initial capver packet tracking version (#2391)

* initial capver packet tracking version

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* Log the minimum version as client version, not only capver

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* remove old versions

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* use capver for integration tests

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* changelog

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* patch through m and n key

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/capver/capver.go

@@ -0,0 +1,92 @@
+package capver
+
+import (
+	"sort"
+	"strings"
+
+	xmaps "golang.org/x/exp/maps"
+	"tailscale.com/tailcfg"
+	"tailscale.com/util/set"
+)
+
+func tailscaleVersSorted() []string {
+	vers := xmaps.Keys(tailscaleToCapVer)
+	sort.Strings(vers)
+	return vers
+}
+
+func capVersSorted() []tailcfg.CapabilityVersion {
+	capVers := xmaps.Keys(capVerToTailscaleVer)
+	sort.Slice(capVers, func(i, j int) bool {
+		return capVers[i] < capVers[j]
+	})
+	return capVers
+}
+
+// TailscaleVersion returns the Tailscale version for the given CapabilityVersion.
+func TailscaleVersion(ver tailcfg.CapabilityVersion) string {
+	return capVerToTailscaleVer[ver]
+}
+
+// CapabilityVersion returns the CapabilityVersion for the given Tailscale version.
+func CapabilityVersion(ver string) tailcfg.CapabilityVersion {
+	if !strings.HasPrefix(ver, "v") {
+		ver = "v" + ver
+	}
+	return tailscaleToCapVer[ver]
+}
+
+// TailscaleLatest returns the n latest Tailscale versions.
+func TailscaleLatest(n int) []string {
+	if n <= 0 {
+		return nil
+	}
+
+	tsSorted := tailscaleVersSorted()
+
+	if n > len(tsSorted) {
+		return tsSorted
+	}
+
+	return tsSorted[len(tsSorted)-n:]
+}
+
+// TailscaleLatestMajorMinor returns the n latest Tailscale versions (e.g. 1.80).
+func TailscaleLatestMajorMinor(n int, stripV bool) []string {
+	if n <= 0 {
+		return nil
+	}
+
+	majors := set.Set[string]{}
+	for _, vers := range tailscaleVersSorted() {
+		if stripV {
+			vers = strings.TrimPrefix(vers, "v")
+		}
+		v := strings.Split(vers, ".")
+		majors.Add(v[0] + "." + v[1])
+	}
+
+	majorSl := majors.Slice()
+	sort.Strings(majorSl)
+
+	if n > len(majorSl) {
+		return majorSl
+	}
+
+	return majorSl[len(majorSl)-n:]
+}
+
+// CapVerLatest returns the n latest CapabilityVersions.
+func CapVerLatest(n int) []tailcfg.CapabilityVersion {
+	if n <= 0 {
+		return nil
+	}
+
+	s := capVersSorted()
+
+	if n > len(s) {
+		return s
+	}
+
+	return s[len(s)-n:]
+}