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The HTTP transaction functions enable you to set up plugin callbacks to HTTP transactions and obtain/modify information about particular HTTP transactions.

As described in the section on HTTP sessions, an HTTP transaction is an object defined for the lifetime of a single request from a client and the corresponding response from Traffic Server. The TSHttpTxn structure is the main handle given to a plugin for manipulating a transaction's internal state. Additionally, an HTTP transaction has a reference back to the HTTP session that created it.

The sample code below illustrates how to register locally to a transaction and associate data to the transaction.

/*
* Simple plugin that illustrates:
* - how to register locally to a transaction
* - how to deal with data that's associated with a tranaction
*
* Note: for readability, error checking is omitted
*/

#include <ts/ts.h>

#define DBG_TAG "txn"

/* Structure to be associated to txns */
typedef struct {
   int i;
   float f;
   char *s;
} TxnData;

/* Allocate memory and init a TxnData structure */
TxnData *
txn_data_alloc()
{
   TxnData *data;
   data = TSmalloc(sizeof(TxnData));

   data->i = 1;
   data->f = 0.5;
   data->s = "Constant String";
   return data;
}

/* Free up a TxnData structure */
void
txn_data_free(TxnData *data)
{
   TSfree(data);
}

/* Handler for event READ_REQUEST and TXN_CLOSE */
static int
local_hook_handler (TSCont contp, TSEvent event, void *edata)
{
   TSHttpTxn txnp = (TSHttpTxn) edata;
   TxnData *txn_data = TSContDataGet(contp);
   switch (event) {
   case TS_EVENT_HTTP_READ_REQUEST_HDR:
      /* Modify values of txn data */
      txn_data->i = 2;
      txn_data->f = 3.5;
      txn_data->s = "Constant String 2";
      break;

   case TS_EVENT_HTTP_TXN_CLOSE:
      /* Print txn data values */
      TSDebug(DBG_TAG, "Txn data i=%d f=%f s=%s", txn_data->i, txn_data->f, txn_data->s);

      /* Then destroy the txn cont and its data */
      txn_data_free(txn_data);
      TSContDestroy(contp);
      break;

   default:
       TSAssert(!"Unexpected event");
       break;
   }

   TSHttpTxnReenable(txnp, TS_EVENT_HTTP_CONTINUE);
   return 1;
}

/* Handler for event TXN_START */
static int
global_hook_handler (TSCont contp, TSEvent event, void *edata)
{
   TSHttpTxn txnp = (TSHttpTxn) edata;
   TSCont txn_contp;
   TxnData *txn_data;

   switch (event) {
   case TS_EVENT_HTTP_TXN_START:
      /* Create a new continuation for this txn and associate data to it */
      txn_contp = TSContCreate(local_hook_handler, TSMutexCreate());
      txn_data = txn_data_alloc();
      TSContDataSet(txn_contp, txn_data);

      /* Registers locally to hook READ_REQUEST and TXN_CLOSE */
      TSHttpTxnHookAdd(txnp, TS_HTTP_READ_REQUEST_HDR_HOOK, txn_contp);
      TSHttpTxnHookAdd(txnp, TS_HTTP_TXN_CLOSE_HOOK, txn_contp);
      break;

   default:
      TSAssert(!"Unexpected event");
      break;
   }

   TSHttpTxnReenable(txnp, TS_EVENT_HTTP_CONTINUE);
   return 1;
}

void
TSPluginInit (int argc, const char *argv[])
{
   TSCont contp;

   /* Note that we do not need a mutex for this txn since it registers globally
      and doesn't have any data associated with it */
   contp = TSContCreate(global_hook_handler, NULL);

   /* Register gloabally */
   TSHttpHookAdd(TS_HTTP_TXN_START_HOOK, contp);
}

See Adding Hooks for background about HTTP transactions and HTTP hooks, as well as HTTP Hooks and Transactions Also see the [HTTP Transaction State Diagram ](HTTPHooksAndTransactions.html(../http-hooks-and-transactions#HHTTPTxStateDiag) for an illustration of the steps involved in a typical HTTP transaction.

The HTTP transaction functions are: