PLAN.md: previews are cached in thumbs.db

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

PLAN.md

@@ -652,16 +652,23 @@ something long in one, switch away and back, refresh — it's all still there.
     0.7 s on the CPU; the 8K Osmo HEVC 1.0 s against 2.9 s. `grid`'s two GPUs are listed in
     node order and both decode the same set (h264, hevc, vp9, mjpeg, mpeg2 — **no AV1 on
     either**, per vainfo, so AV1 is dav1d on the CPU).
-  - **Cached under the machine's data dir**, `<data dir>/thumbs/<xx>/<sha256>.jpg`, keyed by
+  - **Cached in one database file under the machine's data dir**, `<data dir>/thumbs.db`
-    path, size and mtime — a changed file gets a new preview, an unchanged one is never
+    (bbolt — pure Go, so the binary stays static; v0.1.0-202, the first build kept them as
-    decoded twice, and the URL carries `v=<mtime>-<size>` so the browser's own cache is
+    a tree of hash-named JPEGs under `thumbs/`, replaced the same day when Mitchell asked
-    right too (7 days, ETag, 304). A file ffmpeg could not decode is remembered beside the
+    where they were kept: "stored in hamlab, maybe under a DB, up to you"). An entry is
-    JPEGs as `.err` with ffmpeg's reason, answered as 422, and retried only when the file
+    keyed by path, size and mtime — a changed file gets a new preview, an unchanged one is
-    changes; a timeout is not remembered. Nothing expires: a preview is a few KB, and only
+    never decoded twice — and carries the engine, codec, source size and time beside the
+    picture; a count rides in the file so the previews button's tooltip can say "N kept
+    (M MB)" without walking anything. The URL carries `v=<mtime>-<size>` so the browser's
+    own cache is right too (7 days, ETag, 304). A file ffmpeg could not decode is kept with
+    ffmpeg's reason and no picture, answered as 422, retried only when the file changes; a
+    timeout is not kept. A miss never creates the file, so a machine nobody browses with
+    previews on never has one; a cache that cannot be opened is logged and previews are
+    still made and served, just not kept. Nothing expires: a preview is a few KB, and only
     files somebody scrolled past are ever made. At most 2–4 ffmpegs at once per machine
     (half the cores, clamped), one per file however many rows ask, and a preview's work
     runs on a clock of its own so the row that asked first leaving does not cancel it for
-    the rest. Each ffmpeg runs under `nice -n 10`. `hamlet`'s backup job skips the folder.
+    the rest. Each ffmpeg runs under `nice -n 10`. `hamlet`'s backup job skips the file.
   - **Root mode makes them as root** (`hamlab thumb`, the sibling of `hamlab fs`, caps on
     stdin, JSON out), so a file only root can read gets a preview, and the probe runs as
     root too — root opens every render node whatever groups the daemon has. Which matters:

go.mod

@@ -5,6 +5,7 @@ go 1.26.0
 require (
 	github.com/coder/websocket v1.8.15
 	github.com/creack/pty v1.1.24
+	go.etcd.io/bbolt v1.5.0
 	golang.org/x/crypto v0.57.0
 	golang.org/x/term v0.46.0
 )

go.sum

@@ -2,9 +2,21 @@ github.com/coder/websocket v1.8.15 h1:6B2JPeOGlpff2Uz6vOEH1Vzpi0iUz20A+lPVhPHtNU
 github.com/coder/websocket v1.8.15/go.mod h1:NX3SzP+inril6yawo5CQXx8+fk145lPDC6pumgx0mVg=
 github.com/creack/pty v1.1.24 h1:bJrF4RRfyJnbTJqzRLHzcGaZK1NeM5kTC9jGgovnR1s=
 github.com/creack/pty v1.1.24/go.mod h1:08sCNb52WyoAwi2QDyzUCTgcvVFhUzewun7wtTfvcwE=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+go.etcd.io/bbolt v1.5.0 h1:S7GAl7Fxv12yohbwFfIbQCGDWbQbtDGPET4P/bD4lxU=
+go.etcd.io/bbolt v1.5.0/go.mod h1:mkltfYE5aUHQxUct9N9V+Kp7aSjFqjgrhcXIS70Lrdk=
 golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
 golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
+golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
 golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
 golang.org/x/term v0.46.0 h1:3+OXuTbaKDgwk8jTi3aSLHRlmWqHEUDUtxnbFigO4YE=
 golang.org/x/term v0.46.0/go.mod h1:+K02xbkittuwc0Am4abfA3Fc+XRGXkvBXNO88NCXPoc=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/api/thumbs.go

