Initial pass at mDNS support (receiving does not work yet)

src/mdns/mdns.go

@@ -0,0 +1,333 @@
+package mdns
+
+import (
+	"context"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"net"
+	"regexp"
+	"time"
+
+	"github.com/Arceliar/phony"
+	"github.com/gologme/log"
+	"github.com/grandcat/zeroconf"
+
+	"github.com/yggdrasil-network/yggdrasil-go/src/admin"
+	"github.com/yggdrasil-network/yggdrasil-go/src/config"
+	"github.com/yggdrasil-network/yggdrasil-go/src/yggdrasil"
+)
+
+const (
+	MDNSService = "_yggdrasil._tcp"
+	MDNSDomain  = "yggdrasil.local."
+)
+
+type MDNS struct {
+	phony.Inbox
+	core      *yggdrasil.Core                   //
+	config    *config.NodeState                 //
+	log       *log.Logger                       //
+	info      []string                          //
+	instance  string                            //
+	_running  bool                              //
+	_exprs    []*regexp.Regexp                  //
+	_servers  map[string]map[string]*mDNSServer // intf -> ip -> *mDNSServer
+	_resolver *zeroconf.Resolver                //
+	_context  context.Context                   // used by _resolver
+	_cancel   context.CancelFunc                // used by _resolver
+}
+
+type mDNSServer struct {
+	intf     net.Interface
+	server   *zeroconf.Server
+	listener *yggdrasil.TcpListener
+	time     time.Time
+}
+
+func (m *MDNS) Init(core *yggdrasil.Core, state *config.NodeState, log *log.Logger, options interface{}) error {
+	m.core = core
+	m.config = state
+	m.log = log
+	m.info = []string{
+		fmt.Sprintf("ed25519=%s", core.SigningPublicKey()),
+		fmt.Sprintf("curve25519=%s", core.EncryptionPublicKey()),
+		fmt.Sprintf("versionmajor=%d", yggdrasil.ProtocolMajorVersion),
+		fmt.Sprintf("versionminor=%d", yggdrasil.ProtocolMinorVersion),
+	}
+	if nodeid := core.NodeID(); nodeid != nil {
+		m.instance = hex.EncodeToString((*nodeid)[:])[:16]
+	}
+
+	current := m.config.GetCurrent()
+	m._updateConfig(&current)
+
+	m._context, m._cancel = context.WithCancel(context.Background())
+	m._servers = make(map[string]map[string]*mDNSServer)
+
+	return nil
+}
+
+func (m *MDNS) listen(results <-chan *zeroconf.ServiceEntry) {
+	m.log.Info("Listening for other Yggdrasil nodes via mDNS")
+	for entry := range results {
+		log.Info("Received mDNS entry:", entry)
+	}
+	m.log.Info("No longer listening for other Yggdrasil nodes")
+}
+
+func (m *MDNS) Start() error {
+	var err error
+	phony.Block(m, func() {
+		err = m._start()
+	})
+	m.log.Infoln("Started mDNS module")
+	return err
+}
+
+func (m *MDNS) _start() error {
+	var err error
+	if m._running {
+		return errors.New("mDNS module is already running")
+	}
+
+	resolver, err := zeroconf.NewResolver(nil)
+	if err != nil {
+		m.log.Fatalln("Failed to initialize resolver:", err.Error())
+	}
+	m._resolver = resolver
+	incoming := make(chan *zeroconf.ServiceEntry)
+	go m.listen(incoming)
+
+	err = m._resolver.Browse(m._context, MDNSService, MDNSDomain, incoming)
+	if err != nil {
+		m.log.Fatalln("Failed to browse:", err.Error())
+	}
+
+	m._running = true
+	m.Act(m, m._updateInterfaces)
+
+	return nil
+}
+
+func (m *MDNS) Stop() error {
+	var err error
+	phony.Block(m, func() {
+		err = m._stop()
+	})
+	m.log.Infoln("Stopped mDNS module")
+	return err
+}
+
+func (m *MDNS) _stop() error {
+	m._cancel()
+	for _, intf := range m._servers {
+		for _, ip := range intf {
+			ip.server.Shutdown()
+			ip.listener.Stop()
+		}
+	}
+	return nil
+}
+
+func (m *MDNS) UpdateConfig(config *config.NodeConfig) {
+	var err error
+	phony.Block(m, func() {
+		err = m._updateConfig(config)
+	})
+	if err != nil {
+		m.log.Warnf("Failed to update mDNS config: %s", err)
+	} else {
+		m.log.Infof("mDNS configuration updated")
+	}
+}
+
+func (m *MDNS) _updateConfig(config *config.NodeConfig) error {
+	// Now get a list of interface expressions from the
+	// config. This will dictate which interfaces we are
+	// allowed to use.
+	var exprs []*regexp.Regexp
+	// Compile each regular expression
+	for _, exstr := range config.MulticastInterfaces {
+		e, err := regexp.Compile(exstr)
+		if err != nil {
+			return err
+		}
+		exprs = append(exprs, e)
+	}
+	// Update our expression list.
+	m._exprs = exprs
+	return nil
+}
+
+func (m *MDNS) SetupAdminHandlers(a *admin.AdminSocket) {}
+
+func (m *MDNS) IsStarted() bool {
+	var running bool
+	phony.Block(m, func() {
+		running = m._running
+	})
+	return running
+}
+
+func (m *MDNS) _updateInterfaces() {
+	// Start by getting a list of interfaces from the
+	// operating system.
