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mDNS_Support.md

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mDNS Support

The Physical Web is about getting URLs into the physical world. However, this isn't limited to just Bluetooth Low Energy (BLE) beacons. mDNS is a service broadcast technique used in Wi-Fi networks. It has two advantages over BLE:

  1. Only people logged into your Wi-Fi can see the mDNS URLs. This means that in an apartment, your neighbors can't see your devices.
  2. It doesn't have the length restrictions of BLE, so a URL can be as long as you'd like (well, at least up to 100 characters).

Below is an example of how to setup a Raspberry Pi to broadcast a Physical Web URL using mDNS. We hope others are willing to contribute and offer more versions. If so, we'll create an mDNS directory for all the alternatives.

You'll first need a mDNS service on your Raspberry Pi. Avahi is the one we use here:

sudo apt-get install avahi-daemon

You'll then place a .service file into the /etc/avahi/services directory.
Our sample file physical-web-url.service looks like this:

<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">

<service-group>
  <name replace-wildcards="yes">http://www.mycompany.com/xyz.html</name>
  <service>
    <host-name>www.mycompany.com</host-name>
    <type>_http._tcp</type>
    <port>80</port>
    <txt-record>path=/xyz.html</txt-record>
  </service>
</service-group>

Then <name> tag must be unique on your network. We are suggesting that you use the URL as your name to be safe. Finally reload Avahi daemon:

sudo /etc/init.d/avahi-daemon reload

That should be it. If you have the latest client on your phone, the web page http://www.mycompany.com/xyz.html will now show up in your list of nearby devices.

Note: if the URL is global, it shows up just like a BLE beacon with Title, Description, and favicon information. If the URL is local (e.g. 192.x.x.x) the meta data isn't supported yet, only the URL itself will be displayed. We're working on adding the meta data.