// Determine the socket to send from
+	addr := from.(*net.UDPAddr)
+	if addr.IP.To4() != nil {
+		_, err = s.ipv4List.WriteToUDP(buf, addr)
+		return err
+	} else {
+		_, err = s.ipv6List.WriteToUDP(buf, addr)
+		return err
+	}
+}
+
+func (s *Server) unregister() error {
+	sd, ok := s.config.Zone.(*MDNSService)
+	if !ok {
+		return nil
+	}
+
+	atomic.StoreUint32(&sd.TTL, 0)
+	name := fmt.Sprintf("%s.%s.%s.", sd.Instance, trimDot(sd.Service), trimDot(sd.Domain))
+
+	q := new(dns.Msg)
+	q.SetQuestion(name, dns.TypeANY)
+
+	resp := new(dns.Msg)
+	resp.MsgHdr.Response = true
+	resp.Answer = append(resp.Answer, s.config.Zone.Records(q.Question[0])...)
+
+	return s.SendMulticast(resp)
+}
+
+func setCustomPort(port int) {
+	if port != 0 {
+		if mdnsWildcardAddrIPv4.Port != port {
+			mdnsWildcardAddrIPv4.Port = port
+		}
+		if mdnsWildcardAddrIPv6.Port != port {
+			mdnsWildcardAddrIPv6.Port = port
+		}
+		if ipv4Addr.Port != port {
+			ipv4Addr.Port = port
+		}
+		if ipv6Addr.Port != port {
+			ipv6Addr.Port = port
+		}
+	}
+}

util/mdns/server_test.go

@@ -0,0 +1,61 @@
+package mdns
+
+import (
+	"testing"
+	"time"
+)
+
+func TestServer_StartStop(t *testing.T) {
+	s := makeService(t)
+	serv, err := NewServer(&Config{Zone: s})
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer serv.Shutdown()
+}
+
+func TestServer_Lookup(t *testing.T) {
+	serv, err := NewServer(&Config{Zone: makeServiceWithServiceName(t, "_foobar._tcp")})
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer serv.Shutdown()
+
+	entries := make(chan *ServiceEntry, 1)
+	found := false
+	doneCh := make(chan struct{})
+	go func() {
+		select {
+		case e := <-entries:
+			if e.Name != "hostname._foobar._tcp.local." {
+				t.Fatalf("bad: %v", e)
+			}
+			if e.Port != 80 {
+				t.Fatalf("bad: %v", e)
+			}
+			if e.Info != "Local web server" {
+				t.Fatalf("bad: %v", e)
+			}
+			found = true
+
+		case <-time.After(80 * time.Millisecond):
+			t.Fatalf("timeout")
+		}
+		close(doneCh)
+	}()
+
+	params := &QueryParam{
+		Service: "_foobar._tcp",
+		Domain:  "local",
+		Timeout: 50 * time.Millisecond,
+		Entries: entries,
+	}
+	err = Query(params)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	<-doneCh
+	if !found {
+		t.Fatalf("record not found")
+	}
+}

util/mdns/zone.go

@@ -0,0 +1,309 @@
+package mdns
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"strings"
+	"sync/atomic"
+
+	"github.com/miekg/dns"
+)
+
+const (
+	// defaultTTL is the default TTL value in returned DNS records in seconds.
+	defaultTTL = 120
+)
+
+// Zone is the interface used to integrate with the server and
+// to serve records dynamically
+type Zone interface {
+	// Records returns DNS records in response to a DNS question.
+	Records(q dns.Question) []dns.RR
+}
+
+// MDNSService is used to export a named service by implementing a Zone
+type MDNSService struct {
+	Instance     string   // Instance name (e.g. "hostService name")
+	Service      string   // Service name (e.g. "_http._tcp.")
+	Domain       string   // If blank, assumes "local"
+	HostName     string   // Host machine DNS name (e.g. "mymachine.net.")
+	Port         int      // Service Port
+	IPs          []net.IP // IP addresses for the service's host
+	TXT          []string // Service TXT records
+	TTL          uint32
+	serviceAddr  string // Fully qualified service address
+	instanceAddr string // Fully qualified instance address
+	enumAddr     string // _services._dns-sd._udp.<domain>
+}
+
+// validateFQDN returns an error if the passed string is not a fully qualified
+// hdomain name (more specifically, a hostname).
