Add zipfs, an archive/zip-based read-only filesystem

[hillu]

No description provided.

[CLAassistant]

All committers have signed the CLA.

[jcftang]

Would love to see this merged as well, I was about to start on a zipfs backend myself till I saw this.

[hillu]

@bep Are you interested in this PR? If not, it is fine, in that case I would simply publish the zipfs package in a separate repository.

[aviau]

@hillu we might be interested to merge this in https://github.com/absfs/afero

[hillu]

@aviau Please help yourself. :-)
(If you merge it without changes, the constructor is placed in the zipfs package which is different from the rest of the afero package...)

[bep]

I will look more at this in a few days (please bump if I don't). Can I ask, what is your current use case for this?

/cc @spf13

[hillu]

@bep The main (public) use case is contained in https://github.com/DCSO/spyre. The tool can either read its configuration from a ZIP file that has been appended to the executable or from files that have been placed into the same directory as the executable.

[josephlewis42]

@bep another bump for this. Our use-case is something similar, except the zip files are embedded in the executable for legal compliance.

For us, the killer feature Afero provides is support for union filesystems, allowing users to modify/override the embedded files if they desired.

[senghoo]

This package seems panic if check stat of root. would u fix it? @hillu

f, err := fs.Open("/") // this err is not nil. return a File without zipfile field.
f.Stat() // panic on nil access.

[hillu]

@senghoo done.

[hillu]

Thanks!