feat(app): add 'neferbar app' to print the focused window's id, name and title, and show them in the bundled center module

commit: 4bf13d9ee7310e15d0f1f8502648873dca5527e0
author: brice · 17d ago · 2026-10-05 17:26 UTC
parent: b65ab9e
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

8 files · +432 -19

M README.md +14 -0


@@ -232,6 +232,20 @@ neferbar [-config file] [-display socket] [-pprof addr] [-memstats interval]
232	232		\| `-pprof` \| Serve Go profiling on a loopback address, such as `localhost:6060`. \|
233	233		\| `-memstats` \| Log allocation counters at this interval. \|
234	234
	235	+	## Reading the focused window
	236	+
	237	+	`neferbar app` prints fields of the window that has the focus: one line now, then a new one each time the focus or a title changes. It works on compositors that offer `zwlr_foreign_toplevel_manager_v1` (NeferWL, Sway, Hyprland, River, Niri).
	238	+
	239	+	```
	240	+	neferbar app title # Dumber - docs
	241	+	neferbar app id # com.github.bnema.dumber
	242	+	neferbar app name # dumber (the part of the id after the last dot)
	243	+	neferbar app name title # several fields, separated by a tab
	244	+	neferbar app -once title # print once and exit
	245	+	```
	246	+
	247	+	A line is empty when no window has the focus. Control characters are removed from every field, so a title cannot move a terminal's cursor. Scripts started by the bar find the binary in `$NEFERBAR_BIN`.
	248	+
235	249		## Test without touching your desktop
236	250
237	251		```sh


@@ -232,6 +232,20 @@ neferbar [-config file] [-display socket] [-pprof addr] [-memstats interval]
232	\| `-pprof` \| Serve Go profiling on a loopback address, such as `localhost:6060`. \|	232		\| `-pprof` \| Serve Go profiling on a loopback address, such as `localhost:6060`. \|
233	\| `-memstats` \| Log allocation counters at this interval. \|	233		\| `-memstats` \| Log allocation counters at this interval. \|
234		234
		235	+	## Reading the focused window
		236	+
		237	+	`neferbar app` prints fields of the window that has the focus: one line now, then a new one each time the focus or a title changes. It works on compositors that offer `zwlr_foreign_toplevel_manager_v1` (NeferWL, Sway, Hyprland, River, Niri).
		238	+
		239	+	```
		240	+	neferbar app title # Dumber - docs
		241	+	neferbar app id # com.github.bnema.dumber
		242	+	neferbar app name # dumber (the part of the id after the last dot)
		243	+	neferbar app name title # several fields, separated by a tab
		244	+	neferbar app -once title # print once and exit
		245	+	```
		246	+
		247	+	A line is empty when no window has the focus. Control characters are removed from every field, so a title cannot move a terminal's cursor. Scripts started by the bar find the binary in `$NEFERBAR_BIN`.
		248	+
235	## Test without touching your desktop	249		## Test without touching your desktop
236		250
237	```sh	251		```sh

A cmd/neferbar/app.go +69 -0

@@ -0,0 +1,69 @@
	1	+	package main
	2	+
	3	+	import (
	4	+	"context"
	5	+	"flag"
	6	+	"fmt"
	7	+	"os"
	8	+
	9	+	"git.bnema.dev/bnema/neferbar/internal/app"
	10	+	)
	11	+
	12	+	const appUsage = `usage: neferbar app [-once] <field>...
	13	+
	14	+	Prints fields of the window that has the focus: one line now, then one more
	15	+	each time it changes. With several fields, a tab separates them on the line
	16	+	(a title never contains a tab). Fields are empty when no window has the focus.
	17	+
	18	+	fields:
	19	+	id the application id, such as com.github.bnema.dumber
	20	+	name the short form of the id, such as dumber
	21	+	title the window title, without control characters
	22	+
	23	+	flags:
	24	+	`
	25	+
	26	+	// runApp is "neferbar app <field>": the focused window, for scripts.
	27	+	func runApp(ctx context.Context, args []string, display string) error {
	28	+	fs := flag.NewFlagSet("neferbar app", flag.ContinueOnError)
	29	+	once := fs.Bool("once", false, "print the current value and exit")
	30	+	fs.Usage = func() { fmt.Fprint(os.Stderr, appUsage); fs.PrintDefaults() }
	31	+	if err := fs.Parse(args); err != nil {
	32	+	return err
	33	+	}
	34	+	if fs.NArg() == 0 {
	35	+	fs.Usage()
	36	+	return fmt.Errorf("give at least one field: id, name or title")
	37	+	}
	38	+	var picks []func(app.Window) string
	39	+	for _, field := range fs.Args() {
	40	+	switch field {
	41	+	case "id":
	42	+	picks = append(picks, func(w app.Window) string { return app.Clean(w.ID) })
	43	+	case "name":
	44	+	picks = append(picks, func(w app.Window) string { return app.Clean(app.Name(w.ID)) })
	45	+	case "title":
	46	+	picks = append(picks, func(w app.Window) string { return app.Clean(w.Title) })
	47	+	default:
	48	+	return fmt.Errorf("%q is not a field; use id, name or title", field)
	49	+	}
	50	+	}
	51	+	ctx, cancel := context.WithCancel(ctx)
	52	+	defer cancel()
	53	+	return app.Watch(ctx, display, func(w app.Window) error {
	54	+	var line []byte
	55	+	for i, pick := range picks {
	56	+	if i > 0 {
	57	+	line = append(line, '\t')
	58	+	}
	59	+	line = append(line, pick(w)...)
	60	+	}
	61	+	if _, err := os.Stdout.Write(append(line, '\n')); err != nil {
	62	+	return err
	63	+	}
	64	+	if *once {
	65	+	cancel()
	66	+	}
	67	+	return nil
	68	+	})
	69	+	}

