Protocol-relative preconnects are broken

[neoxx]

Following ​https://w3c.github.io/resource-hints/ preconnect supports protocol-relative URLs.

The current implementation removes the double-slashes and you'll end up with

<link rel='preconnect' href='example.org'>

instead of

<link rel='preconnect' href='//example.org'>.

A real-world test in Chrome confirms that such a preconnect does not work.

[swissspidy]

The current implementation removes the double-slashes and you'll end up with

How did you add the URL? Some example code would be helpful.

[neoxx]

Sure thing, here you go:

function wp_resource_hints($hints, $relation_type) {
        if ($relation_type=='preconnect') {
                $hints[]='//example.org';
        }

        return $hints;
}

Though, I currently use the following work-around:

$protocol=(is_ssl()) ? 'https' : 'http';

$hints[]=$protocol.'://example.org';

[swissspidy]

Thanks a bunch for the snippet. 37652.diff​ should fix this.

@voldemortensen What do you think about this?

[peterwilsoncc]

Replying to swissspidy:

Thanks a bunch for the snippet. 37652.diff​ should fix this.

The // prefix can go on the else, the code is nested so only runs on preconnect & dns-prefetch.

I'll upload what I had for the sake of completeness momentarily.

[peterwilsoncc]

Reverting itchy trigger finger.

[swissspidy]

Thanks @peterwilsoncc. We should combine the tests of both patches though as they do slightly different things. For example, test_preconnect() should test various URLs and not just one.

[ocean90]

We're going to break code freeze with #36819 so we can fix this too.

[peterwilsoncc]

Combined version in 37652.3.diff​, preconnect test comes from 37652.diff​, other code and tests from 37652.2.diff​.

[ocean90]

37652.3.diff​ looks good to me.

[ocean90]

In 37652.4.diff​ I've inverted the condition to merge both $url = '//' . $parsed['host']; lines into one.

[azaozz]

37652.4.diff looks good, +1 to commit.

[ocean90]

In 38255:

Script Loader: Fix protocol-relative URLs for the preconnect relation type.

wp_resource_hints() parses the URL for the preconnect and dns-prefetch relation types to ensure correct values for both. While protocol-relative URLs are supported for dns-prefetch, the double slash was lost for preconnect.

Props swissspidy, peterwilsoncc.
Props azaozz for review.
Fixes #37652.

[ocean90]

In 38256:

Script Loader: Fix protocol-relative URLs for the preconnect relation type.

wp_resource_hints() parses the URL for the preconnect and dns-prefetch relation types to ensure correct values for both. While protocol-relative URLs are supported for dns-prefetch, the double slash was lost for preconnect.

Merge of [38255] to the 4.6 branch.

Props swissspidy, peterwilsoncc.
Props azaozz for review.
See #37652.