+	interfaces := make(map[string]map[string]net.Interface)
+	osInterfaces, err := net.Interfaces()
+	if err != nil {
+		return
+	}
+	// Now work through the OS interfaces and work out
+	// which are suitable.
+	for _, intf := range osInterfaces {
+		if intf.Flags&net.FlagUp == 0 {
+			continue
+		}
+		if intf.Flags&net.FlagMulticast == 0 {
+			continue
+		}
+		if intf.Flags&net.FlagPointToPoint != 0 {
+			continue
+		}
+		for _, expr := range m._exprs {
+			// Does the interface match the regular expression? Store it if so
+			if expr.MatchString(intf.Name) {
+				// We should now work out if there are any good candidate
+				// IP addresses on this interface. We will only store it if
+				// there are.
+				addrs, err := intf.Addrs()
+				if err != nil {
+					continue
+				}
+				for _, addr := range addrs {
+					ip, _, err := net.ParseCIDR(addr.String())
+					if err != nil {
+						continue
+					}
+					if ip.IsLinkLocalUnicast() {
+						if _, ok := interfaces[intf.Name]; !ok {
+							interfaces[intf.Name] = make(map[string]net.Interface)
+						}
+						interfaces[intf.Name][ip.String()] = intf
+					}
+				}
+			}
+		}
+	}
+
+	// Work out which interfaces are new.
+	for n, addrs := range interfaces {
+		if _, ok := m._servers[n]; !ok {
+			for addr, intf := range addrs {
+				if err := m._startInterface(intf, addr); err != nil {
+					m.log.Errorf("Failed to start mDNS interface %s on address %s: %s", n, addr, err)
+				} else {
+					m.log.Infof("mDNS started on interface %s address %s", n, addr)
+				}
+			}
+		}
+	}
+
+	// Work out which interfaces have disappeared.
+	for n, _ := range m._servers {
+		if addrs, ok := interfaces[n]; !ok {
+			for addr, server := range m._servers[n] {
+				if err := m._stopInterface(server.intf, addr); err != nil {
+					m.log.Errorf("Failed to stop mDNS interface %s on address %s: %s", n, addr, err)
+				} else {
+					m.log.Infof("mDNS stopped on interface %s address %s", n, addr)
+				}
+			}
+		} else {
+			for addr := range addrs {
+				if intf, ok := interfaces[n][addr]; !ok {
+					if err := m._stopInterface(intf, addr); err != nil {
+						m.log.Errorf("Failed to stop mDNS interface %s on address %s: %s", n, addr, err)
+					} else {
+						m.log.Infof("mDNS stopped on interface %s address %s", n, addr)
+					}
+				}
+			}
+		}
+	}
+
+	time.AfterFunc(time.Second, func() {
+		m.Act(m, m._updateInterfaces)
+	})
+}
+
+func (m *MDNS) _startInterface(intf net.Interface, addr string) error {
+	// Construct a listener on this address.
+	// Work out what the listen address of the new TCP listener should be.
+	ip := net.ParseIP(addr)
+	listenaddr := fmt.Sprintf("[%s%%%s]:%d", ip, intf.Name, 0) // TODO: linklocalport
+	listener, err := m.core.ListenTCP(listenaddr)
+	if err != nil {
+		return fmt.Errorf("m.core.ListenTCP: %w", err)
+	}
+
+	// Resolve it as a TCP endpoint so that we can get the IP address and
+	// port separately.
+	tcpaddr, err := net.ResolveTCPAddr(
+		listener.Listener.Addr().Network(),
+		listener.Listener.Addr().String(),
+	)
+	if err != nil {
+		return fmt.Errorf("net.ResolveTCPAddr: %w", err)
+	}
+
+	// Register a proxy service. This allows us to specify the hostname and
+	// IP addresses to put into the DNS SRV record.
+	server, err := zeroconf.RegisterProxy(
+		m.instance,                    // instance name
+		MDNSService,                   // service name
+		MDNSDomain,                    // service domain
+		tcpaddr.Port,                  // TCP listener port
+		m.instance,                    // our hostname
+		[]string{tcpaddr.IP.String()}, // our IP address
+		m.info,                        // TXT record contents
+		[]net.Interface{intf},         // interfaces to use
+	)
+	if err != nil {
+		return fmt.Errorf("zeroconf.RegisterProxy: %w", err)
+	}
+
+	// Now store information about our new listener and server.
+	if _, ok := m._servers[intf.Name]; !ok {
+		m._servers[intf.Name] = make(map[string]*mDNSServer)
+	}
+	m._servers[intf.Name][addr] = &mDNSServer{
+		intf:     intf,
+		server:   server,
+		listener: listener,
+	}
+
+	return nil
+}
+
+func (m *MDNS) _stopInterface(intf net.Interface, addr string) error {
+	// Check if we know about the interface.
+	addrs, aok := m._servers[intf.Name]
+	if !aok {
+		return fmt.Errorf("interface %q not found", intf.Name)
+	}
+
+	// Check if we know about the address on that interface.
+	server, sok := addrs[addr]
+	if !sok {
+		return fmt.Errorf("address %q not found", addr)
+	}
+
+	// Shut down the mDNS server and the TCP listener.
+	server.server.Shutdown()
+	server.listener.Stop()
+
+	// Clean up.
+	delete(m._servers[intf.Name], addr)
+	if len(m._servers[intf.Name]) == 0 {
+		delete(m._servers, intf.Name)
+	}
+
+	return nil
+}