Preprocessing and Postprocessing

The PyOPC XDAServer class automatically parses incoming SOAP messages and creates appropriate PyOPC objects, which represent the incoming message. After that, the preprocessing stage prepares and handles some of the following options of the outgoing message:

RcvTime:

This option is set to the time, the SOAP message was received by the server.

ClientRequestHandle:

The content of the incoming ClientRequestHandle is automatically copied to the outgoing message.

RevisedLocaleID:

If the requested locale is not available, the server automatically chooses the first available locale and returns it with this options.

ServerState:

This option is set to the ServerState attribute of the server class, the default is ``running''.

After this stage, the server operation methods are executed. Therefore the data from the preprocessing stage is available in these methods and may be modified. For instance, the read operation may check for the option ``RevisedLocaleID'' in the outgoing message and set it to a different locale.

After the server operations are finished, the PyOPC objects, which represent the incoming and outgoing SOAP messages is handed over to the postprocessing stage, which handles and modifies the following options:

Unhandled Items:

As denoted above, the incoming and outgoing OPC items are stored in the ItemPairHolder object. The preprocessing stage will create this object, which contains an incoming ItemContainer object and an associated, empty outgoing ItemContainer object. The operations should then fill this outgoing item with appropriate data. If, however, the outgoing ItemContainer object is still empty¹⁵ in the postprocessing stage, an error of the type ``PYO_E_EMPTYITEM'' is associated with it, denoting that the item contains no data.

ErrorText:

If ReturnErrorText is set to false in the request message, any error text in the outgoing message is deleted. Otherwise the error text will be kept, and if there is none in the outgoing message, it will be set to a blank string.

DiagnosticInfo:

If ReturnDiagnosticInfo is set to false or is omitted in the request message, any diagnostic info in the outgoing message is deleted. Otherwise the diagnostic info will be kept, and if there is none in the outgoing message, it will be set to a blank string.

Timestamp:

If ReturnItemTime is set to false or is omitted in the request message, any item-related timestamp in the outgoing message is deleted. Otherwise the timestamp will be kept, and if there is none in the outgoing message, it will be set to the current time.

ItemPath/ItemName:

If ReturnItemPath/Name is set to false or is omitted in the request message, any ItemPath/Name in the outgoing message is deleted. Otherwise the ItemPath/Name will be kept, and if there is none in the outgoing message, it will be set to a blank string.

ClientItemHandle:

The ClientItemHandle of each incoming item is copied to the according outgoing item.

ReplyTime:

The ReplyTime in the outgoing message is set to the current time, unless it has not been already set a previous server method.