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.. include:: ../../common.defs

.. _admin-plugins-webp-transform:

Webp Transform Plugin
*********************

This plugin converts jpeg and png images and transforms them into webp format for browsers that support webp.
Also, the plugin converts webp images and transforms them to jpeg for browsers that don't support webp
All response with content-type 'image/jpeg' or 'image/png' will go through the transform.
Content-type is changed to 'image/webp' or 'image/jpeg' on successful transformation.

Installation
============

Add the following line to :file:`plugin.config`::

    webp_transform.so [convert_to_jpeg] [convert_to_webp] [max_buffer_size=<size>]


Plugin Arguments
================

The plugin is configured with space-separated arguments. All are optional.

``convert_to_webp``
    Convert ``image/jpeg`` and ``image/png`` responses to ``image/webp`` for
    clients that advertise ``image/webp`` in their ``Accept`` header.

``convert_to_jpeg``
    Convert ``image/webp`` responses to ``image/jpeg`` for clients that do not
    advertise ``image/webp``.

    If neither ``convert_to_webp`` nor ``convert_to_jpeg`` is given, both
    conversions are enabled.

``max_buffer_size=<size>``
    The maximum size of a single response body the plugin will buffer in memory
    before handing it to ImageMagick, which bounds the memory a large image
    response can consume. ``<size>`` is a byte count with an optional ``K``,
    ``M``, or ``G`` suffix (1024-based), for example ``max_buffer_size=32M``.
    The default is 16 MiB.

    There are two distinct over-limit behaviors, depending on whether the size
    is known before the body is read:

    * If the origin advertises a ``Content-Length`` greater than the limit, the
      transform is declined up front and the original response is passed through
      to the client unchanged.

    * If the size is not known in advance (for example a chunked response with
      no usable ``Content-Length``), the body is buffered until it exceeds the
      limit. At that point the transform cannot complete and produces no body,
      so the client receives a ``502 Bad Gateway`` rather than a pass-through of
      the original bytes.


Note
====

This plugin only supports jpeg and png and requires Magick++ from ImageMagick.
Other image formats can easily be supported.

In addition to ``max_buffer_size``, the plugin sets fixed ImageMagick decode
resource limits (image dimensions, pixel-cache memory, and disk) so that a
small image declaring very large dimensions cannot decode into an oversized
pixel buffer. An image that exceeds those limits is passed through in its
original format rather than converted.