+func validateFQDN(s string) error {
+	if len(s) == 0 {
+		return fmt.Errorf("FQDN must not be blank")
+	}
+	if s[len(s)-1] != '.' {
+		return fmt.Errorf("FQDN must end in period: %s", s)
+	}
+	// TODO(reddaly): Perform full validation.
+
+	return nil
+}
+
+// NewMDNSService returns a new instance of MDNSService.
+//
+// If domain, hostName, or ips is set to the zero value, then a default value
+// will be inferred from the operating system.
+//
+// TODO(reddaly): This interface may need to change to account for "unique
+// record" conflict rules of the mDNS protocol.  Upon startup, the server should
+// check to ensure that the instance name does not conflict with other instance
+// names, and, if required, select a new name.  There may also be conflicting
+// hostName A/AAAA records.
+func NewMDNSService(instance, service, domain, hostName string, port int, ips []net.IP, txt []string) (*MDNSService, error) {
+	// Sanity check inputs
+	if instance == "" {
+		return nil, fmt.Errorf("missing service instance name")
+	}
+	if service == "" {
+		return nil, fmt.Errorf("missing service name")
+	}
+	if port == 0 {
+		return nil, fmt.Errorf("missing service port")
+	}
+
+	// Set default domain
+	if domain == "" {
+		domain = "local."
+	}
+	if err := validateFQDN(domain); err != nil {
+		return nil, fmt.Errorf("domain %q is not a fully-qualified domain name: %v", domain, err)
+	}
+
+	// Get host information if no host is specified.
+	if hostName == "" {
+		var err error
+		hostName, err = os.Hostname()
+		if err != nil {
+			return nil, fmt.Errorf("could not determine host: %v", err)
+		}
+		hostName = fmt.Sprintf("%s.", hostName)
+	}
+	if err := validateFQDN(hostName); err != nil {
+		return nil, fmt.Errorf("hostName %q is not a fully-qualified domain name: %v", hostName, err)
+	}
+
+	if len(ips) == 0 {
+		var err error
+		ips, err = net.LookupIP(trimDot(hostName))
+		if err != nil {
+			// Try appending the host domain suffix and lookup again
+			// (required for Linux-based hosts)
+			tmpHostName := fmt.Sprintf("%s%s", hostName, domain)
+
+			ips, err = net.LookupIP(trimDot(tmpHostName))
+
+			if err != nil {
+				return nil, fmt.Errorf("could not determine host IP addresses for %s", hostName)
+			}
+		}
+	}
+	for _, ip := range ips {
+		if ip.To4() == nil && ip.To16() == nil {
+			return nil, fmt.Errorf("invalid IP address in IPs list: %v", ip)
+		}
+	}
+
+	return &MDNSService{
+		Instance:     instance,
+		Service:      service,
+		Domain:       domain,
+		HostName:     hostName,
+		Port:         port,
+		IPs:          ips,
+		TXT:          txt,
+		TTL:          defaultTTL,
+		serviceAddr:  fmt.Sprintf("%s.%s.", trimDot(service), trimDot(domain)),
+		instanceAddr: fmt.Sprintf("%s.%s.%s.", instance, trimDot(service), trimDot(domain)),
+		enumAddr:     fmt.Sprintf("_services._dns-sd._udp.%s.", trimDot(domain)),
+	}, nil
+}
+
+// trimDot is used to trim the dots from the start or end of a string
+func trimDot(s string) string {
+	return strings.Trim(s, ".")
+}
+
+// Records returns DNS records in response to a DNS question.
+func (m *MDNSService) Records(q dns.Question) []dns.RR {
+	switch q.Name {
+	case m.enumAddr:
+		return m.serviceEnum(q)
+	case m.serviceAddr:
+		return m.serviceRecords(q)
+	case m.instanceAddr:
+		return m.instanceRecords(q)
+	case m.HostName:
+		if q.Qtype == dns.TypeA || q.Qtype == dns.TypeAAAA {
+			return m.instanceRecords(q)
+		}
+		fallthrough
+	default:
+		return nil
+	}
+}
+
+func (m *MDNSService) serviceEnum(q dns.Question) []dns.RR {
+	switch q.Qtype {
+	case dns.TypeANY:
+		fallthrough
+	case dns.TypePTR:
+		rr := &dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    atomic.LoadUint32(&m.TTL),
+			},
+			Ptr: m.serviceAddr,
+		}
+		return []dns.RR{rr}
+	default:
+		return nil
+	}
+}
+
+// serviceRecords is called when the query matches the service name
+func (m *MDNSService) serviceRecords(q dns.Question) []dns.RR {
+	switch q.Qtype {
+	case dns.TypeANY:
+		fallthrough
+	case dns.TypePTR:
+		// Build a PTR response for the service
+		rr := &dns.PTR{
+			Hdr: dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: dns.TypePTR,
+				Class:  dns.ClassINET,
+				Ttl:    atomic.LoadUint32(&m.TTL),
+			},
+			Ptr: m.instanceAddr,
+		}
+		servRec := []dns.RR{rr}
+
+		// Get the instance records
+		instRecs := m.instanceRecords(dns.Question{
+			Name:  m.instanceAddr,
+			Qtype: dns.TypeANY,
+		})
+
+		// Return the service record with the instance records
+		return append(servRec, instRecs...)
