feat: SendMessageDraft

messages.setTyping with a sendMessageTypingActionDraft (SendMessageTextDraftAction)
carrying the draft_id and styled text, optionally scoped to a forum topic. Mapping
confirmed against telegram-bot-api 10.1.

sendRichMessageDraft stays deferred: it needs a tg.RichMessage PageBlock tree
built from HTML/markdown, a substantial content parser TDLib runs server-side.
Hermetic test; lint clean.

Author: ernado

send_draft.go

@@ -0,0 +1,69 @@
+package botapi
+
+import (
+	"context"
+
+	"github.com/gotd/td/tg"
+)
+
+// DraftOption configures SendMessageDraft.
+type DraftOption func(*draftConfig)
+
+type draftConfig struct {
+	parseMode       ParseMode
+	entities        []MessageEntity
+	messageThreadID int
+}
+
+// WithDraftParseMode selects the formatting mode for the draft text.
+func WithDraftParseMode(mode ParseMode) DraftOption {
+	return func(c *draftConfig) { c.parseMode = mode }
+}
+
+// WithDraftEntities sets explicit entities for the draft text; they take
+// precedence over a parse mode.
+func WithDraftEntities(entities []MessageEntity) DraftOption {
+	return func(c *draftConfig) { c.entities = entities }
+}
+
+// WithDraftMessageThread targets a specific forum topic / thread.
+func WithDraftMessageThread(messageThreadID int) DraftOption {
+	return func(c *draftConfig) { c.messageThreadID = messageThreadID }
+}
+
+// SendMessageDraft broadcasts a message draft to a chat, so its members see what
+// the bot is preparing. draftID is a unique client-side identifier for the draft.
+func (b *Bot) SendMessageDraft(ctx context.Context, chat ChatID, draftID int64, text string, opts ...DraftOption) error {
+	var cfg draftConfig
+
+	for _, o := range opts {
+		o(&cfg)
+	}
+
+	peer, err := b.resolveInputPeer(ctx, chat)
+	if err != nil {
+		return err
+	}
+
+	textWithEntities, err := b.textWithEntities(ctx, text, cfg.parseMode, cfg.entities)
+	if err != nil {
+		return err
+	}
+
+	req := &tg.MessagesSetTypingRequest{
+		Peer: peer,
+		Action: &tg.SendMessageTextDraftAction{
+			RandomID: draftID,
+			Text:     textWithEntities,
+		},
+	}
+	if cfg.messageThreadID != 0 {
+		req.SetTopMsgID(cfg.messageThreadID)
+	}
+
+	if _, err := b.raw.MessagesSetTyping(ctx, req); err != nil {
+		return asAPIError(err)
+	}
+
+	return nil
+}

send_draft_test.go

@@ -0,0 +1,35 @@
+package botapi
+
+import (
+	"context"
+	"testing"
+
+	"github.com/gotd/td/tg"
+)
+
+func TestSendMessageDraft(t *testing.T) {
+	inv := newMockInvoker()
+	inv.reply(tg.MessagesSetTypingRequestTypeID, &tg.BoolTrue{})
+
+	if err := newMockBot(inv).SendMessageDraft(context.Background(), userRef(10, 20), 999, "draft text",
+		WithDraftMessageThread(5)); err != nil {
+		t.Fatalf("SendMessageDraft: %v", err)
+	}
+
+	var req tg.MessagesSetTypingRequest
+
+	inv.decode(t, tg.MessagesSetTypingRequestTypeID, &req)
+
+	if topMsg, ok := req.GetTopMsgID(); !ok || topMsg != 5 {
+		t.Fatalf("top msg id = %d ok=%v", topMsg, ok)
+	}
+
+	action, ok := req.Action.(*tg.SendMessageTextDraftAction)
+	if !ok {
+		t.Fatalf("action = %#v, want text draft", req.Action)
+	}
+
+	if action.RandomID != 999 || action.Text.Text != "draft text" {
+		t.Fatalf("action = %#v", action)
+	}
+}