feat: add forum topic icons and modern sticker thumbnail methods

GetForumTopicIconStickers (messages.getStickerSet of the default topic
icons set), plus SetStickerSetThumbnail and SetCustomEmojiStickerSetThumbnail
(stickers.setStickerSetThumb). Dedupe the invalid custom_emoji_id error.

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

Author: ernado

errors.go

@@ -90,3 +90,9 @@ func Code(err error) int {
 
 	return 0
 }
+
+// errInvalidCustomEmojiID is returned when a custom_emoji_id is not a valid
+// integer document id.
+func errInvalidCustomEmojiID() *Error {
+	return &Error{Code: 400, Description: "Bad Request: invalid custom_emoji_id"}
+}

forum_topics.go

@@ -0,0 +1,34 @@
+package botapi
+
+import (
+	"context"
+
+	"github.com/gotd/td/tg"
+)
+
+// GetForumTopicIconStickers returns custom emoji stickers that can be used as a
+// forum topic icon by any user.
+func (b *Bot) GetForumTopicIconStickers(ctx context.Context) ([]Sticker, error) {
+	res, err := b.raw.MessagesGetStickerSet(ctx, &tg.MessagesGetStickerSetRequest{
+		Stickerset: &tg.InputStickerSetEmojiDefaultTopicIcons{},
+		Hash:       0,
+	})
+	if err != nil {
+		return nil, asAPIError(err)
+	}
+
+	set, ok := res.(*tg.MessagesStickerSet)
+	if !ok {
+		return nil, &Error{Code: 400, Description: "Bad Request: sticker set not found"}
+	}
+
+	out := make([]Sticker, 0, len(set.Documents))
+
+	for _, d := range set.Documents {
+		if doc, ok := d.(*tg.Document); ok {
+			out = append(out, stickerFromDocument(doc, set.Set.ShortName, StickerCustomEmoji))
+		}
+	}
+
+	return out, nil
+}

reactions.go

@@ -17,7 +17,7 @@ func reactionToTg(r ReactionType) (tg.ReactionClass, error) {
 	case ReactionTypeCustomEmoji:
 		id, err := strconv.ParseInt(v.CustomEmojiID, 10, 64)
 		if err != nil {
-			return nil, &Error{Code: 400, Description: "Bad Request: invalid custom_emoji_id"}
+			return nil, errInvalidCustomEmojiID()
 		}
 
 		return &tg.ReactionCustomEmoji{DocumentID: id}, nil

sticker_edit.go

@@ -160,7 +160,7 @@ func (b *Bot) GetCustomEmojiStickers(ctx context.Context, customEmojiIDs []strin
 	for _, s := range customEmojiIDs {
 		id, err := strconv.ParseInt(s, 10, 64)
 		if err != nil {
-			return nil, &Error{Code: 400, Description: "Bad Request: invalid custom_emoji_id"}
+			return nil, errInvalidCustomEmojiID()
 		}
 
 		ids = append(ids, id)

