Update dependencies

vendor/tailscale.com/wgengine/magicsock/endpoint_tracker.go

@@ -0,0 +1,248 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package magicsock
+
+import (
+	"net/netip"
+	"slices"
+	"sync"
+	"time"
+
+	"tailscale.com/tailcfg"
+	"tailscale.com/tempfork/heap"
+	"tailscale.com/util/mak"
+	"tailscale.com/util/set"
+)
+
+const (
+	// endpointTrackerLifetime is how long we continue advertising an
+	// endpoint after we last see it. This is intentionally chosen to be
+	// slightly longer than a full netcheck period.
+	endpointTrackerLifetime = 5*time.Minute + 10*time.Second
+
+	// endpointTrackerMaxPerAddr is how many cached addresses we track for
+	// a given netip.Addr. This allows e.g. restricting the number of STUN
+	// endpoints we cache (which usually have the same netip.Addr but
+	// different ports).
+	//
+	// The value of 6 is chosen because we can advertise up to 3 endpoints
+	// based on the STUN IP:
+	//    1. The STUN endpoint itself (EndpointSTUN)
+	//    2. The STUN IP with the local Tailscale port (EndpointSTUN4LocalPort)
+	//    3. The STUN IP with a portmapped port (EndpointPortmapped)
+	//
+	// Storing 6 endpoints in the cache means we can store up to 2 previous
+	// sets of endpoints.
+	endpointTrackerMaxPerAddr = 6
+)
+
+// endpointTrackerEntry is an entry in an endpointHeap that stores the state of
+// a given cached endpoint.
+type endpointTrackerEntry struct {
+	// endpoint is the cached endpoint.
+	endpoint tailcfg.Endpoint
+	// until is the time until which this endpoint is being cached.
+	until time.Time
+	// index is the index within the containing endpointHeap.
+	index int
+}
+
+// endpointHeap is an ordered heap of endpointTrackerEntry structs, ordered in
+// ascending order by the 'until' expiry time (i.e. oldest first).
+type endpointHeap []*endpointTrackerEntry
+
+var _ heap.Interface[*endpointTrackerEntry] = (*endpointHeap)(nil)
+
+// Len implements heap.Interface.
+func (eh endpointHeap) Len() int { return len(eh) }
+
+// Less implements heap.Interface.
+func (eh endpointHeap) Less(i, j int) bool {
+	// We want to store items so that the lowest item in the heap is the
+	// oldest, so that heap.Pop()-ing from the endpointHeap will remove the
+	// oldest entry.
+	return eh[i].until.Before(eh[j].until)
+}
+
+// Swap implements heap.Interface.
+func (eh endpointHeap) Swap(i, j int) {
+	eh[i], eh[j] = eh[j], eh[i]
+	eh[i].index = i
+	eh[j].index = j
+}
+
+// Push implements heap.Interface.
+func (eh *endpointHeap) Push(item *endpointTrackerEntry) {
+	n := len(*eh)
+	item.index = n
+	*eh = append(*eh, item)
+}
+
+// Pop implements heap.Interface.
+func (eh *endpointHeap) Pop() *endpointTrackerEntry {
+	old := *eh
+	n := len(old)
+	item := old[n-1]
+	old[n-1] = nil  // avoid memory leak
+	item.index = -1 // for safety
+	*eh = old[0 : n-1]
+	return item
+}
+
+// Min returns a pointer to the minimum element in the heap, without removing
+// it. Since this is a min-heap ordered by the 'until' field, this returns the
+// chronologically "earliest" element in the heap.
+//
+// Len() must be non-zero.
+func (eh endpointHeap) Min() *endpointTrackerEntry {
+	return eh[0]
+}
+
+// endpointTracker caches endpoints that are advertised to peers. This allows
+// peers to still reach this node if there's a temporary endpoint flap; rather
+// than withdrawing an endpoint and then re-advertising it the next time we run
+// a netcheck, we keep advertising the endpoint until it's not present for a
+// defined timeout.
+//
+// See tailscale/tailscale#7877 for more information.
+type endpointTracker struct {
+	mu        sync.Mutex
+	endpoints map[netip.Addr]*endpointHeap
+}
+
+// update takes as input the current sent of discovered endpoints and the
+// current time, and returns the set of endpoints plus any previous-cached and
+// non-expired endpoints that should be advertised to peers.
