Array Filter Converting JSON Data to Object

[kevinfodness]

Summary

The array_filter call here

wp-rest-blocks/src/Data.php

Line 49 in f0c2806

return array_filter(

can cause the resulting data to become encoded in JSON as an object instead of an array if any elements other than just the last one are filtered out by the array_filter call.

Description

In PHP, when using array_filter, elements are removed from the array but the array is not re-indexed by default. When passing a non-sequentially-indexed array to json_encode, it encodes the element as an object with the numerical keys cast to strings. For example:

echo json_encode( array_filter( [ 'a', 'b', 'c' ], fn ( $item ) => 'b' !== $item ) );

Yields:

{"0":"a","2":"c"}

Impact

If the array_filter call linked above removes an item at the beginning or in the middle of the array, the data type of the block_data field changes from an array to an object, and any code that expects it to be an array will fail, especially JavaScript.

Resolution

In order to solve this problem, the array_filter call should be wrapped in a call to array_values which will cause PHP to renumber the array.