From 8b4fefd518f20f231fa416d8ed2054c535a6beb1 Mon Sep 17 00:00:00 2001
From: Katharine Chui <katharine.chui@gmail.com>
Date: Mon, 11 May 2026 14:13:27 +0200
Subject: [PATCH] avoid exposing game to partially written mod files during
 first download

This avoids mod loading failure messages caused by partially
copied mod files after initial download, the same way it is
already avoided while loading files from cache.
---
 src/Network/Resources.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/Network/Resources.cpp b/src/Network/Resources.cpp
index 40dcdac..2869fd9 100644
--- a/src/Network/Resources.cpp
+++ b/src/Network/Resources.cpp
@@ -583,13 +583,17 @@ void NewSyncResources(SOCKET Sock, const std::string& Mods, const std::vector<Mo
                 c = ::tolower(c);
             }
 #endif
+            auto name = std::filesystem::path(GetGamePath()) / "mods/multiplayer" / FName;
+            auto tmp_name = name;
+            tmp_name += ".tmp";
 
             std::error_code ec;
-            fs::copy_file(PathToSaveTo, std::filesystem::path(GetGamePath()) / "mods/multiplayer" / FName, fs::copy_options::overwrite_existing, ec);
+            fs::copy_file(PathToSaveTo, tmp_name, fs::copy_options::overwrite_existing, ec);
             if (ec) {
                 error(beammp_wide("Error in copy_file during download of ") + beammp_fs_string(PathToSaveTo) + beammp_wide(": ") + Utils::ToWString(ec.message()));
                 break;
             }
+            fs::rename(tmp_name, name);
             UpdateModUsage(FName);
         }
         WaitForConfirm();
@@ -748,7 +752,12 @@ void SyncResources(SOCKET Sock) {
             }
 #endif
 
-            fs::copy_file(PathToSaveTo, GetGamePath() / beammp_wide("mods/multiplayer") / Utils::ToWString(FName), fs::copy_options::overwrite_existing);
+            auto name = GetGamePath() / beammp_wide("mods/multiplayer") / Utils::ToWString(FName);
+            auto tmp_name = name;
+            tmp_name += L".tmp";
+
+            fs::copy_file(PathToSaveTo, tmp_name, fs::copy_options::overwrite_existing);
+            fs::rename(tmp_name, name);
             UpdateModUsage(FN->substr(pos));
         }
         WaitForConfirm();