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client.go
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client.go
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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MIT
package mdns
import (
"context"
"fmt"
"log"
"net"
"strings"
"sync/atomic"
"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 // @Deprecated
AddrV6IPAddr *net.IPAddr
Port int
Info string
InfoFields []string
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"
Timeout time.Duration // Lookup timeout, default 1 second
Interface *net.Interface // Multicast interface to use
Entries chan<- *ServiceEntry // Entries Channel
WantUnicastResponse bool // Unicast response desired, as per 5.4 in RFC
DisableIPv4 bool // Whether to disable usage of IPv4 for MDNS operations. Does not affect discovered addresses.
DisableIPv6 bool // Whether to disable usage of IPv6 for MDNS operations. Does not affect discovered addresses.
Logger *log.Logger // Optionally provide a *log.Logger to better manage log output.
}
// 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.
DisableIPv4: false,
DisableIPv6: false,
}
}
// 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 {
return QueryContext(context.Background(), params)
}
// QueryContext 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. QueryContext will attempt to stop the query
// on cancellation.
func QueryContext(ctx context.Context, params *QueryParam) error {
if params.Logger == nil {
params.Logger = log.Default()
}
// Create a new client
client, err := newClient(!params.DisableIPv4, !params.DisableIPv6, params.Logger)
if err != nil {
return err
}
defer client.Close()
go func() {
select {
case <-ctx.Done():
client.Close()
case <-client.closedCh:
return
}
}()
// Set the multicast interface
if params.Interface != nil {
if err := client.setInterface(params.Interface); err != nil {
return err
}
}
// Ensure defaults are set
if params.Domain == "" {
params.Domain = "local"
}
if params.Timeout == 0 {
params.Timeout = time.Second
}
// Run the query
return client.query(params)
}
// 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 {
use_ipv4 bool
use_ipv6 bool
ipv4UnicastConn *net.UDPConn
ipv6UnicastConn *net.UDPConn
ipv4MulticastConn *net.UDPConn
ipv6MulticastConn *net.UDPConn
closed int32
closedCh chan struct{} // TODO(reddaly): This doesn't appear to be used.
log *log.Logger
}
// NewClient creates a new mdns Client that can be used to query
// for records
func newClient(v4 bool, v6 bool, logger *log.Logger) (*client, error) {
if !v4 && !v6 {
return nil, fmt.Errorf("Must enable at least one of IPv4 and IPv6 querying")
}
// TODO(reddaly): At least attempt to bind to the port required in the spec.
// Create a IPv4 listener
var uconn4 *net.UDPConn
var uconn6 *net.UDPConn
var mconn4 *net.UDPConn
var mconn6 *net.UDPConn
var err error
// Establish unicast connections
if v4 {
uconn4, err = net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
if err != nil {
logger.Printf("[ERR] mdns: Failed to bind to udp4 port: %v", err)
}
}
if v6 {
uconn6, err = net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
if err != nil {
logger.Printf("[ERR] mdns: Failed to bind to udp6 port: %v", err)
}
}
if uconn4 == nil && uconn6 == nil {
return nil, fmt.Errorf("failed to bind to any unicast udp port")
}
// Establish multicast connections
if v4 {
mconn4, err = net.ListenMulticastUDP("udp4", nil, ipv4Addr)
if err != nil {
logger.Printf("[ERR] mdns: Failed to bind to udp4 port: %v", err)
}
}
if v6 {
mconn6, err = net.ListenMulticastUDP("udp6", nil, ipv6Addr)
if err != nil {
logger.Printf("[ERR] mdns: Failed to bind to udp6 port: %v", err)
}
}
if mconn4 == nil && mconn6 == nil {
return nil, fmt.Errorf("failed to bind to any multicast udp port")
}
// Check that unicast and multicast connections have been made for IPv4 and IPv6
// and disable the respective protocol if not.
if uconn4 == nil || mconn4 == nil {
logger.Printf("[INFO] mdns: Failed to listen to both unicast and multicast on IPv4")
uconn4 = nil
mconn4 = nil
v4 = false
}
if uconn6 == nil || mconn6 == nil {
logger.Printf("[INFO] mdns: Failed to listen to both unicast and multicast on IPv6")
uconn6 = nil
mconn6 = nil
v6 = false
}
if !v4 && !v6 {
return nil, fmt.Errorf("at least one of IPv4 and IPv6 must be enabled for querying")
}
c := &client{
use_ipv4: v4,
use_ipv6: v6,
ipv4MulticastConn: mconn4,
ipv6MulticastConn: mconn6,
ipv4UnicastConn: uconn4,
ipv6UnicastConn: uconn6,
closedCh: make(chan struct{}),
log: logger,
}
return c, nil
}
// Close is used to cleanup the client
func (c *client) Close() error {
if !atomic.CompareAndSwapInt32(&c.closed, 0, 1) {
// something else already closed it
return nil
}
c.log.Printf("[INFO] mdns: Closing client %v", *c)
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 system
// default if not provided
func (c *client) setInterface(iface *net.Interface) error {
if c.use_ipv4 {
p := ipv4.NewPacketConn(c.ipv4UnicastConn)
if err := p.SetMulticastInterface(iface); err != nil {
return err
}
p = ipv4.NewPacketConn(c.ipv4MulticastConn)
if err := p.SetMulticastInterface(iface); err != nil {
return err
}
}
if c.use_ipv6 {
p2 := ipv6.NewPacketConn(c.ipv6UnicastConn)
if err := p2.SetMulticastInterface(iface); err != nil {
return err
}
p2 = ipv6.NewPacketConn(c.ipv6MulticastConn)
if err := p2.SetMulticastInterface(iface); err != nil {
return err
}
}
return nil
}
// msgAddr carries the message and source address from recv to message processing.
