[Opensync-devel] [RFC] Using OSYNC_START_TYPE_EXTERNAL

[Henrik /K. <he...@ka...>]

Dear all,

I am working on porting mozilla-sync to use OSYNC_START_TYPE_EXTERNAL.

I have a "proof-of-concept" which works "by hand" in a debugging 
environment. I will provide details later on this list for those who 
might me interested.

However, there are two conceptual issues, that I would like to discuss 
with the community:
(1) How to start the external process
(2) How to tell the external process which pipe to use

Currently, in my mozilla-sync "proof-of-concept" I do this:
a) use osynctool to create group and members
b) launch osynctool --discover or --sync
c) manually start the external process and pass it the pipe name on the 
command line (using a pipe name I worked out "manually" using knowledge 
on how OpenSync works, and the groups I created)

In principle, this could also be used in a production environment.

However, this means that it will be the resposability of the caller to 
create the external process, and pass the name of the pipe to it.

This can be a bit tricky, especially if the caller did not create the 
group/members in the first place.

I.e. before launching osynctool (or, in a production environment: before 
starting your own sync in your own GUI), you would need to work out 
which external processes to start, and which pipenames to pass to it, 
and how. It would be difficult for a generic GUI to know how to do this.

Even in the case-in-point (mozilla-sync) it is difficult. Yes the GUI 
plugin could osync_member_get_configdir and append /pluginpipe, but this 
really makes a lot of assumptions on closed OpenSync functionality. And 
if we do a mozilla-sync to mozilla-sync sync, it gets even more long-haired.

So, how do we solve the two issues:
(1) How to start the external process
(2) How to tell the external process which pipe to use

I think that the information on those issues needs to be carried in the 
plugin configurations.

If this could be made to work, "any" generic GUI could just start the 
sync, and the plugin/OpenSync would take care of the rest.

Proposal:

We could add a function called osync_plugin_set_start_external_command 
in opensync_plugin to be called from get_sync_info:

This function could be passed a string in printf format (e.g. 
"start-external-process %s"), and osync_client_proxy_spawn could call 
g_strdup_printf with the pipe name as an argument, and execute the 
resulting command with g_spawn_command_line_async.

I do not know about other external processes, but with blueZync plugin 
installed, if you launch "thunderbird --mozilla-sync=/path/to/pipe" it 
will create a new thunderbird instance if one is not already running, 
otherwise it will connect to the running thunderbird, which is exactly 
what we need.

Comments on this would be most appreciated.

/Henrik