WP_REST_Posts_Controller::get_item

	public function get_item( $request ) {
		$post = $this->get_post( $request['id'] );
		if ( is_wp_error( $post ) ) {
			return $post;
		}

		$data     = $this->prepare_item_for_response( $post, $request );
		$response = rest_ensure_response( $data );

		if ( is_post_type_viewable( get_post_type_object( $post->post_type ) ) ) {
			$response->link_header( 'alternate', get_permalink( $post->ID ), array( 'type' => 'text/html' ) );
		}

		return $response;
	}