From 81c0afafa35a4010b3eeb2c1367ea3719fd0750e Mon Sep 17 00:00:00 2001
From: levlam <levlam@telegram.org>
Date: Mon, 24 Sep 2018 04:25:24 +0300
Subject: [PATCH] Allow limit == -offset in getChatHistory.

GitOrigin-RevId: 8a050a75c0428304bb61c36a2c284b6309c6a8ea
---
 td/generate/scheme/td_api.tl    |  4 ++--
 td/telegram/MessagesManager.cpp | 33 +++++++++++++++++++++++++--------
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/td/generate/scheme/td_api.tl b/td/generate/scheme/td_api.tl
index 0505c0b5..76e69cbb 100644
--- a/td/generate/scheme/td_api.tl
+++ b/td/generate/scheme/td_api.tl
@@ -2505,8 +2505,8 @@ getGroupsInCommon user_id:int32 offset_chat_id:int53 limit:int32 = Chats;
 //-For optimal performance the number of returned messages is chosen by the library. This is an offline request if only_local is true
 //@chat_id Chat identifier
 //@from_message_id Identifier of the message starting from which history must be fetched; use 0 to get results from the last message
-//@offset Specify 0 to get results from exactly the from_message_id or a negative offset to get the specified message and some newer messages
-//@limit The maximum number of messages to be returned; must be positive and can't be greater than 100. If the offset is negative, the limit must be greater than -offset. Fewer messages may be returned than specified by the limit, even if the end of the message history has not been reached
+//@offset Specify 0 to get results from exactly the from_message_id or a negative offset up to 99 to get additionally some newer messages
+//@limit The maximum number of messages to be returned; must be positive and can't be greater than 100. If the offset is negative, the limit must be greater or equal to -offset. Fewer messages may be returned than specified by the limit, even if the end of the message history has not been reached
 //@only_local If true, returns only messages that are available locally without sending network requests
 getChatHistory chat_id:int53 from_message_id:int53 offset:int32 limit:int32 only_local:Bool = Messages;
 
diff --git a/td/telegram/MessagesManager.cpp b/td/telegram/MessagesManager.cpp
index c24763a4..15e0bd76 100644
--- a/td/telegram/MessagesManager.cpp
+++ b/td/telegram/MessagesManager.cpp
@@ -14080,14 +14080,25 @@ tl_object_ptr<td_api::messages> MessagesManager::get_dialog_history(DialogId dia
   if (limit > MAX_GET_HISTORY) {
     limit = MAX_GET_HISTORY;
   }
-  if (limit <= -offset) {
-    promise.set_error(Status::Error(5, "Parameter limit must be greater than -offset"));
-    return nullptr;
-  }
   if (offset > 0) {
     promise.set_error(Status::Error(5, "Parameter offset must be non-positive"));
     return nullptr;
   }
+  if (offset <= -MAX_GET_HISTORY) {
+    promise.set_error(Status::Error(5, "Parameter offset must be greater than -100"));
+    return nullptr;
+  }
+  if (offset < -limit) {
+    promise.set_error(Status::Error(5, "Parameter offset must not be less than -limit"));
+    return nullptr;
+  }
+  bool is_limit_increased = false;
+  if (limit == -offset) {
+    limit++;
+    is_limit_increased = true;
+  }
+  CHECK(0 < limit && limit <= MAX_GET_HISTORY);
+  CHECK(-limit < offset && offset <= 0);
 
   if (from_message_id == MessageId() || from_message_id.get() > MessageId::max().get()) {
     from_message_id = MessageId::max();
@@ -14184,7 +14195,7 @@ tl_object_ptr<td_api::messages> MessagesManager::get_dialog_history(DialogId dia
             << ", offset = " << offset << ", limit = " << limit << ", from_the_end = " << from_the_end;
   vector<tl_object_ptr<td_api::message>> messages;
   if (*p != nullptr && offset == 0) {
-    while (*p != nullptr && limit-- > 0) {
+    while (*p != nullptr && messages.size() < static_cast<size_t>(limit)) {
       messages.push_back(get_message_object(dialog_id, *p));
       from_message_id = (*p)->message_id;
       --p;
@@ -14196,16 +14207,22 @@ tl_object_ptr<td_api::messages> MessagesManager::get_dialog_history(DialogId dia
     CHECK(offset == 0);
     preload_newer_messages(d, MessageId(messages[0]->id_));
     preload_older_messages(d, MessageId(messages.back()->id_));
-  } else if (limit > 0 && (/*d->first_remote_message_id != -1 && */ left_tries != 0)) {
+  } else if (messages.size() < static_cast<size_t>(limit) && left_tries != 0) {
     // there can be more messages on the server, need to load them
     if (from_the_end) {
       from_message_id = MessageId();
     }
-    send_closure_later(actor_id(this), &MessagesManager::load_messages, d->dialog_id, from_message_id, offset, limit,
-                       left_tries, only_local, std::move(promise));
+    send_closure_later(actor_id(this), &MessagesManager::load_messages, d->dialog_id, from_message_id, offset,
+                       limit - static_cast<int32>(messages.size()), left_tries, only_local, std::move(promise));
     return nullptr;
   }
 
+  LOG(INFO) << "Have " << messages.size() << " messages out of requested "
+            << (is_limit_increased ? "increased " : "exact ") << limit;
+  if (is_limit_increased && static_cast<size_t>(limit) == messages.size()) {
+    messages.pop_back();
+  }
+
   LOG(INFO) << "Return " << messages.size() << " messages in result to getChatHistory";
   promise.set_value(Unit());                            // can send some messages
   return get_messages_object(-1, std::move(messages));  // TODO return real total_count of messages in the dialog