Updating metadata via the REST API fails when sanitized values match existing values

[bradyvercher]

WP_REST_Meta_Fields::update_meta_value() checks incoming values to make sure they don't match the existing value, otherwise update_metadata() will return false to prevent extra SQL queries.

However, the check in update_metadata() sanitizes values before doing the comparison, while the method in the REST controller does not, which causes the API request to fail when a meta sanitization callback alters the incoming value and causes it to match the existing value.

[mfolkeseth]

I have a use case which I would like to add to this ticket. If the incoming meta value is a stringified javascript object (JSON), this if check will fail because the incoming meta value is wp_slash-ed and old value is not

[dcavins]

Note that #42069 is related.

[MattGeri]

Ticket #42069 solves the additional use-case reported by @mfolkeseth. I'd suggest that becomes the ticket to get merged.

[boonebgorges]

I'd like to flag this as a Gutenberg blocker, because of the following situation:

1. You have a post with more than one block that uses post meta attributes
2. One or more of those blocks save their data as a JSON-encoded string, as recommended in the documentation ​https://wordpress.org/gutenberg/handbook/block-api/attributes/#considerations
3. You save the post without modifying the data in one or more of the blocks

Because the REST API uses *slashed* data to compare with the existing values, but get_metadata() returns *unslashed* data, most JSON-encoded strings will look "new" to the REST API https://core.trac.wordpress.org/browser/tags/4.9.8/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php?marks=299,301#L287 But update_metadata() correctly compares unslashed-to-unslashed values, so returns false. Not only does this cause an "Updating failed" notice in Gutenberg, but because of the way that the update_value() method returns early out of the foreach() loop, blocks further down the page are not processed. https://core.trac.wordpress.org/browser/tags/4.9.8/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php?marks=131,163-165#L129

[dcavins]

Replying to boonebgorges:
Boone, I'd like to add a test case to the tests in #42069 to cover this case. I added a case using the value

json_encode ( array(
  "one" => "Someone's Text/Value",
  "two" => 2,
  "three" => array( 1, 1, 2, 3, 5 ),
) );

but it appears to pass without the suggested fix. Can you suggest a string or encoded item that currently fails to update via the REST API that I can add to the test cases?

Thanks!

[TimothyBlynJacobs]

Closing as a duplicate of #42069 to consolidate discussion on that ticket.