URL Support

[Benjamin Gilbert]

On Thu, Apr 14, 2016 at 04:40:33PM +0200, Andreas Schmid via openslide-users wrote:
> I am wondering if it would be possible to adapt the Openslide library to
> support also url’s?
> 
> I was able to partially read a zip file via a seekable http range stream.
> 
> I think reading WSI-Formats over http without a tileserver would be amazing.

Hi Andi,

In principle it should be possible, but it would be a lot of work.  The
entire library revolves around opening and reading files, so a lot of code
would need to be changed.  In addition, performance would probably not be
very good, since every read access would need to go to a server potentially
tens of milliseconds away.  A good cache could help to some extent, but
OpenSlide's reads can be small, numerous, and random, so the problem is
non-trivial.  We've considered HTTP support in the past, but concluded that
putting a tile server next to the data would be more efficient.

It's also possible to implement something like this without modifying
OpenSlide, by reading slide files from a virtual filesystem backed by HTTP. 
There should be existing FUSE filesystems that would work.

--Benjamin Gilbert