Close sessions where user is anonymous but is_valid_public_url is false

[kkoz]

Previously, if a request is made where is_valid_public_url is false but is_anonymous is true, a connection would be created but would never be closed. This PR closes those connections to prevent resource leaks.

Testing this PR

1. required setup

• Install this version of omeroweb
• You need a public user (to make is_anonymous True)
• Need to have omero.web.public.url_filter configured without webclient/keepalive_ping (to make is_valid_public_url False for webclient/keepalive_ping requests)

2. actions to perform

• Navigate to a public page (e.g. a pathviewer image) which uses a keepalive ping.
• Open several tabs like this.

3. expected observations

• The thread count used by omeroweb or gunicorn should not increase over time, even as keepalive requests are made by these pages.
• Without this PR, the number of threads in use (e.g. result of ps -Fw -u omero Hh |grep gunicorn |wc -l) will increase over time.

[chris-allan]

Builds failing due to Teemu/pytest-sugar#187; see #152.

/cc @sbesson, @will-moore, @joshmoore

[chris-allan]

Build now passing after merge of #152 and Travis rebuild.

[sbesson]

--include

[will-moore]

Code change makes total sense.
To test the fix as described, I need to set-up public user with the right url regex etc...

[manics]

@kkoz Just out of interest, how did you find this leak? Is there anything we can do to detect these in future?

[chris-allan]

@manics We found it on a customer system where this configuration was present. I can't think of any way off hand to easily detect these in the future aside from monitoring OMERO.web thread counts.

[will-moore]

Instead of pathviewer I added ping every second to webgateway viewer.
Running locally (Mac) as described at https://docs.openmicroscopy.org/omero/5.6.0/developers/Web/Deployment.html#using-wsgi and with 3 viewer tabs open, I don't see any thread increases using

$ pstree | grep gunicorn | wc
       7     132    1903

but I get "Internal Server Error" pages quite quickly without this PR.

With this PR, everything continues to work fine.
👍

[mtbc]

Thank you all for your efforts here.