User:Magick777/Adventures with D-Bus

(→Step 2: dbus-send (actually, a false step))
(→Step 2: dbus-send (actually, a false step))
Line 76: Line 76:
'''"dbus-send does not permit empty containers or nested containers (e.g. arrays of variants)"'''
'''"dbus-send does not permit empty containers or nested containers (e.g. arrays of variants)"'''
-
We can assume that dbus-send isn't going to like an array of dicts any more than it likes an array of variants, ergo, that what we want to do cannot be done with dbus-send. That would explain why there's no simple recipe on the Wiki, then. Well, if we can't use dbus-send, I guess we'll have to resort to python.
+
We can assume that dbus-send isn't going to like an array of dicts any more than it likes an array of variants, ergo, that what we want to do cannot be done with dbus-send. That would explain why there's no simple recipe on the Wiki, then. Well, if we can't use dbus-send, I guess we'll have to resort to python. That's going to be fun; I'm not in the habit of conversing with reptiles.
== Step 3: python ==
== Step 3: python ==

Revision as of 00:48, 16 September 2010

This page started because I'm trying to figure out D-BUS, as a relative newbie to Python and Telepathy, and the documentation is, shall we say, "fragmented". All the D-BUS recipes on the Wiki don't seem to include a simple way to place a call via the sofiasip client. The Telepathy documentation speaks to a vague architecture, not to my N900's implementation of it, and seems better for someone who wants to write a whole new interface than someone who just wants to use an existing one. I've read more source code and more forum posts than you can shake a stick at and I'm still none the wiser. So, this is a generic HOWTO for newbies (written by one) on how to track down an existing application's behaviour on D-BUS and replicate it. Work in progress September 2010.

Step 1: dbus-monitor

After some playing around with dbus-monitor, I've established that when I make a SIP call via the inbuilt Phone application, the first thing that happens on the session bus is: 

method call sender=:1.121 ->
dest=org.freedesktop.Telepathy.AccountManager
serial=439
path=/org/freedesktop/Telepathy/Account/sofiasip/sip/_31030137_40sipgate_2eco_2euk0;
interface=com.nokia.Account.Interface.ChannelRequests;
member=Create
   array [
      dict entry(
         string "org.freedesktop.Telepathy.Channel.TargetHandleType"
         variant             uint32 1
      )
      dict entry(
         string "org.freedesktop.Telepathy.Channel.TargetID"
         variant             string "sip:50000@sipgate.co.uk"
      )
      dict entry(
         string "org.freedesktop.Telepathy.Channel.ChannelType"
         variant             string "org.freedesktop.Telepathy.Channel.Type.StreamedMedia"
      )
   ]
   uint64 14701758
   string ""

and, for a call to a PSTN number, via a different SIP account: 

method call sender=:1.191 ->
dest=org.freedesktop.Telepathy.AccountManager
serial=500
path=/org/freedesktop/Telepathy/Account/sofiasip/sip/_330147398_40sip_2evoipfone_2eco_2euk0; 
interface=com.nokia.Account.Interface.ChannelRequests; 
member=Create
   array [
      dict entry(
         string "org.freedesktop.Telepathy.Channel.TargetHandleType"
         variant             uint32 1
      )
      dict entry(
         string "org.freedesktop.Telepathy.Channel.ChannelType"
         variant             string "org.freedesktop.Telepathy.Channel.Type.StreamedMedia"
      )
      dict entry(
         string "org.freedesktop.Telepathy.Channel.TargetID"
         variant             string "08081703703"
      )
   ]
   uint64 1284595510
   string ""

From this, we can deduce that:

  • we need to make a method call over D-BUS to initiate the SIP call
  • we need to send it to dest=org.freedesktop.Telepathy.AccountManager
  • our path is /org/freedesktop/Telepathy/Account/ plus SofiaSIP account path
    • which can be found via "mc-tool list" (package libmissioncontrol-utils)
    • or, no doubt, via D-BUS, but we'll worry about that later
  • our interface is com.nokia.Account.Interface.ChannelRequests
  • the action we must take on that interface is to Create (a new channel)
  • for which we must supply an array of dicts, a number and an empty string
    • TargetHandleType is 1
    • ChannelType is StreamedMedia
    • Target ID contains our destination SIP address or phone number
    • not sure what that UInt64 is about, some kind of timestamp?

and we can hope that, if we can pack up that set of instructions and deliver it to telepathy-sofiasip, it will (hopefully) place a call for us.

Step 2: dbus-send (actually, a false step)

I spent a while playing with dbus-send and reading forums, until a thread led me to the following statement in the fine manual page:

"dbus-send does not permit empty containers or nested containers (e.g. arrays of variants)"

We can assume that dbus-send isn't going to like an array of dicts any more than it likes an array of variants, ergo, that what we want to do cannot be done with dbus-send. That would explain why there's no simple recipe on the Wiki, then. Well, if we can't use dbus-send, I guess we'll have to resort to python. That's going to be fun; I'm not in the habit of conversing with reptiles.

Step 3: python

Retrieved from "http://bugs.maemo.org/User:Magick777/Adventures_with_D-Bus"