Use of undefined constant LIBXML_HTML_NODEFDTD warning shown in some environments

[ghost]

After the Gutenberg update two days ago (one before last) The following WARNING appeared at the top of the Home page of my website:

Warning: Use of undefined constant LIBXML_HTML_NODEFDTD - assumed 'LIBXML_HTML_NODEFDTD' (this will throw an Error in a future version of PHP) in /var/www/wp-content/plugins/gutenberg/lib/block-supports/index.php on line 64

Warning: A non-numeric value encountered in /var/www/wp-content/plugins/gutenberg/lib/block-supports/index.php on line 64

LINE 64 is a var about GMEDIA. Therefore I immediately contacted GMedia....

RATTUS at GMedia wrote about the error message:: "**That is impossible that in /wp-content/plugins/gutenberg/lib/block-supports/index.php on line 64 was var about Gmedia plugin because it's completely different plugin. Also there is no any constant with name LIBXML_HTML_NODEFDTD in Gmedia Gallery plugin.

You need to ask Gutenberg developers about your problem because error is in their plugin."**

I am posting a Virtual Art Exhibit tomorrow and need immediate resolution to the issue.
PLEASE HELP!!!!
THANK YOU SO MUCH!!!

[skorasaurus]

Hi,

Note: I am not 100% sure whether this advice will work. If you have a critical issue like this, I would highly recommend hiring or website developer and/or WordPress consultant.

To immediately solve the issue for your exhibit tomorrow, you'll need to use a previous version of Gutenberg.
You can temporarily roll back to a previous version of the Gutenberg plugin by using another free plugin WP-Rollback. If this doesn't work, I would recommend to 'roll back' any other plugins you recently updated or contact your webhost provider.

For the long-term, the error message leads me to believe appears that your website maybe using an old version of PHP, a programming language that is installed on your website and is used by WordPress. The version of php used for your website is not controlled by WordPress, it is provided by your website host.

You can check the php version through WordPress by visiting http://nameofyourwebsite.com/wp-admin/site-health.php?tab=debug and click the server tab.

If it says a number less than 7.3; then you're using an older version of PHP that is not recommended by WordPress can lead some to security issues on your website and it's more likely that you'll find errors like this on your website.

Contact your website host to change the PHP version. If you have an important event tomorrow, you should probably wait to change the PHP version until you have time devoted to this.

Note, in the future, this repository is typically for very advanced issues relating to Gutenberg and it's expected that participants have a relatively high level of technical experience. In the future, first try the WordPress support forums or contact a WordPress consultant or web developer.

[ghost]

Thank you for your response, Will. The website is on GoDaddy. The PHP version is not the very latest, but is above 7.3. The error message suggested that a newer version of PHP in the future would generate an error and/or failure. Scary! I can try the WP-Rollback. I am sorry to bother Git-Hub with this issue and greatly appreciate the other links and advice you have taken time to send me. My concern was that there is a bug in the Gutenberg update that may rain havoc on more than just my website and would need to be addressed asap. I have enjoyed using Gutenberg editor, but wondered if I might have to abandon it and what might happen if I deactivate Gutenberg now. Appreciatively, Barbara From: Will Skora <[email protected]> Sent: Monday, September 7, 2020 3:01 PM To: WordPress/gutenberg <[email protected]> Cc: barbarafife <[email protected]>; Author <[email protected]> Subject: Re: [WordPress/gutenberg] Gutenberg update generated invalid error for Gmedia - URGENT!!!!!! HELP REQUESTED!!! (#25122) Hi, Note: I am not 100% sure whether this advice will work. If you have a critical issue like this, I would highly recommend hiring or website developer and/or WordPress consultant. To immediately solve the issue for your exhibit tomorrow, you'll need to use a previous version of Gutenberg. You can temporarily roll back to a previous version of the Gutenberg plugin by using another free plugin WP-Rollback <https://wordpress.org/plugins/wp-rollback/> . For the long-term, the error message leads me to believe appears that your website maybe using an old version of php, a programming language that is installed on your website and is used by WordPress. You can check the php version through WordPress by visiting http://nameofyourwebsite.com/wp-admin/site-health.php?tab=debug and click the server tab. The version of php used for your website is not controlled by WordPress, it is provided by your website host. If it says a number less than 7.3; then you're using an older version of PHP that is not recommended by WordPress <https://make.wordpress.org/hosting/handbook/handbook/server-environment/#php-version> can lead some to security issues on your website and it's more likely that you'll find errors like this on your website. Contact your website host to change the PHP version. If you have an important event tomorrow, you should probably wait to change the PHP version until you have time devoted to this. Note, in the future, this repository is typically for very advanced issues relating to Gutenberg and it's expected that participants have a relatively high level of technical experience. In the future, first try the WordPress support forums <https://wordpress.org/support/welcome/> or contact a WordPress consultant or web developer. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#25122 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQ5AWDBMCTH5OPI7GWBGMODSEUUX7ANCNFSM4Q6WL3SA> . <https://github.com/notifications/beacon/AQ5AWDH4Q6SQHOMDZXN4DKLSEUUX7A5CNFSM4Q6WL3SKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOFEEVBIQ.gif>

