Reading the version number of a .NET assembly in plain C
I recently was assigned the task to write an Autoupdater application for Windows Mobile 6.5. Now my idea was to read the version resource from the application and determine its version and depending on the version propose an update to it or not. Now we all know that this is easy using the GetFileVersionInfo API. So I tried that and then notices that this works well for normal, native applications, but not for .NET Applications. It seems, that they don’t automatically create a Version Info resource section but instead just write the version to some structure that is called “Assembly”.
So I was in need for an API to read that information from the file. After some research, I found an API called Fusion that can be used to read Assembly informations from .NET executables. As it is a COM interface, it can be used from C code. Here is some C++ code that shows how to use this interface for this purpose.
But I wasn’t able to use it on Windows Mobile, because there is no such API on that operating system. This article explains how it works von Windows Mobile. So I finally ended up with parsing the file format and extracting the needed information. It’s not really hard to find the location in the PE file which contains all that tables that also contain Assembly information, but unfortunately, the tables have to be walked and processed according to their size information in order to find the real offset, as there are no RVA-pointers stored in the file that act as an index into the tables, but instead only variable size information is provided. For more information about the format, see this description.
Fortunately I found out that the WINE project already wrote an Assembly parser. So I stripped down the parser to the bare minimum required for getting the version info and packed it into a module that is easy to use. You can download it here.
System programmer