@@ -0,0 +1,69 @@
	1	+	package main
	2	+
	3	+	import (
	4	+	"context"
	5	+	"flag"
	6	+	"fmt"
	7	+	"os"
	8	+
	9	+	"git.bnema.dev/bnema/neferbar/internal/app"
	10	+	)
	11	+
	12	+	const appUsage = `usage: neferbar app [-once] <field>...
	13	+
	14	+	Prints fields of the window that has the focus: one line now, then one more
	15	+	each time it changes. With several fields, a tab separates them on the line
	16	+	(a title never contains a tab). Fields are empty when no window has the focus.
	17	+
	18	+	fields:
	19	+	id the application id, such as com.github.bnema.dumber
	20	+	name the short form of the id, such as dumber
	21	+	title the window title, without control characters
	22	+
	23	+	flags:
	24	+	`
	25	+
	26	+	// runApp is "neferbar app <field>": the focused window, for scripts.
	27	+	func runApp(ctx context.Context, args []string, display string) error {
	28	+	fs := flag.NewFlagSet("neferbar app", flag.ContinueOnError)
	29	+	once := fs.Bool("once", false, "print the current value and exit")
	30	+	fs.Usage = func() { fmt.Fprint(os.Stderr, appUsage); fs.PrintDefaults() }
	31	+	if err := fs.Parse(args); err != nil {
	32	+	return err
	33	+	}
	34	+	if fs.NArg() == 0 {
	35	+	fs.Usage()
	36	+	return fmt.Errorf("give at least one field: id, name or title")
	37	+	}
	38	+	var picks []func(app.Window) string
	39	+	for _, field := range fs.Args() {
	40	+	switch field {
	41	+	case "id":
	42	+	picks = append(picks, func(w app.Window) string { return app.Clean(w.ID) })
	43	+	case "name":
	44	+	picks = append(picks, func(w app.Window) string { return app.Clean(app.Name(w.ID)) })
	45	+	case "title":
	46	+	picks = append(picks, func(w app.Window) string { return app.Clean(w.Title) })
	47	+	default:
	48	+	return fmt.Errorf("%q is not a field; use id, name or title", field)
	49	+	}
	50	+	}
	51	+	ctx, cancel := context.WithCancel(ctx)
	52	+	defer cancel()
	53	+	return app.Watch(ctx, display, func(w app.Window) error {
	54	+	var line []byte
	55	+	for i, pick := range picks {
	56	+	if i > 0 {
	57	+	line = append(line, '\t')
	58	+	}
	59	+	line = append(line, pick(w)...)
	60	+	}
	61	+	if _, err := os.Stdout.Write(append(line, '\n')); err != nil {
	62	+	return err
	63	+	}
	64	+	if *once {
	65	+	cancel()
	66	+	}
	67	+	return nil
	68	+	})
	69	+	}

M cmd/neferbar/main.go +11 -0


@@ -3,6 +3,7 @@ package main
3	3
4	4		import (
5	5		"context"
	6	+	"errors"
6	7		"flag"
7	8		"fmt"
8	9		"log/slog"

@@ -20,6 +21,16 @@ import (
20	21		)
21	22
22	23		func main() {
	24	+	if len(os.Args) > 1 && os.Args[1] == "app" {
	25	+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	26	+	err := runApp(ctx, os.Args[2:], os.Getenv("NEFERBAR_DISPLAY"))
	27	+	stop()
	28	+	if err != nil && !errors.Is(err, flag.ErrHelp) {
	29	+	fmt.Fprintf(os.Stderr, "neferbar app: %v\n", err)
	30	+	os.Exit(1)
	31	+	}
	32	+	return
	33	+	}
23	34		cfgPath := flag.String("config", "", "config file (default: $XDG_CONFIG_HOME/neferbar/config.toml)")
24	35		display := flag.String("display", os.Getenv("NEFERBAR_DISPLAY"), "Wayland socket name or absolute path (default: $NEFERBAR_DISPLAY, then $WAYLAND_DISPLAY)")
25	36		pprofAddr := flag.String("pprof", "", "serve pprof on this loopback address, e.g. localhost:6060")


@@ -3,6 +3,7 @@ package main
3		3
4	import (	4		import (
5	"context"	5		"context"
		6	+	"errors"
6	"flag"	7		"flag"
7	"fmt"	8		"fmt"
8	"log/slog"	9		"log/slog"

@@ -20,6 +21,16 @@ import (
20	)	21		)
21		22
22	func main() {	23		func main() {
		24	+	if len(os.Args) > 1 && os.Args[1] == "app" {
		25	+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
		26	+	err := runApp(ctx, os.Args[2:], os.Getenv("NEFERBAR_DISPLAY"))
		27	+	stop()
		28	+	if err != nil && !errors.Is(err, flag.ErrHelp) {
		29	+	fmt.Fprintf(os.Stderr, "neferbar app: %v\n", err)
		30	+	os.Exit(1)
		31	+	}
		32	+	return
		33	+	}
23	cfgPath := flag.String("config", "", "config file (default: $XDG_CONFIG_HOME/neferbar/config.toml)")	34		cfgPath := flag.String("config", "", "config file (default: $XDG_CONFIG_HOME/neferbar/config.toml)")
24	display := flag.String("display", os.Getenv("NEFERBAR_DISPLAY"), "Wayland socket name or absolute path (default: $NEFERBAR_DISPLAY, then $WAYLAND_DISPLAY)")	35		display := flag.String("display", os.Getenv("NEFERBAR_DISPLAY"), "Wayland socket name or absolute path (default: $NEFERBAR_DISPLAY, then $WAYLAND_DISPLAY)")
25	pprofAddr := flag.String("pprof", "", "serve pprof on this loopback address, e.g. localhost:6060")	36		pprofAddr := flag.String("pprof", "", "serve pprof on this loopback address, e.g. localhost:6060")

M examples/bundle/center.sh +14 -17

@@ -1,23 +1,20 @@
1	1		#!/bin/bash
2		-	# Center: the focused window. NeferWL's state file has the app id but no title;
3		-	# a title needs the compositor's toplevel protocol, which the bar does not read yet.
	2	+	# Center: the focused window, as "icon name title". "neferbar app" asks the
	3	+	# compositor and prints one line each time the focus or a title changes, so this
	4	+	# script sleeps until something happens.
4	5		. "$(dirname "$0")/lib.sh"
5	6
6		-	[ -r "${NEFERWL_STATE:-}" ] \|\| {
7		-	echo
8		-	exec sleep infinity
9		-	}
	7	+	MAX_TITLE=${NEFERBAR_TITLE_MAX:-60} # cells; a longer title ends with an ellipsis
10	8
11		-	draw() {
12		-	local app
13		-	# An app id is chosen by the application: drop control characters, which
14		-	# would otherwise reach the bar as escape sequences.
15		-	app=$(jq -r '(.window.app_id // empty) \| explode \| map(select(. >= 32 and . != 127)) \| implode' "$NEFERWL_STATE" 2>/dev/null) \|\| return
16		-	if [ -n "$app" ]; then
17		-	printf '%s%s%s %s%s%s\f' "$(bg "$BAR")" "$(fg "$NEFERBAR_COLOR3")" "$ICON_APP" "$(fg "$NEFERBAR_FOREGROUND")" "$app" "$RESET"
18		-	else
	9	+	# $NEFERBAR_BIN is the neferbar that started this script. A line ends the bar
	10	+	# when the compositor goes away; the bar then restarts the script.
	11	+	"$NEFERBAR_BIN" app name title \| while IFS=$'\t' read -r name title; do
	12	+	if [ -z "$name$title" ]; then
19	13		printf '\f'
	14	+	continue
20	15		fi
21		-	}
22		-
23		-	state_changed_loop draw
	16	+	((${#title} > MAX_TITLE)) && title="${title:0:MAX_TITLE-1}…"
	17	+	printf '%s%s%s %s%s%s' "$(bg "$BAR")" "$(fg "$NEFERBAR_COLOR3")" "$ICON_APP" "$(fg "$NEFERBAR_FOREGROUND")" "$name" "$RESET"
	18	+	[ -n "$title" ] && printf ' %s%s%s' "$(fg "$DIM")" "$title" "$RESET"
	19	+	printf '\f'
	20	+	done

@@ -1,23 +1,20 @@
1		#!/bin/bash	1		#!/bin/bash
2	-	# Center: the focused window. NeferWL's state file has the app id but no title;	2	+	# Center: the focused window, as "icon name title". "neferbar app" asks the
3	-	# a title needs the compositor's toplevel protocol, which the bar does not read yet.	3	+	# compositor and prints one line each time the focus or a title changes, so this
			4	+	# script sleeps until something happens.
4		. "$(dirname "$0")/lib.sh"	5		. "$(dirname "$0")/lib.sh"
5			6
6	-	[ -r "${NEFERWL_STATE:-}" ] \|\| {	7	+	MAX_TITLE=${NEFERBAR_TITLE_MAX:-60} # cells; a longer title ends with an ellipsis
7	-	echo
8	-	exec sleep infinity
9	-	}
10			8
11	-	draw() {	9	+	# $NEFERBAR_BIN is the neferbar that started this script. A line ends the bar
12	-	local app	10	+	# when the compositor goes away; the bar then restarts the script.
13	-	# An app id is chosen by the application: drop control characters, which	11	+	"$NEFERBAR_BIN" app name title \| while IFS=$'\t' read -r name title; do
14	-	# would otherwise reach the bar as escape sequences.	12	+	if [ -z "$name$title" ]; then
15	-	app=$(jq -r '(.window.app_id // empty) \| explode \| map(select(. >= 32 and . != 127)) \| implode' "$NEFERWL_STATE" 2>/dev/null) \|\| return
16	-	if [ -n "$app" ]; then
17	-	printf '%s%s%s %s%s%s\f' "$(bg "$BAR")" "$(fg "$NEFERBAR_COLOR3")" "$ICON_APP" "$(fg "$NEFERBAR_FOREGROUND")" "$app" "$RESET"
18	-	else
19		printf '\f'	13		printf '\f'
			14	+	continue
20		fi	15		fi
21	-	}	16	+	((${#title} > MAX_TITLE)) && title="${title:0:MAX_TITLE-1}…"
22	-		17	+	printf '%s%s%s %s%s%s' "$(bg "$BAR")" "$(fg "$NEFERBAR_COLOR3")" "$ICON_APP" "$(fg "$NEFERBAR_FOREGROUND")" "$name" "$RESET"
23	-	state_changed_loop draw	18	+	[ -n "$title" ] && printf ' %s%s%s' "$(fg "$DIM")" "$title" "$RESET"
			19	+	printf '\f'
			20	+	done

M go.mod +2 -2


@@ -4,17 +4,17 @@ go 1.27
4	4
5	5		require (
6	6		github.com/BurntSushi/toml v1.6.0
	7	+	github.com/bnema/go-wayland-bindings v0.1.0
7	8		github.com/bnema/neferclient v0.3.0
8	9		github.com/bnema/purego-vulkan v0.6.0
9	10		github.com/bnema/vev-vt v0.6.0
	11	+	github.com/bnema/wlturbo v0.6.2
10	12		golang.org/x/image v0.46.0
11	13		golang.org/x/sys v0.48.0
12	14		)
13	15
14	16		require (
15		-	github.com/bnema/go-wayland-bindings v0.1.0 // indirect
16	17		github.com/bnema/purego v0.13.0-bnema.1 // indirect
17	18		github.com/bnema/purego-xkbcommon v0.2.0 // indirect
18		-	github.com/bnema/wlturbo v0.6.2 // indirect
19	19		golang.org/x/text v0.42.0 // indirect
20	20		)

 require (
 	github.com/BurntSushi/toml v1.6.0
+	github.com/bnema/go-wayland-bindings v0.1.0
 	github.com/bnema/neferclient v0.3.0
 	github.com/bnema/purego-vulkan v0.6.0
 	github.com/bnema/vev-vt v0.6.0
+	github.com/bnema/wlturbo v0.6.2
 	golang.org/x/image v0.46.0
 	golang.org/x/sys v0.48.0
 )
 require (
-	github.com/bnema/go-wayland-bindings v0.1.0 // indirect
 	github.com/bnema/purego v0.13.0-bnema.1 // indirect
 	github.com/bnema/purego-xkbcommon v0.2.0 // indirect
-	github.com/bnema/wlturbo v0.6.2 // indirect
 	golang.org/x/text v0.42.0 // indirect
 )

