xlsx compressed by rubyzip not readable by Excel

Question

I am working on writing code which can read/write Excel xlsx files. xlsx files are simply zip archives of several xml files, so in order to test out if I could write a file,

Answer 1

There are a number of constraints that the OOXML format imposes on the use of Zip in order for the packages to be conformant. For example, the only compression method permitted in the package is DEFLATE.

You might want to check the specification for OPC packages (which .XSLX files are) in Annex C of the standard available here (Zip), and then ensure that the rubyzip library is not doing anything that is not permitted (such as using the IMPLODE compression method).