Dynamic Invoke & Dispatch in Python-client/Java-server app

[KLR2002]

Hello,

I wanted to write a simple application to show how dynamic invoke and dispatch works in Ice. I decided to write the client in python and the server in java. I have looked into the docs, but I have no idea how to do it in practice. When I start up the client I get an Ice.OperationNotExistException. Does anyone know how to do this right? (yeah I know that exception handling in the client is a joke but I don't want to deal with that right now).

IceServer.java:

package sr.ice.server;
import com.zeroc.Ice.*;
import java.lang.Exception;

public class IceServer {
	public void t1(String[] args) {
		int status = 0;
		Communicator communicator = null;

		try {

			communicator = Util.initialize(args);

			ObjectAdapter adapter = communicator.createObjectAdapterWithEndpoints("Adapter1", "tcp -h 127.0.0.2 -p 10000 -z : udp -h 127.0.0.2 -p 10000 -z");
            OperationsI operationsServant = new OperationsI();
			adapter.add(operationsServant, new Identity("add", "add"));


			adapter.activate();

			System.out.println("Entering event processing loop...");

			communicator.waitForShutdown();

		} catch (Exception e) {
			e.printStackTrace(System.err);
			status = 1;
		}
		if (communicator != null) {
			try {
				communicator.destroy();
			} catch (Exception e) {
				e.printStackTrace(System.err);
				status = 1;
			}
		}
		System.exit(status);
	}


	public static void main(String[] args) {
		IceServer app = new IceServer();
		app.t1(args);
	}
}

OperationsI.java:

package sr.ice.server;
import Demo.Operations;
import com.zeroc.Ice.Blobject;
import com.zeroc.Ice.Current;
import com.zeroc.Ice.UserException;
import com.zeroc.Ice.OperationNotExistException;

public class OperationsI implements Blobject  {
    @Override
    public Ice_invokeResult ice_invoke(byte[] inParams, Current current) throws UserException {
        if(current.operation.equals("add"))
        {
            com.zeroc.Ice.Communicator communicator = current.adapter.getCommunicator();
            com.zeroc.Ice.InputStream in = new com.zeroc.Ice.InputStream(communicator, inParams);
            in.startEncapsulation();
            int x = in.readInt();
            int y = in.readInt();
            in.endEncapsulation();

            com.zeroc.Ice.OutputStream out = new com.zeroc.Ice.OutputStream(communicator);
            com.zeroc.Ice.Object.Ice_invokeResult r = new com.zeroc.Ice.Object.Ice_invokeResult();

            out.startEncapsulation();
            out.writeInt(x + y);
            out.endEncapsulation();
            r.outParams = out.finished();
            r.returnValue = true;

            return r;
        }
        else
        {
            OperationNotExistException ex = new OperationNotExistException();
            ex.id = current.id;
            ex.facet = current.facet;
            ex.operation = current.operation;
            throw ex;
        }
    }
}

IceClient.py

import Ice
import Demo

with Ice.initialize() as communicator:
    base = communicator.stringToProxy("add/add:tcp -h 127.0.0.2 -p 10000 -z : udp -h 127.0.0.2 -p 10000 -z")
    demo = Demo.OperationsPrx.checkedCast(base)


    if not demo:
        raise RuntimeError("Invalid proxy")

    try:
        [ok, outParams] = demo.ice_invoke("add", Ice.OperationMode.Normal, [3, 5])

        if ok:
            print("add result:", outParams.returnValue)
        else:
            print("error")

    except Ice.LocalException as ex:
        print("exception")

slice file:

#ifndef OP_ICE
#define OP_ICE

module Demo
{
  interface Operations {
        int add(int a, int b);
   };
};

#endif

[pepone]

It seems that the issue is related to the checkedCast invocation in the following code:

demo = Demo.OperationsPrx.checkedCast(base);

The checkedCast method makes a remote invocation to the ice_isA operation, which is a part of the Ice::Object interface.

Your Blobject implementation is throwing an ObjectNotExistException because it doesn't support the required operation. I would suggest replacing the checkedCast call with uncheckedCast, which does not make any remote calls. This approach is perfectly safe for your use case and should resolve the problem.

Cheers,
Jose

[KLR2002]

Thanks for the reply, indeed now the error is gone. Now it shows me the error that the 3rd argument in ice_invoke should be bytes not list, which is what I expected. Do you know how to prepare the data in python?

in docs there is an example for java:

com.zeroc.Ice.OutputStream out = new com.zeroc.Ice.OutputStream(communicator);
  out.startEncapsulation();
  int x = 100, y = -1;
  out.writeInt(x);
  out.writeInt(y);
  out.endEncapsulation();
  byte[] inParams = out.finished();

but there is nothing like OutputStream for python Ice package and i'm confused

[KLR2002]

I thought it might be enough to pass bytes([3,5]), but I get an exception

exception ::Ice::EncapsulationException
{
    reason = 
}

[bernardnormier]

Do you know how to prepare the data in python?

That's the difficulty. You want to build a byte string with your Slice-encoded arguments, but Ice for Python does not provide "streaming interfaces": https://doc.zeroc.com/ice/3.7/client-server-features/dynamic-ice/streaming-interfaces

For your simple example, you could read about the Slice encoding and encapsulation format and create this byte string "by hand". But for anything somewhat complex, marshaling by hand is not practical.

Ice for Python (and Ruby, PHP) does not provide these streaming interfaces because of the way Ice for Python (Ruby, PHP) marshals/unmarshals data. The marshaling/unmarshaling is delegated to the underlying C++ code instead of being performed using Python (Ruby, PHP) code.

[KLR2002]

I just gave up and wrote the client in C#, but thanks for the reply