A internal/app/app.go +213 -0

@@ -0,0 +1,213 @@
	1	+	// Package app follows the window that has the keyboard focus, using the
	2	+	// wlr-foreign-toplevel-management protocol that NeferWL, Sway, Hyprland, River
	3	+	// and Niri speak.
	4	+	package app
	5	+
	6	+	import (
	7	+	"context"
	8	+	"errors"
	9	+	"fmt"
	10	+	"strings"
	11	+	"sync"
	12	+	"unicode"
	13	+
	14	+	wlr "github.com/bnema/go-wayland-bindings/client/wlrforeigntoplevelmanagement"
	15	+	"github.com/bnema/neferclient"
	16	+	wl "github.com/bnema/wlturbo"
	17	+	)
	18	+
	19	+	// Window is what the bar shows about the focused window. The zero Window means
	20	+	// that nothing has the focus.
	21	+	type Window struct {
	22	+	ID string // the application id, such as "org.mozilla.firefox"
	23	+	Title string
	24	+	}
	25	+
	26	+	// stateActivated is the protocol's "this window has the focus" state.
	27	+	const stateActivated = 2
	28	+
	29	+	// Tracker keeps what the compositor said about each window and answers which
	30	+	// one has the focus. A window's properties apply together when its Done comes,
	31	+	// as the protocol says, so Focused never shows half an update.
	32	+	//
	33	+	// The connection's reader goroutine calls the recording methods while another
	34	+	// goroutine calls Focused, so a mutex guards the state.
	35	+	type Tracker struct {
	36	+	mu sync.Mutex
	37	+	wins map[uint32]*window
	38	+	seq uint64
	39	+	// Changed has a signal waiting whenever Done or Closed may have changed the
	40	+	// focus. Capacity 1: a missed signal is harmless, as Focused is read after.
	41	+	Changed chan struct{}
	42	+	}
	43	+
	44	+	type window struct {
	45	+	pending, shown Window
	46	+	pendingActive bool
	47	+	active bool
	48	+	since uint64 // when it last became active: the newest wins
	49	+	}
	50	+
	51	+	// NewTracker returns an empty tracker.
	52	+	func NewTracker() *Tracker {
	53	+	return &Tracker{wins: map[uint32]*window{}, Changed: make(chan struct{}, 1)}
	54	+	}
	55	+
	56	+	func (t *Tracker) signal() {
	57	+	select {
	58	+	case t.Changed <- struct{}{}:
	59	+	default:
	60	+	}
	61	+	}
	62	+
	63	+	func (t Tracker) get(h uint32) window {
	64	+	w := t.wins[h]
	65	+	if w == nil {
	66	+	w = &window{}
	67	+	t.wins[h] = w
	68	+	}
	69	+	return w
	70	+	}
	71	+
	72	+	// Title, ID and State record an update that applies at the next Done.
	73	+	func (t *Tracker) Title(h uint32, s string) {
	74	+	t.mu.Lock()
	75	+	defer t.mu.Unlock()
	76	+	t.get(h).pending.Title = s
	77	+	}
	78	+
	79	+	func (t *Tracker) ID(h uint32, s string) {
	80	+	t.mu.Lock()
	81	+	defer t.mu.Unlock()
	82	+	t.get(h).pending.ID = s
	83	+	}
	84	+
	85	+	func (t *Tracker) State(h uint32, state []byte) {
	86	+	t.mu.Lock()
	87	+	defer t.mu.Unlock()
	88	+	t.get(h).pendingActive = hasState(state, stateActivated)
	89	+	}
	90	+
	91	+	// Done applies the updates recorded for window h.
	92	+	func (t *Tracker) Done(h uint32) {
	93	+	defer t.signal()
	94	+	t.mu.Lock()
	95	+	defer t.mu.Unlock()
	96	+	w := t.get(h)
	97	+	w.shown = w.pending
	98	+	if w.pendingActive && !w.active {
	99	+	t.seq++
	100	+	w.since = t.seq
	101	+	}
	102	+	w.active = w.pendingActive
	103	+	}
	104	+
	105	+	// Closed forgets window h.
	106	+	func (t *Tracker) Closed(h uint32) {
	107	+	defer t.signal()
	108	+	t.mu.Lock()
	109	+	defer t.mu.Unlock()
	110	+	delete(t.wins, h)
	111	+	}
	112	+
	113	+	// Focused returns the window that has the focus; when several do (one per
	114	+	// seat or output), the one that got it last.
