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To:     linux-bluetooth@vger.kernel.org
From:   Sylvain Leroux <sylvain@chicoree.fr>
Subject: Serial communication over BT using the DBus API
Message-ID: <7246fd0d-022f-0d7b-ab09-1030ac06e0fa@chicoree.fr>
Date:   Tue, 9 Oct 2018 21:30:11 +0200
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Hi everyone,

I'm trying to establish a serial communication between two hosts over
Bluetooth.

Things go well if I start the `bluetoothd` on the server in
_compatibility mode_. That way, I can attach the "serial port" profile
to the channel. Then, using `rfcomm watch` and `rfcomm connect` to
establish the connection between the server and the client, I can
receive "raw" data sent by the server:

----
# Server side
/usr/lib/bluetooth/bluetoothd -C
sdptool add --channel=1 SP
rfcomm watch hci0 1 bash -c 'cat somefile > /dev/rfcomm0'
----

----
#Client side
sudo rfcomm connect /dev/rfcomm0 BB:CC:DD:EE:FF:11 1
sudo cat /dev/rfcomm0
-----

If I do _not_ run the `bluetoothd` server in compatibility mode, SDP is
no longer supported and the data I receive seems to modified by the BT
stack, leading to my data being mixed with garbage--exactly like when I
don't set the "serial port" profile while running in compatibility mode.


I don't like the idea of depending on a deprecated interface. And from
what I read, I understand the new way to go is to use the DBus API.  Any
solution using bluetoothctl, busctl, dbus-send or similar tools would do
the trick. But I can't manage to understand the sequence of operations
required to transmit raw data between the server and the client *from a
shell script* using that new API.

Could you give me some example or point me to the relevant documentation?

Regards,
- Sylvain Leroux