internal/apply/hold.go

@@ -72,6 +72,25 @@ func lookBefore(ctx context.Context, sys system.System, d *declaration.Declarati
 			if present(res.Path) && !recordedPath(known, res.Path) {
 				seen["path:"+res.Path] = true
 			}
+		case *declaration.Archive:
+			// Unpacking over it, and re-owning it recursively, would change the predecessor's
+			// files.
+			if present(res.Path) && !recordedPath(known, res.Path) {
+				seen["path:"+res.Path] = true
+			}
+		case *declaration.Process:
+			// Its unit would be written over and restarted.
+			if !known.Recorded(string(declaration.TypeProcess), res.Name) &&
+				present(filepath.Join(unitDir, res.Name+".service")) {
+				seen["unit-file:"+res.Name] = true
+			}
+		case *declaration.User:
+			// Its shell and groups would be changed.
+			if !known.Recorded(string(declaration.TypeUser), res.Name) {
+				if _, exists, err := system.LookUpUser(ctx, run, res.Name); err == nil && exists {
+					seen["user:"+res.Name] = true
+				}
+			}
 		case *declaration.Service:
 			if known.Recorded(string(declaration.TypeService), res.Unit) {
 				continue
@@ -239,6 +258,12 @@ func holdOnAdopted(ctx context.Context, sys system.System, r declaration.Resourc
 			}
 		case *declaration.Directory:
 			isFound = before["path:"+res.Path]
+		case *declaration.Archive:
+			isFound = before["path:"+res.Path]
+		case *declaration.Process:
+			isFound = before["unit-file:"+res.Name]
+		case *declaration.User:
+			isFound = before["user:"+res.Name]
 		case *declaration.Service:
 			isFound = before["unit:"+res.Unit]
 		}
@@ -396,6 +421,38 @@ func hold(ctx context.Context, sys system.System, r declaration.Resource, module
 			}
 		}
 		detail = "found on the machine; its mode, owner and contents kept until " + module + " is taken"
+	case *declaration.Archive:
+		if _, err := os.Lstat(res.Path); errors.Is(err, os.ErrNotExist) {
+			if !already {
+				return out, h, fmt.Errorf("%s was found and is gone before it could be held", res.Path)
+			}
+			changed = "gone"
+		} else if err != nil {
+			return out, h, err
+		}
+		detail = "something is already at " + res.Path + "; nothing unpacked over it or re-owned until " +
+			module + " is taken"
+	case *declaration.Process:
+		unit := filepath.Join(unitDir, res.Name+".service")
+		if !present(unit) {
+			if !already {
+				return out, h, fmt.Errorf("%s was found and is gone before it could be held", unit)
+			}
+			changed = "gone"
+		}
+		detail = "its unit " + unit + " was found on the machine; not written over or restarted until " +
+			module + " is taken"
+	case *declaration.User:
+		_, exists, err := system.LookUpUser(ctx, run, res.Name)
+		switch {
+		case err != nil:
+			return out, h, err
+		case !exists && !already:
+			return out, h, fmt.Errorf("the user %s was found and is gone before it could be held", res.Name)
+		case !exists:
+			changed = "gone"
+		}
+		detail = "the user was found on the machine; its shell and groups are kept until " + module + " is taken"
 	case *declaration.Service:
 		state, err := sys.ServiceState(ctx, run, res.Unit)
 		switch {

internal/apply/hold_test.go

@@ -24,6 +24,7 @@ type machine struct {
 	// named volumes.
 	units   map[string]*fakeUnit
 	volumes map[string]bool
+	users   map[string]bool
 }
 
