fix(handler): ignore commands targeted at another bot

In groups, Telegram clients append @BotUsername to a command
("/subscribe@other_bot"). The Command predicate ignored the suffix entirely,
so a bot reacted to commands aimed at any bot. Match an untargeted command,
or one whose @username is this bot's own (case-insensitive); the router now
threads the bot's username onto the Update for the check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ernado

CHANGELOG.md

@@ -7,6 +7,12 @@ messages follow [Conventional Commits](https://www.conventionalcommits.org/).
 
 ## [Unreleased]
 
+### Fixed
+
+- **Targeted commands** — a command addressed to another bot (`/cmd@other_bot`,
+  as clients send in groups) no longer matches. `Command`/`OnCommand` now match
+  an untargeted command, or one whose `@username` is this bot's own.
+
 ### Changed
 
 - **Logging port** — the library now logs through `github.com/gotd/log` instead

examples/advanced/main.go

@@ -41,7 +41,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("advanced-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/background/main.go

@@ -48,7 +48,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	sess, err := storage.Open("background-session.bbolt")
+	sess, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/buttons/main.go

@@ -46,7 +46,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("buttons-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/echo/main.go

@@ -31,7 +31,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("echo-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/inline/main.go

@@ -32,7 +32,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("inline-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/media/main.go

@@ -40,7 +40,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("media-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

examples/rich/main.go

@@ -53,7 +53,7 @@ func main() {
 	}
 
 	// Persist session, peers and update state so the bot resumes across restarts.
-	store, err := storage.Open("rich-session.bbolt")
+	store, err := storage.Open("session.bbolt")
 	if err != nil {
 		log.Fatal("Open storage", zap.Error(err))
 	}

handler.go

@@ -75,6 +75,10 @@ func (b *Bot) onWith(handler Handler, mws []Middleware, predicates []Predicate)
 // global middleware. Handler errors are logged, not propagated to the update
 // loop, so one failing handler does not tear down the bot.
 func (b *Bot) route(ctx context.Context, u *Update) {
+	if b.self != nil {
+		u.botUsername = b.self.Username
+	}
+
 	b.router.mu.RLock()
 	routes := b.router.routes
 	mws := b.router.mws

predicates.go

@@ -35,34 +35,44 @@ func (u *Update) Text() string {
 	return ""
 }
 
-// commandName extracts the bot command name from message text: "/start@bot foo"
-// yields ("start", true). Pure.
-func commandName(text string) (string, bool) {
+// commandName extracts the bot command name and its optional @target from
+// message text: "/start@bot foo" yields ("start", "bot", true), "/start foo"
+// yields ("start", "", true). Pure.
+func commandName(text string) (name, target string, ok bool) {
 	if !strings.HasPrefix(text, "/") {
-		return "", false
+		return "", "", false
 	}
 	field := text
 	if i := strings.IndexAny(text, " \t\n"); i >= 0 {
 		field = text[:i]
 	}
 	field = field[1:] // drop leading slash
 	if at := strings.IndexByte(field, '@'); at >= 0 {
+		target = field[at+1:]
 		field = field[:at]
 	}
-	return field, field != ""
+	return field, target, field != ""
 }
 
 // Command matches a message whose first token is the given bot command (with or
-// without a leading slash, and ignoring a trailing @botusername).
+// without a leading slash).
+//
+// A command may be targeted at a specific bot with a trailing @username
+// ("/start@my_bot"), as Telegram clients do in groups. An untargeted command
+// always matches; a targeted one matches only when the @username is this bot's
+// own — so the bot ignores commands aimed at other bots.
 func Command(name string) Predicate {
 	name = strings.TrimPrefix(name, "/")
 	return func(u *Update) bool {
 		m := u.EffectiveMessage()
 		if m == nil {
 			return false
 		}
-		got, ok := commandName(m.Text)
-		return ok && got == name
+		got, target, ok := commandName(m.Text)
+		if !ok || got != name {
+			return false
+		}
+		return target == "" || strings.EqualFold(target, u.botUsername)
 	}
 }