@@ -1,7 +1,7 @@
 package api
 
 // Previews for the Files tab: GET /api/files/thumb hands back one small JPEG of an image or
-// a video, made by internal/thumbs and kept under <data dir>/thumbs/. The work is bounded
+// a video, made by internal/thumbs and kept in <data dir>/thumbs.db. The work is bounded
 // two ways — a handful of ffmpegs at once, and one per file however many rows ask for it —
 // because a folder of a thousand photos asks for every row the moment previews go on.
 //
@@ -32,7 +32,7 @@ const thumbTimeout = 30 * time.Second
 const capsTTL = 10 * time.Minute // how long a probe is believed; a refresh after an install or a group change does not wait
 
 type thumbSvc struct {
-	cache thumbs.Cache
+	cache *thumbs.Cache
 	self  string
 	sem   chan struct{}
 	mu    sync.Mutex
@@ -61,7 +61,7 @@ func newThumbSvc(dataDir, self string) *thumbSvc {
 	if n > 4 {
 		n = 4
 	}
-	return &thumbSvc{cache: thumbs.Cache{Dir: filepath.Join(dataDir, "thumbs")}, self: self, sem: make(chan struct{}, n), caps: map[bool]*capsEntry{}, calls: map[string]*thumbCall{}}
+	return &thumbSvc{cache: thumbs.NewCache(filepath.Join(dataDir, "thumbs.db")), self: self, sem: make(chan struct{}, n), caps: map[bool]*capsEntry{}, calls: map[string]*thumbCall{}}
 }
 
 // capsFor is what previews can be made with, probed once and kept for a while.
@@ -208,7 +208,9 @@ func (s *Server) filesThumb(w http.ResponseWriter, r *http.Request) {
 		var de *thumbs.DecodeError
 		switch {
 		case errors.As(err, &de):
-			_ = s.thumbs.cache.PutFailure(key, de.Msg)
+			if err := s.thumbs.cache.Put(key, thumbs.Entry{Path: p, Failure: de.Msg}); err != nil {
+				log.Printf("thumbs: cache: %v", err)
+			}
 			log.Printf("thumbs: %s: %s", p, de.Msg)
 			jsonErr(w, 422, de.Msg)
 		case errors.Is(err, context.DeadlineExceeded):
@@ -221,21 +223,26 @@ func (s *Server) filesThumb(w http.ResponseWriter, r *http.Request) {
 		}
 		return
 	}
-	if err := s.thumbs.cache.Put(key, res.JPEG); err != nil {
+	if err := s.thumbs.cache.Put(key, thumbs.Entry{Path: p, Engine: res.Engine, Codec: res.Codec, Width: res.Width, Height: res.Height, JPEG: res.JPEG}); err != nil {
-		log.Printf("thumbs: cache %s: %v", key[:8], err)
+		log.Printf("thumbs: cache: %v", err)
 	}
 	writeThumb(w, key, res.JPEG, res.Engine)
 }
 
+// serveCachedThumb answers from the cache when it can. A cache that cannot be read is a
+// miss: the preview is made again rather than refused.
 func (s *Server) serveCachedThumb(w http.ResponseWriter, key string) bool {
-	data, why, found := s.thumbs.cache.Get(key)
+	e, found, err := s.thumbs.cache.Get(key)
+	if err != nil {
+		log.Printf("thumbs: cache: %v", err)
+	}
 	switch {
 	case !found:
 		return false
-	case data == nil:
+	case e.Failure != "":
-		jsonErr(w, 422, why)
+		jsonErr(w, 422, e.Failure)
 	default:
-		writeThumb(w, key, data, "cache")
+		writeThumb(w, key, e.JPEG, "cache ("+e.Engine+")")
 	}
 	return true
 }
@@ -271,7 +278,13 @@ type thumbStatus struct {
 	Install  *thumbInstall `json:"install,omitempty"` // ffmpeg is missing and this can put it on
 	GPUFix   bool          `json:"gpu_fix,omitempty"` // a render node is there but closed to the daemon's user, and this can open it
 	User     string        `json:"user"`
-	CacheDir string        `json:"cache_dir"`
+	Cache    thumbCache    `json:"cache"`
+}
+
+type thumbCache struct {
+	Path    string `json:"path"`
+	Entries int64  `json:"entries"`
+	Bytes   int64  `json:"bytes"`
 }
 