type msgAddr struct {
msg *dns.Msg
src *net.UDPAddr
}
// 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 *msgAddr, 32)
if c.use_ipv4 {
go c.recv(c.ipv4UnicastConn, msgCh)
go c.recv(c.ipv4MulticastConn, msgCh)
}
if c.use_ipv6 {
go c.recv(c.ipv6UnicastConn, msgCh)
go c.recv(c.ipv6MulticastConn, msgCh)
}
// Send the query
m := new(dns.Msg)
m.SetQuestion(serviceAddr, dns.TypePTR)
// 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)
// Listen until we reach the timeout
finish := time.After(params.Timeout)
for {
select {
case resp := <-msgCh:
var inp *ServiceEntry
for _, answer := range append(resp.msg.Answer, resp.msg.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)
case *dns.SRV:
// Check for a target mismatch
if rr.Target != rr.Hdr.Name {
alias(inprogress, rr.Hdr.Name, rr.Target)
}
// Get the port
inp = ensureName(inprogress, rr.Hdr.Name)
inp.Host = rr.Target
inp.Port = int(rr.Port)
case *dns.TXT:
// Pull out the txt
inp = ensureName(inprogress, rr.Hdr.Name)
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)
inp.Addr = rr.A // @Deprecated
inp.AddrV4 = rr.A
case *dns.AAAA:
// Pull out the IP
inp = ensureName(inprogress, rr.Hdr.Name)
inp.Addr = rr.AAAA // @Deprecated
inp.AddrV6 = rr.AAAA // @Deprecated
inp.AddrV6IPAddr = &net.IPAddr{IP: rr.AAAA}
// link-local IPv6 addresses must be qualified with a zone (interface). Zone is
// specific to this machine/network-namespace and so won't be carried in the
// mDNS message itself. We borrow the zone from the source address of the UDP
// packet, as the link-local address should be valid on that interface.
if rr.AAAA.IsLinkLocalUnicast() || rr.AAAA.IsLinkLocalMulticast() {
inp.AddrV6IPAddr.Zone = resp.src.Zone
}
}
}
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:
default:
}
} else {
// Fire off a node specific query
m := new(dns.Msg)
m.SetQuestion(inp.Name, dns.TypePTR)
m.RecursionDesired = false
if err := c.sendQuery(m); err != nil {
c.log.Printf("[ERR] mdns: Failed to query instance %s: %v", inp.Name, err)
}
}
case <-finish:
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 {
_, err = c.ipv4UnicastConn.WriteToUDP(buf, ipv4Addr)
if err != nil {
return err
}
}
if c.ipv6UnicastConn != nil {
_, err = c.ipv6UnicastConn.WriteToUDP(buf, ipv6Addr)
if err != nil {
return err
}
}
return nil
}
// recv is used to receive until we get a shutdown
func (c *client) recv(l *net.UDPConn, msgCh chan *msgAddr) {
if l == nil {
return
}
buf := make([]byte, 65536)
for atomic.LoadInt32(&c.closed) == 0 {
n, addr, err := l.ReadFromUDP(buf)
if atomic.LoadInt32(&c.closed) == 1 {
return
}
if err != nil {
c.log.Printf("[ERR] mdns: Failed to read packet: %v", err)
continue
}
msg := new(dns.Msg)
if err := msg.Unpack(buf[:n]); err != nil {
c.log.Printf("[ERR] mdns: Failed to unpack packet: %v", err)
continue
}
select {
case msgCh <- &msgAddr{
msg: msg,
src: addr,
}:
case <-c.closedCh:
return
}
}
}
// ensureName is used to ensure the named node is in progress
func ensureName(inprogress map[string]*ServiceEntry, name string) *ServiceEntry {
if inp, ok := inprogress[name]; ok {
return inp
}
inp := &ServiceEntry{
Name: name,
}
inprogress[name] = inp
return inp
}
// alias is used to setup an alias between two entries
func alias(inprogress map[string]*ServiceEntry, src, dst string) {
srcEntry := ensureName(inprogress, src)
inprogress[dst] = srcEntry
}