Cache received story viewers.

td/generate/scheme/td_api.tl

@@ -7284,10 +7284,12 @@ openStory story_sender_user_id:int53 story_id:int32 = Ok;
 //@story_id The identifier of the story
 closeStory story_sender_user_id:int53 story_id:int32 = Ok;
 
-//@description Returns viewers of a recent outgoing story. The method can be called if story.can_get_viewers == true
+//@description Returns viewers of a recent outgoing story. The method can be called if story.can_get_viewers == true. The views are returned in a reverse chronological order (i.e., in order of decreasing view_date)
+//-For optimal performance, the number of returned stories is chosen by TDLib
 //@story_id Story identifier
 //@offset_viewer A viewer from which to return next viewers; pass null to get results from the beginning
 //@limit The maximum number of story viewers to return
+//-For optimal performance, the number of returned stories is chosen by TDLib and can be smaller than the specified limit
 getStoryViewers story_id:int32 offset_viewer:messageViewer limit:int32 = MessageViewers;
 
 

td/telegram/MessageViewer.cpp

@@ -53,7 +53,7 @@ MessageViewers::MessageViewers(vector<telegram_api::object_ptr<telegram_api::rea
 }
 
 MessageViewers MessageViewers::get_sublist(const MessageViewer &offset, int32 limit) const {
-  MessageViewers result{vector<telegram_api::object_ptr<telegram_api::storyView>>()};
+  MessageViewers result;
   bool found = offset.is_empty();
   for (auto &message_viewer : message_viewers_) {
     if (found) {
@@ -68,6 +68,25 @@ MessageViewers MessageViewers::get_sublist(const MessageViewer &offset, int32 li
   return result;
 }
 
+void MessageViewers::add_sublist(const MessageViewer &offset, const MessageViewers &sublist) {
+  if (offset.is_empty()) {
+    if (message_viewers_.empty()) {
+      message_viewers_ = sublist.message_viewers_;
+    } else {
+      auto old_viewers = std::move(message_viewers_);
+      for (auto &viewer : sublist.message_viewers_) {
+        if (viewer == old_viewers[0]) {
+          append(message_viewers_, old_viewers);
+          return;
+        }
+        message_viewers_.push_back(viewer);
+      }
+    }
+  } else if (!message_viewers_.empty() && message_viewers_.back() == offset) {
+    append(message_viewers_, sublist.message_viewers_);
+  }
+}
+
 td_api::object_ptr<td_api::messageViewers> MessageViewers::get_message_viewers_object(
     ContactsManager *contacts_manager) const {
   return td_api::make_object<td_api::messageViewers>(

td/telegram/MessageViewer.h

@@ -51,12 +51,20 @@ StringBuilder &operator<<(StringBuilder &string_builder, const MessageViewer &vi
 struct MessageViewers {
   vector<MessageViewer> message_viewers_;
 
+  MessageViewers() = default;
+
   explicit MessageViewers(vector<telegram_api::object_ptr<telegram_api::storyView>> &&story_views);
 
   explicit MessageViewers(vector<telegram_api::object_ptr<telegram_api::readParticipantDate>> &&read_dates);
 
+  bool is_empty() const {
+    return message_viewers_.empty();
+  }
+
   MessageViewers get_sublist(const MessageViewer &offset, int32 limit) const;
 
+  void add_sublist(const MessageViewer &offset, const MessageViewers &sublist);
+
   td_api::object_ptr<td_api::messageViewers> get_message_viewers_object(ContactsManager *contacts_manager) const;
 };
 

td/telegram/StoryInteractionInfo.h

@@ -44,6 +44,10 @@ class StoryInteractionInfo {
     return false;
   }
 
+  int32 get_view_count() const {
+    return view_count_;
+  }
+
   td_api::object_ptr<td_api::storyInteractionInfo> get_story_interaction_info_object(Td *td) const;
 };
 

td/telegram/StoryManager.cpp

@@ -16,7 +16,6 @@
 #include "td/telegram/logevent/LogEventHelper.h"
 #include "td/telegram/MessageEntity.h"
 #include "td/telegram/MessagesManager.h"
-#include "td/telegram/MessageViewer.h"
 #include "td/telegram/OptionManager.h"
 #include "td/telegram/StoryContent.h"
 #include "td/telegram/StoryContentType.h"
@@ -695,6 +694,7 @@ void StoryManager::on_story_can_get_viewers_timeout(int64 story_global_id) {
     send_closure(G()->td(), &Td::send_update,
                  td_api::make_object<td_api::updateStory>(get_story_object(story_full_id, story)));
   }
+  cached_story_viewers_.erase(story_full_id);
 }
 
 bool StoryManager::is_story_owned(DialogId owner_dialog_id) const {
@@ -1100,7 +1100,7 @@ void StoryManager::get_story_viewers(StoryId story_id, const td_api::messageView
   if (limit <= 0) {
     return promise.set_error(Status::Error(400, "Parameter limit must be positive"));
   }
-  if (can_get_story_viewers(story_full_id, story).is_error()) {
+  if (can_get_story_viewers(story_full_id, story).is_error() || story->interaction_info_.get_view_count() == 0) {
     return promise.set_value(td_api::object_ptr<td_api::messageViewers>());
   }
 
