Writing Handler Functions

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 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 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:

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 TSContDestroy() to delete a continuation before you make sure that all incoming events, such as those sent because of TSHttpTxnHookAdd(), have been handled.

Caution

TS_HTTP_SEND_REQUEST_HDR_HOOK may callback several times when the OS crashed. Be careful to use functions such as TSContDestroy in TS_HTTP_SEND_REQUEST_HDR_HOOK hook.

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

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

The continuation functions are listed below: