demo-modify.c

This example modifies a field by a configurable factor, affecting its value in the update packet sent between modules and then published onto DataSource

Note

This example has been written using the legacy API.

Sample configuration:

symbols         /DEMO/*
modify-field    Bid
modify-factor   2.0

Source code:

/*
 *    Transformer - Sample Module
 *
 *    Copyright CAPLIN Systems Ltd 2000-2006
 *
 *    This module modifies the value of a field by a certain factor. This
 *    modified value is then published onto DataSource by the Transformer core 
 *
 */


#include "transformer.h"



static char      **symbols       = NULL;
static int         symbols_num   = 0;

static char       *modify_field  = "dBestBid";
static double      modify_factor = 2.0;



static void        demo_recv_update(int feed, ds_data_t *pkt, time_t arr_tim, int id, void *data);



void mod_init(char *module_name)
{
    char         buf[FILENAME_MAX+1];
    int          i;


    /* Add config option for the symbols we want to receive */
    ds_config_add_array_option("symbols","Symbols to process",DS_CONFIG_STR_ARRAY,&symbols,&symbols_num);

    /* Add a config option for which field to modify */
    ds_config_add_option(0,"modify-field","Fieldname to modify",DS_CONFIG_STR,&modify_field);

    /* Add a config option for the modification factor */
    ds_config_add_option(0,"modify-factor","Modification factor",DS_CONFIG_FLOAT,&modify_factor);

    /* Load a config file based on the name of the module */
    snprintf(buf,sizeof(buf),"%s.conf",module_name);
    mod_config_parse_file(buf);

    /* Check whether any symbols are required, if not then log this condition to the main Transformer
       log file
    */
    if ( symbols_num == 0 ) {
        ds_printf_time(rtas_log,"(%s) No symbols required\n",module_name);
        return;
    }

   
    /* Now register an interest in the symbols */
    for ( i = 0; i < symbols_num; i++ ) {
        register_interest(symbols[i],demo_recv_update,0,NULL);
    }

    return;
}



void mod_exit()
{
    int         i;

    /* We have to loop over all known symbols */
    for ( i = 0; i < symbols_num; i++ ) {
        /* Deregister interests in these symbols */
        deregister_interest(symbols[i],demo_recv_update,0,NULL);
    }
 
    return;
}


static void demo_recv_update(int feed, ds_data_t *pkt, time_t arr_tim, int id, void *data)
{
    char         newvalue_buf[256];
    char        *value_str;
    double       value;

    /* If the Transformer is running in broadcast mode i.e. the config option transformer-active
       is not set in transformer.conf then we must indicate that any update received by
       the Transformer from the source of data is sent onto its peers. We can do this
       by setting the SYMBOL_PUBLISH flag on the flags within the Core. We achieve this
       using the symbol_create() function call which creates the object if it doesn't
       exist (it does in this case) and then sets the flags.

       This flag implies that all packets generated by the core for this particular symbol
       are meant to be published (automatically in the case of broadcast, or upon peer
       request for active mode)
    */
    symbol_create(pkt->subject,SYMBOL_PUBLISH);


    /* Pick out the required field within this received update */
    if ( ( value_str = packet_get_field_byname(pkt,modify_field) ) != NULL ) {
        value = atof(value_str);

        /* Now scale the value appropriately */
        value *= modify_factor;

        /* Print the (scaled) value into a buffer */
        snprintf(newvalue_buf,sizeof(newvalue_buf),"%f",value);

        /* Now, update the field in the original packet. This value will then
           be propogated through the subsequent modules in the Transformer system. This
           packet will then be published onto DataSource (if broadcast or active and requested) 
        */
        packet_update_field_byname(pkt,modify_field,newvalue_buf);
      
    }          
    return;
}