NetPlay: Limit nickname length

Ridiculously long nicknames cause UI silliness, so 30 characters seems
like a reasonable limit, as it's the same as the forum.

Source/Core/Common/StringUtil.cpp

@@ -412,6 +412,12 @@ void StringPopBackIf(std::string* s, char c)
     s->pop_back();
 }
 
+size_t StringUTF8CodePointCount(const std::string& str)
+{
+  return str.size() -
+         std::count_if(str.begin(), str.end(), [](char c) -> bool { return (c & 0xC0) == 0x80; });
+}
+
 #ifdef _WIN32
 
 std::wstring CPToUTF16(u32 code_page, std::string_view input)

Source/Core/Common/StringUtil.h

@@ -167,6 +167,7 @@ void BuildCompleteFilename(std::string& complete_filename, std::string_view path
 bool StringBeginsWith(std::string_view str, std::string_view begin);
 bool StringEndsWith(std::string_view str, std::string_view end);
 void StringPopBackIf(std::string* s, char c);
+size_t StringUTF8CodePointCount(const std::string& str);
 
 std::string CP1252ToUTF8(std::string_view str);
 std::string SHIFTJISToUTF8(std::string_view str);

Source/Core/Core/NetPlayClient.cpp

@@ -252,6 +252,9 @@ bool NetPlayClient::Connect()
     case CON_ERR_GAME_RUNNING:
       m_dialog->OnConnectionError(_trans("The game is currently running."));
       break;
+    case CON_ERR_NAME_TOO_LONG:
+      m_dialog->OnConnectionError(_trans("Nickname is too long."));
+      break;
     default:
       m_dialog->OnConnectionError(_trans("The server sent an unknown error message."));
       break;

Source/Core/Core/NetPlayProto.h

@@ -171,7 +171,8 @@ enum
 {
   CON_ERR_SERVER_FULL = 1,
   CON_ERR_GAME_RUNNING = 2,
-  CON_ERR_VERSION_MISMATCH = 3
+  CON_ERR_VERSION_MISMATCH = 3,
+  CON_ERR_NAME_TOO_LONG = 4
 };
 
 enum
@@ -197,6 +198,7 @@ enum
 
 constexpr u32 NETPLAY_LZO_IN_LEN = 1024 * 64;
 constexpr u32 NETPLAY_LZO_OUT_LEN = NETPLAY_LZO_IN_LEN + (NETPLAY_LZO_IN_LEN / 16) + 64 + 3;
+constexpr u32 MAX_NAME_LENGTH = 30;
 constexpr size_t CHUNKED_DATA_UNIT_SIZE = 16384;
 constexpr u8 CHANNEL_COUNT = 2;
 constexpr u8 DEFAULT_CHANNEL = 0;

Source/Core/Core/NetPlayServer.cpp

@@ -377,9 +377,6 @@ unsigned int NetPlayServer::OnConnect(ENetPeer* socket, sf::Packet& rpac)
   if (m_players.size() >= 255)
     return CON_ERR_SERVER_FULL;
 
-  // cause pings to be updated
-  m_update_pings = true;
-
   Client player;
   player.pid = pid;
   player.socket = socket;
@@ -387,6 +384,12 @@ unsigned int NetPlayServer::OnConnect(ENetPeer* socket, sf::Packet& rpac)
   rpac >> player.revision;
   rpac >> player.name;
 
+  if (StringUTF8CodePointCount(player.name) > MAX_NAME_LENGTH)
+    return CON_ERR_NAME_TOO_LONG;
+
+  // cause pings to be updated
+  m_update_pings = true;
+
   // try to automatically assign new user a pad
   for (PlayerId& mapping : m_pad_map)
   {

Source/Core/DolphinQt/NetPlay/NetPlaySetupDialog.cpp

@@ -17,9 +17,11 @@
 #include <QTabWidget>
 
 #include "Core/Config/NetplaySettings.h"
+#include "Core/NetPlayProto.h"
 
 #include "DolphinQt/GameList/GameListModel.h"
 #include "DolphinQt/QtUtils/ModalMessageBox.h"
+#include "DolphinQt/QtUtils/UTF8CodePointCountValidator.h"
 #include "DolphinQt/Settings.h"
 
 #include "UICommon/NetPlayIndex.h"
@@ -87,6 +89,9 @@ void NetPlaySetupDialog::CreateMainLayout()
   m_reset_traversal_button = new QPushButton(tr("Reset Traversal Settings"));
   m_tab_widget = new QTabWidget;
 
+  m_nickname_edit->setValidator(
+      new UTF8CodePointCountValidator(NetPlay::MAX_NAME_LENGTH, m_nickname_edit));
+
   // Connection widget
   auto* connection_widget = new QWidget;
   auto* connection_layout = new QGridLayout;