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From:   Barry Byford <31baz66@gmail.com>
Date:   Tue, 9 Oct 2018 21:30:49 +0100
Message-ID: <CAAu3APYwnuB+XTuo3jOX=HFsFLWd2X-HW6YdfYnmn51fah=_ag@mail.gmail.com>
Subject: Re: Serial communication over BT using the DBus API
To:     sylvain@chicoree.fr
Cc:     Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Hello Sylvain,

On Tue, 9 Oct 2018 at 20:50, Sylvain Leroux <sylvain@chicoree.fr> wrote:
>
> 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?

You might want to take a look at the Bluedot library that has used the
DBus API to communicate over the Serial Port Profile.
Server:
https://github.com/martinohanlon/BlueDot/blob/master/bluedot/btcomm.py#L141
Client:
https://github.com/martinohanlon/BlueDot/blob/master/bluedot/btcomm.py#L466

The main section using DBus is in:
https://github.com/martinohanlon/BlueDot/blob/master/bluedot/utils.py


Hope that helps.

>
> Regards,
> - Sylvain Leroux