UPnP Discovery with Sonos players

Following on from my previous article on Discovering UPnP Devices this post describes how to be a bit more specific about what we are searching for. Specifically, I will be searching for Sonos music streaming devices.

A crude way of doing this would be to alter the device_proxy_available_cb callback function with an if/then statement that selectively printed out device information based on the values in the model or Friendly Name information, but UPnP provides us with a better approach: When you initiate a discovery, your discovery request includes a specification of what you want to discover. Previously we used the specification upnp:rootdevice which discovered every device. We can limit this by saying we are only interested in certain types of devices.

UPnP devices have a hierarchy. Typically there is a root device which can contain one or more sub-devices. These sub-devices represent specific functionality. Sonos Zoneplayers contain several sub-devices which do different things, but in this case I am interested in the part which plays music. In UPnP terms this is a UPnP AV MediaRenderer.

Each UPnP device type has a URN which identifies what type of device or sub-device it is. The standard URNs for things like UPnP AV are described in the UPnP specification documents at www.upnp.org but these are also available directly from the device itself.

The easiest way to get these is by using a developers too like UPnP Device Spy. Note that Device Spy and similar tools are not "sniffers" as some uninformed people like to claim. They are developer tools. They discover devices and provide an easy way to query them for their capabilities, status and even to execute actions on them.

In this case, examining the UPnP documentation, or using Device Spy and looking at a Zoneplayer, reveals the URN for the UPnP AV Media Renderer is urn:schemas-upnp-org:device:MediaRenderer:1. So if we use that in our discovery, we will only get devices which match this specification returned.

The previous code I present discovered every UPnP device on the network. By modifying this slightly, we can make it so it only returns media player devices. This modified version is shown below with the lines that have changed highlighted:


As you can see, the change is very simple. If we now run this we will get something like the following:
A few things are noteworthy here:

• We only have Media Renderer devices. The firewall and the Sonos WD100 dock no longer show up
• The format of the output is slightly different. This is because we have been returned the MediaRenderer sub-device instead of the root device
• We no longer get the IP address. This isn't a problem as you really should never need it. If you really must have it (e.g. for display info), there are ways to find it.
• In this case we get the Zoneplayer zone name
• In the example above there are no non-Sonos MediaRenderer devices on the network. If there were they would show up in this list

So that is how to restrict UPnP discovery to a specific type of device.