Extending the capability of a C message processing or output node

The types of query that you are likely to want to perform include:

• Obtaining the root element of the required message object
• Accessing the bit stream representation of an element tree
• Navigating or querying the tree by asking for child or sibling elements by name
• Getting the type of the element
• Getting the value of the element

void cniEvaluate( ...               
){                                    
  ...
/* Navigate to the target element */ 
  rootElement = cniRootElement(&rc, message);
  bodyElement = cniLastChild(&rc, rootElement);
  bodyFirstChild = cniFirstChild(&rc, bodyElement);

/* Query the name and value of the target element */
  cniElementName(&rc, bodyFirstChild, (CciChar*)&elementname, sizeof(elementName)); 
  bytes = cniElementCharacterValue(
		&rc, bodyfirstChild, (CciChar*)&eValue, sizeof(eValue));
  ...    
}

For example:

1. To write the incoming message to a new message:

   {
     ...
     context = cniGetMessageContext(&rc, message)); 
     outMsg = cniCreateMessage(&rc, context)); 
     ...
   }

2. To make a copy of the new message:

   cniCopyElementTree(&rc, sourceElement, targetElement);

3. To modify the value of a target element:

     cniSetElementIntegerValue(&rc, targetElement, L"newValue", 8); 

4. After finalizing and propagating the message, you must delete the output message using the cniDeleteMessage function:

    cniDeleteMessage(&rc, outMsg);

As part of the transformation, you might want to create a new message body. To create a new message body, use one of the following functions, which assign a parser to a message tree folder:

cniCreateElementAsFirstChildUsingParser
cniCreateElementAsLastChildUsingParser
cniCreateElementAfterUsingParser
cniCreateElementBeforeUsingParser

When creating a message body, do not use the following functions because they do not associate an owning parser with the folder:

cniCreateElementAsFirstChild
cniCreateElementAsLastChild
cniCreateElementAfter
cniCreateElementBefore

{
  ...
  sqlExpr = cniSqlCreateStatement(&rc, 
   (NODE_CONTEXT_ST *)context->nodeObject,
   L"DB", CCI_SQL_TRANSACTION_AUTO,
   L"SET OutputRoot.XMLNS.Result[] = (SELECT T.C1 AS Col1 FROM Database.TABLE AS T;");
  ...
  cniSqlSelect(&rc, sqlExpr, localEnvironment, exceptionList, message, outMsg);
  cniSqlDeleteStatement(&rc, sqlExpr);
  ...                                                               
}

Before you propagate a message, decide what message flow data you want to propagate, and which terminal is to receive the data.

1. If the message has changed, finalize the message before you propagate it using the cniFinalize function. For example:

         cniFinalize(&rc, outMsg, CCI_FINALIZE_NONE);
   

2. The terminalObject is derived from a list that the user-defined node maintains itself. To propagate the message to the output terminal, use the cniPropagate function:

     if (terminalObject) {
       if (cniIsTerminalAttached(&rc, terminalObject)) {
         if (rc == CCI_SUCCESS) {
           cniPropagate(&rc, terminalObject, localEnvironment, exceptionList, outMsg);
         }
       }

   In the above example, the cniIsTerminalAttached function is used to test whether the message can be propagated to the specified terminal. If you do not use the cniIsTerminalAttached function and the terminal is not attached to another node by a connector, the message is not propagated and no warning message is returned. Use the cniIsTerminalAttached function to prevent this error occurring.

3. If you created a new output message using cniCreateMessage, after propagating the message, delete the output message using the cniDeleteMessage function:

    cniDeleteMessage(&rc, outMsg);

The bit stream can then be accessed and written to an output device. Write the message to a bit stream using the cniWriteBuffer function. For example:

{
  ...
  cniWriteBuffer(&rc, message);
  writeToDevice(cniBufferPointer(&rc, message), cniBufferSize(&rc, message));
  ...                                                               
}

In this example, the method writeToDevice is a user-written method which writes a bit stream to an output device.