Add pre- and post- content filter

README.md

@@ -1218,6 +1218,99 @@ Direct block HTML can be accessed through `$block['innerHTML']`. This may be use
 
 For another example of how this filter can be used to extend block data, we have implemented a default image block filter in [`src/parser/block-additions/core-image.php`][repo-core-image-block-addition]. This filter is automatically called on `core/image` blocks to add `width` and `height` to image attributes.
 
+---
+
+### `vip_block_data_api__before_parse_post_content`
+
+Modify raw post content before it's parsed by the Block Data API. The `$post_content` provided by this filter is directly what is stored in the post database before any processing occurs.
+
+```php
+/**
+ * Filters content before parsing blocks in a post.
+ *
+ * @param string $post_content The content of the post being parsed.
+ * @param int $post_id Post ID associated with the content.
+ */
+$post_content = apply_filters( 'vip_block_data_api__before_parse_post_content', $post_content, $post_id );
+```
+
+For example, this could be used to modify a block's type before parsing. The code below replaces instances of `test/invalid-block` blocks with `core/paragraph`:
+
+```php
+add_filter( 'vip_block_data_api__before_parse_post_content', 'replace_invalid_blocks' );
+
+function replace_invalid_blocks( $post_content, $post_id ) {
+    return str_replace( 'wp:test/invalid-block', 'wp:paragraph', $post_content );
+}
+
+$html = '
+    <!-- wp:test/invalid-block -->
+    <p>Block content!</p>
+    <!-- /wp:test/invalid-block -->
+';
+
+$content_parser = new ContentParser();
+$result         = $content_parser->parse( $html );
+
+// Evaluates to true
+assertEquals( [
+    [
+        'name'       => 'core/paragraph',
+        'attributes' => [
+            'content' => 'Block content!',
+        ],
+    ],
+], $result['blocks'] );
+```
+
+**Warning**
+
+Be careful with content modification before parsing. In the example above, if a block contained the text "wp:test/invalid-block" outside of a block header, this would also be changed to "wp:paragraph". This is likely not the intent of the code.
+
+All block markup is sensitive to changes, even changes in whitespace. We've added this filter to make the plugin flexible, but any transforms to `post_content` should be done with extreme care. Strongly consider adding tests to any usage of this filter.
+
+---
+
+### `vip_block_data_api__after_parse_blocks`
+
+Modify the Block Data API REST endpoint response.
+
+```php
+/**
+ * Filters the API result before returning parsed blocks in a post.
+ *
+ * @param string $result The successful API result, contains 'blocks' key with an array
+ *                       of block data, and optionally 'warnings' and 'debug' keys.
+ * @param int $post_id Post ID associated with the content.
+ */
+$result = apply_filters( 'vip_block_data_api__after_parse_blocks', $result, $post_id );
+```
+
+This filter is called directly before returning a result in the REST API. Use this filter to add additional metadata or debug information to the API output.
+
+```php
+add_action( 'vip_block_data_api__after_parse_blocks', 'add_block_data_debug_info', 10, 2 );
+
+function add_block_data_debug_info( $result, $post_id ) {
+	$result['debug']['my-value'] = 123;
+
+	return $result;
+}
+```
+
+This would add `debug.my-value` to all Block Data API REST results:
+
+```bash
+> curl https://my.site/wp-json/vip-block-data-api/v1/posts/1/blocks
+
+{
+  "debug": {
+    "my-value": 123
+  },
+  "blocks": [ /* ... */ ]
+}
+```
+
 ## Analytics
 
 **Please note that, this is for VIP sites only. Analytics are disabled if this plugin is not being run on VIP sites.**

src/parser/content-parser.php

@@ -128,6 +128,14 @@ public function parse( $post_content, $post_id = null, $filter_options = [] ) {
 		$parsing_error = false;
 
 		try {
+			/**
+			 * Filters content before parsing blocks in a post.
+			 *
+			 * @param string $post_content The content of the post being parsed.
+			 * @param int $post_id Post ID associated with the content.
+			 */
+			$post_content = apply_filters( 'vip_block_data_api__before_parse_post_content', $post_content, $post_id );
+
 			$blocks = parse_blocks( $post_content );
 			$blocks = array_values( array_filter( $blocks, function ( $block ) {
 				$is_whitespace_block = ( null === $block['blockName'] && empty( trim( $block['innerHTML'] ) ) );
@@ -168,6 +176,15 @@ public function parse( $post_content, $post_id = null, $filter_options = [] ) {
 				'details' => $parsing_error->__toString(),
 			] );
 		} else {
+			/**
+			 * Filters the API result before returning parsed blocks in a post.
+			 *
+			 * @param string $result The successful API result, contains 'blocks'
+			 * key with an array of block data, and optionally 'warnings' and 'debug' keys.
+			 * @param int $post_id Post ID associated with the content.
+			 */
+			$result = apply_filters( 'vip_block_data_api__after_parse_blocks', $result, $post_id );
+
 			return $result;
 		}
 	}