control/controlclient, types/netmap: start plumbing delta netmap updates

Currently only the top four most popular changes: endpoints, DERP
home, online, and LastSeen.

Updates #1909

Change-Id: I03152da176b2b95232b56acabfb55dcdfaa16b79
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

types/netmap/nodemut.go

@@ -0,0 +1,168 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package netmap
+
+import (
+	"net/netip"
+	"reflect"
+	"slices"
+	"sync"
+	"time"
+
+	"tailscale.com/tailcfg"
+	"tailscale.com/util/cmpx"
+)
+
+// NodeMutation is the common interface for types that describe
+// the change of a node's state.
+type NodeMutation interface {
+	NodeIDBeingMutated() tailcfg.NodeID
+}
+
+type mutatingNodeID tailcfg.NodeID
+
+func (m mutatingNodeID) NodeIDBeingMutated() tailcfg.NodeID { return tailcfg.NodeID(m) }
+
+// NodeMutationDERPHome is a NodeMutation that says a node
+// has changed its DERP home region.
+type NodeMutationDERPHome struct {
+	mutatingNodeID
+	DERPRegion int
+}
+
+// NodeMutation is a NodeMutation that says a node's endpoints have changed.
+type NodeMutationEndpoints struct {
+	mutatingNodeID
+	Endpoints []netip.AddrPort
+}
+
+// NodeMutationOnline is a NodeMutation that says a node is now online or
+// offline.
+type NodeMutationOnline struct {
+	mutatingNodeID
+	Online bool
+}
+
+// NodeMutationLastSeen is a NodeMutation that says a node's LastSeen
+// value should be set to the current time.
+type NodeMutationLastSeen struct {
+	mutatingNodeID
+	LastSeen time.Time
+}
+
+var peerChangeFields = sync.OnceValue(func() []reflect.StructField {
+	var fields []reflect.StructField
+	rt := reflect.TypeOf((*tailcfg.PeerChange)(nil)).Elem()
+	for i := 0; i < rt.NumField(); i++ {
+		fields = append(fields, rt.Field(i))
+	}
+	return fields
+})
+
+// NodeMutationsFromPatch returns the NodeMutations that
+// p describes. If p describes something not yet supported
+// by a specific NodeMutation type, it returns (nil, false).
+func NodeMutationsFromPatch(p *tailcfg.PeerChange) (_ []NodeMutation, ok bool) {
+	if p == nil || p.NodeID == 0 {
+		return nil, false
+	}
+	var ret []NodeMutation
+	rv := reflect.ValueOf(p).Elem()
+	for i, sf := range peerChangeFields() {
+		if rv.Field(i).IsZero() {
+			continue
+		}
+		switch sf.Name {
+		default:
+			// Unhandled field.
+			return nil, false
+		case "NodeID":
+			continue
+		case "DERPRegion":
+			ret = append(ret, NodeMutationDERPHome{mutatingNodeID(p.NodeID), p.DERPRegion})
+		case "Endpoints":
+			eps := make([]netip.AddrPort, len(p.Endpoints))
+			for i, epStr := range p.Endpoints {
+				var err error
+				eps[i], err = netip.ParseAddrPort(epStr)
+				if err != nil {
+					return nil, false
+				}
+			}
+			ret = append(ret, NodeMutationEndpoints{mutatingNodeID(p.NodeID), eps})
+		case "Online":
+			ret = append(ret, NodeMutationOnline{mutatingNodeID(p.NodeID), *p.Online})
+		case "LastSeen":
+			ret = append(ret, NodeMutationLastSeen{mutatingNodeID(p.NodeID), *p.LastSeen})
+		}
+	}
+	return ret, true
+}
+
+// MutationsFromMapResponse returns all the discrete node mutations described
+// by res. It returns ok=false if res contains any non-patch field as defined
+// by mapResponseContainsNonPatchFields.
+func MutationsFromMapResponse(res *tailcfg.MapResponse, now time.Time) (ret []NodeMutation, ok bool) {
+	if now.IsZero() {
+		now = time.Now()
+	}
+	if mapResponseContainsNonPatchFields(res) {
+		return nil, false
+	}
+	// All that remains is PeersChangedPatch, OnlineChange, and LastSeenChange.
+
+	for _, p := range res.PeersChangedPatch {
+		deltas, ok := NodeMutationsFromPatch(p)
+		if !ok {
+			return nil, false
+		}
+		ret = append(ret, deltas...)
+	}
+	for nid, v := range res.OnlineChange {
+		ret = append(ret, NodeMutationOnline{mutatingNodeID(nid), v})
+	}
+	for nid, v := range res.PeerSeenChange {
+		if v {
+			ret = append(ret, NodeMutationLastSeen{mutatingNodeID(nid), now})
+		}
+	}
+	slices.SortStableFunc(ret, func(a, b NodeMutation) int {
+		return cmpx.Compare(a.NodeIDBeingMutated(), b.NodeIDBeingMutated())
+	})
+	return ret, true
+}
+
+// mapResponseContainsNonPatchFields reports whether res contains only "patch"
+// fields set (PeersChangedPatch primarily, but also including the legacy
+// PeerSeenChange and OnlineChange fields).
+//
+// It ignores any of the meta fields that are handled by PollNetMap before the
+// peer change handling gets involved.
+//
+// The purpose of this function is to ask whether this is a tricky enough
+// MapResponse to warrant a full netmap update. When this returns false, it
+// means the response can be handled incrementally, patching up the local state.
+func mapResponseContainsNonPatchFields(res *tailcfg.MapResponse) bool {
+	return res.Node != nil ||
+		res.DERPMap != nil ||
+		res.DNSConfig != nil ||
+		res.Domain != "" ||
+		res.CollectServices != "" ||
+		res.PacketFilter != nil ||
+		res.UserProfiles != nil ||
+		res.Health != nil ||
+		res.SSHPolicy != nil ||
+		res.TKAInfo != nil ||
+		res.DomainDataPlaneAuditLogID != "" ||
+		res.Debug != nil ||
+		res.ControlDialPlan != nil ||
+		res.ClientVersion != nil ||
+		res.Peers != nil ||
+		res.PeersRemoved != nil ||
+		// PeersChanged is too coarse to be considered a patch. Also, we convert
+		// PeersChanged to PeersChangedPatch in patchifyPeersChanged before this
+		// function is called, so it should never be set anyway. But for
+		// completedness, and for tests, check it too:
+		res.PeersChanged != nil
+}