README
¶
MDNS 
MDNS is a simple mdns client/server library by Hashicorp.
We maintain a fork with updates for PRs and issues they have not merged or addressed.
Overview
MDNS or Multicast DNS can be used to discover services on the local network without the use of an authoritative DNS server. This enables peer-to-peer discovery. It is important to note that many networks restrict the use of multicasting, which prevents mDNS from functioning. Notably, multicast cannot be used in any sort of cloud, or shared infrastructure environment. However it works well in most office, home, or private infrastructure environments.
Usage
Using the library is very simple, here is an example of publishing a service entry:
package main
import (
"github.com/micro/mdns"
"os"
)
func main() {
// Setup our service export
host, _ := os.Hostname()
info := []string{"My awesome service"}
service, _ := mdns.NewMDNSService(host, "_foobar._tcp", "", "", 8000, nil, info)
// Create the mDNS server, defer shutdown
server, _ := mdns.NewServer(&mdns.Config{Zone: service})
defer server.Shutdown()
}
Doing a lookup for service providers is also very simple:
package main
import (
"fmt"
"github.com/micro/mdns"
)
func main() {
// Make a channel for results and start listening
entriesCh := make(chan *mdns.ServiceEntry, 8)
go func() {
for entry := range entriesCh {
fmt.Printf("Got new entry: %v\n", entry)
}
}()
// Start the lookup
err := mdns.Lookup("_foobar._tcp", entriesCh)
if err != nil {
fmt.Println(err)
}
close(entriesCh)
}
Documentation
¶
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Listen ¶
func Listen(entries chan<- *ServiceEntry, exit chan struct{}) error
Listen listens indefinitely for multicast updates
func Lookup ¶
func Lookup(service string, entries chan<- *ServiceEntry) error
Lookup is the same as Query, however it uses all the default parameters
func Query ¶
func Query(params *QueryParam) error
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.
Types ¶
type Config ¶
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
}
Config is used to configure the mDNS server
type DNSSDService ¶
type DNSSDService struct {
MDNSService *MDNSService
}
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()
func (*DNSSDService) Records ¶
func (s *DNSSDService) Records(q dns.Question) []dns.RR
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.
type MDNSService ¶
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
// contains filtered or unexported fields
}
MDNSService is used to export a named service by implementing a Zone
func NewMDNSService ¶
func NewMDNSService(instance, service, domain, hostName string, port int, ips []net.IP, txt []string) (*MDNSService, error)
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.
type QueryParam ¶
type QueryParam struct {
Service string // Service to lookup
Domain string // Lookup domain, default "local"
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
}
QueryParam is used to customize how a Lookup is performed
func DefaultParams ¶
func DefaultParams(service string) *QueryParam
DefaultParams is used to return a default set of QueryParam's
type Server ¶
type Server struct {
// contains filtered or unexported fields
}
mDNS server is used to listen for mDNS queries and respond if we have a matching local record
func (*Server) SendMulticast ¶
multicastResponse us used to send a multicast response packet
Source Files
Directories