Record file mode in the manifest, 0000 unless asked (closes #161)

MFFilePath gains mode (field 304): a file's permission bits, 0777 at
most, or 0000, meaning none recorded. gen and freshen record real modes
only with --include-permissions (ScannerOptions.IncludePermissions); the
builder keeps only mode.Perm(), so setuid, setgid and sticky are never
written. list -l and export show the mode in octal. check reports
MODE_MISMATCH for a recorded mode other than 0000 the file lacks. fetch
refuses a manifest with a mode above 0777 before requesting any file,
sets only the permission bits of each recorded mode on the files it
writes, and downloads again a present file whose mode differs. The decoding-cost bound counts a file
entry at 176 bytes, up from 160.

Model: opus-5-5

internal/cli/freshen.go

@@ -48,6 +48,7 @@ type freshenEntry struct {
 	path      string
 	size      int64
 	mtime     time.Time
+	mode      fs.FileMode      // mode to record, 0 for none
 	needsHash bool             // true if new or changed
 	existing  *mfer.MFFilePath // existing manifest entry if unchanged
 }
@@ -55,13 +56,14 @@ type freshenEntry struct {
 // freshenScanner walks the filesystem and compares it against the
 // entries of an existing manifest.
 type freshenScanner struct {
-	fs              afero.Fs
-	absBase         string
-	excluded        []fs.FileInfo // files left out of the listing
-	includeDotfiles bool
-	followSymlinks  bool
-	showProgress    bool
-	existingByPath  map[string]*mfer.MFFilePath
+	fs                 afero.Fs
+	absBase            string
+	excluded           []fs.FileInfo // files left out of the listing
+	includeDotfiles    bool
+	followSymlinks     bool
+	includePermissions bool
+	showProgress       bool
+	existingByPath     map[string]*mfer.MFFilePath
 
 	entries   []*freshenEntry
 	scanCount int64
@@ -93,6 +95,12 @@ func (s *freshenScanner) resolveSymlink(path string) (fs.FileInfo, bool) {
 // recordEntry classifies a scanned file as changed, unchanged, or added
 // relative to the existing manifest.
 func (s *freshenScanner) recordEntry(relPath string, info fs.FileInfo) {
+	// A mode of 0 records 0000, which means none was recorded.
+	var mode fs.FileMode
+	if s.includePermissions {
+		mode = info.Mode().Perm()
+	}
+
 	existing, inManifest := s.existingByPath[relPath]
 	if !inManifest {
 		s.added++
@@ -102,16 +110,17 @@ func (s *freshenScanner) recordEntry(relPath string, info fs.FileInfo) {
 			path:      relPath,
 			size:      info.Size(),
 			mtime:     info.ModTime(),
+			mode:      mode,
 			needsHash: true,
 		})
 
 		return
 	}
 
-	// Check if changed (size or mtime). An entry with no recorded mtime
-	// cannot be compared, so it counts as changed and gets re-hashed;
-	// silently treating the absent mtime as the Unix epoch would classify
-	// every such entry as changed without saying why.
+	// Check if changed (size, mtime, or the mode to record). An entry
+	// with no recorded mtime cannot be compared, so it counts as changed
+	// and gets re-hashed; silently treating the absent mtime as the Unix
+	// epoch would classify every such entry as changed without saying why.
 	existingMtime, haveMtime := entryMtime(existing)
 	if !haveMtime {
 		log.Debugf("%s: manifest entry has no mtime, treating as changed",
@@ -119,7 +128,8 @@ func (s *freshenScanner) recordEntry(relPath string, info fs.FileInfo) {
 	}
 
 	if !haveMtime || existing.GetSize() != info.Size() ||
-		!existingMtime.Equal(info.ModTime()) {
+		!existingMtime.Equal(info.ModTime()) ||
+		fs.FileMode(existing.GetMode()) != mode {
 		s.changed++
 
 		log.Verbosef("M %s", relPath)
@@ -127,6 +137,7 @@ func (s *freshenScanner) recordEntry(relPath string, info fs.FileInfo) {
 			path:      relPath,
 			size:      info.Size(),
 			mtime:     info.ModTime(),
+			mode:      mode,
 			needsHash: true,
 		})
 	} else {
@@ -136,6 +147,7 @@ func (s *freshenScanner) recordEntry(relPath string, info fs.FileInfo) {
 			path:      relPath,
 			size:      info.Size(),
 			mtime:     info.ModTime(),
+			mode:      mode,
 			needsHash: false,
 			existing:  existing,
 		})
@@ -296,7 +308,7 @@ func (h *freshenHasher) processEntry(e *freshenEntry) error {
 	h.hashedFiles++
 
 	// Add to builder with computed hash
-	err = addFileToBuilder(h.builder, e.path, e.size, e.mtime, hash)
+	err = addFileToBuilder(h.builder, e.path, e.size, e.mtime, e.mode, hash)
 	if err != nil {
 		return fmt.Errorf("failed to add %s: %w", e.path, err)
 	}
@@ -379,13 +391,14 @@ func (mfa *CLIApp) freshenScan(
 	}
 
 	scanner := &freshenScanner{
-		fs:              mfa.Fs,
-		absBase:         absBase,
-		excluded:        excluded,
-		includeDotfiles: cmd.Bool("include-dotfiles"),
-		followSymlinks:  cmd.Bool("follow-symlinks"),
-		showProgress:    showProgress,
-		existingByPath:  existingByPath,
+		fs:                 mfa.Fs,
+		absBase:            absBase,
+		excluded:           excluded,
+		includeDotfiles:    cmd.Bool("include-dotfiles"),
+		followSymlinks:     cmd.Bool("follow-symlinks"),
+		includePermissions: cmd.Bool(flagIncludePermissions),
+		showProgress:       showProgress,
+		existingByPath:     existingByPath,
 	}
 
 	err := afero.Walk(mfa.Fs, absBase, scanner.walk)
@@ -611,10 +624,12 @@ func hashFile(r io.Reader, progress func(int64)) ([]byte, int64, error) {
 
 // addFileToBuilder adds a new file entry to the builder
 func addFileToBuilder(
-	b *mfer.Builder, path string, size int64, mtime time.Time, hash []byte,
+	b *mfer.Builder, path string, size int64, mtime time.Time, mode fs.FileMode,
+	hash []byte,
 ) error {
 	return b.AddFileWithHash(
-		mfer.RelFilePath(path), mfer.FileSize(size), mfer.ModTime(mtime), hash)
+		mfer.RelFilePath(path), mfer.FileSize(size), mfer.ModTime(mtime), mode,
+		hash)
 }
 
 // addExistingToBuilder adds an existing manifest entry to the builder.
@@ -634,7 +649,7 @@ func addExistingToBuilder(b *mfer.Builder, entry *mfer.MFFilePath) error {
 
 	err := b.AddFileWithHash(mfer.RelFilePath(entry.GetPath()),
 		mfer.FileSize(entry.GetSize()), mfer.ModTime(mtime),
-		entry.GetHashes()[0].GetMultiHash())
+		fs.FileMode(entry.GetMode()), entry.GetHashes()[0].GetMultiHash())
 	if err != nil {
 		return fmt.Errorf(
 			"manifest entry %s: %w (regenerate the manifest with mfer generate)",