Support bluetooth connections

[jcapona]

Status	Ticket/Issue
Hold	Ticket

Main changes

Support bluetooth connections by adding a GATT server with a service and several characteristics to interact with the frontend app.

Screenshots (feature, test output, profiling, dev tools etc)

[insert screenshots here]

Other notes (e.g. implementation quirks, edge cases, questions / issues)

Manual testing tips

• Download deb
• Make sure that the unstable apt repository is installed. You can install it by running:

sudo apt update
sudo apt install pi-top-os-unstable-apt-source
# Run again to update source
sudo apt update

• Install deb artifact by running sudo apt install ./<file>. It should automatically fetch the new dependencies from the unstable repository.
• Restart the further-link and bluetooth services

sudo systemctl daemon-reload
sudo systemctl restart further-link
sudo systemctl restart bluetooth

• Install miniscreen app using the deb file from this PR.
• Enable pairing mode from Overview page of miniscreen app
• Use this frontend branch for testing.

Tag anyone who definitely needs to review or help

[codecov]

Codecov Report

Attention: 171 lines in your changes are missing coverage. Please review.

Comparison is base (0d6e230) 72.83% compared to head (fd182a9) 73.52%.

Files	Patch %	Lines
further_link/endpoint/run.py	72.82%	25 Missing ⚠️
further_link/util/bluetooth/pairing.py	0.00%	25 Missing ⚠️
further_link/util/bluetooth/encryption.py	0.00%	24 Missing ⚠️
further_link/util/state.py	54.54%	20 Missing ⚠️
further_link/util/bluetooth/service.py	88.15%	18 Missing ⚠️
further_link/util/bluetooth/utils.py	37.93%	18 Missing ⚠️
...er_link/util/bluetooth/messages/chunked_message.py	84.74%	9 Missing ⚠️
further_link/util/bluetooth/messages/format.py	87.69%	8 Missing ⚠️
further_link/util/bluetooth/server.py	82.50%	7 Missing ⚠️
further_link/util/ipc.py	58.82%	7 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #156      +/-   ##
==========================================
+ Coverage   72.83%   73.52%   +0.68%     
==========================================
  Files          25       38      +13     
  Lines        1119     1760     +641     
==========================================
+ Hits          815     1294     +479     
- Misses        304      466     +162     

Flag	Coverage Δ
unittests	73.52% <74.88%> (+0.68%)	⬆️

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[angusjfw]

we shouldn't really need this - the clients should send valid json

[angusjfw]

When sending as well as as chunking outgoing messages we probably need to handle buffering additional messages that are being sent while the previous one is still going out. An alternative would be to support simultaneous messages which are tagged by a message id.

Once we have finalised the chunking protocol we should add unit tests for it - we'll need to implement it in javascript and python so we want it to be pretty stable.

[angusjfw]

We discussed going with a message id approach rather than buffering. We'll drop support for unchunked messages. So chunked messages have the format:
[2-bytes id][3-bytes end chunk index][3-bytes chunk index][data]

receiving logic is like:

• if there's no open message with the id create a new one
• if there is an open message with the id use that one
• append the chunk (for now if it's not the next expected index that's an error, could start skipping these messages)
• if the chunk index is the end chunk index close and handle the message

[angusjfw]

run steps:

• install deb
• sudo pip3 install dbus-next bless

sudo apt install -y bluez

# Run bluetooth service in experimental mode
sudo sed -i '/^ExecStart=/ExecStart=/usr/libexec/bluetooth/bluetoothd --experimental' /lib/systemd/system/bluetooth.service
sudo sed -i '/^ExecStart=/ExecStart=/usr/libexec/bluetooth/bluetoothd --experimental' /etc/systemd/system/bluetooth.service
sudo systemctl daemon-reload
sudo systemctl restart bluetooth```