(In reply to comment #0)
>  1x git branch implementing the said feature.

* I don't like how we use integer flags to efficiently switch off debug messages, but the sender stuff bypasses that, always allocates and formats a debug string, and does a hash lookup to get back the string domain on every potentially no-op debug statement. Get everything back under that flag check?

* log_to_debug_sender: just keep a static reference to the logger instead of useless reffing and unreffing for every log message?

(In reply to comment #1)
> * I don't like how we use integer flags to efficiently switch off debug
> messages, but the sender stuff bypasses that, always allocates and formats a
> debug string, and does a hash lookup to get back the string domain on every
> potentially no-op debug statement. Get everything back under that flag check?

I got explained that the logger is disabled by default.
We need something like tp_debug_sender_is_enabled() (see the dependency bug #26393), so you don't have to run a property get every time you want to check if the logger is enabled before formatting varargs into the message and handing it to the logger.

After some pondering and explanation, I retract the objections made in comment #1.
The branch is merged to remote master.

The fix is merged upstream and available under tag telepathy-sofiasip-0.6.0, pending a proper fd.o release Real Soon Now.