FR: Send Peers delta in MapResponse

[kev-the-dev]

Feature request

I'm currently working on this feature and will submit my patch upstream, but creating a ticket to prevent duplicate work

This is a ticket to implement the sending of Peers list as deltas rather then the full list each time, per this TODO

headscale/api_common.go

Line 72 in d011373

// TODO(kradalby): Implement:

.

In addition to improving performance, there is at least one bug I've found associated with not sending deltas:

• There are two nodes in a tailnet, A and B
• Node B is deleted
• A MapResponse is generated for node A. Node A no longer has any peers, so len(MapResponse.Peers) == 0
• Tailscale interprets len(MapResponse.Peers) == 0 as no change, meaning it isn't notified of node B being deleted https://github.com/tailscale/tailscale/blob/43819309e18ac7d496643fcd86489a2ee0927964/control/controlclient/map.go#L227
• Node B remains on tailnet after being deleted, causing a security vulnerability for deleted nodes

[loprima-l]

How is it going ? Do you have any issues ?

[kev-the-dev]

I have a working patch, just cleaning up and should be able to submit next week

[loprima-l]

Nice, that's a good step on Headscale optimization, thanks for your investment.

[kradalby]

This is implemented as part of #1492.