Reset Tight zlib stream when deflater is recreated mid-session

Also scrub brand-name references from comments.

client/vnc/server/extclipboard.go

@@ -54,11 +54,11 @@ const (
 
 // buildExtClipCaps emits the Caps payload. The flags word advertises every
 // action we support in the high byte (Caps + Request + Peek + Notify +
-// Provide) and every format we accept in the low 16 bits. noVNC uses these
-// action bits to decide whether to auto-Request on Notify; without
-// Request in our Caps it silently drops our Notify messages. After the
-// flags word we emit one uint32 max size per format bit set, in ascending
-// bit order.
+// Provide) and every format we accept in the low 16 bits. Clients use
+// these action bits to decide whether to auto-Request on Notify; without
+// Request in our Caps a conforming client silently drops our Notify
+// messages. After the flags word we emit one uint32 max size per format
+// bit set, in ascending bit order.
 func buildExtClipCaps() []byte {
 	flags := extClipActionCaps | extClipActionRequest | extClipActionPeek |
 		extClipActionNotify | extClipActionProvide | extClipFormatText

client/vnc/server/input_darwin.go

@@ -632,10 +632,10 @@ var specialKeyMap = map[uint32]uint16{
 	0xffea: 0x3D, // Alt_R (Option)
 	0xffe7: 0x37, // Meta_L (Command)
 	0xffe8: 0x36, // Meta_R (Command)
-	0xffeb: 0x37, // Super_L (Command) - noVNC sends this
+	0xffeb: 0x37, // Super_L (Command)
 	0xffec: 0x36, // Super_R (Command)
 
-	// Mode_switch / ISO_Level3_Shift (sent by noVNC for macOS Option remap)
+	// Mode_switch / ISO_Level3_Shift (for macOS Option remap on layouts)
 	0xff7e: 0x3A, // Mode_switch -> Option
 	0xfe03: 0x3D, // ISO_Level3_Shift -> Right Option
 
@@ -674,7 +674,7 @@ var specialKeyMap = map[uint32]uint16{
 	0x002e: 0x2F, // period .
 	0x002f: 0x2C, // slash /
 
-	// Shifted punctuation (noVNC sends these as separate keysyms)
+	// Shifted punctuation (clients sometimes send these as separate keysyms)
 	0x005f: 0x1B, // underscore _ (shift+minus)
 	0x002b: 0x18, // plus + (shift+equal)
 	0x007b: 0x21, // braceleft { (shift+[)

client/vnc/server/input_windows.go

@@ -206,7 +206,7 @@ func (w *WindowsInputInjector) InjectKey(keysym uint32, down bool) {
 // InjectKeyScancode queues a raw-scancode key event. PC AT Set 1 maps
 // directly onto what SendInput's KEYEVENTF_SCANCODE flag wants, so the
 // only translation is splitting the optional 0xE0 prefix off into the
-// KEYEVENTF_EXTENDEDKEY flag. keysym is the noVNC-provided fallback we
+// KEYEVENTF_EXTENDEDKEY flag. keysym is the client-provided fallback we
 // reach for if the scancode is zero.
 func (w *WindowsInputInjector) InjectKeyScancode(scancode uint32, keysym uint32, down bool) {
 	if scancode == 0 {

client/vnc/server/rfb.go

@@ -69,10 +69,9 @@ const (
 	pseudoEncDesktopName             = -307
 	pseudoEncExtendedDesktopSize     = -308
 
-	// Quality/Compression level pseudo-encodings (TightVNC extension). The
-	// client picks one value from each range to tune JPEG quality and zlib
-	// effort. 0 is lowest quality / fastest, 9 is highest quality / best
-	// compression.
+	// Quality/Compression level pseudo-encodings. The client picks one
+	// value from each range to tune JPEG quality and zlib effort. 0 is
+	// lowest quality / fastest, 9 is highest quality / best compression.
 	pseudoEncQualityLevelMin  = -32
 	pseudoEncQualityLevelMax  = -23
 	pseudoEncCompressLevelMin = -256
@@ -445,6 +444,12 @@ type tightState struct {
 	// whether a SetEncodings refresh needs to recreate the tight state.
 	qualityLevel  int
 	compressLevel int
+	// pendingZlibReset becomes true when this tightState replaces an
+	// in-use one (e.g. CompressLevel change mid-session). The next Basic
+	// rect we emit ORs the stream-0 reset bit into its sub-encoding byte
+	// so the client's inflater drops its now-stale dictionary; cleared
+	// after one emission.
+	pendingZlibReset bool
 }
 
 func newTightState() *tightState {
@@ -618,9 +623,15 @@ func encodeTightBasic(img *image.RGBA, x, y, w, h int, t *tightState) ([]byte, b
 		}
 	}
 
-	// Sub-encoding byte: stream 0, no resets, basic encoding (top nibble
-	// = 0x40 = explicit filter follows).
+	// Sub-encoding byte: stream 0, basic encoding (top nibble = 0x40 =
+	// explicit filter follows). The low nibble carries per-stream reset
+	// flags; bit 0 here tells the client to reset its stream-0 inflater
+	// when our deflater was just recreated.
 	subenc := byte(tightBasicFilter)
+	if t.pendingZlibReset {
+		subenc |= 0x01
+		t.pendingZlibReset = false
+	}
 	filter := byte(tightFilterCopy)
 
 	if pixelStream < 12 {

client/vnc/server/server.go

@@ -32,7 +32,7 @@ const (
 )
 
 // RFB security-failure reason codes sent to the client. These prefixes are
-// stable so dashboard/noVNC integrations can branch on them without parsing
+// stable so dashboard integrations can branch on them without parsing
 // free text. Format: "CODE: human message".
 const (
 	RejectCodeJWTMissing    = "AUTH_JWT_MISSING"

client/vnc/server/session.go

@@ -77,7 +77,7 @@ type session struct {
 
 	// captureErrLast throttles "capture (transient)" logs while the
 	// capturer is in a sustained failure state (e.g. X server died but a
-	// noVNC tab is still open). Owned by the encoder goroutine.
+	// client is still connected). Owned by the encoder goroutine.
 	captureErrLast time.Time
 	captureErrSeen bool
 
@@ -290,7 +290,15 @@ func (s *session) handleSetEncodings() error {
 	if s.useTight && (s.tight == nil ||
 		s.tight.qualityLevel != s.clientJPEGQuality ||
 		s.tight.compressLevel != s.clientZlibLevel) {
+		// When we replace an in-use tightState the client's stream-0
+		// inflater carries dictionary state from the old deflater. Carry
+		// the pending-reset flag so the next Basic rect tells the client
+		// to reset its inflater before decoding.
+		replacing := s.tight != nil
 		s.tight = newTightStateWithLevels(s.clientJPEGQuality, s.clientZlibLevel)
+		if replacing {
+			s.tight.pendingZlibReset = true
+		}
 	}
 	sendExtClipCaps := s.clientSupportsExtClipboard && !s.extClipCapsSent
 	if sendExtClipCaps {