Add snapshot files to list a snapshot's files without restoring it (closes #435)

`vaultik snapshot files <snapshot-id> [path] [--json]` downloads and
decrypts the snapshot database, as restore does, and prints mode, size,
modification time and path for every file at or under the path. A path
that matches nothing is an error. It needs the private key. The mode is
in Go's file-mode notation, which the README spells out.

Named `files` because `ls` is already the alias of `snapshot list`.
The missing-key error no longer says "for restore", since this command
and deep verify return it too. The README opening now states the
private-key rule first.

Model: opus-5-5

internal/cli/app.go

@@ -38,10 +38,11 @@ const (
 	// prune, remote nuke) write the local index or the remote store. They
 	// hold the PID lock so that at most one runs at a time.
 	mutating lockMode = iota
-	// readOnly commands (info, snapshot list, snapshot verify, remote info,
-	// snapshot restore) do not write the local index or the remote store,
-	// so they run without the lock and are never blocked by a running
-	// mutator. restore writes only to the target directory it is given.
+	// readOnly commands (info, snapshot list, snapshot files, snapshot
+	// verify, remote info, snapshot restore) do not write the local index
+	// or the remote store, so they run without the lock and are never
+	// blocked by a running mutator. restore writes only to the target
+	// directory it is given.
 	readOnly
 )
 
@@ -310,7 +311,7 @@ func RunOperation(
 }
 
 // runVaultikApp runs the standard single-operation command lifecycle
-// shared by the snapshot list/purge/remove and remote nuke subcommands:
+// shared by the snapshot list/files/purge/remove and remote nuke subcommands:
 // resolve the config, then run op against the Vaultik instance through
 // RunOperation, reporting a failure prefixed with failMsg on stderr. mode
 // says whether the command takes the PID lock. jsonOutput marks a command

internal/cli/entry_snapshot_files_test.go

@@ -0,0 +1,47 @@
+package cli //nolint:testpackage // shares runEntry and the backup config helpers
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/vaultik"
+)
+
+// cmdFiles is the word of `snapshot files`, used to build argument
+// vectors below.
+const cmdFiles = "files"
+
+// TestEntrySnapshotFilesListsOnlyThePath backs up two files and runs
+// `snapshot files` with the snapshot ID and the path of one of them,
+// which must be the only file listed.
+//
+//nolint:paralleltest // replaces os.Args, os.Stdout, os.Stderr and the xdg globals
+func TestEntrySnapshotFilesListsOnlyThePath(t *testing.T) {
+	configPath, _ := writeBackupConfigWithPrivateKey(t)
+
+	// writeBackupConfig puts file.txt in the source directory beside the
+	// config file.
+	sourceDir := filepath.Join(filepath.Dir(configPath), "source")
+	listed := filepath.Join(sourceDir, "file.txt")
+
+	require.NoError(t, os.WriteFile(
+		filepath.Join(sourceDir, "other.txt"), []byte("other"), 0o600))
+
+	code, _, stderr := runEntry(t,
+		flagConfig, configPath, cmdSnapshot, cmdCreate)
+	require.Equal(t, 0, code, stderr)
+
+	code, stdout, stderr := runEntry(t, flagConfig, configPath, cmdSnapshot,
+		cmdFiles, onlySnapshotID(t, configPath), listed, flagJSON)
+	require.Equal(t, 0, code, stderr)
+
+	var entries []vaultik.ListedFile
+
+	require.NoError(t, json.Unmarshal([]byte(stdout), &entries))
+	require.Len(t, entries, 1, "only the path given may be listed")
+	assert.Equal(t, listed, entries[0].Path)
+}

internal/cli/entry_test.go

@@ -48,7 +48,7 @@ func TestCLIEntry(t *testing.T) {
 	} else {
 		// Check snapshot subcommands
 		expectedSubCommands := []string{
-			"create", "list", "purge", "verify", "remove", "restore",
+			"create", "list", "files", "purge", "verify", "remove", "restore",
 		}
 		for _, expected := range expectedSubCommands {
 			found := false

internal/cli/snapshot.go

@@ -9,6 +9,10 @@ import (
 	"sneak.berlin/go/vaultik/internal/vaultik"
 )
 
