gatkin / dnssd

DNS Service Discovery for Go

DNS-Based Service Discovery for Go

DNS-Based service discovery, or DNS-SD (RFC 6763), can be used to discover services on a local area network advertised over Multicast DNS, or mDNS (RFC 6762), enabling peer-to-peer discovery.

This library provides DNS-SD capabilities in Go. To use it, you first create a resolver by specifying the interfaces and address family on which to browse for services.

ifi, err := net.InterfaceByName("en0")
if err != nil {
    log.Fatal(err)
}

resolver, err := dnssd.NewResolver(dnssd.AddrFamilyIPv4, []net.Interface{*ifi})
if err != nil {
    log.Fatal(err)
}
defer resolver.Close()

Next, you provide the names of the services which you wish to browse for to the resolver. The same resolver can be used to browse for multiple services.

resolver.BrowseService("_http._tcp.local.")
resolver.BrowseService("_googlecast._tcp.local.")

Finally, you can query the resolver for the set of fully resolved service instances by either retrieving all resolved instances or only instances for a particular service.

instances := resolver.GetAllResolvedInstances()
for _, instance := range instances {
    fmt.Printf("%v\n", instance)
}

chromecasts := resolver.GetResolvedInstances("_googlecast._tcp.local.")
for _, instance := range instances {
    fmt.Printf("%v\n", instance)
}

We can put all of this together to discover all instances of the _http._tcp service on the local network

package main

import (
    "fmt"
    "log"
    "net"
    "time"

    "github.com/gatkin/dnssd"
)

func main() {
    ifi, err := net.InterfaceByName("en0")
    if err != nil {
        log.Fatal(err)
    }

    resolver, err := dnssd.NewResolver(dnssd.AddrFamilyIPv4, []net.Interface{*ifi})
    if err != nil {
        log.Fatal(err)
    }
    defer resolver.Close()

    resolver.BrowseService("_http._tcp.local.")
    resolver.BrowseService("_googlecast._tcp.local.")

    // Wait some time to allow all service instances to be discovered.
    time.Sleep(1 * time.Second)

    instances := resolver.GetAllResolvedInstances()
    for _, instance := range instances {
        fmt.Printf("%v\n", instance)
    }
}