Bonjour / mDNS / ZeroConf support in App::HTTPThis

App::HTTPThis can advertise your local web server on your network so other devices can find it without you having to tell them an IP address and port.

This document explains the what, the how, and the how do I check it’s working?

1) What is Bonjour / Rendezvous / mDNS / ZeroConf / Avahi?

The 30‑second version

mDNS (multicast DNS) is the core technology: DNS‑like name lookups performed on the local network using multicast rather than a central DNS server.
DNS‑SD (DNS Service Discovery) is the convention layered on top that says how a service advertises itself (service type, name, port, and optional metadata).
Bonjour is Apple’s implementation/branding of mDNS + DNS‑SD.
Rendezvous was Apple’s earlier name for the same thing.
ZeroConf is a broader term (“zero configuration networking”) that includes mDNS + DNS‑SD and related ideas.
Avahi is the common Linux implementation of mDNS + DNS‑SD.

So when people say “Bonjour” (or “Rendezvous”, “mDNS”, “ZeroConf”, “Avahi”), they’re usually talking about the same family of technologies: advertise a service on the local network and let clients discover it automatically.

What it does for App::HTTPThis

When you start http_this with a name, it can publish a service of type:

$ http_this --name MyService .

_http._tcp on the local domain

That means other machines on the same network that speak mDNS/DNS‑SD can discover something like:

Service name: MyService
Service type: _http._tcp
Address/port: e.g. 172.24.198.3:7007

(Exact details depend on your network and how many interfaces you have.)

2) How do I use it with `http_this`?

Basic usage

Start the server and publish it via mDNS/DNS‑SD:

http_this --name MyService

--name is the service instance name that other devices will see.
If you omit --name, the server will still run, but it will not advertise itself over mDNS.

What Perl modules do I need?

Publishing is implemented via Net::Rendezvous::Publish.

You will also need an appropriate backend module for your platform, typically:

Net::Rendezvous::Publish::Backend::Avahi (common on Linux)

In other words:

Publishing (what http_this does): Net::Rendezvous::Publish + a Net::Rendezvous::Publish::Backend::*.

Notes and gotchas

“Bonjour” is just the ecosystem name. App::HTTPThis does not require Apple libraries; it publishes an mDNS/DNS‑SD service that any Bonjour/mDNS client can discover.
Multiple interfaces are normal. On machines with Docker, WSL2, VPNs, etc., your service may appear once per interface.
The advertised name is not a hostname. It’s a service instance label shown in service browsers.

3) How do I see my advertised service?

Option A: Avahi tools (Linux)

If you’re on Linux with Avahi installed, you can browse all advertised services:

avahi-browse -at

You should see entries like:

Service name (e.g. MyService)
Service type (_http._tcp)
Domain (local)

To filter to HTTP services only:

avahi-browse -rt _http._tcp

Option B: A graphical browser

On many platforms there are “Bonjour browser” apps that show advertised services. These are handy for a quick sanity check.

(Any mDNS/DNS‑SD browser should work — you’re just looking for _http._tcp with the instance name you chose.)

Option C: Discover from Perl

To discover services from Perl, use Net::Bonjour.

Net::Bonjour can browse and resolve services to host/port information.

A minimal example (adapted from the Net::Bonjour documentation):

use strict;
use warnings;

use Net::Bonjour;

my $browser = Net::Bonjour->new('http');
$browser->discover;

for my $service ($browser->services) {
  $service->resolve;
  next unless $service->name; # defensive
  printf "%s %s:%s\n",
    $service->name,
    ($service->addresses)[0] // 'unknown',
    $service->port // 'unknown';
}

If you started:

http_this --name MyService

…you should see output that includes something like:

MyService 172.24.198.3:7007

Interpreting what you see

Seeing MyService means the advertisement is happening.
Seeing an address/port means the client successfully resolved the service.
If you see multiple MyService entries, you’re likely seeing multiple network interfaces.

Troubleshooting

I don’t see anything in my browser
- Ensure you started with --name.
- Ensure the publish modules are installed (Net::Rendezvous::Publish + backend).
- Ensure mDNS isn’t blocked by firewall rules on your machine or network.
It shows up, but I can’t connect
- Confirm which address/port was advertised.
- Confirm your server is listening on the interface reachable from the client.
- Check if you’re in an environment with tricky networking (WSL2, Docker bridges, VPNs).
What should I tell users to connect to?
- Many service browsers will let you click through.
- Otherwise, tell them the resolved http://<address>:<port>/.