@@ -1110,11 +1110,22 @@ void StoryManager::get_story_viewers(StoryId story_id, const td_api::messageView
     offset_date = offset->view_date_;
     offset_user_id = offset->user_id_;
   }
+  MessageViewer offset_viewer{UserId(offset_user_id), offset_date};
+
+  auto &cached_viewers = cached_story_viewers_[story_full_id];
+  if (cached_viewers != nullptr && story->content_ != nullptr &&
+      (cached_viewers->total_count_ == story->interaction_info_.get_view_count() || !offset_viewer.is_empty())) {
+    auto result = cached_viewers->viewers_.get_sublist(offset_viewer, limit);
+    if (!result.is_empty()) {
+      return promise.set_value(result.get_message_viewers_object(td_->contacts_manager_.get()));
+    }
+  }
 
   auto query_promise = PromiseCreator::lambda(
-      [actor_id = actor_id(this), story_id, promise = std::move(promise)](
+      [actor_id = actor_id(this), story_id, offset_viewer, promise = std::move(promise)](
           Result<telegram_api::object_ptr<telegram_api::stories_storyViewsList>> result) mutable {
-        send_closure(actor_id, &StoryManager::on_get_story_viewers, story_id, std::move(result), std::move(promise));
+        send_closure(actor_id, &StoryManager::on_get_story_viewers, story_id, offset_viewer, std::move(result),
+                     std::move(promise));
       });
 
   td_->create_handler<GetStoryViewsListQuery>(std::move(query_promise))
@@ -1122,7 +1133,8 @@ void StoryManager::get_story_viewers(StoryId story_id, const td_api::messageView
 }
 
 void StoryManager::on_get_story_viewers(
-    StoryId story_id, Result<telegram_api::object_ptr<telegram_api::stories_storyViewsList>> r_view_list,
+    StoryId story_id, MessageViewer offset,
+    Result<telegram_api::object_ptr<telegram_api::stories_storyViewsList>> r_view_list,
     Promise<td_api::object_ptr<td_api::messageViewers>> &&promise) {
   G()->ignore_result_if_closing(r_view_list);
   if (r_view_list.is_error()) {
@@ -1140,11 +1152,29 @@ void StoryManager::on_get_story_viewers(
 
   td_->contacts_manager_->on_get_users(std::move(view_list->users_), "on_get_story_viewers");
 
-  if (story->content_ != nullptr && story->interaction_info_.set_view_count(view_list->count_)) {
-    on_story_changed(story_full_id, story, true, true);
+  auto total_count = view_list->count_;
+  if (total_count < 0 || static_cast<size_t>(total_count) < view_list->views_.size()) {
+    LOG(ERROR) << "Receive total_count = " << total_count << " and " << view_list->views_.size() << " story viewers";
+    total_count = static_cast<int32>(view_list->views_.size());
   }
 
   MessageViewers story_viewers(std::move(view_list->views_));
+  if (story->content_ != nullptr) {
+    if (story->interaction_info_.set_view_count(view_list->count_)) {
+      on_story_changed(story_full_id, story, true, true);
+    }
+    auto &cached_viewers = cached_story_viewers_[story_full_id];
+    if (cached_viewers == nullptr) {
+      cached_viewers = make_unique<CachedStoryViewers>();
+    }
+    if (total_count < cached_viewers->total_count_) {
+      LOG(ERROR) << "Total viewer count decreased from " << cached_viewers->total_count_ << " to " << total_count;
+    } else {
+      cached_viewers->total_count_ = total_count;
+    }
+    cached_viewers->viewers_.add_sublist(offset, story_viewers);
+  }
+
   promise.set_value(story_viewers.get_message_viewers_object(td_->contacts_manager_.get()));
 }
 

td/telegram/StoryManager.h

@@ -11,6 +11,7 @@
 #include "td/telegram/files/FileSourceId.h"
 #include "td/telegram/FullMessageId.h"
 #include "td/telegram/MessageEntity.h"
+#include "td/telegram/MessageViewer.h"
 #include "td/telegram/StoryFullId.h"
 #include "td/telegram/StoryId.h"
 #include "td/telegram/StoryInteractionInfo.h"
@@ -82,6 +83,11 @@ class StoryManager final : public Actor {
     vector<StoryId> story_ids_;
   };
 
+  struct CachedStoryViewers {
+    int32 total_count_ = -1;
+    MessageViewers viewers_;
+  };
+
  public:
   StoryManager(Td *td, ActorShared<> parent);
   StoryManager(const StoryManager &) = delete;
@@ -284,7 +290,7 @@ class StoryManager final : public Actor {
 
   void on_synchronized_archive_all_stories(bool set_archive_all_stories, Result<Unit> result);
 
-  void on_get_story_viewers(StoryId story_id,
+  void on_get_story_viewers(StoryId story_id, MessageViewer offset,
                             Result<telegram_api::object_ptr<telegram_api::stories_storyViewsList>> r_view_list,
                             Promise<td_api::object_ptr<td_api::messageViewers>> &&promise);
 
@@ -312,6 +318,8 @@ class StoryManager final : public Actor {
 
   FlatHashMap<StoryFullId, uint32, StoryFullIdHash> opened_owned_stories_;
 
+  FlatHashMap<StoryFullId, unique_ptr<CachedStoryViewers>, StoryFullIdHash> cached_story_viewers_;
+
   uint32 send_story_count_ = 0;
 
   int64 max_story_global_id_ = 0;