Encoding a Series of Messages Using the C Encode Functions

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A common application of BER encoding is the repetitive encoding of a series of the same type of message over and over again. For example, a TAP3 batch application might read billing data out of a database table and encode each of the records for a batch transmission.

If a user was to repeatedly allocate/free memory and reinitialize the C objects involved in the encoding of a message, performance would suffer. This is not necessary however, because the C objects and memory heap can be reused to allow multiple messages to be encoded. As example showing how to do this is as follows:

    #include employee.h         /* include file generated by ASN1C */
 

 
    main ()
 
    {
 
        const OSOCTET* msgptr;
 
        OSOCTET   msgbuf[1024];
 
        int       msglen;
 
        OSCTXT    ctxt;
 
        PersonnelRecord data;
 

 
        /* Init context structure */
 

 
        if ((stat = rtInitContext (&ctxt)) != 0) {
 
           printf ("rtInitContext failed; stat = %d\n", stat);
 
           return -1;
 
        }
 

 
        /* Encode loop starts here, this will repeatedly use the 
 
         * objects declared above to encode the messages */
 

 
        for (;;) {
 

 
           xe_setp (&ctxt, msgbuf, sizeof(msgbuf));
 

 
           /* logic here to read record from some source (database, 
 
            * flat file, socket, etc.).. */
 

           /* populate structure with data to be encoded */
 

 
           data.name = "SMITH";
 
           ...
 

 
            /* call encode function */
 

 
            if ((msglen = asn1E_PersonnelRecord (&ctxt, &data, ASN1EXPL)) > 0) {
 

 
                /* encoding successful, get pointer to start of message */
 

 
                msgptr = xe_getp (&ctxt);
 

 
                /* do something with the encoded message */
 

 
                ...
 
            }
 
            else
 
               error processing...
 

 
            /* Call rtxMemReset to reset the memory heap for the next
 
             * iteration. Note, all data allocated by rtxMemAlloc will 
 
             * become invalid after this call. */
 

 
            rtxMemReset (&ctxt);
 
        }
 

 
        rtFreeContext (&ctxt);
 
    }
 

 

The rtxMemReset call does not free memory; instead, it marks it as empty so that it may be reused in the next iteration. Thus, all memory allocated by rtxMemAlloc will be overwritten and data will be lost.