 type fakeUnit struct {
@@ -80,6 +81,12 @@ func (m *machine) run(_ context.Context, name string, args ...string) (string, e
 	if name == "systemctl" {
 		return m.systemctl(args)
 	}
+	if name == "getent" {
+		if m.users[args[len(args)-1]] {
+			return args[len(args)-1] + ":x:1500:1500::/home/" + args[len(args)-1] + ":/bin/bash\n", nil
+		}
+		return "", errors.New("exit status 2")
+	}
 	if name != "docker" {
 		return "", nil
 	}
@@ -680,3 +687,70 @@ func TestAnActionInAHeldContainerIsHeldUntilItsModuleIsTaken(t *testing.T) {
 		t.Errorf("holds outlived the take: %+v", state.Held)
 	}
 }
+
+const sixtyFourZeros = "0000000000000000000000000000000000000000000000000000000000000000"
+
+func TestAnArchiveOverSomethingFoundIsNotUnpacked(t *testing.T) {
+	dir := t.TempDir()
+	at := filepath.Join(dir, "site")
+	if err := os.Mkdir(at, 0o750); err != nil {
+		t.Fatal(err)
+	}
+	theirs := filepath.Join(at, "index.html")
+	_ = os.WriteFile(theirs, []byte("the predecessor's site\n"), 0o640)
+	m := &machine{containers: map[string]*fakeContainer{}}
+	// The source is unreachable: fetching it would fail the apply, so a pass means it was not tried.
+	report, state := applyAdopted(t, adopted(t, untaken("hello-web.site"),
+		`{"id":"hello-web.site","type":"archive","source":"http://192.0.2.1/site.tar.gz",
+		  "digest":"sha256:`+sixtyFourZeros+`","path":"`+at+`","owner":"root"}`), store.State{}, m, dir)
+	if o := outcomeOf(report, "hello-web.site"); o.Action != "held" || !strings.Contains(o.Detail, "nothing unpacked") {
+		t.Errorf("an archive over found files was not held: %+v", o)
+	}
+	if got, _ := os.ReadFile(theirs); string(got) != "the predecessor's site\n" {
+		t.Errorf("the found files were touched: %q", got)
+	}
+	if _, ok := state.HeldAt("hello-web.site"); !ok {
+		t.Error("the hold was not recorded")
+	}
+}
+
+func TestAProcessWhoseUnitIsFoundIsNotWrittenOverOrRestarted(t *testing.T) {
+	dir := t.TempDir()
+	was := unitDir
+	unitDir = dir
+	t.Cleanup(func() { unitDir = was })
+	unit := filepath.Join(dir, "hello-daemon.service")
+	_ = os.WriteFile(unit, []byte("[Service]\nExecStart=/opt/predecessor/hello\n"), 0o644)
+	m := &machine{containers: map[string]*fakeContainer{}}
+	report, state := applyAdopted(t, adopted(t, untaken("hello-web.daemon"),
+		`{"id":"hello-web.daemon","type":"process","name":"hello-daemon","source":"http://192.0.2.1/d.tar.gz",
+		  "digest":"sha256:`+sixtyFourZeros+`","run":["hello"]}`), store.State{}, m, dir)
+	if o := outcomeOf(report, "hello-web.daemon"); o.Action != "held" || !strings.Contains(o.Detail, "not written over or restarted") {
+		t.Errorf("a process whose unit was found was not held: %+v", o)
+	}
+	if got, _ := os.ReadFile(unit); string(got) != "[Service]\nExecStart=/opt/predecessor/hello\n" {
+		t.Errorf("the found unit was written over: %q", got)
+	}
+	if m.did("systemctl") {
+		t.Errorf("the found unit was touched: %v", m.asked)
+	}
+	if _, ok := state.HeldAt("hello-web.daemon"); !ok {
+		t.Error("the hold was not recorded")
+	}
+}
+
+func TestAUserFoundOnTheMachineKeepsItsShellAndGroups(t *testing.T) {
+	dir := t.TempDir()
+	m := &machine{containers: map[string]*fakeContainer{}, users: map[string]bool{"hello": true}}
+	report, _ := applyAdopted(t, adopted(t, untaken("hello-web.user"),
+		`{"id":"hello-web.user","type":"user","name":"hello","shell":"/bin/zsh","groups":["docker"]}`),
+		store.State{}, m, dir)
+	if o := outcomeOf(report, "hello-web.user"); o.Action != "held" || !strings.Contains(o.Detail, "shell and groups") {
+		t.Errorf("a found user was not held: %+v", o)
+	}
+	for _, a := range m.asked {
+		if strings.HasPrefix(a, "usermod") || strings.HasPrefix(a, "useradd") {
+			t.Errorf("a found user was changed: %s", a)
+		}
+	}
+}

internal/apply/process.go

@@ -32,8 +32,9 @@ import (
 // owners end up disagreeing about one path.
 const daemonRoot = "/var/lib/mesh/daemons"
 
-// unitDir is where the mesh writes the units it owns.
-const unitDir = "/etc/systemd/system"
+// unitDir is where the mesh writes the units it owns. A variable only so a test can point it at a
+// directory of its own.
+var unitDir = "/etc/systemd/system"
 
 func applyProcess(ctx context.Context, r *declaration.Process, run Runner,
 	changed map[string]bool, previous store.Applied) (Outcome, error) {