	115	+	func (t *Tracker) Focused() Window {
	116	+	t.mu.Lock()
	117	+	defer t.mu.Unlock()
	118	+	var best *window
	119	+	for _, w := range t.wins {
	120	+	if w.active && (best == nil \|\| w.since > best.since) {
	121	+	best = w
	122	+	}
	123	+	}
	124	+	if best == nil {
	125	+	return Window{}
	126	+	}
	127	+	return best.shown
	128	+	}
	129	+
	130	+	// hasState reports whether a state array (native-endian uint32 values) has s.
	131	+	func hasState(state []byte, s uint32) bool {
	132	+	for i := 0; i+4 <= len(state); i += 4 {
	133	+	v := uint32(state[i]) \| uint32(state[i+1])<<8 \| uint32(state[i+2])<<16 \| uint32(state[i+3])<<24
	134	+	if v == s {
	135	+	return true
	136	+	}
	137	+	}
	138	+	return false
	139	+	}
	140	+
	141	+	// Name is the short form of an application id: the part after the last dot,
	142	+	// so "com.github.bnema.dumber" is "dumber". An id without a dot is its own name.
	143	+	func Name(id string) string {
	144	+	if i := strings.LastIndexByte(id, '.'); i >= 0 && i < len(id)-1 {
	145	+	return id[i+1:]
	146	+	}
	147	+	return id
	148	+	}
	149	+
	150	+	// Clean removes control characters. An application chooses its own title, and
	151	+	// a title must never be able to move the cursor or end a line in a terminal.
	152	+	func Clean(s string) string {
	153	+	return strings.Map(func(r rune) rune {
	154	+	if unicode.IsControl(r) {
	155	+	return -1
	156	+	}
	157	+	return r
	158	+	}, s)
	159	+	}
	160	+
	161	+	// Watch calls emit with the focused window once, and again each time it
	162	+	// changes, until ctx ends or the connection fails. display is the Wayland
	163	+	// socket; empty uses $WAYLAND_DISPLAY.
	164	+	func Watch(ctx context.Context, display string, emit func(Window) error) error {
	165	+	conn, err := neferclient.Connect(ctx, display)
	166	+	if err != nil {
	167	+	return fmt.Errorf("cannot connect to the compositor: %w", err)
	168	+	}
	169	+	defer conn.Close()
	170	+
	171	+	t := NewTracker()
	172	+	_, _, err = conn.Bind("zwlr_foreign_toplevel_manager_v1", 3, func(c wl.Context) wlr.ForeignToplevelManager {
	173	+	m := wlr.NewForeignToplevelManager(c)
	174	+	m.OnToplevel(func(h *wlr.ForeignToplevelHandle) {
	175	+	id := h.ID()
	176	+	h.OnTitle(func(s string) { t.Title(id, s) })
	177	+	h.OnAppId(func(s string) { t.ID(id, s) })
	178	+	h.OnState(func(b []byte) { t.State(id, b) })
	179	+	h.OnDone(func() { t.Done(id) })
	180	+	h.OnClosed(func() { t.Closed(id); _ = h.Destroy() })
	181	+	})
	182	+	return m
	183	+	})
	184	+	if errors.Is(err, neferclient.ErrGlobalNotFound) {
	185	+	return errors.New("this compositor does not offer zwlr_foreign_toplevel_manager_v1, so the focused window is unknown")
	186	+	}
	187	+	if err != nil {
	188	+	return fmt.Errorf("cannot ask the compositor for its windows: %w", err)
	189	+	}
	190	+	// The windows that exist now arrive after one round trip.
	191	+	if err = conn.Roundtrip(); err != nil {
	192	+	return err
	193	+	}
	194	+	var last Window
	195	+	first := true
	196	+	for {
	197	+	if err = conn.Dispatch(nil); err != nil {
	198	+	return fmt.Errorf("lost the connection to the compositor: %w", err)
	199	+	}
	200	+	if now := t.Focused(); first \|\| now != last {
	201	+	first, last = false, now
	202	+	if err = emit(now); err != nil {
	203	+	return err
	204	+	}
	205	+	}
	206	+	select {
	207	+	case <-ctx.Done():
	208	+	return nil
	209	+	case <-conn.Wake(): // the connection's own events: drain them
	210	+	case <-t.Changed: // the compositor changed a window
	211	+	}
	212	+	}
	213	+	}

