When saving, write the save to a temporary file first

TheForceEngine/TFE_FileSystem/filestream.cpp

@@ -30,6 +30,14 @@ bool FileStream::exists(const char* filename)
 	return res;
 }
 
+bool FileStream::renameFile(const char* oldName, const char* newName)
+{
+	remove(newName);
+	int status = rename(oldName, newName);
+	if (status < 0) { return false; }
+	return true;
+}
+
 bool FileStream::open(const char* filename, AccessMode mode)
 {
 	const char* modeStrings[] = { "rb", "wb", "rb+" };

TheForceEngine/TFE_FileSystem/filestream.h

@@ -16,6 +16,7 @@ class FileStream : public Stream
 	~FileStream();
 
 	bool exists(const char* filename);
+	bool renameFile(const char* oldName, const char* newName);
 	bool open(const char* filename, AccessMode mode);
 	bool open(const FilePath* filePath, AccessMode mode);
 	void close();

TheForceEngine/TFE_Game/saveSystem.cpp

@@ -187,17 +187,27 @@ namespace TFE_SaveSystem
 
 	bool saveGame(const char* filename, const char* saveName)
 	{
+		// We first write the new save to a temporary file, then rename the temporary file.
+		// This way, if we are saving into an existing slot and something goes wrong during
+		// the save process, we won't overwrite a valid save with a corrupted save.
+
+		char tempFilePath[TFE_MAX_PATH];
 		char filePath[TFE_MAX_PATH];
+		string tempFilename = string(filename) + ".tmp";
+		sprintf(tempFilePath, "%s%s", s_gameSavePath, tempFilename.c_str());
 		sprintf(filePath, "%s%s", s_gameSavePath, filename);
 
 		bool ret = false;
 		FileStream stream;
-		if (stream.open(filePath, Stream::MODE_WRITE))
+		if (stream.open(tempFilePath, Stream::MODE_WRITE))
 		{
 			saveHeader(&stream, saveName);
 			ret = s_game->serializeGameState(&stream, filename, true);
 			stream.close();
 		}
+
+		stream.renameFile(tempFilePath, filePath);
+
 		return ret;
 	}