Add GoVPP integration and GetVPPInfo gRPC call

VPP client (internal/vpp/)
- New package managing connections to both VPP API and stats sockets,
  treated as a unit: if either drops, both are torn down and
  re-established together.
- Run() loop: connect, fetch version via vpe.ShowVersion, read
  /sys/boottime from the stats segment, log vpp-connect, then monitor
  with control_ping every 10s. On failure, disconnect both, retry
  after 5s.
- Registers as client name "vpp-maglev" (visible in VPP's
  "show api clients").
- Flags: --vpp-api-addr (default /run/vpp/api.sock) and
  --vpp-stats-addr (default /run/vpp/stats.sock). Empty api addr
  disables VPP integration entirely.

gRPC / proto
- Add GetVPPInfo RPC returning VPPInfo: version, build_date,
  build_directory, pid, boottime_ns, connecttime_ns. Both times are
  unix timestamps in nanoseconds — the client computes durations
  locally for display.
- Returns codes.Unavailable if VPP is disabled or not connected.

maglevc
- Add 'show vpp info' command displaying version, build-date,
  build-dir, vpp-pid, vpp-boottime (with duration), and connected
  time (with duration).

cmd/maglevc/commands.go

@@ -71,11 +71,20 @@ func buildTree() *Node {
 		Children: []*Node{showHealthCheckName},
 	}
 
+	// show vpp info
+	showVPPInfo := &Node{Word: "info", Help: "Show VPP version, uptime, and connection status", Run: runShowVPPInfo}
+	showVPP := &Node{
+		Word:     "vpp",
+		Help:     "VPP dataplane information",
+		Children: []*Node{showVPPInfo},
+	}
+
 	show.Children = []*Node{
 		showVersion,
 		showFrontends,
 		showBackends,
 		showHealthChecks,
+		showVPP,
 	}
 
 	// set backend <name> pause|resume|disabled|enabled
@@ -201,6 +210,31 @@ func dynNone(_ context.Context, _ grpcapi.MaglevClient) []string { return nil }
 
 // ---- run functions ---------------------------------------------------------
 
+func runShowVPPInfo(ctx context.Context, client grpcapi.MaglevClient, _ []string) error {
+	ctx, cancel := context.WithTimeout(ctx, callTimeout)
+	defer cancel()
+	info, err := client.GetVPPInfo(ctx, &grpcapi.GetVPPInfoRequest{})
+	if err != nil {
+		return err
+	}
+	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
+	fmt.Fprintf(w, "%s\t%s\n", label("version"), info.Version)
+	fmt.Fprintf(w, "%s\t%s\n", label("build-date"), info.BuildDate)
+	fmt.Fprintf(w, "%s\t%s\n", label("build-dir"), info.BuildDirectory)
+	fmt.Fprintf(w, "%s\t%d\n", label("vpp-pid"), info.Pid)
+	if info.BoottimeNs > 0 {
+		bootTime := time.Unix(0, info.BoottimeNs)
+		fmt.Fprintf(w, "%s\t%s (%s)\n", label("vpp-boottime"),
+			bootTime.Format("2006-01-02 15:04:05"),
+			formatDuration(time.Since(bootTime)))
+	}
+	connTime := time.Unix(0, info.ConnecttimeNs)
+	fmt.Fprintf(w, "%s\t%s (%s)\n", label("connected"),
+		connTime.Format("2006-01-02 15:04:05"),
+		formatDuration(time.Since(connTime)))
+	return w.Flush()
+}
+
 func runShowVersion(_ context.Context, _ grpcapi.MaglevClient, _ []string) error {
 	fmt.Printf("maglevc %s (commit %s, built %s)\n",
 		buildinfo.Version(), buildinfo.Commit(), buildinfo.Date())

cmd/maglevc/tree_test.go

@@ -28,6 +28,7 @@ func TestExpandPathsRoot(t *testing.T) {
 		"watch events",
 		"watch events <opt>",
 		"config check",
+		"show vpp info",
 		"config reload",
 		"quit",
 		"exit",
@@ -59,9 +60,9 @@ func TestExpandPathsShow(t *testing.T) {
 		}
 	}
 	// version, frontends, frontends <name>, backends, backends <name>,
-	// healthchecks, healthchecks <name> = 7 lines
-	if len(lines) != 7 {
-		t.Errorf("expected exactly 7 show subcommands, got %d", len(lines))
+	// healthchecks, healthchecks <name>, vpp info = 8 lines
+	if len(lines) != 8 {
+		t.Errorf("expected exactly 8 show subcommands, got %d", len(lines))
 	}
 }