+func (et *endpointTracker) update(now time.Time, eps []tailcfg.Endpoint) (epsPlusCached []tailcfg.Endpoint) {
+	var inputEps set.Slice[netip.AddrPort]
+	for _, ep := range eps {
+		inputEps.Add(ep.Addr)
+	}
+
+	et.mu.Lock()
+	defer et.mu.Unlock()
+
+	// Extend endpoints that already exist in the cache. We do this before
+	// we remove expired endpoints, below, so we don't remove something
+	// that would otherwise have survived by extending.
+	until := now.Add(endpointTrackerLifetime)
+	for _, ep := range eps {
+		et.extendLocked(ep, until)
+	}
+
+	// Now that we've extended existing endpoints, remove everything that
+	// has expired.
+	et.removeExpiredLocked(now)
+
+	// Add entries from the input set of endpoints into the cache; we do
+	// this after removing expired ones so that we can store as many as
+	// possible, with space freed by the entries removed after expiry.
+	for _, ep := range eps {
+		et.addLocked(now, ep, until)
+	}
+
+	// Finally, add entries to the return array that aren't already there.
+	epsPlusCached = eps
+	for _, heap := range et.endpoints {
+		for _, ep := range *heap {
+			// If the endpoint was in the input list, or has expired, skip it.
+			if inputEps.Contains(ep.endpoint.Addr) {
+				continue
+			} else if now.After(ep.until) {
+				// Defense-in-depth; should never happen since
+				// we removed expired entries above, but ignore
+				// it anyway.
+				continue
+			}
+
+			// We haven't seen this endpoint; add to the return array
+			epsPlusCached = append(epsPlusCached, ep.endpoint)
+		}
+	}
+
+	return epsPlusCached
+}
+
+// extendLocked will update the expiry time of the provided endpoint in the
+// cache, if it is present. If it is not present, nothing will be done.
+//
+// et.mu must be held.
+func (et *endpointTracker) extendLocked(ep tailcfg.Endpoint, until time.Time) {
+	key := ep.Addr.Addr()
+	epHeap, found := et.endpoints[key]
+	if !found {
+		return
+	}
+
+	// Find the entry for this exact address; this loop is quick since we
+	// bound the number of items in the heap.
+	//
+	// TODO(andrew): this means we iterate over the entire heap once per
+	// endpoint; even if the heap is small, if we have a lot of input
+	// endpoints this can be expensive?
+	for i, entry := range *epHeap {
+		if entry.endpoint == ep {
+			entry.until = until
+			heap.Fix(epHeap, i)
+			return
+		}
+	}
+}
+
+// addLocked will store the provided endpoint(s) in the cache for a fixed
+// period of time, ensuring that the size of the endpoint cache remains below
+// the maximum.
+//
+// et.mu must be held.
+func (et *endpointTracker) addLocked(now time.Time, ep tailcfg.Endpoint, until time.Time) {
+	key := ep.Addr.Addr()
+
+	// Create or get the heap for this endpoint's addr
+	epHeap := et.endpoints[key]
+	if epHeap == nil {
+		epHeap = new(endpointHeap)
+		mak.Set(&et.endpoints, key, epHeap)
+	}
+
+	// Find the entry for this exact address; this loop is quick
+	// since we bound the number of items in the heap.
+	found := slices.ContainsFunc(*epHeap, func(v *endpointTrackerEntry) bool {
+		return v.endpoint == ep
+	})
+	if !found {
+		// Add address to heap; either the endpoint is new, or the heap
+		// was newly-created and thus empty.
+		heap.Push(epHeap, &endpointTrackerEntry{endpoint: ep, until: until})
+	}
+
+	// Now that we've added everything, pop from our heap until we're below
+	// the limit. This is a min-heap, so popping removes the lowest (and
+	// thus oldest) endpoint.
+	for epHeap.Len() > endpointTrackerMaxPerAddr {
+		heap.Pop(epHeap)
+	}
+}
+
+// removeExpired will remove all expired entries from the cache.
+//
+// et.mu must be held.
+func (et *endpointTracker) removeExpiredLocked(now time.Time) {
+	for k, epHeap := range et.endpoints {
+		// The minimum element is oldest/earliest endpoint; repeatedly
+		// pop from the heap while it's in the past.
+		for epHeap.Len() > 0 {
+			minElem := epHeap.Min()
+			if now.After(minElem.until) {
+				heap.Pop(epHeap)
+			} else {
+				break
+			}
+		}
+
+		if epHeap.Len() == 0 {
+			// Free up space in the map by removing the empty heap.
+			delete(et.endpoints, k)
+		}
+	}
+}