+	default:
+		return nil
+	}
+}
+
+// serviceRecords is called when the query matches the instance name
+func (m *MDNSService) instanceRecords(q dns.Question) []dns.RR {
+	switch q.Qtype {
+	case dns.TypeANY:
+		// Get the SRV, which includes A and AAAA
+		recs := m.instanceRecords(dns.Question{
+			Name:  m.instanceAddr,
+			Qtype: dns.TypeSRV,
+		})
+
+		// Add the TXT record
+		recs = append(recs, m.instanceRecords(dns.Question{
+			Name:  m.instanceAddr,
+			Qtype: dns.TypeTXT,
+		})...)
+		return recs
+
+	case dns.TypeA:
+		var rr []dns.RR
+		for _, ip := range m.IPs {
+			if ip4 := ip.To4(); ip4 != nil {
+				rr = append(rr, &dns.A{
+					Hdr: dns.RR_Header{
+						Name:   m.HostName,
+						Rrtype: dns.TypeA,
+						Class:  dns.ClassINET,
+						Ttl:    atomic.LoadUint32(&m.TTL),
+					},
+					A: ip4,
+				})
+			}
+		}
+		return rr
+
+	case dns.TypeAAAA:
+		var rr []dns.RR
+		for _, ip := range m.IPs {
+			if ip.To4() != nil {
+				// TODO(reddaly): IPv4 addresses could be encoded in IPv6 format and
+				// putinto AAAA records, but the current logic puts ipv4-encodable
+				// addresses into the A records exclusively.  Perhaps this should be
+				// configurable?
+				continue
+			}
+
+			if ip16 := ip.To16(); ip16 != nil {
+				rr = append(rr, &dns.AAAA{
+					Hdr: dns.RR_Header{
+						Name:   m.HostName,
+						Rrtype: dns.TypeAAAA,
+						Class:  dns.ClassINET,
+						Ttl:    atomic.LoadUint32(&m.TTL),
+					},
+					AAAA: ip16,
+				})
+			}
+		}
+		return rr
+
+	case dns.TypeSRV:
+		// Create the SRV Record
+		srv := &dns.SRV{
+			Hdr: dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: dns.TypeSRV,
+				Class:  dns.ClassINET,
+				Ttl:    atomic.LoadUint32(&m.TTL),
+			},
+			Priority: 10,
+			Weight:   1,
+			Port:     uint16(m.Port),
+			Target:   m.HostName,
+		}
+		recs := []dns.RR{srv}
+
+		// Add the A record
+		recs = append(recs, m.instanceRecords(dns.Question{
+			Name:  m.instanceAddr,
+			Qtype: dns.TypeA,
+		})...)
+
+		// Add the AAAA record
+		recs = append(recs, m.instanceRecords(dns.Question{
+			Name:  m.instanceAddr,
+			Qtype: dns.TypeAAAA,
+		})...)
+		return recs
+
+	case dns.TypeTXT:
+		txt := &dns.TXT{
+			Hdr: dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: dns.TypeTXT,
+				Class:  dns.ClassINET,
+				Ttl:    atomic.LoadUint32(&m.TTL),
+			},
+			Txt: m.TXT,
+		}
+		return []dns.RR{txt}
+	}
+	return nil
+}

util/mdns/zone_test.go

@@ -0,0 +1,275 @@
+package mdns
+
+import (
+	"bytes"
+	"net"
+	"reflect"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func makeService(t *testing.T) *MDNSService {
+	return makeServiceWithServiceName(t, "_http._tcp")
+}
+
+func makeServiceWithServiceName(t *testing.T, service string) *MDNSService {
+	m, err := NewMDNSService(
+		"hostname",
+		service,
+		"local.",
+		"testhost.",
+		80, // port
+		[]net.IP{net.IP([]byte{192, 168, 0, 42}), net.ParseIP("2620:0:1000:1900:b0c2:d0b2:c411:18bc")},
+		[]string{"Local web server"}) // TXT
+
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	return m
+}
+
+func TestNewMDNSService_BadParams(t *testing.T) {
+	for _, test := range []struct {
+		testName string
+		hostName string
+		domain   string
+	}{
+		{
+			"NewMDNSService should fail when passed hostName that is not a legal fully-qualified domain name",
+			"hostname", // not legal FQDN - should be "hostname." or "hostname.local.", etc.
