ruby win32api & structs (VerQueryValue) - windows

Question

I am trying to call the standard Win32 API functions to get file version info, using the win32-api library.
The 3 version.dll functions are GetFileVersionInfoSize, GetFileVersionInfo, and VerQueryValue. Then I call RtlMoveMemory in kernel32.dll to get a copy of the VS_FIXEDFILEINFO struct (see Microsoft documentation: http://msdn.microsoft.com/en-us/library/ms646997%28VS.85%29.aspx).
I drew from an example I saw using VB: http://support.microsoft.com/kb/139491.
My problem is that the data that finally gets returned doesn't seem to match the expected struct, in fact it doesn't even return a consistent value. I suspect the data is getting mangled at some point, probably in VerQueryValue or RtlMoveMemory.
Here is the code:
GetFileVersionInfoSize = Win32::API.new('GetFileVersionInfoSize','PP','I','version.dll')
GetFileVersionInfo = Win32::API.new('GetFileVersionInfo','PIIP','I', 'version.dll')
VerQueryValue = Win32::API.new('VerQueryValue','PPPP','I', 'version.dll')
RtlMoveMemory = Win32::API.new('RtlMoveMemory', 'PPI', 'V', 'kernel32.dll')
buf = [0].pack('L')
version_size = GetFileVersionInfoSize.call(myfile + "\0", buf)
raise Exception.new if version_size == 0 #TODO
version_info = 0.chr * version_size
version_ok = GetFileVersionInfo.call(file, 0, version_size, version_info)
raise Exception.new if version_ok == 0 #TODO
addr = [0].pack('L')
size = [0].pack('L')
query_ok = VerQueryValue.call(version_info, "\\\0", addr, size)
raise Exception.new if query_ok == 0 #TODO
# note that at this point, size == 4 -- is that right?
fixed_info = Array.new(13,0).pack('L*')
RtlMoveMemory.call(fixed_info, addr, fixed_info.length)
# fixed_info.unpack('L*') #=> seemingly random data, usually only the first two dwords' worth and the rest 0.

Answer 1

This is the full code I got to work, in case others are looking for such a function.
Returns an array with four parts of product/file version number (i.e., what is called "File Version" in a dll file properties window):
def file_version ref, options = {}
options = {:path => LIBDIR, :extension => 'dll'}.merge(options)
begin
file = File.join(ROOT, options[:path],"#{ref}.#{options[:extension]}").gsub(/\//,"\\")
buf = [0].pack('L')
version_size = GetFileVersionInfoSize.call(file + "\0", buf)
raise Exception.new if version_size == 0 #TODO
version_info = 0.chr * version_size
version_ok = GetFileVersionInfo.call(file, 0, version_size, version_info)
raise Exception.new if version_ok == 0 #TODO
addr = [0].pack('L')
size = [0].pack('L')
query_ok = VerQueryValue.call(version_info, "\\\0", addr, size)
raise Exception.new if query_ok == 0 #TODO
fixed_info = Array.new(18,0).pack('LSSSSSSSSSSLLLLLLL')
RtlMoveMemory.call(fixed_info, addr.unpack('L')[0], fixed_info.length)
fixed_info.unpack('LSSSSSSSSSSLLLLLLL')[5..8].reverse
rescue
[]
end
end

Answer 2

The answer in https://stackoverflow.com/a/2224681/3730446 isn't strictly correct: the VS_FIXEDFILEINFO struct contains separate FileVersion and ProductVersion. That code returns a version number consisting of the two more-significant components of the ProductVersion and the two less-significant components of the FileVersion. Most times I've seen, that wouldn't matter because both Product- and FileVersion have the same value, but you never know what you might encounter in the wild.
We can see this by comparing the VS_FIXEDFILEINFO struct from http://msdn.microsoft.com/en-us/library/windows/desktop/ms646997(v=vs.85).aspx and the format string we're using to pack and unpack the buffer:
typedef struct tagVS_FIXEDFILEINFO {
DWORD dwSignature; // 0: L
DWORD dwStrucVersion; // 1: S
// 2: S
DWORD dwFileVersionMS; // 3: S
// 4: S
DWORD dwFileVersionLS; // 5: S
// 6: S
DWORD dwProductVersionMS; // 7: S
// 8: S
DWORD dwProductVersionLS; // 9: S
// 10: S
DWORD dwFileFlagsMask; // 11: L
DWORD dwFileFlags; // 12: L
DWORD dwFileOS; // 13: L
DWORD dwFileType; // 14: L
DWORD dwFileSubtype; // 15: L
DWORD dwFileDateMS; // 16: L
DWORD dwFileDateLS; // 17: L
} VS_FIXEDFILEINFO;
Subscripts 5 to 8, then, consists of dwFileVersionLS and dwProductVersionMS. Getting FileVersion and ProductVersion correctly would look like this:
info = fixed_info.unpack('LSSSSSSSSSSLLLLLLL')
file_version = [ info[4], info[3], info[6], info[5] ]
product_version = [ info[8], info[7], info[10], info[9] ]