feat(answer): implement AnswerCallbackQuery

Respond to inline-keyboard callback queries via
messages.setBotCallbackAnswer, with options for text, alert, URL and
cache time. Add a Context.AnswerCallback helper for the handler
framework.

AnswerInlineQuery and the payment answers (PreCheckout/Shipping) are
deferred: they need the InlineQueryResult union and payment update
plumbing respectively, neither of which is wired yet.

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

Author: ernado

answer.go

@@ -0,0 +1,73 @@
+package botapi
+
+import (
+	"context"
+	"strconv"
+
+	"github.com/gotd/td/tg"
+)
+
+// AnswerCallbackQueryOption configures an AnswerCallbackQuery call.
+type AnswerCallbackQueryOption func(*answerCallbackConfig)
+
+type answerCallbackConfig struct {
+	text      string
+	showAlert bool
+	url       string
+	cacheTime int
+}
+
+// WithCallbackText sets the notification text shown to the user (0-200
+// characters). By default nothing is shown.
+func WithCallbackText(text string) AnswerCallbackQueryOption {
+	return func(c *answerCallbackConfig) { c.text = text }
+}
+
+// WithCallbackAlert shows the notification as an alert dialog instead of a
+// top-of-screen toast.
+func WithCallbackAlert() AnswerCallbackQueryOption {
+	return func(c *answerCallbackConfig) { c.showAlert = true }
+}
+
+// WithCallbackURL sets a URL to open. Telegram restricts which URLs are
+// accepted (game URLs, or t.me/your_bot?start= links).
+func WithCallbackURL(url string) AnswerCallbackQueryOption {
+	return func(c *answerCallbackConfig) { c.url = url }
+}
+
+// WithCallbackCacheTime sets, in seconds, how long the result may be cached
+// client-side.
+func WithCallbackCacheTime(seconds int) AnswerCallbackQueryOption {
+	return func(c *answerCallbackConfig) { c.cacheTime = seconds }
+}
+
+// AnswerCallbackQuery responds to a callback query sent from an inline keyboard.
+// The callbackQueryID is the CallbackQuery.ID from the update.
+func (b *Bot) AnswerCallbackQuery(ctx context.Context, callbackQueryID string, opts ...AnswerCallbackQueryOption) error {
+	var cfg answerCallbackConfig
+	for _, o := range opts {
+		o(&cfg)
+	}
+
+	queryID, err := strconv.ParseInt(callbackQueryID, 10, 64)
+	if err != nil {
+		return &Error{Code: 400, Description: "Bad Request: invalid callback query id"}
+	}
+
+	req := &tg.MessagesSetBotCallbackAnswerRequest{
+		Alert:     cfg.showAlert,
+		QueryID:   queryID,
+		CacheTime: cfg.cacheTime,
+	}
+	if cfg.text != "" {
+		req.SetMessage(cfg.text)
+	}
+	if cfg.url != "" {
+		req.SetURL(cfg.url)
+	}
+
+	if _, err := b.raw.MessagesSetBotCallbackAnswer(ctx, req); err != nil {
+		return asAPIError(err)
+	}
+	return nil
+}

answer_test.go

@@ -0,0 +1,19 @@
+package botapi
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestAnswerCallbackQueryInvalidID(t *testing.T) {
+	b := &Bot{}
+	err := b.AnswerCallbackQuery(context.Background(), "not-a-number")
+	if err == nil {
+		t.Fatal("expected error for non-numeric callback query id")
+	}
+	var apiErr *Error
+	if !errors.As(err, &apiErr) || apiErr.Code != 400 {
+		t.Fatalf("want 400 Error, got %v", err)
+	}
+}

context.go

@@ -49,3 +49,13 @@ func (c *Context) Reply(text string, opts ...SendOption) (*Message, error) {
 	opts = append([]SendOption{ReplyTo(m.MessageID)}, opts...)
 	return c.Bot.SendMessage(c, ID(m.Chat.ID), text, opts...)
 }
+
+// AnswerCallback answers the update's callback query. It is an error to call it
+// when the update is not a callback query.
+func (c *Context) AnswerCallback(opts ...AnswerCallbackQueryOption) error {
+	cq := c.Update.CallbackQuery
+	if cq == nil {
+		return &Error{Code: 400, Description: "Bad Request: update has no callback query to answer"}
+	}
+	return c.Bot.AnswerCallbackQuery(c, cq.ID, opts...)
+}