[fpc-pascal] Web Service Toolkit - Notify the Client

[Michael Van Canneyt]

On Sun, 3 Jun 2007, Johann Glaser wrote:

> Hi!
> 
> I'm going to implement a data logger and a GUI frontend in FreePascal.
> One (daemon) program gets data from a device connected via USB and
> stores it to a file. A second program, the GUI frontend, connects to the
> daemon and can retrieve the measured data and other stuff. Additionally
> it can send commands to change the measurement settings. 
> 
> All this is quite a typical application for RPC, so I plan to use the
> Web Service Toolkit with SOAP.
> 
> Usually the frontend does a remote procedure call to the backend. There
> is one important problem I'm facing now. I want the backend (service
> provider) to notify the frontend (service consumer) as soon as a new
> measurement value has arrived. So this is the reverse direction of
> communication.
> 
> Is this possible? Can you please point me to information how to
> accomplish this?

This is not possible in SOAP, unless you do continuous polling.

I believe there are some Microsoft extensions which allow asynchronous
notifications, but they are not implemented in SOAP and also not in WST.

Michael.