Photon: Force only Photon URLs to HTTPS

[aduth]

Fixes #6073

Changes proposed in this Pull Request:

This pull request seeks to resolve an issue where providing one's own Photon domain via the jetpack_photon_domain would not have its scheme respected and instead forced to HTTPS, regardless of whether the custom domain is capable of supporting it.

The changes here force only those URLs we detect to be Photon to HTTPS. Combined with previous changes in 0fa10d4, this should ensure all Photon URLs use HTTPS while still respecting custom domains provided through the filter.

Further, it resolves an issue where if a custom domain is provided for Photon that is already "network_path" and a valid scheme is provided, that scheme should be reflected in the return value.

Testing instructions:

Verify newly added unit tests are passing:

WP_DEVELOP_DIR=/path/to/wordpress-develop/tests/phpunit phpunit tests/php/test_functions.photon.php 

Replace WP_DEVELOP_DIR with a path to a checkout of the WordPress develop repository.

(See original testing instructions)

cc @danielbachhuber @jeherve

[danielbachhuber]

No unit tests?

[aduth]

Good call, they'd not existed 'til semi-recently. I'll add cases based on testing instructions.

[aduth]

Added unit tests and updated testing instructions accordingly.

I also changed behavior to not try to override the scheme of a URL which is already "Photonized". It seems as though we should respect the scheme of the Photon domain*, though I think this might need to be part of a larger set of changes to deprecate the $scheme parameter altogether and simply enforce the scheme of the Photon domain.

* In other words, I think jetpack_photon_url( 'http://i0.wp.com/example.com/img.jpg' ) should probably return https://i0.wp.com/example.com/img.jpg, but with the implementation here will preserve the original scheme.

[georgestephanis]

@aduth The unit tests added seem to have a couple failures in PHP 5.2/5.3 --

test_photon_url_filter_network_path_photonized_http
test_photon_url_filter_network_path_photonized_https
test_photon_url_filter_network_path_photonized_to_https

If you need me to, I can dig into what's causing the failures, just let me know.

[aduth]

@georgestephanis I may or may not have time to take a look this week, but I suspect it could be an existing issue with URL parsing related to this PHP Changelog note from 5.4.7:

Fixed host recognition when scheme is omitted and a leading component separator is present.

http://php.net/manual/en/function.parse-url.php#refsect1-function.parse-url-changelog

At this line:

https://github.com/Automattic/jetpack/blob/df97b9d/functions.photon.php#L101

[georgestephanis]

I'll put a reminder on it and try to hit it later this week if you don't beat me to it.

Alternately, if anyone finds this still open after next week, please hunt me down and beat me with a whisky bottle until I fix it.

Then leave the bottle when you're done.

[aduth]

In 2e53352, added jetpack_photon_parse_url as a wrapper to parse_url which prepends an assumed scheme for schema-less URLs. Might make sense as something more generic than how it is currently (i.e. not specific to Photon).

[eliorivero]

Tests well 🐑