Find a better way to name persistent storage directories

[phenaproxima]

Right now, when the plugin sets up the persistent storage location for TUF metadata in the context of a particular repository, it uses this line of code to name the directory:

preg_replace('/[^[:alnum:]\.]/', '-', $repoUrl)

This can be problematic because URLs like site.coop.info/packages and site.coop/info/packages will collide. This is probably something of an edge case, but it's enough of a concern that it should block a 1.0.0 release of this plugin. We need to find a better way to name these directories.

One option is to use a SHA-256 hash of the URL, but that could be quite obscure. Other thoughts welcome...

[phenaproxima]

Assigning to @davidstrauss, since I think his opinion might be useful here.

[davidstrauss]

I see a couple options to balance these needs:

• Use a true escaping method that doesn't create collisions. For example, I think URL encoding may provide a conservative subset of what a filename is allowed to contain.
• Combine the current naming with a hash, eliminating collision risk while preserving readability for most purposes. I would put the hash later in the name to improve sorting and tab completion experiences.

I slightly prefer the latter, as the readable part remains more readable/tab-completable. The common case won't be collision, anyway.

[phenaproxima]

Combine the current naming with a hash, eliminating collision risk while preserving readability for most purposes. I would put the hash later in the name to improve sorting and tab completion experiences.

I think that's a pretty good idea.