+			"local.",   // legal
+		},
+		{
+			"NewMDNSService should fail when passed domain that is not a legal fully-qualified domain name",
+			"hostname.", // legal
+			"local",     // should be "local."
+		},
+	} {
+		_, err := NewMDNSService(
+			"instance name",
+			"_http._tcp",
+			test.domain,
+			test.hostName,
+			80, // port
+			[]net.IP{net.IP([]byte{192, 168, 0, 42})},
+			[]string{"Local web server"}) // TXT
+		if err == nil {
+			t.Fatalf("%s: error expected, but got none", test.testName)
+		}
+	}
+}
+
+func TestMDNSService_BadAddr(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "random",
+		Qtype: dns.TypeANY,
+	}
+	recs := s.Records(q)
+	if len(recs) != 0 {
+		t.Fatalf("bad: %v", recs)
+	}
+}
+
+func TestMDNSService_ServiceAddr(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "_http._tcp.local.",
+		Qtype: dns.TypeANY,
+	}
+	recs := s.Records(q)
+	if got, want := len(recs), 5; got != want {
+		t.Fatalf("got %d records, want %d: %v", got, want, recs)
+	}
+
+	if ptr, ok := recs[0].(*dns.PTR); !ok {
+		t.Errorf("recs[0] should be PTR record, got: %v, all records: %v", recs[0], recs)
+	} else if got, want := ptr.Ptr, "hostname._http._tcp.local."; got != want {
+		t.Fatalf("bad PTR record %v: got %v, want %v", ptr, got, want)
+	}
+
+	if _, ok := recs[1].(*dns.SRV); !ok {
+		t.Errorf("recs[1] should be SRV record, got: %v, all reccords: %v", recs[1], recs)
+	}
+	if _, ok := recs[2].(*dns.A); !ok {
+		t.Errorf("recs[2] should be A record, got: %v, all records: %v", recs[2], recs)
+	}
+	if _, ok := recs[3].(*dns.AAAA); !ok {
+		t.Errorf("recs[3] should be AAAA record, got: %v, all records: %v", recs[3], recs)
+	}
+	if _, ok := recs[4].(*dns.TXT); !ok {
+		t.Errorf("recs[4] should be TXT record, got: %v, all records: %v", recs[4], recs)
+	}
+
+	q.Qtype = dns.TypePTR
+	if recs2 := s.Records(q); !reflect.DeepEqual(recs, recs2) {
+		t.Fatalf("PTR question should return same result as ANY question: ANY => %v, PTR => %v", recs, recs2)
+	}
+}
+
+func TestMDNSService_InstanceAddr_ANY(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "hostname._http._tcp.local.",
+		Qtype: dns.TypeANY,
+	}
+	recs := s.Records(q)
+	if len(recs) != 4 {
+		t.Fatalf("bad: %v", recs)
+	}
+	if _, ok := recs[0].(*dns.SRV); !ok {
+		t.Fatalf("bad: %v", recs[0])
+	}
+	if _, ok := recs[1].(*dns.A); !ok {
+		t.Fatalf("bad: %v", recs[1])
+	}
+	if _, ok := recs[2].(*dns.AAAA); !ok {
+		t.Fatalf("bad: %v", recs[2])
+	}
+	if _, ok := recs[3].(*dns.TXT); !ok {
+		t.Fatalf("bad: %v", recs[3])
+	}
+}
+
+func TestMDNSService_InstanceAddr_SRV(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "hostname._http._tcp.local.",
+		Qtype: dns.TypeSRV,
+	}
+	recs := s.Records(q)
+	if len(recs) != 3 {
+		t.Fatalf("bad: %v", recs)
+	}
+	srv, ok := recs[0].(*dns.SRV)
+	if !ok {
+		t.Fatalf("bad: %v", recs[0])
+	}
+	if _, ok := recs[1].(*dns.A); !ok {
+		t.Fatalf("bad: %v", recs[1])
+	}
+	if _, ok := recs[2].(*dns.AAAA); !ok {
