piwik (matomo) plugin - malformed URL

[ctgraham]

Describe the bug
https://forum.pkp.sfu.ca/t/ojs-v3-1-2-piwik-plugin-error/53349/2

OJS seems to change the piwik url which I insert into the configuration of the plugin. It changes the url from https://piwik.ub.uni-muenchen.de to //https://piwik.ub.uni-muenchen.de/

To Reproduce
Steps to reproduce the behavior:

1. Enable and configure piwik plugin
2. View HTTP requests made against matomo URL

What application are you using?
OJS or OMP version 3.1.2

Additional information
Piwik plugin Settings form requires a URL:
https://github.com/pkp/piwik/blob/910bfd6b6464fb383dc7d476771d9551b8d6b308/PiwikSettingsForm.inc.php#L38
as of
pkp/piwik@e78646c

This setting is used as if it is a DNS name, or DNS name + path:
https://github.com/pkp/piwik/blob/910bfd6b6464fb383dc7d476771d9551b8d6b308/PiwikPlugin.inc.php#L122

[ctgraham]

If we let (require) the user enter a full URL with protocol, we'll need to either require this be https to prevent failure of mixed protocol requests, or we'll need to strip the protocol before usage.

If we let the user enter just a arbitrary DNS + path, we need to clarify the expectation within the form. The form error currently says "http://" is required.
https://github.com/pkp/piwik/blob/910bfd6b6464fb383dc7d476771d9551b8d6b308/locale/en_US/locale.xml#L24

[ctgraham]

@dennmuel , @mpbraendle, can you test the proposed PR?

[mpbraendle]

Works on our test server. Thank you.

[dennmuel]

Same here. :) Thanks!

[asmecher]

Thanks, @ctgraham!

[asmecher]

Added a new release of Piwik (v1.0.2-1) to the plugin gallery with this fix included.