Proposal: Fix incorrectly entered prefetches

[webtrainingwheels]

I see incorrect prefetch entries all the time:

Could we automatically fix them?

Steps to Reproduce:

• In Preload tab > Prefetch DNS Requests
• Add an incorrect prefetch entry like http://example.com (or https://example.com)
• This should be automatically corrected to //example.com (i.e. no protocol) when a user clicks Save Settings

Backlog Grooming

• Reproduce the problem
• Identify the root cause
• Scope a solution
• Estimate the effort

[Tabrisrp]

Reproduce the issue ✅
Reproduced on my local test site

Identify the root cause ✅
In the sanitize_callback() method, we sanitize the field but we don't have anything to remove the scheme from the entries:

wp-rocket/inc/classes/admin/settings/class-settings.php

Line 250 in 8cf329c

$input['dns_prefetch'] = rocket_sanitize_textarea_field( 'dns_prefetch', $input['dns_prefetch'] );

Scope a solution ✅
We can add an additional sanitize to remove the http(s) scheme from each URL in the textarea field.

Estimate the effort ✅
The code change itself is low effort. The current state of the sanitize_callback() method though might make writing automatic tests for this change very complicated.

[Tabrisrp]

@hellofromtonya will need your input for the testing part of sanitize_callback()

[arunbasillal]

Acceptance criteria

Customer inputs any of these:

• http://domain.com
• https://domain.com
• http://domain.com/example

WP Rocket converts this to:

• //domain.com

What if:

• customer inputs http:///domain.com (triple or more slashes)
  ^ My suggestion is that we ignore this for now. This is invalid input. The output will be ///domain.com

@GeekPress Inviting your thought on this ^

• customer inputs http://domain.com/ (trailing slash)
  ^ We keep the trailing slash. It's okay for dns-prefetch to have trailing slash.

• customer inputs ftp://domain.com (other protocols)
  ^ we can ignore all other protocols for now and do nothing. Just as we do in WP Rocket 3.5.0.x

[hellofromtonya]

Moving this one to 3.5.2 for us to do the following requirements:

• Detect malformed URLs, such as http:///domain.com or more more \
• Repair these URLs.