 type thumbInstall struct {
@@ -287,7 +300,8 @@ func (s *Server) thumbsStatus(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	caps, err := s.thumbs.capsFor(r.Context(), root, r.URL.Query().Get("refresh") == "1")
-	st := thumbStatus{GPUs: []thumbs.GPU{}, User: s.user, CacheDir: s.thumbs.cache.Dir}
+	st := thumbStatus{GPUs: []thumbs.GPU{}, User: s.user, Cache: thumbCache{Path: s.thumbs.cache.Path}}
+	st.Cache.Entries, st.Cache.Bytes = s.thumbs.cache.Stats()
 	if root {
 		st.User = "root"
 	}

internal/thumbs/cache.go

@@ -2,20 +2,51 @@ package thumbs
 
 import (
 	"crypto/sha256"
+	"encoding/binary"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"os"
-	"path/filepath"
 	"strconv"
+	"sync"
+	"time"
+
+	bolt "go.etcd.io/bbolt"
 )
 
-// Cache keeps finished previews on disk, under Ham Lab's own data directory: one JPEG per
+// Cache keeps finished previews in one database file under Ham Lab's own data directory —
-// (path, size, mtime), so a file that changes gets a new preview and an unchanged one is
+// thumbs.db, a bbolt key/value store: pure Go, so the binary stays static, and one file
-// never decoded twice. A file ffmpeg could not decode is remembered the same way, with
+// per machine rather than a tree of hash-named JPEGs. An entry is one file's preview keyed
-// ffmpeg's reason beside it, so a folder of odd files does not re-run ffmpeg on every
+// by its path, size and mtime, so a file that changes gets a new preview and an unchanged
+// one is never decoded twice. A file ffmpeg could not decode is kept the same way, with
+// ffmpeg's reason and no picture, so a folder of odd files does not re-run ffmpeg on every
 // visit. Nothing expires: a preview is a few kilobytes, and only files somebody actually
-// scrolled past are ever made.
+// scrolled past are ever made. The file is opened the first time something is stored, so a
-type Cache struct{ Dir string }
+// machine nobody browses with previews on never has one.
+type Cache struct {
+	Path string
+	mu   sync.Mutex
+	db   *bolt.DB
+	err  error
+}
+
+// Entry is one cached preview, or the remembered reason there is none.
+type Entry struct {
+	Path    string    `json:"path"`
+	Engine  string    `json:"engine,omitempty"`
+	Codec   string    `json:"codec,omitempty"`
+	Width   int       `json:"width,omitempty"`
+	Height  int       `json:"height,omitempty"`
+	Made    time.Time `json:"made"`
+	Failure string    `json:"failure,omitempty"` // set instead of JPEG when ffmpeg refused the file
+	JPEG    []byte    `json:"-"`
+}
+
+var (
+	bucketThumbs = []byte("thumbs")
+	bucketMeta   = []byte("meta")
+	keyCount     = []byte("count")
+)
 
 // Key identifies one file's preview. "v1" is the preview format: bump it to retire every
 // cached preview at once.
@@ -24,55 +55,164 @@ func Key(path string, size, mtime int64) string {
 	return hex.EncodeToString(h[:])
 }
 
-func (c Cache) file(key, ext string) string { return filepath.Join(c.Dir, key[:2], key+ext) }
+func NewCache(path string) *Cache { return &Cache{Path: path} }
 
-// Get returns the preview, or the remembered reason it could not be made.
+// open the database once; an open that failed is not retried, and previews still get made
-func (c Cache) Get(key string) (jpeg []byte, failure string, found bool) {
+// and served — they are simply not kept, and the log says why.
-	if len(key) < 2 {
+func (c *Cache) open() (*bolt.DB, error) {
-		return nil, "", false
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.db != nil || c.err != nil {
+		return c.db, c.err
 	}
-	if b, err := os.ReadFile(c.file(key, ".jpg")); err == nil && len(b) > 0 {
+	db, err := bolt.Open(c.Path, 0o600, &bolt.Options{Timeout: 2 * time.Second})
-		return b, "", true
+	if err != nil {
+		c.err = err
+		return nil, err
 	}
-	if b, err := os.ReadFile(c.file(key, ".err")); err == nil {
+	if err := db.Update(func(tx *bolt.Tx) error {
-		return nil, string(b), true
+		if _, err := tx.CreateBucketIfNotExists(bucketThumbs); err != nil {
+			return err
+		}
+		_, err := tx.CreateBucketIfNotExists(bucketMeta)
+		return err
+	}); err != nil {
+		db.Close()
+		c.err = err
+		return nil, err
 	}
-	return nil, "", false
+	c.db = db
+	return db, nil
 }
 
