Scratching my own itch, or how to publish multicast DNS records in Go

DHCP handles allocating IP addresses to the devices on my home network, but that leaves me with the problem of mapping IP addresses to names. The Macs and Linux hosts sort this out with Bonjour and Avahi, but annoyingly two devices, my router and my NAS don’t support it.

Now, I could hack my /etc/hosts file for those two hosts, but that doesn’t work well for embedded devices like iPad. Alternatively, I could install Avahi on my NAS, which is running Debian Sid armel, but space on it’s tiny root file system is always at a premium.

Fortunately, my NAS is also one of my Go development systems, so after some prodding from +Brian Ketelsen, I wrote a package to replicate the parts of Avahi that I needed. Here it is

https://github.com/davecheney/mdns/

Here is a simple example of how to use the package.

import (
        "net"
        "github.com/davecheney/mdns"
)

func main() {
        // Publish a SVR record for ssh running on port 22 for my home NAS.

        // Publish an A record for the host
        mdns.PublishA("stora.local.", 3600, net.IPv4(192, 168, 1, 200))

        // Publish a PTR record for the _ssh._tcp DNS-SD type
        mdns.PublishPTR("_ssh._tcp.local.", 3600, "stora._ssh._tcp.local.")

        // Publish a SRV record typing the _ssh._tcp record to an A record and a port.
        mdns.PublishSRV("stora._ssh._tcp.local.", 3600, "stora.local.", 22)

        // Most mDNS browsing tools expect a TXT record for the service even if there
        // are not records defined by RFC 2782.
        mdns.PublishTXT("stora._ssh._tcp.local.", 3600, "")

        select{}
}

So that’s it. This package has scratched my itch and I hope it is useful for others. I’d love to hear feedback and suggestions you’ve found it to be useful.

updated 16/10/2011 Thanks to @eneff for the select{} tip.

Related posts:

  1. Introducing gmx, runtime instrumentation for Go applications
  2. Bash trick ‘o the day
  3. Go 1.1 performance improvements, part 3
  4. Netgear Stora as an ARM development platform

4 thoughts on “Scratching my own itch, or how to publish multicast DNS records in Go”

  1. davewongillies

    Another way to do it would be to put the hosts in /etc/avahi/hosts on a linux box that’s always on (well if you have that). Its pretty much multicast /etc/hosts.

  2. Dave Cheney

    Yeah, I could have compiled Avahi somewhere else to avoid the dire situation on the root partition, but then I wouldn’t have had a story to tell about it afterwards.

  3. Andrew Gerrand

    Nice library. :-)BTW, the canonical way to block indefinitely is an empty select statement (`select{}`) – saves you an allocation. :-)

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