Editing User:Magick777/Adventures with D-Bus

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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 [[Nokia N900|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 <code>dbus-monitor</code>, 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:

<pre>
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 ""
</pre>

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

<pre>
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 ""
</pre>

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 <code>org.freedesktop.Telepathy.AccountManager</code>
* our path is <code>/org/freedesktop/Telepathy/Account/</code> 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 <code>com.nokia.Account.Interface.ChannelRequests</code>
* 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 <code>uint64</code> 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 <code>dbus-send</code> 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 <code>dbus-send</code>. That would explain why there's no simple recipe on the Wiki, then. Well, if we can't use <code>dbus-send</code>, 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 ==

The only example I could find of a shell script making a D-Bus method call is the "athome" script on the [[DbusScripts]] page, which in theory should act as a starting point for what I want to do.

<source lang="python">
#!/usr/bin/python

import dbus
import sys
import re
import telepathy

# This gets us a connnection to the session bus
bus = dbus.SessionBus()

# This would seem to set up a proxy object, referring to our target SIP  account
account = bus.get_object('org.freedesktop.Telepathy.AccountManager',
                         '/org/freedesktop/Telepathy/Account/sofiasip/sip/_309517129090')

# This would seem to make a method call on the object
#account.Set('org.freedesktop.Telepathy.Account', 'RequestedPresence', \
#               dbus.Struct(( dbus.UInt32( presence_const) ,  presence_text,  ""), signature='uss'),
#               dbus_interface='org.freedesktop.DBus.Properties')

# We need to make a method call to Create a new channel

account.Set('org.freedesktop.Telepathy.Account', 'RequestedPresence', \
               dbus.Struct(( dbus.UInt32( presence_const) ,  presence_text,  ""), signature='uss'),
               dbus_interface='org.freedesktop.DBus.Properties')
</source>

[[Category:Python]]

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Editing User:Magick777/Adventures with D-Bus

@@ Line 76: / Line 76: @@
 == Step 2: dbus-send (actually, a false step) ==
-I spent a while playing with dbus-send and reading the forums, until a thread led me to the following statement in the (fine) manual page:
+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)"'''