Not all messaging protocols are the same. Different protocols may offer
different messaging features, for example contact presence, avatars,
geolocation, Voice-over-IP, etc. Sometimes a particular server
implementation/version/instance won't have certain features enabled.
Telepathy exposes the various available features for a connection as
D-Bus interfaces.
The same might apply to channels. A text channel may be a one-to-one
chat, or it may be a multi-user chat. The interfaces present on the
channel tell us what its capabilities are.
Telepathy objects can be assumed to implement their base interface
(e.g. Connection,
Channel).
The additional interfaces available on a Telepathy object are retreivable
either via the
Interfaces property (preferred) or the
older GetInterfaces method call (e.g. for
Connection, deprecated).
Note that the Interfaces property (or the
GetInterfaces method) should be used instead
of the standard D-Bus Introspectable
interface.
The interfaces for a connection/channel depend on the
capabilities/type of the object.
In general, most D-Bus language bindings make it very difficult to
implement D-Bus objects with a dynamic set of interfaces, thus making
it difficult for a connection manager to export a dynamic set of
interfaces via D-Bus introspection.
If you use a D-Bus introspection tool (e.g.
D-Feet to look at a Telepathy connection
object, you'll find it announces support for all interfaces, even the
ones it doesn't support. If you query the object's
Interfaces property, you'll see which interfaces
really are supported.
When using telepathy-glib, you can simply call the
tp_proxy_has_interface function for
TpConnectionManager,
TpConnection, or
TpChannel objects.
The Telepathy specification is still being improved and sometimes the
specification provides two ways to achieve the same goal. Although one
of the methods/interfaces will be deprecated, it's possible that some
older connection managers do not yet implement the latest
specification. In this case, it could be possible for your client to fall
back to the older method. In general, deprecated interfaces and methods
are not documented in this manual.
