For a Zip file is there an official way to tell a directoy from a 0 length file?

I'm writing some code to parse a zip file headers. I've read through the specification and can't seem to find an answer for telling apart directory names from file names. C# seems to use the convention that directories end with a trailing slash but the spec doesn't say anything about it, so I'm wondering if this is just convention or if there is a better way to do it.