R-124 recipe root namespace as PBS spells it; R-118 no root size for an absent drive; R-269 rotated-out token rejected at once; R-317 dnsmasq install probed by its unit (burn-down round 2)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/lanresolver/ensure_dnsmasq_test.go

@@ -0,0 +1,122 @@
+package lanresolver
+
+import (
+	"context"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+)
+
+// recRunner records every privileged command EnsureDnsmasq would run and succeeds — nothing reaches
+// apt, systemctl or the root checker.
+type recRunner struct {
+	mu    sync.Mutex
+	calls []string
+}
+
+func (r *recRunner) Run(_ context.Context, name string, args ...string) ([]byte, []byte, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.calls = append(r.calls, strings.Join(append([]string{name}, args...), " "))
+	return nil, nil, nil
+}
+
+func (r *recRunner) RunStdin(ctx context.Context, _ io.Reader, name string, args ...string) ([]byte, []byte, error) {
+	return r.Run(ctx, name, args...)
+}
+
+func (r *recRunner) installed() bool {
+	for _, c := range r.calls {
+		if strings.HasPrefix(c, "apt-get install") && strings.HasSuffix(c, " dnsmasq") {
+			return true
+		}
+	}
+	return false
+}
+
+// fixtureRoot builds a fake host root holding exactly the given relative files and points the REAL
+// probe at it for the test's duration.
+func fixtureRoot(t *testing.T, files ...string) {
+	t.Helper()
+	root := t.TempDir()
+	for _, f := range files {
+		p := filepath.Join(root, f)
+		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(p, nil, 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+	prev := hostRoot
+	hostRoot = root
+	t.Cleanup(func() { hostRoot = prev })
+}
+
+func ensure(t *testing.T) *recRunner {
+	t.Helper()
+	r := &recRunner{}
+	m := NewManager(r, "192.0.2.10", []string{"1.1.1.1"}, slog.New(slog.NewTextHandler(io.Discard, nil)))
+	if err := m.EnsureDnsmasq(context.Background()); err != nil {
+		t.Fatalf("EnsureDnsmasq: %v", err)
+	}
+	return r
+}
+
+// R-317: a host with `dnsmasq-base` (the /usr/sbin/dnsmasq binary) but WITHOUT the `dnsmasq` package
+// (the service unit) must get the package installed — else the following `systemctl enable --now
+// dnsmasq` hits a unit that does not exist and LAN name resolution silently never comes up.
+//
+// RED-PROOF: probe "usr/sbin/dnsmasq" instead of the unit paths in dnsmasqUnitInstalled → this fails
+// with "install was skipped".
+func TestEnsureDnsmasq_BinaryWithoutUnitInstalls(t *testing.T) {
+	fixtureRoot(t, "usr/sbin/dnsmasq")
+	r := ensure(t)
+	if !r.installed() {
+		t.Fatalf("install was skipped on a dnsmasq-base-only host (binary present, unit absent) — "+
+			"the enable that follows targets a missing unit (R-317). calls: %q", r.calls)
+	}
+}
+
+func TestEnsureDnsmasq_UnitPresentSkipsInstall(t *testing.T) {
+	for _, unit := range []string{"usr/lib/systemd/system/dnsmasq.service", "lib/systemd/system/dnsmasq.service"} {
+		t.Run(unit, func(t *testing.T) {
+			fixtureRoot(t, "usr/sbin/dnsmasq", unit)
+			if r := ensure(t); r.installed() {
+				t.Fatalf("apt-get install ran although the dnsmasq unit is present at %s: %q", unit, r.calls)
+			}
+		})
+	}
+}
+
+func TestEnsureDnsmasq_NothingPresentInstalls(t *testing.T) {
+	fixtureRoot(t)
+	if r := ensure(t); !r.installed() {
+		t.Fatalf("install skipped on a host with no dnsmasq at all: %q", r.calls)
+	}
+}
+
+// Production wiring for the hostRoot seam: the shipped probe resolves against the real root and asks
+// about the unit the `dnsmasq` package owns — never the dnsmasq-base binary.
+func TestEnsureDnsmasq_ProductionProbeIsTheUnit(t *testing.T) {
+	if hostRoot != "/" {
+		t.Fatalf("hostRoot default = %q, want \"/\" — the production probe would look in the wrong tree", hostRoot)
+	}
+	var sawUsrLib bool
+	for _, p := range dnsmasqUnitPaths {
+		full := filepath.Join(hostRoot, p)
+		if strings.HasSuffix(full, "/sbin/dnsmasq") || strings.HasSuffix(full, "/bin/dnsmasq") {
+			t.Errorf("probe path %s is the dnsmasq-base binary, not the dnsmasq unit (R-317)", full)
+		}
+		if full == "/usr/lib/systemd/system/dnsmasq.service" {
+			sawUsrLib = true
+		}
+	}
+	if !sawUsrLib {
+		t.Errorf("probe paths %q miss /usr/lib/systemd/system/dnsmasq.service (dpkg -S: owned by dnsmasq)", dnsmasqUnitPaths)
+	}
+}

internal/lanresolver/lanresolver.go

@@ -101,11 +101,35 @@ func NewManager(runner proxmox.Runner, hostIP string, upstreams []string, logger
 	}
 }
 
+// hostRoot is the filesystem root the install probe resolves against: "/" in production; a test
+// points it at a fixture tree so the REAL probe runs against files it controls.
+var hostRoot = "/"
+
+// dnsmasqUnitPaths are where the `dnsmasq` package ships its systemd unit (Debian; /lib is the
+// pre-usrmerge spelling). R-317: probe the UNIT, never /usr/sbin/dnsmasq — that binary belongs to
+// `dnsmasq-base`, so a host carrying dnsmasq-base without dnsmasq used to skip the install and then
+// `systemctl enable --now dnsmasq` failed against a unit that is not there (resolver never up).
+// Pinned by TestEnsureDnsmasq_BinaryWithoutUnitInstalls.
+var dnsmasqUnitPaths = []string{
+	"usr/lib/systemd/system/dnsmasq.service",
+	"lib/systemd/system/dnsmasq.service",
+}
+
+// dnsmasqUnitInstalled reports whether the dnsmasq service unit (the `dnsmasq` package) is present.
+func dnsmasqUnitInstalled() bool {
+	for _, p := range dnsmasqUnitPaths {
+		if _, err := os.Stat(filepath.Join(hostRoot, p)); err == nil {
+			return true
+		}
+	}
+	return false
+}
+
 // EnsureDnsmasq makes dnsmasq present + enabled and writes the host base config. Idempotent: it
 // installs the package only when absent, and writes the base drop-in only when its content changes.
 func (m *Manager) EnsureDnsmasq(ctx context.Context) error {
-	if _, err := os.Stat("/usr/sbin/dnsmasq"); err != nil { // metadata read, no privilege needed
-		m.logger.Info("lanresolver: dnsmasq absent — installing")
+	if !dnsmasqUnitInstalled() { // metadata read, no privilege needed
+		m.logger.Info("lanresolver: dnsmasq service unit absent — installing")
 		if out, errOut, ierr := m.runner.Run(ctx, "apt-get", "install", "-y", "-q", "dnsmasq"); ierr != nil {
 			return fmt.Errorf("install dnsmasq: %s: %w", strings.TrimSpace(string(errOut))+string(out), ierr)
 		}