@@ -0,0 +1,213 @@
	1	+	// Package app follows the window that has the keyboard focus, using the
	2	+	// wlr-foreign-toplevel-management protocol that NeferWL, Sway, Hyprland, River
	3	+	// and Niri speak.
	4	+	package app
	5	+
	6	+	import (
	7	+	"context"
	8	+	"errors"
	9	+	"fmt"
	10	+	"strings"
	11	+	"sync"
	12	+	"unicode"
	13	+
	14	+	wlr "github.com/bnema/go-wayland-bindings/client/wlrforeigntoplevelmanagement"
	15	+	"github.com/bnema/neferclient"
	16	+	wl "github.com/bnema/wlturbo"
	17	+	)
	18	+
	19	+	// Window is what the bar shows about the focused window. The zero Window means
	20	+	// that nothing has the focus.
	21	+	type Window struct {
	22	+	ID string // the application id, such as "org.mozilla.firefox"
	23	+	Title string
	24	+	}
	25	+
	26	+	// stateActivated is the protocol's "this window has the focus" state.
	27	+	const stateActivated = 2
	28	+
	29	+	// Tracker keeps what the compositor said about each window and answers which
	30	+	// one has the focus. A window's properties apply together when its Done comes,
	31	+	// as the protocol says, so Focused never shows half an update.
	32	+	//
	33	+	// The connection's reader goroutine calls the recording methods while another
	34	+	// goroutine calls Focused, so a mutex guards the state.
	35	+	type Tracker struct {
	36	+	mu sync.Mutex
	37	+	wins map[uint32]*window
	38	+	seq uint64
	39	+	// Changed has a signal waiting whenever Done or Closed may have changed the
	40	+	// focus. Capacity 1: a missed signal is harmless, as Focused is read after.
	41	+	Changed chan struct{}
	42	+	}
	43	+
	44	+	type window struct {
	45	+	pending, shown Window
	46	+	pendingActive bool
	47	+	active bool
	48	+	since uint64 // when it last became active: the newest wins
	49	+	}
	50	+
	51	+	// NewTracker returns an empty tracker.
	52	+	func NewTracker() *Tracker {
	53	+	return &Tracker{wins: map[uint32]*window{}, Changed: make(chan struct{}, 1)}
	54	+	}
	55	+
	56	+	func (t *Tracker) signal() {
	57	+	select {
	58	+	case t.Changed <- struct{}{}:
	59	+	default:
	60	+	}
	61	+	}
	62	+
	63	+	func (t Tracker) get(h uint32) window {
	64	+	w := t.wins[h]
	65	+	if w == nil {
	66	+	w = &window{}
	67	+	t.wins[h] = w
	68	+	}
	69	+	return w
	70	+	}
	71	+
	72	+	// Title, ID and State record an update that applies at the next Done.
	73	+	func (t *Tracker) Title(h uint32, s string) {
	74	+	t.mu.Lock()
	75	+	defer t.mu.Unlock()
	76	+	t.get(h).pending.Title = s
	77	+	}
	78	+
	79	+	func (t *Tracker) ID(h uint32, s string) {
	80	+	t.mu.Lock()
	81	+	defer t.mu.Unlock()
	82	+	t.get(h).pending.ID = s
	83	+	}
	84	+
	85	+	func (t *Tracker) State(h uint32, state []byte) {
	86	+	t.mu.Lock()
	87	+	defer t.mu.Unlock()
	88	+	t.get(h).pendingActive = hasState(state, stateActivated)
	89	+	}
	90	+
	91	+	// Done applies the updates recorded for window h.
	92	+	func (t *Tracker) Done(h uint32) {
	93	+	defer t.signal()
	94	+	t.mu.Lock()
	95	+	defer t.mu.Unlock()
	96	+	w := t.get(h)
	97	+	w.shown = w.pending
	98	+	if w.pendingActive && !w.active {
	99	+	t.seq++
	100	+	w.since = t.seq
	101	+	}
	102	+	w.active = w.pendingActive
	103	+	}
	104	+
	105	+	// Closed forgets window h.
	106	+	func (t *Tracker) Closed(h uint32) {
	107	+	defer t.signal()
	108	+	t.mu.Lock()
	109	+	defer t.mu.Unlock()
	110	+	delete(t.wins, h)
	111	+	}
	112	+
	113	+	// Focused returns the window that has the focus; when several do (one per
	114	+	// seat or output), the one that got it last.
	115	+	func (t *Tracker) Focused() Window {
	116	+	t.mu.Lock()
	117	+	defer t.mu.Unlock()
	118	+	var best *window
	119	+	for _, w := range t.wins {
	120	+	if w.active && (best == nil \|\| w.since > best.since) {
	121	+	best = w
	122	+	}
	123	+	}
	124	+	if best == nil {
	125	+	return Window{}
	126	+	}
	127	+	return best.shown
	128	+	}
	129	+
	130	+	// hasState reports whether a state array (native-endian uint32 values) has s.
	131	+	func hasState(state []byte, s uint32) bool {
	132	+	for i := 0; i+4 <= len(state); i += 4 {
	133	+	v := uint32(state[i]) \| uint32(state[i+1])<<8 \| uint32(state[i+2])<<16 \| uint32(state[i+3])<<24
	134	+	if v == s {
	135	+	return true
	136	+	}
	137	+	}
	138	+	return false
	139	+	}
	140	+
	141	+	// Name is the short form of an application id: the part after the last dot,
	142	+	// so "com.github.bnema.dumber" is "dumber". An id without a dot is its own name.
	143	+	func Name(id string) string {
	144	+	if i := strings.LastIndexByte(id, '.'); i >= 0 && i < len(id)-1 {
	145	+	return id[i+1:]
	146	+	}
	147	+	return id
	148	+	}
	149	+
	150	+	// Clean removes control characters. An application chooses its own title, and
	151	+	// a title must never be able to move the cursor or end a line in a terminal.
	152	+	func Clean(s string) string {
	153	+	return strings.Map(func(r rune) rune {
	154	+	if unicode.IsControl(r) {
	155	+	return -1
	156	+	}
	157	+	return r
	158	+	}, s)
	159	+	}
	160	+
	161	+	// Watch calls emit with the focused window once, and again each time it
	162	+	// changes, until ctx ends or the connection fails. display is the Wayland
	163	+	// socket; empty uses $WAYLAND_DISPLAY.
	164	+	func Watch(ctx context.Context, display string, emit func(Window) error) error {
	165	+	conn, err := neferclient.Connect(ctx, display)
	166	+	if err != nil {
	167	+	return fmt.Errorf("cannot connect to the compositor: %w", err)
	168	+	}
	169	+	defer conn.Close()
	170	+
	171	+	t := NewTracker()
	172	+	_, _, err = conn.Bind("zwlr_foreign_toplevel_manager_v1", 3, func(c wl.Context) wlr.ForeignToplevelManager {
	173	+	m := wlr.NewForeignToplevelManager(c)
	174	+	m.OnToplevel(func(h *wlr.ForeignToplevelHandle) {
	175	+	id := h.ID()
	176	+	h.OnTitle(func(s string) { t.Title(id, s) })
	177	+	h.OnAppId(func(s string) { t.ID(id, s) })
	178	+	h.OnState(func(b []byte) { t.State(id, b) })
	179	+	h.OnDone(func() { t.Done(id) })
	180	+	h.OnClosed(func() { t.Closed(id); _ = h.Destroy() })
	181	+	})
	182	+	return m
	183	+	})
	184	+	if errors.Is(err, neferclient.ErrGlobalNotFound) {
	185	+	return errors.New("this compositor does not offer zwlr_foreign_toplevel_manager_v1, so the focused window is unknown")
	186	+	}
	187	+	if err != nil {
	188	+	return fmt.Errorf("cannot ask the compositor for its windows: %w", err)
	189	+	}
	190	+	// The windows that exist now arrive after one round trip.
	191	+	if err = conn.Roundtrip(); err != nil {
	192	+	return err
	193	+	}
	194	+	var last Window
	195	+	first := true
	196	+	for {
	197	+	if err = conn.Dispatch(nil); err != nil {
	198	+	return fmt.Errorf("lost the connection to the compositor: %w", err)
	199	+	}
	200	+	if now := t.Focused(); first \|\| now != last {
	201	+	first, last = false, now
	202	+	if err = emit(now); err != nil {
	203	+	return err
	204	+	}
	205	+	}
	206	+	select {
	207	+	case <-ctx.Done():
	208	+	return nil
	209	+	case <-conn.Wake(): // the connection's own events: drain them
	210	+	case <-t.Changed: // the compositor changed a window
	211	+	}
	212	+	}
	213	+	}