-// Put keeps a preview; PutFailure keeps the reason there is none.
+// Close releases the file. Previews after it are made but not kept.
-func (c Cache) Put(key string, jpeg []byte) error {
+func (c *Cache) Close() error {
-	if len(jpeg) == 0 {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.db == nil {
+		return nil
+	}
+	err := c.db.Close()
+	c.db, c.err = nil, errors.New("cache closed")
+	return err
+}
+
+// Get returns the entry for a key. A database that does not exist yet is a miss, not a reason
+// to make one.
+func (c *Cache) Get(key string) (Entry, bool, error) {
+	c.mu.Lock()
+	db := c.db
+	c.mu.Unlock()
+	if db == nil {
+		if _, err := os.Stat(c.Path); err != nil {
+			return Entry{}, false, nil
+		}
+		var err error
+		if db, err = c.open(); err != nil {
+			return Entry{}, false, err
+		}
+	}
+	var e Entry
+	found := false
+	err := db.View(func(tx *bolt.Tx) error {
+		v := tx.Bucket(bucketThumbs).Get([]byte(key))
+		if v == nil {
+			return nil
+		}
+		var err error
+		e, err = decode(v) // copies: a value is only valid inside the transaction
+		found = err == nil
+		return err
+	})
+	return e, found, err
+}
+
+// Put stores an entry, replacing any under the same key.
+func (c *Cache) Put(key string, e Entry) error {
+	if len(e.JPEG) == 0 && e.Failure == "" {
 		return errors.New("empty preview")
 	}
-	return c.write(c.file(key, ".jpg"), jpeg)
+	if e.Made.IsZero() {
-}
+		e.Made = time.Now()
-
-func (c Cache) PutFailure(key, reason string) error {
-	return c.write(c.file(key, ".err"), []byte(reason))
-}
-
-// write lands the file whole or not at all: a reader never sees a half-written JPEG.
-func (c Cache) write(dst string, b []byte) error {
-	if err := os.MkdirAll(filepath.Dir(dst), 0o700); err != nil {
-		return err
 	}
-	tmp, err := os.CreateTemp(filepath.Dir(dst), ".tmp-*")
+	db, err := c.open()
 	if err != nil {
 		return err
 	}
-	if _, err := tmp.Write(b); err != nil {
+	v, err := encode(e)
-		tmp.Close()
+	if err != nil {
-		os.Remove(tmp.Name())
 		return err
 	}
-	if err := tmp.Close(); err != nil {
+	return db.Update(func(tx *bolt.Tx) error {
-		os.Remove(tmp.Name())
+		b := tx.Bucket(bucketThumbs)
-		return err
+		k := []byte(key)
+		fresh := b.Get(k) == nil
+		if err := b.Put(k, v); err != nil {
+			return err
+		}
+		if fresh {
+			m := tx.Bucket(bucketMeta)
+			return m.Put(keyCount, be64(count(m)+1))
+		}
+		return nil
+	})
+}
+
+// Stats is how many previews are kept and how big the file is.
+func (c *Cache) Stats() (entries int64, bytes int64) {
+	st, err := os.Stat(c.Path)
+	if err != nil {
+		return 0, 0
 	}
-	if err := os.Rename(tmp.Name(), dst); err != nil {
+	bytes = st.Size()
-		os.Remove(tmp.Name())
+	db, err := c.open()
-		return err
+	if err != nil {
+		return 0, bytes
 	}
-	return nil
+	_ = db.View(func(tx *bolt.Tx) error { entries = count(tx.Bucket(bucketMeta)); return nil })
+	return entries, bytes
+}
+
+func count(m *bolt.Bucket) int64 {
+	if v := m.Get(keyCount); len(v) == 8 {
+		return int64(binary.BigEndian.Uint64(v))
+	}
+	return 0
+}
+
+func be64(n int64) []byte {
+	b := make([]byte, 8)
+	binary.BigEndian.PutUint64(b, uint64(n))
+	return b
+}
+
+// A value is a 4-byte header length, the header as JSON, then the JPEG bytes.
+func encode(e Entry) ([]byte, error) {
+	hdr, err := json.Marshal(e)
+	if err != nil {
+		return nil, err
+	}
+	v := make([]byte, 4+len(hdr)+len(e.JPEG))
+	binary.BigEndian.PutUint32(v, uint32(len(hdr)))
+	copy(v[4:], hdr)
+	copy(v[4+len(hdr):], e.JPEG)
+	return v, nil
+}
+
+func decode(v []byte) (Entry, error) {
+	if len(v) < 4 {
+		return Entry{}, errors.New("short value")
+	}
+	n := int(binary.BigEndian.Uint32(v))
+	if 4+n > len(v) {
+		return Entry{}, errors.New("bad header length")
+	}
+	var e Entry
+	if err := json.Unmarshal(v[4:4+n], &e); err != nil {
+		return Entry{}, err
+	}
+	if rest := v[4+n:]; len(rest) > 0 {
+		e.JPEG = append([]byte(nil), rest...)
+	}
+	return e, nil
 }

