make a backup of save data before writing to it

src/g_game.c

@@ -4635,6 +4635,7 @@ void G_SaveGameData(void)
 	INT32 i, j;
 	UINT8 btemp;
 	savebuffer_t save = {0};
+	char backupfile[MAX_WADPATH+4];
 
 	if (!gamedataloaded)
 		return; // If never loaded (-nodata), don't save
@@ -4652,6 +4653,23 @@ void G_SaveGameData(void)
 		return;
 	}
 
+	// Create backup of the save data
+	snprintf(backupfile, sizeof(backupfile), "%s.bak", gamedatafilename);
+	backupfile[sizeof(backupfile) - 1] = '\0';
+
+	FILE *gamedata = fopen(gamedatafilename, "r");
+
+	if (gamedata != NULL)
+	{
+		fclose(gamedata);
+
+		if (!FIL_CopyFile(gamedatafilename, backupfile))
+		{
+			CONS_Alert(CONS_WARNING,"Failed to create a backup of save data. Will not attempt to write to save data\n");
+			return;
+		}
+	}
+
 	// Version test
 	WRITEUINT32(save.p, GD_VERSIONCHECK); // 4
 

src/m_misc.cpp

@@ -363,6 +363,38 @@ boolean FIL_FileOK(char const *name)
 	return access(name,6)+1; //R_OK|W_OK
 }
 
+/** Copies contents of one file to another
+ *
+ * \param src   File to copy from
+ * \param dst   File to write into
+ * \return true if copy was succesful, false if it doesn't.
+ */
+boolean FIL_CopyFile(const char *src, const char *dst)
+{
+	FILE *srcFile = fopen(src, "rb");
+
+	if (srcFile == NULL)
+		return false;
+
+	FILE *dstFile = fopen(dst, "wb");
+
+	if (dstFile == NULL)
+	{
+		fclose(srcFile);
+		return false;
+	}
+
+	char buffer[1024];
+	size_t n;
+
+	while ((n = fread(buffer, 1, sizeof(buffer), srcFile)) > 0)
+		fwrite(buffer, 1, n, dstFile);
+
+	fclose(srcFile);
+	fclose(dstFile);
+
+	return true;
+}
 
 /** Checks if a pathname has a file extension and adds the extension provided
   * if not.
@@ -573,11 +605,28 @@ void M_SaveConfig(const char *filename)
 {
 	FILE *f;
 	char *filepath;
+	char backupfile[MAX_WADPATH+4];
 
 	// make sure not to write back the config until it's been correctly loaded
 	if (!gameconfig_loaded)
 		return;
 
+	// Create backup of the config file
+	snprintf(backupfile, sizeof backupfile, "%s.bak", configfile);
+	backupfile[sizeof backupfile - 1] = '\0';
+
+	FILE *config = fopen(configfile, "r");
+
+	if (config != NULL)
+	{
+		fclose(config);
+		if (FIL_CopyFile(configfile, backupfile) == false)
+		{
+			CONS_Alert(CONS_WARNING,"Failed to create a backup of the configuration file. Will not attempt to write to file\n");
+			return;
+		}
+	}
+
 	// can change the file name
 	if (filename)
 	{

src/m_misc.h

@@ -56,6 +56,7 @@ boolean FIL_FileExists(const char *name);
 boolean FIL_WriteFileOK(char const *name);
 boolean FIL_ReadFileOK(char const *name);
 boolean FIL_FileOK(char const *name);
+boolean FIL_CopyFile(const char *src, const char *dst);
 
 void FIL_DefaultExtension (char *path, const char *extension);
 void FIL_ForceExtension(char *path, const char *extension);