+		t.Fatalf("bad: %v", recs[2])
+	}
+
+	if srv.Port != uint16(s.Port) {
+		t.Fatalf("bad: %v", recs[0])
+	}
+}
+
+func TestMDNSService_InstanceAddr_A(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "hostname._http._tcp.local.",
+		Qtype: dns.TypeA,
+	}
+	recs := s.Records(q)
+	if len(recs) != 1 {
+		t.Fatalf("bad: %v", recs)
+	}
+	a, ok := recs[0].(*dns.A)
+	if !ok {
+		t.Fatalf("bad: %v", recs[0])
+	}
+	if !bytes.Equal(a.A, []byte{192, 168, 0, 42}) {
+		t.Fatalf("bad: %v", recs[0])
+	}
+}
+
+func TestMDNSService_InstanceAddr_AAAA(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "hostname._http._tcp.local.",
+		Qtype: dns.TypeAAAA,
+	}
+	recs := s.Records(q)
+	if len(recs) != 1 {
+		t.Fatalf("bad: %v", recs)
+	}
+	a4, ok := recs[0].(*dns.AAAA)
+	if !ok {
+		t.Fatalf("bad: %v", recs[0])
+	}
+	ip6 := net.ParseIP("2620:0:1000:1900:b0c2:d0b2:c411:18bc")
+	if got := len(ip6); got != net.IPv6len {
+		t.Fatalf("test IP failed to parse (len = %d, want %d)", got, net.IPv6len)
+	}
+	if !bytes.Equal(a4.AAAA, ip6) {
+		t.Fatalf("bad: %v", recs[0])
+	}
+}
+
+func TestMDNSService_InstanceAddr_TXT(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "hostname._http._tcp.local.",
+		Qtype: dns.TypeTXT,
+	}
+	recs := s.Records(q)
+	if len(recs) != 1 {
+		t.Fatalf("bad: %v", recs)
+	}
+	txt, ok := recs[0].(*dns.TXT)
+	if !ok {
+		t.Fatalf("bad: %v", recs[0])
+	}
+	if got, want := txt.Txt, s.TXT; !reflect.DeepEqual(got, want) {
+		t.Fatalf("TXT record mismatch for %v: got %v, want %v", recs[0], got, want)
+	}
+}
+
+func TestMDNSService_HostNameQuery(t *testing.T) {
+	s := makeService(t)
+	for _, test := range []struct {
+		q    dns.Question
+		want []dns.RR
+	}{
+		{
+			dns.Question{Name: "testhost.", Qtype: dns.TypeA},
+			[]dns.RR{&dns.A{
+				Hdr: dns.RR_Header{
+					Name:   "testhost.",
+					Rrtype: dns.TypeA,
+					Class:  dns.ClassINET,
+					Ttl:    120,
+				},
+				A: net.IP([]byte{192, 168, 0, 42}),
+			}},
+		},
+		{
+			dns.Question{Name: "testhost.", Qtype: dns.TypeAAAA},
+			[]dns.RR{&dns.AAAA{
+				Hdr: dns.RR_Header{
+					Name:   "testhost.",
+					Rrtype: dns.TypeAAAA,
+					Class:  dns.ClassINET,
+					Ttl:    120,
+				},
+				AAAA: net.ParseIP("2620:0:1000:1900:b0c2:d0b2:c411:18bc"),
+			}},
+		},
+	} {
+		if got := s.Records(test.q); !reflect.DeepEqual(got, test.want) {
+			t.Errorf("hostname query failed: s.Records(%v) = %v, want %v", test.q, got, test.want)
+		}
+	}
+}
+
+func TestMDNSService_serviceEnum_PTR(t *testing.T) {
+	s := makeService(t)
+	q := dns.Question{
+		Name:  "_services._dns-sd._udp.local.",
+		Qtype: dns.TypePTR,
+	}
+	recs := s.Records(q)
+	if len(recs) != 1 {
+		t.Fatalf("bad: %v", recs)
+	}
+	if ptr, ok := recs[0].(*dns.PTR); !ok {
+		t.Errorf("recs[0] should be PTR record, got: %v, all records: %v", recs[0], recs)
+	} else if got, want := ptr.Ptr, "_http._tcp.local."; got != want {
+		t.Fatalf("bad PTR record %v: got %v, want %v", ptr, got, want)
+	}
+}