vendor.github.com.pion.mdns.conn.go Maven / Gradle / Ivy
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// SPDX-FileCopyrightText: 2023 The Pion community
// SPDX-License-Identifier: MIT
package mdns
import (
"context"
"errors"
"fmt"
"net"
"sync"
"time"
"github.com/pion/logging"
"golang.org/x/net/dns/dnsmessage"
"golang.org/x/net/ipv4"
)
// Conn represents a mDNS Server
type Conn struct {
mu sync.RWMutex
log logging.LeveledLogger
socket *ipv4.PacketConn
dstAddr *net.UDPAddr
queryInterval time.Duration
localNames []string
queries []*query
ifaces []net.Interface
closed chan interface{}
}
type query struct {
nameWithSuffix string
queryResultChan chan queryResult
}
type queryResult struct {
answer dnsmessage.ResourceHeader
addr net.Addr
}
const (
defaultQueryInterval = time.Second
destinationAddress = "224.0.0.251:5353"
maxMessageRecords = 3
responseTTL = 120
// maxPacketSize is the maximum size of a mdns packet.
// From RFC 6762:
// Even when fragmentation is used, a Multicast DNS packet, including IP
// and UDP headers, MUST NOT exceed 9000 bytes.
// https://datatracker.ietf.org/doc/html/rfc6762#section-17
maxPacketSize = 9000
)
var errNoPositiveMTUFound = errors.New("no positive MTU found")
// Server establishes a mDNS connection over an existing conn.
//
// Currently, the server only supports listening on an IPv4 connection, but internally
// it supports answering with IPv6 AAAA records if this were ever to change.
func Server(conn *ipv4.PacketConn, config *Config) (*Conn, error) {
if config == nil {
return nil, errNilConfig
}
ifaces := config.Interfaces
if ifaces == nil {
var err error
ifaces, err = net.Interfaces()
if err != nil {
return nil, err
}
}
inboundBufferSize := 0
joinErrCount := 0
ifacesToUse := make([]net.Interface, 0, len(ifaces))
for i, ifc := range ifaces {
if !config.IncludeLoopback && ifc.Flags&net.FlagLoopback == net.FlagLoopback {
continue
}
if err := conn.JoinGroup(&ifaces[i], &net.UDPAddr{IP: net.IPv4(224, 0, 0, 251)}); err != nil {
joinErrCount++
continue
}
ifcCopy := ifc
ifacesToUse = append(ifacesToUse, ifcCopy)
if ifaces[i].MTU > inboundBufferSize {
inboundBufferSize = ifaces[i].MTU
}
}
if inboundBufferSize == 0 {
return nil, errNoPositiveMTUFound
}
if inboundBufferSize > maxPacketSize {
inboundBufferSize = maxPacketSize
}
if joinErrCount >= len(ifaces) {
return nil, errJoiningMulticastGroup
}
dstAddr, err := net.ResolveUDPAddr("udp", destinationAddress)
if err != nil {
return nil, err
}
loggerFactory := config.LoggerFactory
if loggerFactory == nil {
loggerFactory = logging.NewDefaultLoggerFactory()
}
localNames := []string{}
for _, l := range config.LocalNames {
localNames = append(localNames, l+".")
}
c := &Conn{
queryInterval: defaultQueryInterval,
queries: []*query{},
socket: conn,
dstAddr: dstAddr,
localNames: localNames,
ifaces: ifacesToUse,
log: loggerFactory.NewLogger("mdns"),
closed: make(chan interface{}),
}
if config.QueryInterval != 0 {
c.queryInterval = config.QueryInterval
}
if err := conn.SetControlMessage(ipv4.FlagInterface, true); err != nil {
c.log.Warnf("Failed to SetControlMessage on PacketConn %v", err)
}
if config.IncludeLoopback {
// this is an efficient way for us to send ourselves a message faster instead of it going
// further out into the network stack.
if err := conn.SetMulticastLoopback(true); err != nil {
c.log.Warnf("Failed to SetMulticastLoopback(true) on PacketConn %v; this may cause inefficient network path communications", err)
}
}
// https://www.rfc-editor.org/rfc/rfc6762.html#section-17
// Multicast DNS messages carried by UDP may be up to the IP MTU of the
// physical interface, less the space required for the IP header (20
// bytes for IPv4; 40 bytes for IPv6) and the UDP header (8 bytes).
go c.start(inboundBufferSize-20-8, config)
return c, nil
}
// Close closes the mDNS Conn
func (c *Conn) Close() error {
select {
case <-c.closed:
return nil
default:
}
if err := c.socket.Close(); err != nil {
return err
}
<-c.closed
return nil
}
// Query sends mDNS Queries for the following name until
// either the Context is canceled/expires or we get a result
func (c *Conn) Query(ctx context.Context, name string) (dnsmessage.ResourceHeader, net.Addr, error) {
select {
case <-c.closed:
return dnsmessage.ResourceHeader{}, nil, errConnectionClosed
default:
}
nameWithSuffix := name + "."
queryChan := make(chan queryResult, 1)
query := &query{nameWithSuffix, queryChan}
c.mu.Lock()
c.queries = append(c.queries, query)
c.mu.Unlock()
defer func() {
c.mu.Lock()
defer c.mu.Unlock()
for i := len(c.queries) - 1; i >= 0; i-- {
if c.queries[i] == query {
c.queries = append(c.queries[:i], c.queries[i+1:]...)
}
}
}()
ticker := time.NewTicker(c.queryInterval)
defer ticker.Stop()
c.sendQuestion(nameWithSuffix)
for {
select {
case <-ticker.C:
c.sendQuestion(nameWithSuffix)
case <-c.closed:
return dnsmessage.ResourceHeader{}, nil, errConnectionClosed
case res := <-queryChan:
// Given https://datatracker.ietf.org/doc/html/draft-ietf-mmusic-mdns-ice-candidates#section-3.2.2-2
// An ICE agent SHOULD ignore candidates where the hostname resolution returns more than one IP address.
//
// We will take the first we receive which could result in a race between two suitable addresses where
// one is better than the other (e.g. localhost vs LAN).
return res.answer, res.addr, nil
case <-ctx.Done():
return dnsmessage.ResourceHeader{}, nil, errContextElapsed
}
}
}
type ipToBytesError struct {
ip net.IP
expectedType string
}
func (err ipToBytesError) Error() string {
return fmt.Sprintf("ip (%s) is not %s", err.ip, err.expectedType)
}
func ipv4ToBytes(ip net.IP) ([4]byte, error) {
rawIP := ip.To4()
if rawIP == nil {
return [4]byte{}, ipToBytesError{ip, "IPv4"}
}
// net.IPs are stored in big endian / network byte order
var out [4]byte
copy(out[:], rawIP[:])
return out, nil
}
func ipv6ToBytes(ip net.IP) ([16]byte, error) {
rawIP := ip.To16()
if rawIP == nil {
return [16]byte{}, ipToBytesError{ip, "IPv6"}
}
// net.IPs are stored in big endian / network byte order
var out [16]byte
copy(out[:], rawIP[:])
return out, nil
}
func interfaceForRemote(remote string) (net.IP, error) {
conn, err := net.Dial("udp", remote)
if err != nil {
return nil, err
}
localAddr, ok := conn.LocalAddr().(*net.UDPAddr)
if !ok {
return nil, errFailedCast
}
if err := conn.Close(); err != nil {
return nil, err
}
return localAddr.IP, nil
}
func (c *Conn) sendQuestion(name string) {
packedName, err := dnsmessage.NewName(name)
if err != nil {
c.log.Warnf("Failed to construct mDNS packet %v", err)
return
}
msg := dnsmessage.Message{
Header: dnsmessage.Header{},
Questions: []dnsmessage.Question{
{
Type: dnsmessage.TypeA,
Class: dnsmessage.ClassINET,
Name: packedName,
},
},
}
rawQuery, err := msg.Pack()
if err != nil {
c.log.Warnf("Failed to construct mDNS packet %v", err)
return
}
c.writeToSocket(0, rawQuery, false)
}
func (c *Conn) writeToSocket(ifIndex int, b []byte, srcIfcIsLoopback bool) {
if ifIndex != 0 {
ifc, err := net.InterfaceByIndex(ifIndex)
if err != nil {
c.log.Warnf("Failed to get interface for %d: %v", ifIndex, err)
return
}
if srcIfcIsLoopback && ifc.Flags&net.FlagLoopback == 0 {
// avoid accidentally tricking the destination that itself is the same as us
c.log.Warnf("Interface is not loopback %d", ifIndex)
return
}
if err := c.socket.SetMulticastInterface(ifc); err != nil {
c.log.Warnf("Failed to set multicast interface for %d: %v", ifIndex, err)
} else {
if _, err := c.socket.WriteTo(b, nil, c.dstAddr); err != nil {
c.log.Warnf("Failed to send mDNS packet on interface %d: %v", ifIndex, err)
}
}
return
}
for ifcIdx := range c.ifaces {
if srcIfcIsLoopback && c.ifaces[ifcIdx].Flags&net.FlagLoopback == 0 {
// avoid accidentally tricking the destination that itself is the same as us
continue
}
if err := c.socket.SetMulticastInterface(&c.ifaces[ifcIdx]); err != nil {
c.log.Warnf("Failed to set multicast interface for %d: %v", c.ifaces[ifcIdx].Index, err)
} else {
if _, err := c.socket.WriteTo(b, nil, c.dstAddr); err != nil {
c.log.Warnf("Failed to send mDNS packet on interface %d: %v", c.ifaces[ifcIdx].Index, err)
}
}
}
}
func createAnswer(name string, addr net.IP) (dnsmessage.Message, error) {
packedName, err := dnsmessage.NewName(name)
if err != nil {
return dnsmessage.Message{}, err
}
msg := dnsmessage.Message{
Header: dnsmessage.Header{
Response: true,
Authoritative: true,
},
Answers: []dnsmessage.Resource{
{
Header: dnsmessage.ResourceHeader{
Type: dnsmessage.TypeA,
Class: dnsmessage.ClassINET,
Name: packedName,
TTL: responseTTL,
},
},
},
}
if ip4 := addr.To4(); ip4 != nil {
ipBuf, err := ipv4ToBytes(addr)
if err != nil {
return dnsmessage.Message{}, err
}
msg.Answers[0].Body = &dnsmessage.AResource{
A: ipBuf,
}
} else {
ipBuf, err := ipv6ToBytes(addr)
if err != nil {
return dnsmessage.Message{}, err
}
msg.Answers[0].Body = &dnsmessage.AAAAResource{
AAAA: ipBuf,
}
}
return msg, nil
}
func (c *Conn) sendAnswer(name string, ifIndex int, addr net.IP) {
answer, err := createAnswer(name, addr)
if err != nil {
c.log.Warnf("Failed to create mDNS answer %v", err)
return
}
rawAnswer, err := answer.Pack()
if err != nil {
c.log.Warnf("Failed to construct mDNS packet %v", err)
return
}
c.writeToSocket(ifIndex, rawAnswer, addr.IsLoopback())
}
func (c *Conn) start(inboundBufferSize int, config *Config) { //nolint gocognit
defer func() {
c.mu.Lock()
defer c.mu.Unlock()
close(c.closed)
}()
b := make([]byte, inboundBufferSize)
p := dnsmessage.Parser{}
for {
n, cm, src, err := c.socket.ReadFrom(b)
if err != nil {
if errors.Is(err, net.ErrClosed) {
return
}
c.log.Warnf("Failed to ReadFrom %q %v", src, err)
continue
}
var ifIndex int
if cm != nil {
ifIndex = cm.IfIndex
}
var srcIP net.IP
switch addr := src.(type) {
case *net.UDPAddr:
srcIP = addr.IP
case *net.TCPAddr:
srcIP = addr.IP
default:
c.log.Warnf("Failed to determine address type %T for source address %s", src, src)
continue
}
srcIsIPv4 := srcIP.To4() != nil
func() {
c.mu.RLock()
defer c.mu.RUnlock()
if _, err := p.Start(b[:n]); err != nil {
c.log.Warnf("Failed to parse mDNS packet %v", err)
return
}
for i := 0; i <= maxMessageRecords; i++ {
q, err := p.Question()
if errors.Is(err, dnsmessage.ErrSectionDone) {
break
} else if err != nil {
c.log.Warnf("Failed to parse mDNS packet %v", err)
return
}
for _, localName := range c.localNames {
if localName == q.Name.String() {
if config.LocalAddress != nil {
c.sendAnswer(q.Name.String(), ifIndex, config.LocalAddress)
} else {
var localAddress net.IP
// prefer the address of the interface if we know its index, but otherwise
// derive it from the address we read from. We do this because even if
// multicast loopback is in use or we send from a loopback interface,
// there are still cases where the IP packet will contain the wrong
// source IP (e.g. a LAN interface).