+// filesMaxArgs is the maximum positional argument count of
+// `snapshot files <snapshot-id> [path]`.
+const filesMaxArgs = 2
+
 var (
 	errSnapshotIDRequired  = errors.New("snapshot ID required")
 	errWrongArgCount       = errors.New("wrong argument count")
@@ -52,6 +56,7 @@ func NewSnapshotCommand() *cobra.Command {
 	// Add subcommands
 	cmd.AddCommand(newSnapshotCreateCommand())
 	cmd.AddCommand(newSnapshotListCommand())
+	cmd.AddCommand(newSnapshotFilesCommand())
 	cmd.AddCommand(newSnapshotPurgeCommand())
 	cmd.AddCommand(newSnapshotVerifyCommand())
 	cmd.AddCommand(newSnapshotRemoveCommand())
@@ -172,6 +177,44 @@ func newSnapshotListCommand() *cobra.Command {
 	return cmd
 }
 
+// newSnapshotFilesCommand creates the 'snapshot files' subcommand
+func newSnapshotFilesCommand() *cobra.Command {
+	var jsonOutput bool
+
+	cmd := &cobra.Command{
+		Use:   "files <snapshot-id> [path]",
+		Short: "List the files in a snapshot",
+		Long: `Lists the path, size, mode and modification time of every file in a
+snapshot, without restoring it. With a path, lists only that path and
+what is under it; a path that matches nothing is an error.
+
+The snapshot may be named by its ID or, on a host with no local index,
+by the remote key that 'snapshot list' prints for a remote-only snapshot
+(an unambiguous leading part is enough).
+
+The file list is only in the snapshot's encrypted database, so this
+downloads and decrypts it, and requires the age private key in the
+VAULTIK_AGE_SECRET_KEY environment variable, as 'snapshot restore' does.`,
+		Args: cobra.RangeArgs(1, filesMaxArgs),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			path := ""
+			if len(args) == filesMaxArgs {
+				path = args[1]
+			}
+
+			return runVaultikApp(cmd, readOnly, jsonOutput,
+				"Failed to list snapshot files",
+				func(v *vaultik.Vaultik) error {
+					return v.ListSnapshotFiles(args[0], path, jsonOutput)
+				})
+		},
+	}
+
+	cmd.Flags().BoolVar(&jsonOutput, "json", false, "Output in JSON format")
+
+	return cmd
+}
+
 // newSnapshotPurgeCommand creates the 'snapshot purge' subcommand
 func newSnapshotPurgeCommand() *cobra.Command {
 	opts := &vaultik.SnapshotPurgeOptions{}

internal/vaultik/restore.go

@@ -31,7 +31,7 @@ var (
 	errPathsNotInSnapshot    = errors.New("requested path(s) not in the snapshot")
 	errFilesFailedVerify     = errors.New("files failed verification")
 	errDecryptionKeyRequired = errors.New(
-		"decryption key required for restore\n\n" +
+		"decryption key required\n\n" +
 			"Set the VAULTIK_AGE_SECRET_KEY environment variable to your " +
 			"age private key file:\n" +
 			"  export VAULTIK_AGE_SECRET_KEY=\"$(cat vaultik_backup_private_key.txt)\"")
@@ -153,18 +153,7 @@ func (v *Vaultik) Restore(opts *RestoreOptions) error {
 		return fmt.Errorf("downloading snapshot database: %w", err)
 	}
 
-	defer func() {
-		err := tempDB.Close()
-		if err != nil {
-			log.Debug("Failed to close temp database", "error", err)
-		}
-		// Remove the whole private directory, so the decrypted database
-		// and any SQLite side files it produced are gone on every path.
-		err = v.Fs.RemoveAll(tempDir)
-		if err != nil {
-			log.Debug("Failed to remove temp database directory", "error", err)
-		}
-	}()
+	defer v.closeSnapshotDB(tempDB, tempDir)
 
 	repos := database.NewRepositories(tempDB)
 
@@ -880,6 +869,21 @@ func (v *Vaultik) downloadSnapshotDB(
 	return db, tempDir, nil
 }
 
