I dug into this area some more.
The GTFS spec does not specify /which/ ZIP standard must be used. The original spec came from PKWARE and is entitled "APPNOTE.TXT - .ZIP File Format Specification". It can be found here:
This was eventually made into ISO standard, but there's a fee just to get a copy of that standard. However, Wikipedia describes it as a subset of the PKWARE standard, lacking features that are no used in GTFS anyway, like encryption.
However, the most popular CLI tool for Mac and Linux is "Info-ZIP". It provides the familiar `zip` and `unzip` binaries.
The detail I'm interested in-- file permissions-- I believe is referred to in the sec as "external file attributes", which are considered host-dependent. In other words, I think for Unix file permissions to work, you may need to both create and unzip a zip archive on Unix.
I reviewed the `zip` and `unzip` tools from the "Info-ZIP" project and I couldn't actually find how to tell them to ignore file permissions, so that if an archive was created with a "read-only" file permissions, I might be able to ignore that when opening, using my Unix user's default permissions.
In summary:
* I don't think it's appropriate to add the spec that the files should have "at least readable permissions", because it turns out the permissions are host-dependent and I believe could be completely ignored depending on what tools are involved.
* It could be useful to clarify which "ZIP" file format specification must be followed, but this is not as a clear-cut as I might hope. It's difficult to recommend standard which people have to pay just to read the thing. Meanwhile, one of the most popular tools, Info-ZIP, has it's own extensions, although they might not matter for practical use. So it worth explicitlying mentioning the PKZIP standard? Maybe.
In the end, I'm less clear that's a great way to avoid rare permission problems using the spec, so I withdraw this proposal.
Thanks,