I think <p> and <br /> are fine for all usecases

includes/class-activitypub.php

@@ -39,6 +39,8 @@ class Activitypub {
 
 		\add_action( 'in_plugin_update_message-' . ACTIVITYPUB_PLUGIN_BASENAME, array( self::class, 'plugin_update_message' ) );
 
+		\add_filter( 'wp_kses_allowed_html', array( self::class, 'allowed_comment_html' ), 15, 2 );
+
 		// register several post_types
 		self::register_post_types();
 	}
@@ -335,6 +337,32 @@ class Activitypub {
 		);
 	}
 
+	/**
+	 * Adds line breaks to the list of allowed comment tags.
+	 *
+	 * @param  array  $allowed_tags Allowed HTML tags.
+	 * @param  string $context      Context.
+	 *
+	 * @return array Filtered tag list.
+	 */
+	public static function allowed_comment_html( $allowed_tags, $context = '' ) {
+		if ( 'pre_comment_content' !== $context ) {
+			// Do nothing.
+			return $allowed_tags;
+		}
+
+		// Add `p` and `br` to the list of allowed tags.
+		if ( ! array_key_exists( 'br', $allowed_tags ) ) {
+			$allowed_tags['br'] = array();
+		}
+
+		if ( ! array_key_exists( 'p', $allowed_tags ) ) {
+			$allowed_tags['p'] = array();
+		}
+
+		return $allowed_tags;
+	}
+
 	/**
 	 * Register the "Followers" Taxonomy
 	 *

includes/collection/class-interactions.php

@@ -82,11 +82,9 @@ class Interactions {
 				return 'inactive';
 			}
 		);
-		\add_filter( 'wp_kses_allowed_html', array( self::class, 'allowed_comment_html' ), 10, 2 );
 
 		$comment = \wp_new_comment( $commentdata, true );
 
-		\remove_filter( 'wp_kses_allowed_html', array( self::class, 'allowed_comment_html' ), 10 );
 		\remove_filter( 'pre_option_require_name_email', '__return_false' );
 
 		// re-add flood control
@@ -132,11 +130,9 @@ class Interactions {
 				return 'inactive';
 			}
 		);
-		\add_filter( 'wp_kses_allowed_html', array( self::class, 'allowed_comment_html' ), 10, 2 );
 
 		$comment = \wp_update_comment( $commentdata, true );
 
-		\remove_filter( 'wp_kses_allowed_html', array( self::class, 'allowed_comment_html' ), 10 );
 		\remove_filter( 'pre_option_require_name_email', '__return_false' );
 
 		// re-add flood control
@@ -208,29 +204,4 @@ class Interactions {
 		$comment_query = new WP_Comment_Query( $args );
 		return $comment_query->comments;
 	}
-
-	/**
-	 * Adds line breaks to the list of allowed comment tags.
-	 *
-	 * @param  array  $allowedtags Allowed HTML tags.
-	 * @param  string $context     Context.
-	 * @return array               Filtered tag list.
-	 */
-	public static function allowed_comment_html( $allowedtags, $context = '' ) {
-		if ( 'pre_comment_content' !== $context ) {
-			// Do nothing.
-			return $allowedtags;
-		}
-
-		// Add `p` and `br` to the list of allowed tags.
-		if ( ! array_key_exists( 'br', $allowedtags ) ) {
-			$allowedtags['br'] = array();
-		}
-
-		if ( ! array_key_exists( 'p', $allowedtags ) ) {
-			$allowedtags['p'] = array();
-		}
-
-		return $allowedtags;
-	}
 }

tests/test-class-activitypub-interactions.php

@@ -47,6 +47,21 @@ class Test_Activitypub_Interactions extends WP_UnitTestCase {
 		);
 	}
 
+	public function create_test_rich_object( $id = 'https://example.com/123' ) {
+		return array(
+			'actor' => $this->user_url,
+			'id' => 'https://example.com/id/' . microtime( true ),
+			'to' => [ $this->user_url ],
+			'cc' => [ 'https://www.w3.org/ns/activitystreams#Public' ],
+			'object' => array(
+				'id'        => $id,
+				'url'       => 'https://example.com/example',
+				'inReplyTo' => $this->post_permalink,
+				'content'   => 'Hello<br />example<p>example</p><img src="https://example.com/image.jpg" />',
+			),
+		);
+	}
+
 	public function test_handle_create_basic() {
 		$comment_id = Activitypub\Collection\Interactions::add_comment( $this->create_test_object() );
 		$comment   = get_comment( $comment_id, ARRAY_A );
@@ -65,6 +80,13 @@ class Test_Activitypub_Interactions extends WP_UnitTestCase {
 		$this->assertEquals( 'activitypub', get_comment_meta( $comment_id, 'protocol', true ) );
 	}
 
+	public function test_handle_create_rich() {
+		$comment_id = Activitypub\Collection\Interactions::add_comment( $this->create_test_rich_object() );
+		$comment   = get_comment( $comment_id, ARRAY_A );
+
+		$this->assertEquals( 'Hello<br />example<p>example</p>', $comment['comment_content'] );
+	}
+
 	public function test_convert_object_to_comment_not_reply_rejected() {
 		$object = $this->create_test_object();
 		unset( $object['object']['inReplyTo'] );