Decoding a Series of Messages Using the C++ Control Class Interface

---

The above example is fine as a sample for decoding a single message, but what happens in the more typical scenario of having a long-running loop that continuously decodes messages? The logic shown above would not be optimal from a performance standpoint because of the constant creation and destruction of the message processing objects. It would be much better to create all of the required objects outside of the loop and then reuse them to decode and process each message.

A code fragment showing a way to do this is as follows:

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

 
    main ()
 
    {
 
        OSOCTET msgbuf[1024];
 
        ASN1TAG   msgtag;
 
        int       msglen, status;
 

 
        // Create message buffer, ASN1T, and ASN1C objects
 

 
        ASN1BERDecodeBuffer decodeBuffer (msgbuf, len);
 
        ASN1T_PersonnelRecord employeeData;
 
        ASN1C_PersonnelRecord employee (decodeBuffer, employeeData);
 

 
        for (;;) {
 

          .. logic to read message into msgbuf ..
 

 
          status = decodeBuffer.ParseTagLen (msgtag, msglen);
 

 
          if (status != 0) {
 
            // handle error
 
            ...
 
          }
 

 
         // Now switch on initial tag value to determine what type of 
 
         // message was received..
 

 
         switch (msgtag)
 
         {
 
           case TV_PersonnelRecord:  // compiler generated constant
 
           {
 
              if ((status = employee.Decode ()) == 0)
 
              {
 
                 // decoding successful, data in employeeData
 

 
                 process received data..
 
              }
 
              else
 
                 error processing...
 
           }
 
           break;
 

 
           default:
 
              // handle unknown message type here
 

 
          }  // switch
 

 
          // Need to reinitialize objects for next iteration
 

 
          if (!isLastIteration) employee.memFreeAll ();
 

 
        }  // end of loop
 

This is quite similar to the first example. Note that we have pulled the ASN1T_Employee and ASN1C_Employee object creation logic out of the switch statement and moved it above the loop. These objects can now be reused to process each received message.

The only other change was the call to employee.memFreeAll that was added at the bottom of the loop. Since we can't count on the objects being deleted to automatically release allocated memory, we need to do it manually. This call will free all memory held within the decoding context. This will allow the loop to start again with no outstanding memory allocations for the next pass.

If the buffer already contains multiple BER messages encoded back-to-back then it is necessary to modify the buffer pointer in each iteration. The getByteIndex method should be used at the end of loop to get the current offset in the buffer. This offset should be used with the decode buffer object's setBuffer method call at the beginning of the loop to determine the correct buffer pointer and length:

        OSUINT32 offset = 0;
 
        for ( ; offset < msglen;) {
 

// set buffer pointer and its length to decode

           decodeBuffer.setBuffer (&msgbuf[offset], msglen - offset);
 
           int curlen = (int)(msglen - offset);
 

 
           status = decodeBuffer.ParseTagLen (msgtag, curlen);
 

 
           if (status != 0) {
 
               // handle error
 
               ...
 
           }
 

 
           // Now switch on initial tag value to determine what type of 
 
           // message was received..
 

 
           switch (msgtag)
 
           {
 
              case TV_PersonnelRecord:  // compiler generated constant
 
              {
 
                 if ((status = employee.Decode ()) == 0)
 
                 {
 
                    // decoding successful, data in employeeData
 

 
                    process received data..
 
                 }
 
                 else
 
                    error processing...
 
               }
 
               break;
 

 
             default:
 
               // handle unknown message type here
 

 
           }  // switch
 

 
           // get new offset
 
           offset += decodeBuffer.getByteIndex ();
 

 
           // Need to reinitialize objects for next iteration (if it is not
 
           // last iteration)
 

 
           if (offset < msglen) employee.memFreeAll ();
 

 
        }  // end of loop