Allow precompute size of serialized tags.

ui/text/text_entity.cpp

@@ -1950,6 +1950,20 @@ void Trim(TextWithEntities &result) {
 	}
 }
 
+int SerializeTagsSize(const TextWithTags::Tags &tags) {
+	auto result = qint32(0);
+	if (tags.isEmpty()) {
+		return result;
+	}
+	result += sizeof(qint32);
+	for (const auto &tag : tags) {
+		result += 2 * sizeof(qint32) // offset, length
+			+ sizeof(quint32) // id.size
+			+ tag.id.size() * sizeof(ushort);
+	}
+	return result;
+}
+
 QByteArray SerializeTags(const TextWithTags::Tags &tags) {
 	if (tags.isEmpty()) {
 		return QByteArray();

ui/text/text_entity.h

@@ -344,10 +344,13 @@ inline QString PrepareForSending(const QString &text, PrepareTextOption option =
 // Replace bad symbols with space and remove '\r'.
 void ApplyServerCleaning(TextWithEntities &result);
 
-QByteArray SerializeTags(const TextWithTags::Tags &tags);
+[[nodiscard]] int SerializeTagsSize(const TextWithTags::Tags &tags);
-TextWithTags::Tags DeserializeTags(QByteArray data, int textLength);
+[[nodiscard]] QByteArray SerializeTags(const TextWithTags::Tags &tags);
-QString TagsMimeType();
+[[nodiscard]] TextWithTags::Tags DeserializeTags(
-QString TagsTextMimeType();
+	QByteArray data,
+	int textLength);
+[[nodiscard]] QString TagsMimeType();
+[[nodiscard]] QString TagsTextMimeType();
 
 inline const auto kMentionTagStart = qstr("mention://user.");