..  include:: /Includes.rst.txt

..  _crawlers:

========
Crawlers
========

The extension uses crawlers to visit all URLs configured for cache
warmup. While visiting a URL, the appropriate page cache gets warmed.
Learn more about which crawlers are available by default and how to
implement a custom crawler on this page.

..  php:namespace:: EliasHaeussler\CacheWarmup\Crawler

..  php:interface:: CrawlerInterface

    Interface for crawlers used to crawl and warm up URLs.

    ..  php:method:: crawl($urls)

        Crawl a given list of URLs.

        :param array $urls: List of URLs to be crawled.
        :returntype: EliasHaeussler\\CacheWarmup\\Result\\CacheWarmupResult

..  _default-crawlers:

Default crawlers
================

The extension ships with two default crawlers:

-   :php:class:`EliasHaeussler\\Typo3Warming\\Crawler\\ConcurrentUserAgentCrawler`:
    Used for cache warmup triggered within the **TYPO3 backend**
-   :php:class:`EliasHaeussler\\Typo3Warming\\Crawler\\OutputtingUserAgentCrawler`:
    Used for cache warmup executed from the **command-line**

Both crawlers use a custom `User-Agent` header for all warmup
requests. By using this custom header, it is possible to exclude
warmup requests from the statistics of analysis tools, for example.
The header is generated by a HMAC hash of the string
`TYPO3/tx_warming_crawler`.

The generated header value can be copied form the cache warmup modal
in the TYPO3 backend. Alternatively, a command `warming:showuseragent`
is available which can be used to read the current `User-Agent` header.

..  _implement-a-custom-crawler:

Implement a custom crawler
==========================

..  _available-interfaces:

Available interfaces
--------------------

The actual cache warmup is done via the library
`eliashaeussler/cache-warmup <https://github.com/eliashaeussler/cache-warmup>`__.
It provides the
:php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\CrawlerInterface`,
which must be implemented when developing your own crawler. There is
also a
:php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\VerboseCrawlerInterface`
that redirects user-oriented output to an instance of
:php:interface:`Symfony\\Component\\Console\\Output\\OutputInterface`.

..  _configurable-crawlers:

Configurable crawlers
---------------------

Custom crawlers can also implement the
:php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\ConfigurableCrawlerInterface`,
allowing users to configure warmup requests themselves.

..  seealso::

    `Feature #59 - Introduce configurable crawlers <https://github.com/eliashaeussler/cache-warmup/pull/59>`__
    of `eliashaeussler/cache-warmup` library

..  _steps-to-implement-a-new-crawler:

Steps to implement a new crawler
--------------------------------

..  rst-class:: bignums

1.  Create a new crawler

    The new crawler must implement one of the following interfaces:

    -   :php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\CrawlerInterface`
    -   :php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\VerboseCrawlerInterface`
    -   :php:interface:`EliasHaeussler\\CacheWarmup\\Crawler\\ConfigurableCrawlerInterface`

2.  Configure the new crawler

    Add the new crawler to the :ref:`extension configuration <extension-configuration>`.
    Note that you should configure either the `crawler` or
    `verboseCrawler` option, depending on what interface you have
    implemented.

3.  Flush system caches

    Finally, flush all system caches to ensure the correct crawler
    class is used for further cache warmup requests.

..  seealso::
    View the sources on GitHub:

    -   `CrawlerInterface <https://github.com/eliashaeussler/cache-warmup/blob/main/src/Crawler/CrawlerInterface.php>`__
    -   `ConfigurableCrawlerInterface <https://github.com/eliashaeussler/cache-warmup/blob/main/src/Crawler/ConfigurableCrawlerInterface.php>`__
    -   `VerboseCrawlerInterface <https://github.com/eliashaeussler/cache-warmup/blob/main/src/Crawler/VerboseCrawlerInterface.php>`__
    -   `ConcurrentUserAgentCrawler <https://github.com/eliashaeussler/typo3-warming/blob/main/Classes/Crawler/ConcurrentUserAgentCrawler.php>`__
    -   `OutputtingUserAgentCrawler <https://github.com/eliashaeussler/typo3-warming/blob/main/Classes/Crawler/OutputtingUserAgentCrawler.php>`__