internal/thumbs/thumbs_test.go

@@ -107,30 +107,54 @@ func TestAttempts(t *testing.T) {
 }
 
 func TestCache(t *testing.T) {
-	c := Cache{Dir: t.TempDir()}
+	c := NewCache(filepath.Join(t.TempDir(), "thumbs.db"))
 	k := Key("/a", 1, 2)
-	if _, _, found := c.Get(k); found {
+	if _, found, err := c.Get(k); found || err != nil {
-		t.Fatal("empty cache found something")
+		t.Fatal("an empty cache found something, or complained")
 	}
-	if err := c.Put(k, []byte("jpeg")); err != nil {
+	if _, err := os.Stat(c.Path); err == nil {
+		t.Fatal("a miss must not create the database")
+	}
+	if n, b := c.Stats(); n != 0 || b != 0 {
+		t.Fatal("stats of nothing")
+	}
+	if err := c.Put(k, Entry{Path: "/a", Engine: "cpu", Codec: "png", Width: 640, Height: 360, JPEG: []byte("jpeg")}); err != nil {
 		t.Fatal(err)
 	}
-	if b, _, found := c.Get(k); !found || string(b) != "jpeg" {
+	e, found, err := c.Get(k)
-		t.Fatal("put then get")
+	if err != nil || !found || string(e.JPEG) != "jpeg" || e.Engine != "cpu" || e.Width != 640 || e.Path != "/a" || e.Made.IsZero() {
+		t.Fatalf("put then get: %+v %v %v", e, found, err)
 	}
 	k2 := Key("/b", 1, 2)
-	if err := c.PutFailure(k2, "no video stream"); err != nil {
+	if err := c.Put(k2, Entry{Path: "/b", Failure: "no video stream"}); err != nil {
 		t.Fatal(err)
 	}
-	if b, why, found := c.Get(k2); !found || b != nil || why != "no video stream" {
+	if e, found, _ := c.Get(k2); !found || e.JPEG != nil || e.Failure != "no video stream" {
 		t.Fatal("a failure is remembered with its reason")
 	}
-	if err := c.Put(k, nil); err == nil {
+	if err := c.Put(k, Entry{}); err == nil {
 		t.Fatal("an empty preview must not be kept")
 	}
-	if left, _ := filepath.Glob(filepath.Join(c.Dir, "*", ".tmp-*")); len(left) != 0 {
+	// replacing an entry does not count it twice
-		t.Fatal("temp files left behind")
+	if err := c.Put(k, Entry{Path: "/a", JPEG: []byte("jpeg2")}); err != nil {
+		t.Fatal(err)
 	}
+	n, b := c.Stats()
+	if n != 2 || b == 0 {
+		t.Fatalf("stats = %d entries, %d bytes", n, b)
+	}
+	// survives a reopen
+	if err := c.Close(); err != nil {
+		t.Fatal(err)
+	}
+	c2 := NewCache(c.Path)
+	if e, found, _ := c2.Get(k); !found || string(e.JPEG) != "jpeg2" {
+		t.Fatal("not there after reopening")
+	}
+	if n, _ := c2.Stats(); n != 2 {
+		t.Fatal("count lost on reopen")
+	}
+	c2.Close()
 }
 