+// closeSnapshotDB closes a database returned by downloadSnapshotDB and
+// removes its private directory, so the decrypted database and any SQLite
+// side files it produced are gone.
+func (v *Vaultik) closeSnapshotDB(db *database.DB, tempDir string) {
+	err := db.Close()
+	if err != nil {
+		log.Debug("Failed to close temp database", "error", err)
+	}
+
+	err = v.Fs.RemoveAll(tempDir)
+	if err != nil {
+		log.Debug("Failed to remove temp database directory", "error", err)
+	}
+}
+
 // verifySnapshotDBIdentity confirms the decrypted metadata database really
 // is the snapshot named by remoteKey. age decryption proves the database
 // is readable, not that the object served at

internal/vaultik/snapshot_files.go

@@ -0,0 +1,114 @@
+package vaultik
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"text/tabwriter"
+	"time"
+
+	"sneak.berlin/go/vaultik/internal/database"
+)
+
+// ListedFile is one entry printed by `snapshot files`. Mode is the Go
+// file mode string, which shows the entry type and the permission bits
+// (for example -rw-r--r-- or drwxr-xr-x).
+type ListedFile struct {
+	Path  string    `json:"path"`
+	Size  int64     `json:"size"`
+	Mode  string    `json:"mode"`
+	MTime time.Time `json:"mtime"`
+}
+
+// ListSnapshotFiles prints the path, size, mode and modification time of
+// every file the snapshot holds at or under path, or of every file when
+// path is empty. The file list is only in the snapshot's encrypted
+// database, so this downloads and decrypts it as restore does, and needs
+// the private key.
+func (v *Vaultik) ListSnapshotFiles(snapshotID, path string, jsonOutput bool) error {
+	identities, err := v.restoreIdentities()
+	if err != nil {
+		return err
+	}
+
+	remoteKey, err := v.resolveSnapshotRemoteKey(snapshotID)
+	if err != nil {
+		return err
+	}
+
+	db, tempDir, err := v.downloadSnapshotDB(snapshotID, remoteKey, identities)
+	if errors.Is(err, errWrongPrivateKey) {
+		return err
+	}
+
+	if err != nil {
+		return fmt.Errorf("downloading snapshot database: %w", err)
+	}
+
+	defer v.closeSnapshotDB(db, tempDir)
+
+	repos := database.NewRepositories(db)
+
+	var files []*database.File
+
+	if path == "" {
+		files, err = repos.Files.ListAll(v.ctx)
+	} else {
+		files, err = repos.Files.ListUnderPath(v.ctx, filepath.Clean(path))
+	}
+
+	if err != nil {
+		return fmt.Errorf("listing files: %w", err)
+	}
+
+	if path != "" && len(files) == 0 {
+		return fmt.Errorf("%w: %s", errPathsNotInSnapshot, path)
+	}
+
+	entries := make([]ListedFile, 0, len(files))
+
+	for _, file := range files {
+		entries = append(entries, ListedFile{
+			Path:  file.Path.String(),
+			Size:  file.Size,
+			Mode:  os.FileMode(file.Mode).String(),
+			MTime: file.MTime,
+		})
+	}
+
+	if jsonOutput {
+		encoder := json.NewEncoder(v.Stdout)
+		encoder.SetIndent("", "  ")
+
+		return encoder.Encode(entries)
+	}
+
+	if v.UI.Quiet() {
+		return nil
+	}
+
+	return v.printListedFileTable(entries)
+}
+
+// printListedFileTable writes the entries as a plain table to stdout.
+func (v *Vaultik) printListedFileTable(entries []ListedFile) error {
+	w := tabwriter.NewWriter(v.Stdout, 0, 0, tabPadding, ' ', 0)
+
+	_, err := fmt.Fprintln(w, "MODE\tSIZE\tMODIFIED\tPATH")
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range entries {
+		_, err = fmt.Fprintf(w, "%s\t%d\t%s\t%s\n",
+			entry.Mode, entry.Size,
+			entry.MTime.Format(time.RFC3339), entry.Path)
+		if err != nil {
+			return err
+		}
+	}
+
+	return w.Flush()
+}

