doc/developer-guide/api/functions/TSVConnArgs.en.rst

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.. include:: ../../../common.defs
.. default-domain:: c

TSVConnArgs
************

Synopsis
========

.. note::

   This set of API is obsoleted as of ATS v9.0.0, and will be removed with ATS v10.0.0!
   For details of the new APIs, see :ref:`tsuserargs`.


.. code-block:: cpp

    #include <ts/ts.h>

.. function:: TSReturnCode TSVConnArgIndexReserve(const char * name, const char * description, int * arg_idx)
.. function:: TSReturnCode TSVConnArgIndexNameLookup(const char * name, int * arg_idx, const char ** description)
.. function:: TSReturnCode TSVConnArgIndexLookup(int arg_idx, const char ** name, const char ** description)
.. function:: void TSVConnArgSet(TSVConn vc, int arg_idx, void * arg)
.. function:: void * TSVConnArgGet(TSVConn vc, int arg_idx)

Description
===========

Virtual connection objects (API type :c:type:`TSVConn`) support an array of :code:`void *` values that
are controlled entirely by plugins. These are not used in any way by the core. This allows plugins
to store data associated with a specific virtual connection for later retrieval by the same plugin
in a different hook or by another plugin. Because the core does not interact with these values any
cleanup is the responsibility of the plugin.

To avoid collisions between plugins a plugin should first *reserve* an index in the array by calling
:func:`TSVConnArgIndexReserve` passing it an identifying name, a description, and a pointer to an
integer which will get the reserved index. The function returns :code:`TS_SUCCESS` if an index was
reserved, :code:`TS_ERROR` if not (most likely because all of the indices have already been
reserved). Generally this will be a file or library scope global which is set at plugin
initialization. Note the reservation is by convention - nothing stops a plugin from interacting with
a :code:`TSVConn` arg it has not reserved.

To look up the owner of a reserved index use :func:`TSVConnArgIndexNameLookup`. If the :arg:`name` is
found as an owner, the function returns :code:`TS_SUCCESS` and :arg:`arg_index` is updated with the
index reserved under that name. If :arg:`description` is not :code:`nullptr` then it will be updated
with the description for that reserved index. This enables communication between plugins where
plugin "A" reserves an index under a well known name and plugin "B" locates the index by looking it
up under that name.

The owner of a reserved index can be found with :func:`TSVConnArgIndexLookup`. If :arg:`arg_index` is
reserved then the function returns :code:`TS_SUCCESS` and :arg:`name` and :arg:`description` are
updated. :arg:`name` must point at a valid character pointer but :arg:`description` can be
:code:`nullptr`.

Manipulating the array is simple. :func:`TSVConnArgSet` sets the array slot at :arg:`arg_idx` for
the :arg:`vc` to the value :arg:`arg`. Note this sets the value only for the specific
:c:type:`TSVConn`. The values can be retrieved with :func:`TSVConnArgGet` which returns the
specified value. Values that have not been set are :code:`nullptr`.

Hooks
=====

Although these can be used from any hook that has access to a :c:type:`TSVConn` it will generally be
the case that :func:`TSVConnArgSet` will be used in early intervention hooks and
:func:`TSVConnArgGet` in session / transaction hooks. Cleanup should be done on the
:code:`TS_VCONN_CLOSE_HOOK`.

.. rubric:: Appendix

.. note::
   This is originally from `Issue 2388 <https://github.com/apache/trafficserver/issues/2388>`__. It
   has been extended based on discussions with Kees and Leif Hedstrom at the ATS summit.