 // The real thing, when ffmpeg is here: a PNG and a generated video each come back as a

web/src/Files.tsx

@@ -192,7 +192,7 @@ export default function Files({ onOpenInTerminal }: { onOpenInTerminal?: (cmd: s
   const [thumbs, setThumbs] = useState<ThumbStatus | null>(null)
   const [listEl, setListEl] = useState<HTMLDivElement | null>(null)
   const near = useMemo(() => (listEl && previews ? new Near(listEl) : null), [listEl, previews])
-  const readThumbs = useCallback((refresh = false) => { api.thumbStatus(sudo, refresh).then(setThumbs).catch((e) => setThumbs({ ok: false, engine: '', summary: '', gpus: [], error: e instanceof Error ? e.message : 'failed', user: '', cache_dir: '' })) }, [sudo])
+  const readThumbs = useCallback((refresh = false) => { api.thumbStatus(sudo, refresh).then(setThumbs).catch((e) => setThumbs({ ok: false, engine: '', summary: '', gpus: [], error: e instanceof Error ? e.message : 'failed', user: '', cache: { path: '', entries: 0, bytes: 0 } })) }, [sudo])
   useEffect(() => { try { localStorage.setItem(PREVIEWS_KEY, previews ? '1' : '0') } catch { /* private mode */ } }, [previews])
   useEffect(() => { if (previews) readThumbs(); else setThumbs(null) }, [previews, readThumbs])
 
@@ -279,7 +279,7 @@ export default function Files({ onOpenInTerminal }: { onOpenInTerminal?: (cmd: s
         <div className="files-tools">
           <button className={'btn' + (sudo ? ' on' : '')} title="browse as root" onClick={() => setSudo(!sudo)}>{sudo ? 'root' : 'sudo'}</button>
           <button className={'btn' + (hidden ? ' on' : '')} title="show hidden files" onClick={() => setHidden(!hidden)}>.hidden</button>
-          <button className={'btn' + (previews ? ' on' : '')} title={'thumbnails for images and videos' + (thumbs ? ` — ${thumbs.summary}` : '')} onClick={() => setPreviews(!previews)}>previews</button>
+          <button className={'btn' + (previews ? ' on' : '')} title={'thumbnails for images and videos' + (thumbs ? ` — ${thumbs.summary}` + (thumbs.cache.entries ? ` · ${thumbs.cache.entries} kept (${fmtBytes(thumbs.cache.bytes)})` : '') : '')} onClick={() => setPreviews(!previews)}>previews</button>
           <select className="btn" value={sort} onChange={(e) => setSort(e.target.value as Sort)}><option value="name">name</option><option value="size">size</option><option value="mtime">modified</option></select>
           <input className="filter" placeholder="filter" value={q} onChange={(e) => setQ(e.target.value)} />
           <button className="btn" onClick={mkdir}>+ folder</button>

web/src/api.ts

@@ -252,7 +252,7 @@ export interface ARCView { detail: ARCDetail; live: ARCLive | null }
 export interface FileEntry { name: string; type: 'dir' | 'file' | 'link' | 'other'; size: number; mode: string; perm: string; mtime: number; user: string; group: string; target?: string; broken?: boolean; preview?: 'image' | 'video' }
 export interface ThumbGPU { api: string; device: string; name?: string; codecs?: string[]; reason?: string; permission?: boolean }
 // How previews get made on the machine: ok with an engine, or why not and what would fix it.
-export interface ThumbStatus { ok: boolean; engine: 'gpu' | 'cpu' | ''; summary: string; ffmpeg?: string; gpus: ThumbGPU[]; unusable?: ThumbGPU[]; error?: string; install?: { pm: string; package: string }; gpu_fix?: boolean; user: string; cache_dir: string }
+export interface ThumbStatus { ok: boolean; engine: 'gpu' | 'cpu' | ''; summary: string; ffmpeg?: string; gpus: ThumbGPU[]; unusable?: ThumbGPU[]; error?: string; install?: { pm: string; package: string }; gpu_fix?: boolean; user: string; cache: { path: string; entries: number; bytes: number } }
 export interface FileInfo extends FileEntry { path: string; text: boolean }
 
 const q = (path: string, sudo: boolean, extra = '') => `path=${encodeURIComponent(path)}${sudo ? '&sudo=1' : ''}${extra}`