Re: Background CoreBluetooth
Re: Background CoreBluetooth
- Subject: Re: Background CoreBluetooth
- From: soan saini via Bluetooth-dev <email@hidden>
- Date: Thu, 7 May 2020 23:37:59 +0000 (UTC)
Hey,
Thanks for Writeup, i am also trying to understand this process. If Apps are
getting connected and not just reading Advertised Packets, To record close
proximity with user.
Will it cause issues like loosing disconnection with Headsets. As i understand
there is a limit on how many simultaneous connections can be made from phone.
On Friday, 8 May 2020, 09:25:25 GMT+10, Darren Jones via Bluetooth-dev
<email@hidden> wrote:
Thanks for the write up. Your findings are pretty much the same as mine.
I wonder how long the ‘keep alive’ can last. Possibly forever?If you are in a
household with multiple iOS users that install the app, an initial connection
could stay connected constantly while in range. I wonder what effect that would
have on battery life.They’ve been very clever with the way Android can wake up
iOS, so in a crowded area with many devices there’s a good chance the app will
work.Walking to a local shop on your own and bumping into a few people, there’s
a good chance it won’t.
Sent from my iPhone
On 8 May 2020, at 00:09, Nick Brook <email@hidden> wrote:
I’ve been playing around with this today, testing with my own code and looking
at the NHS App.
- The NHS App is doing nothing special, as far as I can see
- It advertises a service, and in the background iOS puts the service in the
“overflow” (one-hot encoded)
- Android looks for this specific one hot encoded value. Actually, it
doesn’t look for a specific bit set, but a fixed set of bytes, so if other Apps
are advertising services in the background on iOS the NHS App on Android might
fail to discover it. This seems like a bug, although I’m not sure if they could
work around it
- It attempts to keep connections (and the process) alive for as long as
possible by sending “keep alive” data every 8s (under the 10s execution window
apple provides)
- It is susceptible to the problems other Apps are (restarting the phone,
quitting the app etc can break scanning and discovery) but it helps to overcome
this through notifications to the user to reopen the app.
- I’m not sure if Apple imposes a time limit on scanning for/advertising
services in the background although presumably there is a notification for this
in the NHS App if it does.
With the user notifications, if users actually respond to them it might work
well enough to be effective. But I could see users ignoring the notifications
if there are too many, and particular when out and about and busy these may get
ignored. If they are ignored, the App may not work for a long period of time.
It seems the UK government may be reconsidering the centralised approach now
anyway:
https://www.telegraph.co.uk/news/2020/05/06/nhs-explores-feasibility-moving-contact-tracing-app-apple-google/?fbclid=IwAR2qT77qzPkMlefQWYRFKmy-zj3Y_z2-Ip2peuUE9nCdokHldxuEIC1Ze64
I’d be keen to hear any further insight into how the App is working or
background bluetooth can made to work better.
Nick Brook
NRB TechW: https://nrbtech.io
On 7 May 2020, at 21:17, Darren Jones via Bluetooth-dev
<email@hidden> wrote:
There is no location permission in the app.Which is a good job as the questions
over privacy would explode more than they already have.
Sent from my iPhone
On 7 May 2020, at 21:14, Diego Alfarache <email@hidden> wrote:
These apps are going to have background location permission, which effectively
gives them free reign to run almost anything in the background. I created a
framework for a client that would act as both a peripheral and central while
executing in the background, but only when they had “always” location
permission. Diego From: "Jan Lübeck via Bluetooth-dev (Fyrastudio)"
<email@hidden>
Reply-To: "Jan Lübeck (Fyrastudio)" <email@hidden>
Date: Thursday, May 7, 2020 at 3:04 PM
To: Darren Jones <email@hidden>
Cc: <email@hidden>
Subject: Re: Background CoreBluetooth Apple did announce that they are sharing
their APIs with specific developers. Maybe UK NHS is one of them?
______Jan LübeckChief Technology Officerfyrastudio.com On Thu, May 7, 2020
at 3:48 PM Darren Jones via Bluetooth-dev <email@hidden> wrote:
Unless you have your head buried in the sand, I’m sure everyone has noticed the
sagas going on with countries creating their own COVID-19 contact tracing apps.
I have personally tried many times over the years to create an app that can
broadcast and scan in the background to trigger a ‘contact trace’ and always
failed. Yet the UK NHS are claiming they have an app that does just that.
I’d love to hear from anyone that’s had experience with background BT. Is it
possible? Can a background CBPeripheral be detected by a background CBCentral?
If not, is there a definitive time period when discovery becomes impossible?
Thanks
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