clientupdate: add support for QNAP (#10179)

Use the `qpkg_cli` to check for updates and install them. There are a
couple special things about this compare to other updaters:
* qpkg_cli can tell you when upgrade is available, but not what the
  version is
* qpkg_cli --add Tailscale works for new installs, upgrades and
  reinstalling existing version; even reinstall of existing version
  takes a while

Updates #10178

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

clientupdate/clientupdate.go

@@ -180,6 +180,8 @@ func (up *Updater) getUpdateFunction() (fn updateFunction, canAutoUpdate bool) {
 			// plugin manager to be persistent.
 			// TODO(awly): implement Unraid updates using the 'plugin' CLI.
 			return nil, false
+		case distro.QNAP:
+			return up.updateQNAP, true
 		}
 		switch {
 		case haveExecutable("pacman"):
@@ -1067,6 +1069,77 @@ func (up *Updater) unpackLinuxTarball(path string) error {
 	return nil
 }
 
+func (up *Updater) updateQNAP() (err error) {
+	if up.Version != "" {
+		return errors.New("installing a specific version on QNAP is not supported")
+	}
+	if err := requireRoot(); err != nil {
+		return err
+	}
+
+	defer func() {
+		if err != nil {
+			err = fmt.Errorf(`%w; you can try updating using "qpkg_cli --add Tailscale"`, err)
+		}
+	}()
+
+	out, err := exec.Command("qpkg_cli", "--upgradable", "Tailscale").CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to check if Tailscale is upgradable using qpkg_cli: %w, output: %q", err, out)
+	}
+
+	// Output should look like this:
+	//
+	// $ qpkg_cli -G Tailscale
+	// [Tailscale]
+	// upgradeStatus = 1
+	statusRe := regexp.MustCompile(`upgradeStatus = (\d)`)
+	m := statusRe.FindStringSubmatch(string(out))
+	if len(m) < 2 {
+		return fmt.Errorf("failed to check if Tailscale is upgradable using qpkg_cli, output: %q", out)
+	}
+	status, err := strconv.Atoi(m[1])
+	if err != nil {
+		return fmt.Errorf("cannot parse upgradeStatus from qpkg_cli output %q: %w", out, err)
+	}
+	// Possible status values:
+	//  0:can upgrade
+	//  1:can not upgrade
+	//  2:error
+	//  3:can not get rss information
+	//  4:qpkg not found
+	//  5:qpkg not installed
+	//
+	// We want status 0.
+	switch status {
+	case 0: // proceed with upgrade
+	case 1:
+		up.Logf("no update available")
+		return nil
+	case 2, 3, 4:
+		return fmt.Errorf("failed to check update status with qpkg_cli (upgradeStatus = %d)", status)
+	case 5:
+		return errors.New("Tailscale was not found in the QNAP App Center")
+	default:
+		return fmt.Errorf("failed to check update status with qpkg_cli (upgradeStatus = %d)", status)
+	}
+
+	// There doesn't seem to be a way to fetch what the available upgrade
+	// version is. Use the generic "latest" version in confirmation prompt.
+	if up.Confirm != nil && !up.Confirm("latest") {
+		return nil
+	}
+
+	up.Logf("c2n: running qpkg_cli --add Tailscale")
+	cmd := exec.Command("qpkg_cli", "--add", "Tailscale")
+	cmd.Stdout = up.Stdout
+	cmd.Stderr = up.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("failed tailscale update using qpkg_cli: %w", err)
+	}
+	return nil
+}
+
 func writeFile(r io.Reader, path string, perm os.FileMode) error {
 	if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
 		return fmt.Errorf("failed to remove existing file at %q: %w", path, err)

ipn/ipnlocal/c2n.go

@@ -31,6 +31,7 @@ import (
 	"tailscale.com/util/httpm"
 	"tailscale.com/util/syspolicy"
 	"tailscale.com/version"
+	"tailscale.com/version/distro"
 )
 
 var c2nLogHeap func(http.ResponseWriter, *http.Request) // non-nil on most platforms (c2n_pprof.go)
@@ -341,6 +342,14 @@ func findCmdTailscale() (string, error) {
 		if self == "/usr/local/sbin/tailscaled" || self == "/usr/local/bin/tailscaled" {
 			ts = "/usr/local/bin/tailscale"
 		}
+		if distro.Get() == distro.QNAP {
+			// The volume under /share/ where qpkg are installed is not
+			// predictable. But the rest of the path is.
+			ok, err := filepath.Match("/share/*/.qpkg/Tailscale/tailscaled", self)
+			if err == nil && ok {
+				ts = filepath.Join(filepath.Dir(self), "tailscale")
+			}
+		}
 	case "windows":
 		ts = filepath.Join(filepath.Dir(self), "tailscale.exe")
 	case "freebsd":