Core/Players: Prevent creating characters with duplicate name by reserving name early in the process

Closes #21656
Closes #21809

(cherry picked from commit fdb2b90685ebc3852740c424170101a196c29ebb)

src/server/game/Cache/CharacterCache.cpp

@@ -30,6 +30,7 @@ namespace
 {
     std::unordered_map<ObjectGuid, CharacterCacheEntry> _characterCacheStore;
     std::unordered_map<std::string, CharacterCacheEntry*> _characterCacheByNameStore;
+    std::unordered_set<std::string> _characterCreationNameStore;
 }
 
 CharacterCache::CharacterCache()
@@ -225,6 +226,21 @@ CharacterCacheEntry const* CharacterCache::GetCharacterCacheByName(std::string c
     return nullptr;
 }
 
+std::shared_ptr<std::string const> CharacterCache::TryCreateCharacterWithName(std::string const& name) const
+{
+    auto itr = _characterCacheByNameStore.find(name);
+    if (itr != _characterCacheByNameStore.end())
+        return nullptr;
+
+    auto insertResult = _characterCreationNameStore.insert(name);
+    if (!insertResult.second)
+        return nullptr;
+
+    // shared_ptr with custom deleter that erases its held value from _characterCreationNameStore instead of deleting it (points to value inside the container)
+    return std::shared_ptr<std::string const>(&(*insertResult.first),
+        [this](std::string const* storedName) { _characterCreationNameStore.erase(*storedName); });
+}
+
 ObjectGuid CharacterCache::GetCharacterGuidByName(std::string const& name) const
 {
     auto itr = _characterCacheByNameStore.find(name);

src/server/game/Cache/CharacterCache.h

@@ -58,7 +58,7 @@ class TC_GAME_API CharacterCache
         bool HasCharacterCacheEntry(ObjectGuid const& guid) const;
         CharacterCacheEntry const* GetCharacterCacheByGuid(ObjectGuid const& guid) const;
         CharacterCacheEntry const* GetCharacterCacheByName(std::string const& name) const;
-
+        std::shared_ptr<std::string const> TryCreateCharacterWithName(std::string const& name) const;
         ObjectGuid GetCharacterGuidByName(std::string const& name) const;
         bool GetCharacterNameByGuid(ObjectGuid guid, std::string& name) const;
         uint32 GetCharacterTeamByGuid(ObjectGuid guid) const;

src/server/game/Handlers/CharacterHandler.cpp

@@ -704,6 +704,14 @@ void WorldSession::HandleCharCreateOpcode(WorldPackets::Character::CreateCharact
     }
 
     std::shared_ptr<WorldPackets::Character::CharacterCreateInfo> createInfo = charCreate.CreateInfo;
+    // Reserve the name for the duration of callback chain
+    createInfo->NameToken = sCharacterCache->TryCreateCharacterWithName(createInfo->Name);
+    if (!createInfo->NameToken)
+    {
+        SendCharCreate(CHAR_CREATE_NAME_IN_USE);
+        return;
+    }
+
     CharacterDatabasePreparedStatement* stmt = CharacterDatabase.GetPreparedStatement(CHAR_SEL_CHECK_NAME);
     stmt->setString(0, charCreate.CreateInfo->Name);
 

src/server/game/Server/Packets/CharacterPackets.h

@@ -68,6 +68,7 @@ namespace WorldPackets
 
             /// Server side data
             uint8 CharCount  = 0;
+            std::shared_ptr<std::string const> NameToken;
         };
 
         struct CharacterRenameInfo