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/gen/main.go

@@ -0,0 +1,157 @@
+package main
+
+//go:generate go run main.go
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+
+	xmaps "golang.org/x/exp/maps"
+	"tailscale.com/tailcfg"
+)
+
+const (
+	releasesURL = "https://api.github.com/repos/tailscale/tailscale/releases"
+	rawFileURL  = "https://github.com/tailscale/tailscale/raw/refs/tags/%s/tailcfg/tailcfg.go"
+	outputFile  = "../capver_generated.go"
+)
+
+type Release struct {
+	Name string `json:"name"`
+}
+
+func getCapabilityVersions() (map[string]tailcfg.CapabilityVersion, error) {
+	// Fetch the releases
+	resp, err := http.Get(releasesURL)
+	if err != nil {
+		return nil, fmt.Errorf("error fetching releases: %w", err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("error reading response body: %w", err)
+	}
+
+	var releases []Release
+	err = json.Unmarshal(body, &releases)
+	if err != nil {
+		return nil, fmt.Errorf("error unmarshalling JSON: %w", err)
+	}
+
+	// Regular expression to find the CurrentCapabilityVersion line
+	re := regexp.MustCompile(`const CurrentCapabilityVersion CapabilityVersion = (\d+)`)
+
+	versions := make(map[string]tailcfg.CapabilityVersion)
+
+	for _, release := range releases {
+		version := strings.TrimSpace(release.Name)
+		if !strings.HasPrefix(version, "v") {
+			version = "v" + version
+		}
+
+		// Fetch the raw Go file
+		rawURL := fmt.Sprintf(rawFileURL, version)
+		resp, err := http.Get(rawURL)
+		if err != nil {
+			fmt.Printf("Error fetching raw file for version %s: %v\n", version, err)
+			continue
+		}
+		defer resp.Body.Close()
+
+		body, err := io.ReadAll(resp.Body)
+		if err != nil {
+			fmt.Printf("Error reading raw file for version %s: %v\n", version, err)
+			continue
+		}
+
+		// Find the CurrentCapabilityVersion
+		matches := re.FindStringSubmatch(string(body))
+		if len(matches) > 1 {
+			capabilityVersionStr := matches[1]
+			capabilityVersion, _ := strconv.Atoi(capabilityVersionStr)
+			versions[version] = tailcfg.CapabilityVersion(capabilityVersion)
+		} else {
+			fmt.Printf("Version: %s, CurrentCapabilityVersion not found\n", version)
+		}
+	}
+
+	return versions, nil
+}
+
+func writeCapabilityVersionsToFile(versions map[string]tailcfg.CapabilityVersion) error {
+	// Open the output file
+	file, err := os.Create(outputFile)
+	if err != nil {
+		return fmt.Errorf("error creating file: %w", err)
+	}
+	defer file.Close()
+
+	// Write the package declaration and variable
+	file.WriteString("package capver\n\n")
+	file.WriteString("//Generated DO NOT EDIT\n\n")
+	file.WriteString(`import "tailscale.com/tailcfg"`)
+	file.WriteString("\n\n")
+	file.WriteString("var tailscaleToCapVer = map[string]tailcfg.CapabilityVersion{\n")
+
+	sortedVersions := xmaps.Keys(versions)
+	sort.Strings(sortedVersions)
+	for _, version := range sortedVersions {
+		file.WriteString(fmt.Sprintf("\t\"%s\": %d,\n", version, versions[version]))
+	}
+	file.WriteString("}\n")
+
+	file.WriteString("\n\n")
+	file.WriteString("var capVerToTailscaleVer = map[tailcfg.CapabilityVersion]string{\n")
+
+	capVarToTailscaleVer := make(map[tailcfg.CapabilityVersion]string)
+	for _, v := range sortedVersions {
+		cap := versions[v]
+		log.Printf("cap for v: %d, %s", cap, v)
+
+		// If it is already set, skip and continue,
+		// we only want the first tailscale vsion per
+		// capability vsion.
+		if _, ok := capVarToTailscaleVer[cap]; ok {
+			log.Printf("Skipping %d, %s", cap, v)
+			continue
+		}
+		log.Printf("Storing %d, %s", cap, v)
+		capVarToTailscaleVer[cap] = v
+	}
+
+	capsSorted := xmaps.Keys(capVarToTailscaleVer)
+	sort.Slice(capsSorted, func(i, j int) bool {
+		return capsSorted[i] < capsSorted[j]
+	})
+	for _, capVer := range capsSorted {
+		file.WriteString(fmt.Sprintf("\t%d:\t\t\"%s\",\n", capVer, capVarToTailscaleVer[capVer]))
+	}
+	file.WriteString("}\n")
+
+	return nil
+}
+
+func main() {
+	versions, err := getCapabilityVersions()
+	if err != nil {
+		fmt.Println("Error:", err)
+		return
+	}
+
+	err = writeCapabilityVersionsToFile(versions)
+	if err != nil {
+		fmt.Println("Error writing to file:", err)
+		return
+	}
+
+	fmt.Println("Capability versions written to", outputFile)
+}