xDrip+ Sync service (powered by bluejay) to operate over a more-standard port in order to reduce chance of traffic being blocked

[dbames]

Subject of the issue

xDrip+ Sync traffic (over port 25935) can be blocked on some wifi networks

Discussion thread: #3772 relates to this issue.
Bluejay (the replacement for Google firebase messaging) now used by the xDrip+ Sync Service, operates (by default) over port 25935. On some restricted access (e.g. school) networks, non-standard high ports like this are blocked. When this happens, followers will not obtain any xDrip+ sync data on downstream devices.

I suspect that the reverse is also true (i.e. if a follower attempts to connect to xDrip+ Cloud to receive data from the master, this will also fail). I have not validated this scenario, but it seems likely, and should therefore be considered when implementing a solution.

During this time, the push to Nightscout continues to be successful - at this is operated over 443 (and is not blocked).

Your environment

Version: 2024.11.08, but applies to all versions since the switch from Google Firebase messaging to Bluejay was implemented
G6 with BYOD app, patched to broadcast. xDrip+ configured for 640G/EverSense. xDrip+ pushes to Nightscout and is configured for xDrip+ Sync using "new cloud" option.

Expected behavior

xDrip+ Sync Service should be configured in such a way to ensure that it maximises its chances of working correctly on restricted networks, by using a more-standard port (e.g. 443 for encrypted HTTPS). Or if a connection to 25935 failed, then fall back to an alternative port that is less likely to be blocked. (Some consideration may also need to be given to layer 7 packet inspection, when considering a suitable port to use - in-case such inspection might interfere with the transmission of data).

Actual behavior

On networks where port 25935 is not opened, any followers of a xDrip+ Master, will not receive any data until the Master device connects to a different data service (i.e. at the end of a school day).

Steps to reproduce the behavior:

Block outbound traffic to port 25935
xDrip+ will fail to connect to the bluejay messaging service and log the message: "Connection lost, retrying in " + reconnectTime + " ... " + e);