Hi Andrzej,
On Fri, Mar 11, 2016 at 2:24 PM, Andrzej Kaczmarek
<andrzej.kaczmarek@xxxxxxxxxxx> wrote:
> Hi Luiz,
>
>
> On Fri, Mar 11, 2016 at 12:23 PM, Luiz Augusto von Dentz
> <luiz.dentz@xxxxxxxxx> wrote:
>> Hi Andrzej,
>>
>> On Fri, Mar 11, 2016 at 1:05 PM, Andrzej Kaczmarek
>> <andrzej.kaczmarek@xxxxxxxxxxx> wrote:
>>> Hi Luiz,
>>>
>>> On Thu, Mar 10, 2016 at 5:16 PM, Luiz Augusto von Dentz
>>> <luiz.dentz@xxxxxxxxx> wrote:
>>>> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
>>>>
>>>> GattServices is not really doing was it was meant to do which was to
>>>> track progress of service discovery since it only worked for the very
>>>> first time a device is connected but since we no longer remove the
>>>> attributes an application would have the false impression the service are
>>>> all resolved by the time it reconnects when in fact the service may have
>>>> changed.
>>>>
>>>> Futhermore object tracking like it is doing has been obsolete by
>>>> ObjectManager so this propose to replace the service discovery tracking
>>>> with a boolean property which works both with SDP as well as GATT
>>>> discovery.
>>>> ---
>>>> doc/device-api.txt | 9 +++------
>>>> src/device.c | 58 +++++++++++-------------------------------------------
>>>> 2 files changed, 14 insertions(+), 53 deletions(-)
>>>>
>>>> diff --git a/doc/device-api.txt b/doc/device-api.txt
>>>> index a8076a2..9e58664 100644
>>>> --- a/doc/device-api.txt
>>>> +++ b/doc/device-api.txt
>>>> @@ -212,10 +212,7 @@ Properties string Address [readonly]
>>>> Service advertisement data. Keys are the UUIDs in
>>>> string format followed by its byte array value.
>>>>
>>>> - array{object} GattServices [readonly, optional]
>>>> + bool Discovering [readonly, optional, experimental]
>>>
>>> It's not optional - there's no exists method (which is fine).
>>
>> Indeed, I will fix it.
>>
>>> I think a better name for this would be "Discovered" which has initial
>>> value of false (once device is connected) and then changes to true
>>> (once services are ready, either from cache or an actual discovery).
>>> It could also change back to false once re-discovery due to Service
>>> Changed is in progress which I think is also fine.
>>>
>>> With "Discovering" the problem is still that once "Connected" changes
>>> to true, reading "Discovering" will return false so you don't quite
>>> know whether discovery already finished or has not yet started.
>>> Application would need to wait for complete sequence to be sure:
>>> Connected=false, Discovering=false
>>> Connected=true, Discovering=false
>>> Connected=false, Discovering=true
>>> Connected=false, Discovering=false
>>>
>>> With "Discovered" this is not a problem since sequence is as follows:
>>> Connected=false, Discovered=false
>>> Connected=true, Discovered=false
>>> Connected=true, Discovered=true
>>
>> I was actually thinking in using the same terminology we used in the
>> source code such as ResolvingServices, but changing to Discovered
>> don't actually fix the problem since you may still end up with
>> Connected=true, Discovered=true but the flag can still change to
>> Discovered=false. Anyway Im currently discussing about this changes
>> makes sense in Web Bluetooth, because Service Changed may come in
>> later on and there is no API to push the services added/removed to the
>> application.
>
> When Service Changed is received, BlueZ removes old objects and then
> adds new ones. And once there's change to Discovered=false it means
> device in its current state is not fully discovered, e.g. there's
> re-discovery due to Service Changed in this case which makes sense to
> me. So what's the problem here?
If that was the case, again this is for Web Bluetooth, we wouldn't
need to notify this at all because the application would receive the
updates directly, but since the Web Bluetooth is not designed in this
way you just get the current services if anything is updated later it
causes this problem where the services get updated but the application
don't realize it has happened. So it is all about when the application
actually list the objects, again Im talking about Web Bluetooth
applications, if by the time it calls getPrimaryServices the discovery
is active there is a chance it will return outdated services.
Essentially it is a polling API.
You can read more about this issue here:
https://github.com/thegecko/web-bluetooth-dfu/issues/12#issuecomment-194973956
--
Luiz Augusto von Dentz
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