sticker_thumb.go

@@ -0,0 +1,66 @@
+package botapi
+
+import (
+	"context"
+	"strconv"
+
+	"github.com/gotd/td/tg"
+)
+
+// SetStickerSetThumbnail sets the thumbnail of a regular or mask sticker set
+// owned by the bot. The thumbnail is referenced by file_id or uploaded; format
+// selects the uploaded file's encoding. This is the format-aware counterpart of
+// SetStickerSetThumb.
+func (b *Bot) SetStickerSetThumbnail(ctx context.Context, name string, thumb InputFile, format StickerFormat) error {
+	var doc tg.InputDocumentClass
+
+	switch f := thumb.(type) {
+	case InputFileID:
+		d, err := inputDocumentFromFileID(string(f))
+		if err != nil {
+			return err
+		}
+
+		doc = d
+	case *InputFileUpload:
+		uploaded, err := b.uploadStickerDocument(ctx, f, format)
+		if err != nil {
+			return err
+		}
+
+		doc = &tg.InputDocument{ID: uploaded.ID, AccessHash: uploaded.AccessHash, FileReference: uploaded.FileReference}
+	default:
+		return &Error{Code: 400, Description: "Bad Request: thumbnail must be a file_id or an uploaded file"}
+	}
+
+	req := &tg.StickersSetStickerSetThumbRequest{Stickerset: &tg.InputStickerSetShortName{ShortName: name}}
+	req.SetThumb(doc)
+
+	if _, err := b.raw.StickersSetStickerSetThumb(ctx, req); err != nil {
+		return asAPIError(err)
+	}
+
+	return nil
+}
+
+// SetCustomEmojiStickerSetThumbnail sets the thumbnail of a custom emoji sticker
+// set owned by the bot to one of its stickers, referenced by custom_emoji_id. An
+// empty customEmojiID drops the set thumbnail.
+func (b *Bot) SetCustomEmojiStickerSetThumbnail(ctx context.Context, name, customEmojiID string) error {
+	req := &tg.StickersSetStickerSetThumbRequest{Stickerset: &tg.InputStickerSetShortName{ShortName: name}}
+
+	if customEmojiID != "" {
+		id, err := strconv.ParseInt(customEmojiID, 10, 64)
+		if err != nil {
+			return errInvalidCustomEmojiID()
+		}
+
+		req.SetThumbDocumentID(id)
+	}
+
+	if _, err := b.raw.StickersSetStickerSetThumb(ctx, req); err != nil {
+		return asAPIError(err)
+	}
+
+	return nil
+}

sticker_thumb_test.go

@@ -0,0 +1,69 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+func TestGetForumTopicIconStickers(t *testing.T) {
+	inv := newMockInvoker()
+	inv.reply(tg.MessagesGetStickerSetRequestTypeID, &tg.MessagesStickerSet{
+		Set: tg.StickerSet{ShortName: "topics", Emojis: true},
+		Documents: []tg.DocumentClass{
+			&tg.Document{
+				ID:       1,
+				MimeType: "image/webp",
+				Attributes: []tg.DocumentAttributeClass{
+					&tg.DocumentAttributeSticker{Alt: "🎯", Stickerset: &tg.InputStickerSetEmpty{}},
+				},
+			},
+		},
+	})
+
+	stickers, err := newMockBot(inv).GetForumTopicIconStickers(context.Background())
+	if err != nil {
+		t.Fatalf("GetForumTopicIconStickers: %v", err)
+	}
+
+	if len(stickers) != 1 || stickers[0].Type != StickerCustomEmoji {
+		t.Fatalf("stickers = %#v", stickers)
+	}
+}
+
+func TestSetStickerSetThumbnail(t *testing.T) {
+	fid := documentFileID(t, 0x61)
+
+	inv := newMockInvoker()
+	inv.reply(tg.StickersSetStickerSetThumbRequestTypeID, &tg.MessagesStickerSet{Set: tg.StickerSet{ShortName: "s"}})
+
+	if err := newMockBot(inv).SetStickerSetThumbnail(context.Background(), "s", FileID(fid), StickerFormatStatic); err != nil {
+		t.Fatalf("SetStickerSetThumbnail: %v", err)
+	}
+
+	var req tg.StickersSetStickerSetThumbRequest
+
+	inv.decode(t, tg.StickersSetStickerSetThumbRequestTypeID, &req)
+
+	if _, ok := req.GetThumb(); !ok {
+		t.Fatal("thumb not set")
+	}
+}
+
+func TestSetCustomEmojiStickerSetThumbnail(t *testing.T) {
+	inv := newMockInvoker()
+	inv.reply(tg.StickersSetStickerSetThumbRequestTypeID, &tg.MessagesStickerSet{Set: tg.StickerSet{ShortName: "s"}})
+
+	if err := newMockBot(inv).SetCustomEmojiStickerSetThumbnail(context.Background(), "s", "777"); err != nil {
+		t.Fatalf("SetCustomEmojiStickerSetThumbnail: %v", err)
+	}
+
+	var req tg.StickersSetStickerSetThumbRequest
+
+	inv.decode(t, tg.StickersSetStickerSetThumbRequestTypeID, &req)
+
+	if id, ok := req.GetThumbDocumentID(); !ok || id != 777 {
+		t.Fatalf("thumb document id = %d, ok=%v", id, ok)
+	}
+}