A internal/app/app_test.go +104 -0

@@ -0,0 +1,104 @@
	1	+	package app
	2	+
	3	+	import (
	4	+	"encoding/binary"
	5	+	"testing"
	6	+	)
	7	+
	8	+	func state(vals ...uint32) []byte {
	9	+	var b []byte
	10	+	for _, v := range vals {
	11	+	b = binary.NativeEndian.AppendUint32(b, v)
	12	+	}
	13	+	return b
	14	+	}
	15	+
	16	+	// open maps a window: its properties and its state, then the done that applies them.
	17	+	func open(t *Tracker, h uint32, id, title string, st ...uint32) {
	18	+	t.ID(h, id)
	19	+	t.Title(h, title)
	20	+	t.State(h, state(st...))
	21	+	t.Done(h)
	22	+	}
	23	+
	24	+	func TestNothingFocusedIsTheZeroWindow(t *testing.T) {
	25	+	tr := NewTracker()
	26	+	if tr.Focused() != (Window{}) {
	27	+	t.Fatal("an empty tracker must have no focus")
	28	+	}
	29	+	open(tr, 1, "a", "A") // mapped, not activated
	30	+	if tr.Focused() != (Window{}) {
	31	+	t.Fatalf("a window without the activated state has no focus: %+v", tr.Focused())
	32	+	}
	33	+	}
	34	+
	35	+	func TestFocusFollowsTheActivatedState(t *testing.T) {
	36	+	tr := NewTracker()
	37	+	open(tr, 1, "org.mozilla.firefox", "Docs", 0, stateActivated) // maximized + activated
	38	+	open(tr, 2, "kitty", "~")
	39	+	if got := tr.Focused(); got != (Window{"org.mozilla.firefox", "Docs"}) {
	40	+	t.Fatalf("focused = %+v", got)
	41	+	}
	42	+	// Focus moves: 1 loses it, 2 gets it.
	43	+	open(tr, 1, "org.mozilla.firefox", "Docs", 0)
	44	+	open(tr, 2, "kitty", "~", stateActivated)
	45	+	if got := tr.Focused(); got != (Window{"kitty", "~"}) {
	46	+	t.Fatalf("after the focus moved: %+v", got)
	47	+	}
	48	+	}
	49	+
	50	+	func TestATitleChangeAppliesOnlyAtDone(t *testing.T) {
	51	+	tr := NewTracker()
	52	+	open(tr, 1, "kitty", "one", stateActivated)
	53	+	tr.Title(1, "two")
	54	+	if got := tr.Focused().Title; got != "one" {
	55	+	t.Fatalf("title changed before done: %q", got)
	56	+	}
	57	+	tr.Done(1)
	58	+	if got := tr.Focused().Title; got != "two" {
	59	+	t.Fatalf("title after done: %q", got)
	60	+	}
	61	+	}
	62	+
	63	+	func TestClosingTheFocusedWindowClearsTheFocus(t *testing.T) {
	64	+	tr := NewTracker()
	65	+	open(tr, 1, "kitty", "~", stateActivated)
	66	+	tr.Closed(1)
	67	+	if tr.Focused() != (Window{}) {
	68	+	t.Fatalf("a closed window still has the focus: %+v", tr.Focused())
	69	+	}
	70	+	}
	71	+
	72	+	func TestTheWindowThatGotTheFocusLastWins(t *testing.T) {
	73	+	tr := NewTracker()
	74	+	open(tr, 1, "a", "A", stateActivated)
	75	+	open(tr, 2, "b", "B", stateActivated) // two seats, two focused windows
	76	+	if got := tr.Focused().ID; got != "b" {
	77	+	t.Fatalf("focused = %q, want b (the newest)", got)
	78	+	}
	79	+	open(tr, 1, "a", "A2", stateActivated) // still active, only its title changed
	80	+	if got := tr.Focused().ID; got != "b" {
	81	+	t.Fatalf("a title change must not steal the focus: %q", got)
	82	+	}
	83	+	}
	84	+
	85	+	func TestCleanRemovesControlCharacters(t *testing.T) {
	86	+	in := "fire\x1b[2Jfox\n\ttab\x07 ok \u00e9"
	87	+	if got, want := Clean(in), "fire[2Jfoxtab ok \u00e9"; got != want {
	88	+	t.Fatalf("Clean = %q, want %q", got, want)
	89	+	}
	90	+	}
	91	+
	92	+	func TestNameIsTheLastPartOfTheID(t *testing.T) {
	93	+	for id, want := range map[string]string{
	94	+	"com.github.bnema.dumber": "dumber",
	95	+	"org.mozilla.firefox": "firefox",
	96	+	"kitty": "kitty",
	97	+	"": "",
	98	+	"trailing.": "trailing.",
	99	+	} {
	100	+	if got := Name(id); got != want {
	101	+	t.Errorf("Name(%q) = %q, want %q", id, got, want)
	102	+	}
	103	+	}
	104	+	}

