How to serialize a Gutenberg block from block attributes in PHP?

Question

I am writing a migration script which has to read the post_content of posts and then dynamically change some attributes of some custom Gutenberg blocks.

I was able to read the post_content and then convert them into block objects by using the parse_blocks function. I was also able to dynamically change the attributes of the custom blocks by manipulating the block objects.

But I am not able to convert these block objects into the special HTML comments that Gutenberg uses to serialize them so that I can update the post_content.

I found that the PHP part of WordPress core only has parse_blocks function to parse the special HTML comments into block objects and render_block function to render the blocks, but there is no serialize_block function.

I found that in JavaScript there is a function called serializeBlock which does this. But is there an equivalent of it in PHP which I can call from my migration scripts?

Answer 1

This markup is generated on the js side of things and saved in the content of the block editor, which is why there doesn't seem to be a native PHP function for this.

However, I found a PHP method that does exactly this in an "experimental" class in the Gutenberg plugin. You can see this here: https://github.com/WordPress/gutenberg/blob/master/lib/class-experimental-wp-widget-blocks-manager.php#L265

You could add it as a method in your own class or convert to a standard function like so:

/**
 * Serializes a block.
 *
 * @param array $block Block object.
 * @return string String representing the block.
 */
function serialize_block( $block ) {
    if ( ! isset( $block['blockName'] ) ) {
        return false;
    }
    $name = $block['blockName'];
    if ( 0 === strpos( $name, 'core/' ) ) {
        $name = substr( $name, strlen( 'core/' ) );
    }
    if ( empty( $block['attrs'] ) ) {
        $opening_tag_suffix = '';
    } else {
        $opening_tag_suffix = ' ' . json_encode( $block['attrs'] );
    }
    if ( empty( $block['innerHTML'] ) ) {
        return sprintf(
            '<!-- wp:%s%s /-->',
            $name,
            $opening_tag_suffix
        );
    } else {
        return sprintf(
            '<!-- wp:%1$s%2$s -->%3$s<!-- /wp:%1$s -->',
            $name,
            $opening_tag_suffix,
            $block['innerHTML']
        );
    }
}

Answer 2

March 2020 update: Looks like serialize_block() is included with WP since 5.3.1, though i think it's undocumented right now. Here's the source on Trac. The docstring says:

/* [...]
 *
 * Returns the content of a block, including comment delimiters, serializing all
 * attributes from the given parsed block.
 *
 * This should be used when preparing a block to be saved to post content.
 * Prefer `render_block` when preparing a block for display. Unlike
 * `render_block`, this does not evaluate a block's `render_callback`, and will
 * instead preserve the markup as parsed.
 */

It seems to work fine from a few simple tests I did, but I'm not sure if it's intended for public usage yet, because there's also this Trac ticket with a different implementation (marked as "awaiting review" as of 2020.03.20): #47375 - Blocks API: Add server-side serialize_block()