WP_REST_Attachments_Controller::create_item_permissions_check() WordPress Method

	public function create_item_permissions_check( $request ) {
		$ret = parent::create_item_permissions_check( $request );

		if ( ! $ret || is_wp_error( $ret ) ) {
			return $ret;
		}

		if ( ! current_user_can( 'upload_files' ) ) {
			return new WP_Error(
				'rest_cannot_create',
				__( 'Sorry, you are not allowed to upload media on this site.' ),
				array( 'status' => 400 )
			);
		}

		// Attaching media to a post requires ability to edit said post.
		if ( ! empty( $request['post'] ) && ! current_user_can( 'edit_post', (int) $request['post'] ) ) {
			return new WP_Error(
				'rest_cannot_edit',
				__( 'Sorry, you are not allowed to upload media to this post.' ),
				array( 'status' => rest_authorization_required_code() )
			);
		}

		return true;
	}