[talldan]

It looks like the AMP plugin also encountered a similar issue, with the cause being that the libxml library is old/outdated:

• https://wordpress.org/support/topic/php-warning-use-of-undefined-constant-libxml_html_nodefdtd-assumed-libxml_h/
• PHP throws warning for missing LIBXML_HTML_NODEFDTD constant ampproject/amp-wp#4485
• Only use LIBXML_HTML_NODEFDTD is available ampproject/amp-wp#4486

[ReisingerWolfgang]

I have a similar error but in line 66 after upgrade to new WP and Gutenberg version....

Warning: Use of undefined constant LIBXML_HTML_NODEFDTD - assumed 'LIBXML_HTML_NODEFDTD' (this will throw an Error in a future version of PHP) in .../web/WPVB/wp-content/plugins/gutenberg/lib/block-supports/index.php on line 66 Warning: A non-numeric value encountered in .../web/WPVB/wp-content/plugins/gutenberg/lib/block-supports/index.php on line 66

Line 66 in Code:
$success = $dom->loadHTML( $wrapped_block_html, LIBXML_HTML_NODEFDTD | LIBXML_COMPACT );

Wordpress: 5.5.1
PHP: 7.3.21
Gutenberg: 8.9.2

[getsource]

We talked about this in today's dev meeting:
https://wordpress.slack.com/archives/C02RQBWTW/p1602652885487500

Tests started failing on GoDaddy and AMIMOTO around when r49135 landed.

@talldan pointed out https://github.com/WordPress/gutenberg/blob/master/lib/block-supports/index.php#L66, which matches with the timeline due to the block-supports merge included in r49135.

The full test results can be found linked in the host names above, but it's 24 test failures -- here's the first one:

WP_Block_Context_Test::test_provides_block_context
Use of undefined constant LIBXML_HTML_NODEFDTD - assumed 'LIBXML_HTML_NODEFDTD' (this will throw an Error in a future version of PHP)

/tmp/wp-test-runner/build/wp-includes/block-supports/index.php:73
/tmp/wp-test-runner/build/wp-includes/class-wp-hook.php:287
/tmp/wp-test-runner/build/wp-includes/plugin.php:206
/tmp/wp-test-runner/build/wp-includes/class-wp-block.php:237
/tmp/wp-test-runner/build/wp-includes/class-wp-block.php:211
/tmp/wp-test-runner/build/wp-includes/blocks.php:721
/tmp/wp-test-runner/tests/phpunit/tests/blocks/block-context.php:132

I'll add additional hosts as well, if I find them when looking through the results.

Will reach out to GoDaddy about the version of libxml, too, to see whether it's a custom compile as mentioned in this PR or not.

I noticed that both hosts in question have redhat notes in the environment info reported, so this makes me think it might be a standard CentOS package.

Either way, since there are two hosts with this issue that we know of already, I think it'd be a good idea to fix / add backcompat for this for 5.6, since there are likely others on the long tail.

[getsource]

Added PR #26210 that looks to solve the issue with the code in the appropriate location on the core side in the GoDaddy test environment.

It's a port from https://github.com/ampproject/amp-wp/pull/4486/files, which @talldan mentioned above.
The amp-wp plugin is GPL v2: https://github.com/ampproject/amp-wp/blob/develop/LICENSE

[getsource]

After #26192, this code isn't in the project anymore.

This looks to be solved in core now, when merged in https://core.trac.wordpress.org/changeset/49226

It's passing in tests at both GoDaddy and AMIMOTO now.

For anyone coming across this ticket later, libxml2 2.7.6-21 is the newest version of libxml available for CentOS 6, which is supported until the end of November (2020).

Recommend closing the issue.

[talldan]

Thanks @getsource for looking into the issue!