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[online_image] support HTTP caching #4906

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[online_image] support HTTP caching #4906

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22 changes: 22 additions & 0 deletions components/online_image.rst
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Expand Up @@ -66,6 +66,28 @@ Automations

- **on_download_finished** (*Optional*, :ref:`Automation <automation>`): An automation to perform when the image has been successfully downloaded.

The variable ``cached`` is a boolean available in :ref:`lambdas <config-lambda>` that indicates cache status:
- ``true`` if the image was loaded from cache (cache hit).
- ``false`` if the image was freshly downloaded (cache miss).

Caching follows standard HTTP mechanisms (see `HTTP caching <https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching>`_), utilizing the ``Last-Modified`` and ``ETag`` headers.

For example:

.. code-block:: yaml

online_image:
- url: "https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/PNG_transparency_demonstration_1.png/280px-PNG_transparency_demonstration_1.png"
format: png
id: my_online_image
on_download_finished:
lambda: |-
if (cached) {
ESP_LOGD("online_image", "Cache hit: using cached image");
} else {
ESP_LOGD("online_image", "Cache miss: fresh download");
}

A good example for that is to update the display component after the download succeeded.

- **on_error** (*Optional*, :ref:`Automation <automation>`): An automation to perform when an error happened during download or decode.
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