doc/sdk/io-guide/guide-to-cache-api.en.rst

Guide to the Cache API
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.. toctree::
   :maxdepth: 2

   guide-to-cache-api/how-to-do-a-cache-write.en
   guide-to-cache-api/how-to-do-a-cache-remove.en
   guide-to-cache-api/errors.en
   guide-to-cache-api/example.en


The cache API enables plugins to read, write, and remove objects in the
Traffic Server cache. All cache APIs are keyed by an object called an
``TSCacheKey``; cache keys are created via ``TSCacheKeyCreate``; keys
are destroyed via ``TSCacheKeyDestroy``. Use ``TSCacheKeyDigestSet`` to
set the hash of the cache key.

Note that the cache APIs differentiate between HTTP data and plugin
data. The cache APIs do not allow you to write HTTP docs in the cache;
you can only write plugin-specific data (a specific type of data that
differs from the HTTP type).

**Example:**

.. code-block:: c

        const unsigned char *key_name = "example key name";

        TSCacheKey key;
        TSCacheKeyCreate (&key);
        TSCacheKeyDigestSet (key, (unsigned char *) key_name , strlen(key_name));
        TSCacheKeyDestroy (key);

How to Do a Cache Read
~~~~~~~~~~~~~~~~~~~~~~

``TSCacheRead`` does not really read - it is used for lookups (see the
sample Protocol plugin). Possible callback events include:

-  ``TS_EVENT_CACHE_OPEN_READ`` - indicates the lookup was successful.
   The data passed back along with this event is a cache vconnection
   that can be used to initiate a read on this keyed data.

-  ``TS_EVENT_CACHE_OPEN_READ_FAILED`` - indicates the lookup was
   unsuccessful. Reasons for this event could be that another
   continuation is writing to that cache location, or the cache key
   doesn't refer to a cached resource. Data payload for this event
   indicates the possible reason the read failed (``TSCacheError``).