[wp-trac] [WordPress Trac] #38715: Facilitate posts storing raw JSON in post_content by short-circuiting KSES and other filters

[WordPress Trac]

#38715: Facilitate posts storing raw JSON in post_content by short-circuiting KSES
and other filters
-------------------------------+----------------------------
 Reporter:  westonruter        |      Owner:
     Type:  enhancement        |     Status:  new
 Priority:  normal             |  Milestone:  Future Release
Component:  Posts, Post Types  |    Version:
 Severity:  normal             |   Keywords:
  Focuses:                     |
-------------------------------+----------------------------
 When attempting to store arbitrary JSON in WordPress, the `post_content`
 field is the logical choice. Using `post_content` to store arbitrary JSON
 instead of postmeta is more performant and it also means that the JSON
 content will automatically get support for revisions.

 Storing JSON is done in core now for `customize_changeset` posts and it is
 done in the `widget_instance` post type in the Customize Widgets Plus
 plugin. In both cases, however, there are challenges when storing the JSON
 due to filters that may apply on `content_save_pre`. In particular, the
 KSES filters will apply on the `post_content` and strip out markup that is
 intended to be contained within JSON strings. The solution taken by
 changesets is to wrap the updates to the `customize_changeset` post type
 by the `\WP_Customize_Manager::save_changeset_post()` method. Before this
 method calls `wp_update_post()`/`wp_insert_post()` it suspends the KSES
 filters temporarily:

 {{{#!php
 <?php
 $has_kses = ( false !== has_filter( 'content_save_pre',
 'wp_filter_post_kses' ) );
 if ( $has_kses ) {
         kses_remove_filters(); // Prevent KSES from corrupting JSON in
 post_content.
 }
 wp_update_post( /*...*/ );
 if ( $has_kses ) {
         kses_init_filters();
 }
 }}}

 This works, however it is ugly. It also means that post updates via WP-CLI
 and via the REST API won't work as expected because the filters won't be
 suspended as in this wrapper method.

 One idea is that we could introduce a new `post_type_support` for
 `json_content`, and when the post type supports that, it could bypass any
 `content_save_pre` filters applying.

 See also #15515.

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Ticket URL: <https://core.trac.wordpress.org/ticket/38715>
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