wpcom_vip_maybe_skip_old_slug_redirect(): Improve compatibility with local setups

[GaryJones]

Description

Add support for local development servers that do not have $_SERVER['DOCUMENT_URI'] defined.

Fixes #976.

Needs actual testing.

Checklist

Please make sure the items below have been covered before requesting a review:

• This change works and has been tested locally (or has an appropriate fallback).
• This change works and has been tested on a Go sandbox.
• This change has relevant unit tests (if applicable).
• This change has relevant documentation additions / updates (if applicable).

Steps to Test

1. Create a setup where $_SERVER['DOCUMENT_URI'] is undefined.
2. Check that function does what it was still meant to, once PR is applied.

[brandon-m-skinner]

Just one minor typo/carry over from a previous version of the function.

[brandon-m-skinner]

Since you're comparing to e.g.: http://othersite.com/random_text and looking to match the start of the string, this should be comparisons to 0 since string indexes start at 0.

Suggested change

	if ( is_404() && ( 1 === strpos( $uri, 'http:' ) || 1 === strpos( $uri, 'https:' ) ) ) {
	if ( is_404() && ( 0 === strpos( $uri, 'http:' ) || 0 === strpos( $uri, 'https:' ) ) ) {

[GaryJones]

@brandon-m-skinner How does that match up with the comment then?

//We look to see if a malformed url (represented by 'http:' ) is right after the starting / in DOCUMENT_URI hence position 1

As per the function DocBlock, what we're looking for is an invalid URL e.g. http://example.com/http://othersite.com/random_text, which means the DOCUMENT_URI and REQUEST_URI would be /http:..., so looking for http: or https: starting at index 1.

We could just start at index 0 and look for /http: or /https: if that makes it easier to understand? (I think it would be)

Also, do we really need to check for DOCUMENT_URI if REQUEST_URI seems to be the most popular key to check? Compare instances of DOCUMENT_URI to instances of REQUEST_URI just in this repo.

[GaryJones]

Re-jigged, and rebased on to latest master.

[brandon-m-skinner]

r961-stacks