Writing Handler Functions
*************************

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   http://www.apache.org/licenses/LICENSE-2.0

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.. default-domain:: c

The handler function is the key component of a continuation. It is
supposed to examine the event and event data, and then do something
appropriate. The probable action might be to schedule another event for
the continuation to received, to open up a connection to a server, or
simply to destroy itself.

The continuation's handler function is a function of type
:type:`TSEventFunc`. Its arguments are a continuation, an event, and a
pointer to some data (this data is passed to the continuation by the
caller - do not confuse this data with the continuation's own data,
associated by :func:`TSContDataSet`). When the continuation is called back,
the continuation and an event are passed to the handler function. The
continuation is a handle to the same continuation that is invoked. The
handler function typically has a switch statement to handle the events
it receives:

.. code-block:: c

   static int some_handler (TScont contp, TSEvent event, void *edata)
   {
      // .....
      switch(event) {
         case TS_EVENT_SOME_EVENT_1:
            do_some_thing_1;
            return;
         case TS_EVENT_SOME_EVENT_2:
            do_some_thing_2;
            return;
         case TS_EVENT_SOME_EVENT_3:
            do_some_thing_3;
            return;
         default: break;
      }
      return 0;
   }

.. caution::

   You might notice that a continuation cannot determine if more events are
   "in flight" toward it. Do not use :func:`TSContDestroy` to delete a
   continuation before you make sure that all incoming events, such as
   those sent because of :func:`TSHttpTxnHookAdd`, have been handled.

The following table lists events and the corresponding type of
`void* data` passed to handler functions:

============================================ =========================================== ==========================
Event                                        Event Sender                                Data Type
============================================ =========================================== ==========================
:data:`TS_EVENT_HTTP_READ_REQUEST_HDR`       :data:`TS_HTTP_READ_REQUEST_HDR_HOOK`       :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_OS_DNS`                 :data:`TS_HTTP_OS_DNS_HOOK`                 :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_SEND_REQUEST_HDR`       :data:`TS_HTTP_SEND_REQUEST_HDR_HOOK`       :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_READ_CACHE_HDR`         :data:`TS_HTTP_READ_CACHE_HDR_HOOK`         :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_READ_RESPONSE_HDR`      :data:`TS_HTTP_READ_RESPONSE_HDR_HOOK`      :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_SEND_RESPONSE_HDR`      :data:`TS_HTTP_SEND_RESPONSE_HDR_HOOK`      :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_SELECT_ALT`             :data:`TS_HTTP_SELECT_ALT_HOOK`             :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_TXN_START`              :data:`TS_HTTP_TXN_START_HOOK`              :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_TXN_CLOSE`              :data:`TS_HTTP_TXN_CLOSE_HOOK`              :type:`TSHttpTxn`
:data:`TS_EVENT_HTTP_SSN_START`              :data:`TS_HTTP_SSN_START_HOOK`              :type:`TSHttpSsn`
:data:`TS_EVENT_HTTP_SSN_CLOSE`              :data:`TS_HTTP_SSN_CLOSE_HOOK`              :type:`TSHttpSsn`
:data:`TS_EVENT_NONE`
:data:`TS_EVENT_CACHE_LOOKUP_COMPLETE`       :data:`TS_HTTP_CACHE_LOOKUP_COMPLETE_HOOK`  :type:`TSHttpTxn`
:data:`TS_EVENT_IMMEDIATE`                   :func:`TSVConnClose`
                                             :func:`TSVIOReenable`
                                             :func:`TSContSchedule`
:data:`TS_EVENT_IMMEDIATE`                   :data:`TS_HTTP_REQUEST_TRANSFORM_HOOK`
:data:`TS_EVENT_IMMEDIATE`                   :data:`TS_HTTP_RESPONSE_TRANSFORM_HOOK`
:data:`TS_EVENT_CACHE_OPEN_READ`             :func:`TSCacheRead`                         Cache VC
:data:`TS_EVENT_CACHE_OPEN_READ_FAILED`      :func:`TSCacheRead`                         TS_CACHE_ERROR code
:data:`TS_EVENT_CACHE_OPEN_WRITE`            :func:`TSCacheWrite`                        Cache VC
:data:`TS_EVENT_CACHE_OPEN_WRITE_FAILED`     :func:`TSCacheWrite`                        TS_CACHE_ERROR code
:data:`TS_EVENT_CACHE_REMOVE`                :func:`TSCacheRemove`
:data:`TS_EVENT_CACHE_REMOVE_FAILED`         :func:`TSCacheRemove`                       TS_CACHE_ERROR code
:data:`TS_EVENT_NET_ACCEPT`                  :func:`TSNetAccept`                         :type:`TSNetVConnection`
                                             :func:`TSHttpTxnServerIntercept`
                                             :func:`TSHttpTxnIntercept`
:data:`TS_EVENT_NET_ACCEPT_FAILED`           :func:`TSNetAccept`
                                             :func:`TSHttpTxnServerIntercept`
                                             :func:`TSHttpTxnIntercept`
:data:`TS_EVENT_HOST_LOOKUP`                 :func:`TSHostLookup`                        :type:`TSHostLookupResult`
:data:`TS_EVENT_TIMEOUT`                     :func:`TSContSchedule`
:data:`TS_EVENT_ERROR`
:data:`TS_EVENT_VCONN_READ_READY`            :func:`TSVConnRead`                         :type:`TSVIO`
:data:`TS_EVENT_VCONN_WRITE_READY`           :func:`TSVConnWrite`                        :type:`TSVIO`
:data:`TS_EVENT_VCONN_READ_COMPLETE`         :func:`TSVConnRead`                         :type:`TSVIO`
:data:`TS_EVENT_VCONN_WRITE_COMPLETE`        :func:`TSVConnWrite`                        :type:`TSVIO`
:data:`TS_EVENT_VCONN_EOS`                   :func:`TSVConnRead`                         :type:`TSVIO`
:data:`TS_EVENT_NET_CONNECT`                 :func:`TSNetConnect`                        :type:`TSVConn`
:data:`TS_EVENT_NET_CONNECT_FAILED`          :func:`TSNetConnect`                        :type:`TSVConn`
:data:`TS_EVENT_HTTP_CONTINUE`
:data:`TS_EVENT_HTTP_ERROR`
:data:`TS_EVENT_MGMT_UPDATE`                 :func:`TSMgmtUpdateRegister`
============================================ =========================================== ==========================

The continuation functions are listed below:

-  :func:`TSContCall`
-  :func:`TSContCreate`
-  :func:`TSContDataGet`
-  :func:`TSContDataSet`
-  :func:`TSContDestroy`
-  :func:`TSContMutexGet`
-  :func:`TSContSchedule`
