Persistent URL store

[dr-chase-g3ka1]

Is your feature request related to a problem? Please describe.
When the upload is interrupted by for example a power outage, the upload must restart. That is because only MemoryURLStore exists.

Describe the solution you'd like
There should be a persistent URL store which could be loaded after a restart of the computer.

Can you provide help with implementing this feature?
I have some code and I will create a pull request.

Additional context
It's a feature that was requested by my boss, but we are moving to AWS cloud, so our old infrastructure will not be updated. Thus I don't want my efforts wasted, the tus team might like this solution. I hope.

[Acconut]

Thank you very much for your work on this feature. In general, we are interested in adding such a persistent URL storage.

It's a feature that was requested by my boss, but we are moving to AWS cloud, so our old infrastructure will not be updated. Thus I don't want my efforts wasted

That's very noble of you! Would you still be open for modification on your PR? I am mostly thinking about adding tests and discussing the actual data format (is XML really the best choice here?).

[dr-chase-g3ka1]

I am open to continue to work on the PR, I have some time during evenings. I think XML (JAXB) is good enough if we assume the typical client uploads 1-2 large files at a time because of bandwidth limitation. JAXB with these annotations is very simple in the code, easy to maintain. Also, the xml file is in temp folder, so operating system should be able to pick up and clean automatically. Only concern is JAXB is not included after JRE1.8 so that might be an issue. Other solution could be SQLite maybe. If you have a better solution in mind feel free to share.

[Acconut]

Thanks for your work! We continued the discussion in #68.