internal/vaultik/snapshot_files_test.go

@@ -0,0 +1,164 @@
+package vaultik_test
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/vaultik/internal/database"
+	"sneak.berlin/go/vaultik/internal/log"
+	"sneak.berlin/go/vaultik/internal/storage"
+	"sneak.berlin/go/vaultik/internal/vaultik"
+)
+
+// These tests cover https://git.eeqj.de/sneak/vaultik/issues/435:
+// `snapshot files` lists what a snapshot holds without restoring it.
+
+// backUpForFileListing backs up the fault source tree and returns a
+// reader whose stdout is out, the snapshot ID, and the source directory.
+func backUpForFileListing(
+	t *testing.T, out *bytes.Buffer,
+) (*vaultik.Vaultik, string, string) {
+	t.Helper()
+
+	fs := afero.NewOsFs()
+	tempDir := t.TempDir()
+	dataDir := filepath.Join(tempDir, "src")
+	dbPath := filepath.Join(tempDir, "index.sqlite")
+
+	ctx := context.Background()
+	cfg := faultTestConfig()
+
+	writeFaultSourceTree(t, fs, dataDir)
+
+	store, err := storage.NewFileStorer(t.TempDir())
+	require.NoError(t, err)
+
+	db, err := database.New(ctx, dbPath)
+	require.NoError(t, err)
+
+	id := fullFaultBackup(ctx, t, fs, store, cfg,
+		database.NewRepositories(db), dataDir, dbPath, "files")
+	require.NoError(t, db.Close())
+
+	v := newReaderVaultik(ctx, cfg, store, nil, fs)
+	v.Stdout = out
+
+	return v, id, dataDir
+}
+
+func TestSnapshotFilesJSONListsEveryFileWithItsMetadata(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	var out bytes.Buffer
+
+	v, id, dataDir := backUpForFileListing(t, &out)
+
+	require.NoError(t, v.ListSnapshotFiles(id, "", true))
+
+	var entries []vaultik.ListedFile
+
+	require.NoError(t, json.Unmarshal(out.Bytes(), &entries))
+
+	byPath := make(map[string]vaultik.ListedFile, len(entries))
+	for _, entry := range entries {
+		byPath[entry.Path] = entry
+	}
+
+	for _, rel := range []string{"small.txt", "a.bin", "sub", "sub/b.bin", "sub/c.bin"} {
+		path := filepath.Join(dataDir, rel)
+
+		entry, ok := byPath[path]
+		require.True(t, ok, "%s must be listed", path)
+
+		info, err := afero.NewOsFs().Stat(path)
+		require.NoError(t, err)
+
+		assert.Equal(t, info.Mode().String(), entry.Mode, path)
+		assert.True(t, info.ModTime().Equal(entry.MTime),
+			"%s: mtime %v, listed %v", path, info.ModTime(), entry.MTime)
+
+		if !info.IsDir() {
+			assert.Equal(t, info.Size(), entry.Size, path)
+		}
+	}
+}
+
+func TestSnapshotFilesListsOnlyWhatIsUnderThePath(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	var out bytes.Buffer
+
+	v, id, dataDir := backUpForFileListing(t, &out)
+
+	require.NoError(t, v.ListSnapshotFiles(id, filepath.Join(dataDir, "sub"), false))
+
+	text := out.String()
+	assert.Contains(t, text, filepath.Join(dataDir, "sub", "b.bin"))
+	assert.Contains(t, text, filepath.Join(dataDir, "sub", "c.bin"))
+	assert.NotContains(t, text, filepath.Join(dataDir, "small.txt"))
+	assert.True(t, strings.HasPrefix(text, "MODE"), "the table must have a header")
+}
+
+// TestSnapshotFilesQuietSuppressesTableNotJSON is the --quiet contract
+// for `snapshot files`: the table is silenced, but the --json document a
+// script depends on is still written.
+func TestSnapshotFilesQuietSuppressesTableNotJSON(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	var out bytes.Buffer
+
+	v, id, _ := backUpForFileListing(t, &out)
+	v.UI.SetQuiet(true)
+
+	require.NoError(t, v.ListSnapshotFiles(id, "", false))
+	require.Empty(t, out.String(), "the table must be silenced under --quiet")
+
+	require.NoError(t, v.ListSnapshotFiles(id, "", true))
+
+	var entries []vaultik.ListedFile
+
+	require.NoError(t, json.Unmarshal(out.Bytes(), &entries))
+	assert.NotEmpty(t, entries,
+		"the --json document must still be written under --quiet")
+}
+
+func TestSnapshotFilesFailsOnAPathThatMatchesNothing(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	var out bytes.Buffer
+
+	v, id, dataDir := backUpForFileListing(t, &out)
+	missing := filepath.Join(dataDir, "typo.txt")
+
+	err := v.ListSnapshotFiles(id, missing, false)
+
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), missing, "the error must name the path")
+	assert.Empty(t, out.String(), "nothing must be printed")
+}
+
+func TestSnapshotFilesRequiresThePrivateKey(t *testing.T) {
+	log.Initialize(log.Config{})
+	t.Parallel()
+
+	var out bytes.Buffer
+
+	v, id, _ := backUpForFileListing(t, &out)
+	v.Config.AgeSecretKey = ""
+
+	err := v.ListSnapshotFiles(id, "", false)
+
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "VAULTIK_AGE_SECRET_KEY")
+}