bound notification delivery and expand placeholders once

Give the notification queue a buffer and drop events when it is full.
The channel was unbuffered, so a slow or hung notification command
blocked whichever UI or network callback happened to raise the event.

Expand the command placeholders in a single pass.
Substituting %event, then %who, then %what meant text arriving in an
earlier field could contain a later placeholder and have it expanded,
letting a remote user inject their own text into the command.

Move the command runner behind a build tag and drop the POSIX default
on Windows.
The helper script it pointed at does not exist there, so the default
was a command that could only fail.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

config/notification_unix.go

@@ -0,0 +1,7 @@
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+
+package config
+
+func defaultNotifyCommand() string {
+	return "/usr/share/barnard/barnard-sound.sh \"%event\" \"%who\" \"%what\""
+}

config/notification_windows.go

@@ -0,0 +1,9 @@
+//go:build windows
+
+package config
+
+// Windows installations do not ship the POSIX notification helper. Users can
+// configure a cmd.exe-compatible command explicitly if they want notifications.
+func defaultNotifyCommand() string {
+	return ""
+}

config/user_config.go

@@ -150,7 +150,7 @@ func (c *Config) LoadConfig() {
 		jc.Username = &username
 	}
 	if c.config.NotifyCommand == nil {
-		ncmd := string("/usr/share/barnard/barnard-sound.sh \"%event\" \"%who\" \"%what\"")
+		ncmd := defaultNotifyCommand()
 		jc.NotifyCommand = &ncmd
 	}
 	if c.config.NoiseSuppressionEnabled == nil {

main.go

@@ -9,7 +9,6 @@ import (
 	"log"
 	"net/http"
 	"os"
-	"os/exec"
 	"strings"
 	"time"
 
@@ -45,31 +44,28 @@ func do_list_devices() {
 	show_devs("Inputs:", idevs)
 }
 
-func setup_notify_runner(notify_command string) chan []string {
+const notificationQueueSize = 32
-	t := make(chan []string)
+
-	var do_nothing = false
+func setup_notify_runner(notifyCommand string) chan []string {
-	var err error
+	events := make(chan []string, notificationQueueSize)
-	if err != nil {
+	go func() {
+		for event := range events {
+			if notifyCommand != "" {
+				runNotification(expandNotification(notifyCommand, event))
 			}
-	if notify_command == "" {
-		do_nothing = true
 		}
-	go func(events chan []string, cmd_template string, dummy bool) {
+	}()
-		for {
+	return events
-			event := <-events
+}
-			if !dummy {
+
-				t := string(cmd_template)
+// expandNotification replaces placeholders in one pass so text supplied for
-				t = strings.ReplaceAll(t, "%event", shellescape.Quote(event[0]))
+// one field cannot cause another placeholder to be expanded recursively.
-				t = strings.ReplaceAll(t, "%who", shellescape.Quote(event[1]))
+func expandNotification(template string, event []string) string {
-				t = strings.ReplaceAll(t, "%what", shellescape.Quote(event[2]))
+	return strings.NewReplacer(
-				cmd := "/bin/sh"
+		"%event", shellescape.Quote(event[0]),
-				args := []string{"-c", t}
+		"%who", shellescape.Quote(event[1]),
-				x := exec.Command(cmd, args...)
+		"%what", shellescape.Quote(event[2]),
-				x.Run()
+	).Replace(template)
-			} //if we actually have a command to run
-		} //for
-	}(t, notify_command, do_nothing)
-	return t
 }
 
 func main() {

notification_unix.go

@@ -0,0 +1,9 @@
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+
+package main
+
+import "os/exec"
+
+func runNotification(command string) {
+	_ = exec.Command("/bin/sh", "-c", command).Run()
+}

notification_windows.go

@@ -0,0 +1,9 @@
+//go:build windows
+
+package main
+
+import "os/exec"
+
+func runNotification(command string) {
+	_ = exec.Command("cmd.exe", "/C", command).Run()
+}

ui.go

@@ -39,7 +39,12 @@ func esc(str string) string {
 }
 
 func (b *Barnard) Notify(event string, who string, what string) {
-	b.notifyChannel <- []string{event, who, what}
+	// Notifications are best-effort: a slow external command must not block a
+	// UI or network callback. New events are dropped once the bounded queue is full.
+	select {
+	case b.notifyChannel <- []string{event, who, what}:
+	default:
+	}
 }
 
 func (b *Barnard) Beep() {