// For example, we can have a packet that has:
// Source: 192.168.65.3
// Destination: 224.0.0.251
// Interface Index: 1
// Interface Addresses @ 1: [127.0.0.1/8 ::1/128]
if ifIndex != 0 {
ifc, netErr := net.InterfaceByIndex(ifIndex)
if netErr != nil {
c.log.Warnf("Failed to get interface for %d: %v", ifIndex, netErr)
continue
}
addrs, addrsErr := ifc.Addrs()
if addrsErr != nil {
c.log.Warnf("Failed to get addresses for interface %d: %v", ifIndex, addrsErr)
continue
}
if len(addrs) == 0 {
c.log.Warnf("Expected more than one address for interface %d", ifIndex)
continue
}
var selectedIP net.IP
for _, addr := range addrs {
var ip net.IP
switch addr := addr.(type) {
case *net.IPNet:
ip = addr.IP
case *net.IPAddr:
ip = addr.IP
default:
c.log.Warnf("Failed to determine address type %T from interface %d", addr, ifIndex)
continue
}
// match up respective IP types
if ipv4 := ip.To4(); ipv4 == nil {
if srcIsIPv4 {
continue
} else if !isSupportedIPv6(ip) {
continue
}
} else if !srcIsIPv4 {
continue
}
selectedIP = ip
break
}
if selectedIP == nil {
c.log.Warnf("Failed to find suitable IP for interface %d; deriving address from source address instead", ifIndex)
} else {
localAddress = selectedIP
}
} else if ifIndex == 0 || localAddress == nil {
localAddress, err = interfaceForRemote(src.String())
if err != nil {
c.log.Warnf("Failed to get local interface to communicate with %s: %v", src.String(), err)
continue
}
}
c.sendAnswer(q.Name.String(), ifIndex, localAddress)
}
}
}
}
for i := 0; i <= maxMessageRecords; i++ {
a, err := p.AnswerHeader()
if errors.Is(err, dnsmessage.ErrSectionDone) {
return
}
if err != nil {
c.log.Warnf("Failed to parse mDNS packet %v", err)
return
}
if a.Type != dnsmessage.TypeA && a.Type != dnsmessage.TypeAAAA {
continue
}
for i := len(c.queries) - 1; i >= 0; i-- {
if c.queries[i].nameWithSuffix == a.Name.String() {
ip, err := ipFromAnswerHeader(a, p)
if err != nil {
c.log.Warnf("Failed to parse mDNS answer %v", err)
return
}
c.queries[i].queryResultChan <- queryResult{a, &net.IPAddr{
IP: ip,
}}
c.queries = append(c.queries[:i], c.queries[i+1:]...)
}
}
}
}()
}
}
func ipFromAnswerHeader(a dnsmessage.ResourceHeader, p dnsmessage.Parser) (ip []byte, err error) {
if a.Type == dnsmessage.TypeA {
resource, err := p.AResource()
if err != nil {
return nil, err
}
ip = resource.A[:]
} else {
resource, err := p.AAAAResource()
if err != nil {
return nil, err
}
ip = resource.AAAA[:]
}
return
}
// The conditions of invalidation written below are defined in
// https://tools.ietf.org/html/rfc8445#section-5.1.1.1
func isSupportedIPv6(ip net.IP) bool {
if len(ip) != net.IPv6len ||
isZeros(ip[0:12]) || // !(IPv4-compatible IPv6)
ip[0] == 0xfe && ip[1]&0xc0 == 0xc0 || // !(IPv6 site-local unicast)
ip.IsLinkLocalUnicast() ||
ip.IsLinkLocalMulticast() {
return false
}
return true
}
func isZeros(ip net.IP) bool {
for i := 0; i < len(ip); i++ {
if ip[i] != 0 {
return false
}
}
return true
}