Crash when disconnecting network adapter

This feels like a tricky situation.

I have no doubt we can do something to make sure we don't crash when accessing a network adapter that has disappeared (provided we have the hardware to reproduce it, which I currently don't). A tarball of the logs (e.g., /var/log/installer + /var/crash + journal) would help BTW.

OTOH, if the network adapter gets disconnected and does not come back up before we start downloading packages from the archive, there's little we can do to prevent the install from failing. A manual retry option would be ideal, I guess, but it feels like substantial effort.

Yea, either the install has access to a mirror or it doesn't. If access disappears half way through, well, what can we do? If the user knows in advance this is a possibility, they can disable networking by hand.

This was still early on: installation hadn't actually begun. IIRC that could happen while the installer was checking the network status.

What I wanted to try but hadn't the time to do yet is whether that happens with several adapters and only one of them being disconnected. As a user I would expect that adapter and the related network configuration to disappear rather than a crash.

Ah yes before installation it should be tolerated. If it happens again can you capture the logs?

I reproduced with a brand new USB to ethernet adapter:

2023-03-28 07:42:12,315 DEBUG root:37 start: subiquity/Network/_send_update: DEL enx00e04c680717
2023-03-28 07:42:12,315 DEBUG subiquity.server.controllers.network:355 dev_info enx00e04c680717 {'dhcp4': True}
2023-03-28 07:42:12,315 ERROR root:37 finish: subiquity/Network/_send_update: FAIL: 'NoneType' object has no attribute 'is_connected'
2023-03-28 07:42:12,315 ERROR subiquity.server.server:422 top level error
Traceback (most recent call last):
  File "/snap/subiquity/4542/usr/lib/python3.10/asyncio/events.py", line 80, in _run
    self._context.run(self._callback, *self._args)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/subiquitycore/controllers/network.py", line 215, in _data_ready
    self.observer.data_ready(fd)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/probert/network.py", line 667, in data_ready
    with CoalescedCalls(self):
  File "/snap/subiquity/4542/usr/lib/python3.10/contextlib.py", line 142, in __exit__
    next(self.gen)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/probert/network.py", line 630, in CoalescedCalls
    meth(obj, action, data)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/probert/network.py", line 680, in link_change
    self.receiver.del_link(ifindex)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/subiquitycore/controllers/network.py", line 72, in del_link
    self.controller.del_link(netdev)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/subiquity/server/controllers/network.py", line 379, in del_link
    self._send_update(LinkAction.DEL, dev)
  File "/snap/subiquity/4542/lib/python3.10/site-packages/subiquity/server/controllers/network.py", line 356, in _send_update
    dev_info = dev.netdev_info()
  File "/snap/subiquity/4542/lib/python3.10/site-packages/subiquitycore/models/network.py", line 201, in netdev_info
    is_connected = bool(self.info.is_connected)
AttributeError: 'NoneType' object has no attribute 'is_connected'
2023-03-28 07:42:12,320 DEBUG subiquity.common.errorreport:384 generating crash report
2023-03-28 07:42:12,320 INFO subiquity.common.errorreport:406 saving crash report 'unknown error crashed with AttributeError' to /var/crash/1679989332.320252895.unknown.crash

When a link disappears, SubiquityNetworkEventReceiver.del_link() calls model.del_link() which sets dev.info to None. Then, the code flows to NetworkController.del_link() which expects dev.info not to be None.

This feels wrong and I suspect the bug could occur without the adapter being disconnected.

https://github.com/canonical/subiquity/pull/1789