WP_REST_Server::is_dispatching()
Method: Returns whether the REST server is currently dispatching / responding to a request.
Source: wp-includes/rest-api/class-wp-rest-server.php:1063
wp_is_rest_endpoint()
Function: Checks whether a REST API endpoint request is currently being handled.
Source: wp-includes/rest-api.php:3332
wp_is_rest_endpoint
Filter Hook: Filters whether a REST endpoint request is currently being handled.
Source: wp-includes/rest-api.php:3353
wp_is_serving_rest_request()
Function: Determines whether WordPress is currently serving a REST API request.
Source: wp-includes/functions.php:4719
wp_get_image_mime()
Function: Returns the real mime type of an image file.
Source: wp-includes/functions.php:3273