The source code file mongo/util/file.h contains a File class based on a FileInterface class that is not used by any other derived class. All code for the File class is in the header file; there is no file.cpp. The code for Windows and non-Windows versions of the member functions do not align well; they print different messages on errors and in one case one version throws an massert while the other just logs a message. Neither version does a very good job of logging what failed on some errors. There is some code that might be moved into a "file" area, but it doesn't belong in a header file and so isn't easy to move.