Bug Description

When a form element has a relative URL (such as ../) or a query (such as ?foo=bar) for the action attribute, the value is incorrectly sanitized and a malformed URL is produced.

For example, given that the request URL is https://example.org/about/?amp with Transitional mode active, the following can be observed:

This is also reproducible in Standard mode.

Do note that actions with relative anchor tags (eg. #foo) are correctly converted, which was fixed by #4003.

Steps to reproduce

1. Activate Transitional mode

2. Create a post and add a Custom HTML block with the following content:

<form method="post" action="../"></form> 
<form method="post" action="?foo=bar"></form> 

3. View the AMP version of the post

4. Given that the current URL is https://example.org/about/?amp, the following malformed action-xhr URL values for each form element can be observed:

<form method="post" action-xhr="//example.com/about/?amp/__/&_wp_amp_action_xhr_converted=1&amp">...</form>

<form method="post" action-xhr="//example.com/about/?amp?foo=bar&_wp_amp_action_xhr_converted=1&amp">...</form>

Screenshots

Additional context

• WordPress version:
• Plugin version:
• Gutenberg plugin version (if applicable):
• AMP plugin template mode:
• PHP version:
• OS:
• Browser: [e.g. chrome, safari]
• Device: [e.g. iPhone6]

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Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry