android: handle network state changes

[iwanbk]

Mobile phone have certain behaviors that different with server or PC/laptop: connection lost (and connected again) is not uncommon, for many reasons.

While mycelium should already handle connection lost, there are more about it in mobile phone:

• we will save battery by stopping mycelium while the connection is lost
• it gives more visibility when things going wrong, for example when mycelium disconnected while we thought that it should be connected
• our android log will be cleaner from unnecessary connection failure logs

Android has builtin class for this : NetworkCallback. It can give notification for various network state changes events:

• onAvailable
• onBlockedStatusChanged
• onCapabilitiesChanged
• onLinkPropertiesChanged
• onLosing
• onLost
• onUnavailable

[iwanbk]

Some research has been done to other platform about how they handle network state event.

yggdrasil only handle onAvailable event

https://github.com/yggdrasil-network/yggdrasil-android/blob/aa94ccad26435de615cfbae4ae13740e12db1040/app/src/main/java/eu/neilalexander/yggdrasil/NetworkStateCallback.kt#L15-L35

If we follow the code, it will call their Go engine

https://github.com/yggdrasil-network/yggdrasil-go/blob/v0.5.5/contrib/mobile/mobile.go#L183-L186

// Retry resets the peer connection timer and tries to dial them immediately.
func (m *Yggdrasil) RetryPeersNow() {
    m.core.RetryPeersNow()
}

from the comment and quick read, looks like yggdrasil resets all the connections.

I think this way is quite simple and reliable

[iwanbk]

I also looked at wireguard-android and found nothing so far. But i found that wireguard-apple do have the handles as i mentioned in https://github.com/threefoldtech/myceliumflut/issues/35#issuecomment-2138686759

To summarize, wireguard-apple do these:

• network lost: stop wireguard
• if network available after lost : start wireguard
• network available when wireguard state is started: bump sockets:
  • close existing socket
  • re-open socket
  • send keepalive to peers

[iwanbk]

looks like yggdrasil resets all the connections.

network available when wireguard state is started: bump sockets:

• close existing socket
• re-open socket
• send keepalive to peers

All of above things are done in their respective engine (yggdrasil-go and wireguard-go), so we might need to do that as well in mycelium

[iwanbk]

The NetworkCallback already added and below are my observations:

• the network available and lost events are not about connected or disconnected, but more like about the interfaces (mobile, wifi, etc) up or down
• when we got network lost event, it doesn't mean that we have no connection anymore, because there might be another interface that still up. For example:
  • wifi down
  • mobile still active can take over
• when mycelium disconnected for too long, there is no NetworkCallback event
• wireguard-android doesn't have any NetworkCallback handler
• yggdrasil only refresh the peers when network become available, this functionality doesn't exist in mycelium
• mycelium can handle network lost -> available perfectly

For now i will push the NetworkCallback code but only in listening mode, no specific actions taken when any events fired