@@ -0,0 +1,104 @@
	1	+	package app
	2	+
	3	+	import (
	4	+	"encoding/binary"
	5	+	"testing"
	6	+	)
	7	+
	8	+	func state(vals ...uint32) []byte {
	9	+	var b []byte
	10	+	for _, v := range vals {
	11	+	b = binary.NativeEndian.AppendUint32(b, v)
	12	+	}
	13	+	return b
	14	+	}
	15	+
	16	+	// open maps a window: its properties and its state, then the done that applies them.
	17	+	func open(t *Tracker, h uint32, id, title string, st ...uint32) {
	18	+	t.ID(h, id)
	19	+	t.Title(h, title)
	20	+	t.State(h, state(st...))
	21	+	t.Done(h)
	22	+	}
	23	+
	24	+	func TestNothingFocusedIsTheZeroWindow(t *testing.T) {
	25	+	tr := NewTracker()
	26	+	if tr.Focused() != (Window{}) {
	27	+	t.Fatal("an empty tracker must have no focus")
	28	+	}
	29	+	open(tr, 1, "a", "A") // mapped, not activated
	30	+	if tr.Focused() != (Window{}) {
	31	+	t.Fatalf("a window without the activated state has no focus: %+v", tr.Focused())
	32	+	}
	33	+	}
	34	+
	35	+	func TestFocusFollowsTheActivatedState(t *testing.T) {
	36	+	tr := NewTracker()
	37	+	open(tr, 1, "org.mozilla.firefox", "Docs", 0, stateActivated) // maximized + activated
	38	+	open(tr, 2, "kitty", "~")
	39	+	if got := tr.Focused(); got != (Window{"org.mozilla.firefox", "Docs"}) {
	40	+	t.Fatalf("focused = %+v", got)
	41	+	}
	42	+	// Focus moves: 1 loses it, 2 gets it.
	43	+	open(tr, 1, "org.mozilla.firefox", "Docs", 0)
	44	+	open(tr, 2, "kitty", "~", stateActivated)
	45	+	if got := tr.Focused(); got != (Window{"kitty", "~"}) {
	46	+	t.Fatalf("after the focus moved: %+v", got)
	47	+	}
	48	+	}
	49	+
	50	+	func TestATitleChangeAppliesOnlyAtDone(t *testing.T) {
	51	+	tr := NewTracker()
	52	+	open(tr, 1, "kitty", "one", stateActivated)
	53	+	tr.Title(1, "two")
	54	+	if got := tr.Focused().Title; got != "one" {
	55	+	t.Fatalf("title changed before done: %q", got)
	56	+	}
	57	+	tr.Done(1)
	58	+	if got := tr.Focused().Title; got != "two" {
	59	+	t.Fatalf("title after done: %q", got)
	60	+	}
	61	+	}
	62	+
	63	+	func TestClosingTheFocusedWindowClearsTheFocus(t *testing.T) {
	64	+	tr := NewTracker()
	65	+	open(tr, 1, "kitty", "~", stateActivated)
	66	+	tr.Closed(1)
	67	+	if tr.Focused() != (Window{}) {
	68	+	t.Fatalf("a closed window still has the focus: %+v", tr.Focused())
	69	+	}
	70	+	}
	71	+
	72	+	func TestTheWindowThatGotTheFocusLastWins(t *testing.T) {
	73	+	tr := NewTracker()
	74	+	open(tr, 1, "a", "A", stateActivated)
	75	+	open(tr, 2, "b", "B", stateActivated) // two seats, two focused windows
	76	+	if got := tr.Focused().ID; got != "b" {
	77	+	t.Fatalf("focused = %q, want b (the newest)", got)
	78	+	}
	79	+	open(tr, 1, "a", "A2", stateActivated) // still active, only its title changed
	80	+	if got := tr.Focused().ID; got != "b" {
	81	+	t.Fatalf("a title change must not steal the focus: %q", got)
	82	+	}
	83	+	}
	84	+
	85	+	func TestCleanRemovesControlCharacters(t *testing.T) {
	86	+	in := "fire\x1b[2Jfox\n\ttab\x07 ok \u00e9"
	87	+	if got, want := Clean(in), "fire[2Jfoxtab ok \u00e9"; got != want {
	88	+	t.Fatalf("Clean = %q, want %q", got, want)
	89	+	}
	90	+	}
	91	+
	92	+	func TestNameIsTheLastPartOfTheID(t *testing.T) {
	93	+	for id, want := range map[string]string{
	94	+	"com.github.bnema.dumber": "dumber",
	95	+	"org.mozilla.firefox": "firefox",
	96	+	"kitty": "kitty",
	97	+	"": "",
	98	+	"trailing.": "trailing.",
	99	+	} {
	100	+	if got := Name(id); got != want {
	101	+	t.Errorf("Name(%q) = %q, want %q", id, got, want)
	102	+	}
	103	+	}
	104	+	}

M internal/module/module.go +5 -0


@@ -151,6 +151,11 @@ func (m *Module) runOnce(ctx context.Context) error {
151	151		cmd.Cancel = func() error { return syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM) }
152	152		cmd.WaitDelay = 2 * time.Second
153	153		cmd.Env = append(append(os.Environ(), m.Env...), "NEFERBAR_MODULE="+m.Name)
	154	+	// Scripts call "$NEFERBAR_BIN app title" and friends: the path of the very
	155	+	// binary that started them, which need not be in $PATH.
	156	+	if exe, err := os.Executable(); err == nil {
	157	+	cmd.Env = append(cmd.Env, "NEFERBAR_BIN="+exe)
	158	+	}
154	159		out, err := cmd.StdoutPipe()
155	160		if err != nil {
156	161		return err


@@ -151,6 +151,11 @@ func (m *Module) runOnce(ctx context.Context) error {
151	cmd.Cancel = func() error { return syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM) }	151		cmd.Cancel = func() error { return syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM) }
152	cmd.WaitDelay = 2 * time.Second	152		cmd.WaitDelay = 2 * time.Second
153	cmd.Env = append(append(os.Environ(), m.Env...), "NEFERBAR_MODULE="+m.Name)	153		cmd.Env = append(append(os.Environ(), m.Env...), "NEFERBAR_MODULE="+m.Name)
		154	+	// Scripts call "$NEFERBAR_BIN app title" and friends: the path of the very
		155	+	// binary that started them, which need not be in $PATH.
		156	+	if exe, err := os.Executable(); err == nil {
		157	+	cmd.Env = append(cmd.Env, "NEFERBAR_BIN="+exe)
		158	+	}
154	out, err := cmd.StdoutPipe()	159		out, err := cmd.StdoutPipe()
155	if err != nil {	160		if err != nil {
156	return err	161		return err