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Broker ActiveX Control provides five Broker functions to enable publishing and subscription. Publish and subscribe enables an application to send a message (publication) to multiple receivers (subscribers).

This functionality is supported by the native COM interface as well as by the Transaction Object Repository interface (TOR file).

Some examples of publish and subscribe for the native interface are given below.

This document covers the following topics:

• Writing Subscriber Applications

• Writing Publisher Applications

Writing Subscriber Applications

A subscriber receives the publications that are sent by the publisher. Subscribers will only receive publications that are sent after they have subscribed to a topic. Similarly, publishers can only send a publication if at least one subscriber has already subscribed to a topic.

To learn more about a particular topic, see Writing Applications: Publish and Subscribe.

The methods, functions, properties and steps required to operate as subscriber are described here.

Methods

Functions

These will be set in the function property. For all function calls, the UserID, Password (if security Broker), Token and Topic properties must be set.

Properties

Important:
Please check the Error Status regularly; at least after every InvokeBrokerFunction.

To operate as subscriber

1. Set the APIVersion property to 8, the functionality Publish and Subscribe is only available with API version 8 and above.

2. Set the BrokerID property for your EntireX Broker.

3. Set the UserID, Password (if required), Token and Topic properties.

4. Set the Option property to 0 (None).

5. Set the Function property to 9 (Logon). You must be logged on to use the publish-and-subscribe functionality.

6. Call the method InvokeBrokerFunction to perform the logon function. The application has now been logged on to the EntireX Broker.

7. After successful logon to the Broker, set the function property to 19 (subscribe).

8. Call the method InvokeBrokerFunction to subscribe. The application has now been subscribed as a non-durable subscriber for this topic. If you want to be a durable subscriber, set the Option property to Durable when calling the method InvokeBrokerFunction. To learn more about the difference between durable and non-durable subscribers, see Concepts of Persistent Messaging.

9. Set the Wait property to the required value, for example 60s (s = seconds).

10. Set the Option property to 0 (None).

11. Set the PublicationID property to NEW.

12. Set the Function property to 18 (Receive Publication).

13. Set the ReceiveBufferLength property to your maximum expected publication length (can be up to 2048).

14. Call the method InvokeBrokerFunction to receive publications. The application will now wait to receive a publication. With the current settings the application would receive a publication within 60 seconds or time out after 60 seconds. If the publication is larger than 2048 characters, Broker ActiveX Control will return an error. Assuming that an application has received a publication, that publication now has a publication ID, assigned to it by the EntireX Broker.

15. Get the received data with the method GetReceiveData.

16. The current status of the publication is stored in the UOWstatus property. Check this UOWstatus now. A UOWstatus of 12 (Received Only), means that the received publication has only one message. A UOWstatus of 9 (Received First) means that you have received the first message of a multi-message publication. In this case you should request the other messages of this publication, until a UOWstatus of 11 (Received Last) is returned. See Concepts of Persistent Messaging for more information. To inform the EntireX Broker that the subscriber has received and retrieved the publication the subscriber must commit this.

17. Do not change the PublicationID property. This is required to refer to the received publication.

18. Set the Option property to 10 (Commit).

19. Set the Function property to 21 (Control Publication).

20. Call the method InvokeBrokerFunction to control the publication.

21. Get the UOWstatus property and check the status. The value of the UOWstatus should now be 5 (Processed). Your application may now run in a loop between steps 9 and 21 to receive several publications.

22. Set the Option property to 0 (None).

23. Set the Function property to 20 (Unsubscribe).

24. Call the method InvokeBrokerFunction to unsubscribe. The application has now been unsubscribed from the topic.

25. Set the Function property to 10 (Log off).

26. Call the method InvokeBrokerFunction to log off. The application has now been logged off from the EntireX Broker.

C# Example with a simple Subscriber who has Received only one Publication

using System;
// add the "EntireX Broker ActiveX Control" in COM references
using BrokerLib;

namespace Pubsub
{
    class Class1
    {
        static BrokerClass ebx;
        // EntireX Broker ACI definitions.
        const int function_logon = 9;
        const int function_logoff = 10;
        const int function_subscribe = 19;
        const int function_unsubscribe = 20;
        const int function_receive_publication = 18;
        const int function_control_publication = 21;
        const int option_none = 0;
        const int option_commit = 10;
        const int uowstatus_receive_only = 12;
        const int uowstatus_receive_last = 11;

        // procedure to invoke an entirex broker function call.
        static bool invokeEBX(short function, short option)
        {
            bool rc = true;
            ebx.Option = option;
            ebx.Function = function;
            ebx.InvokeBrokerFunction();
            // check the error status after the broker call.
            if (ebx.ErrorCode != "00000000") 
            {
                Console.WriteLine(ebx.ErrorMsg);
                rc = false;
            }
            return rc;
        }

        [STAThread]
        static void Main(string[] args)
        {
            bool receive_error = false;
            bool subscribe_error = false;
            ebx = new BrokerClass();

            ebx.APIVersion = 8;
            ebx.BrokerID = "localhost";
            ebx.UserID = "EBXUSER";
            ebx.Token  = "EBXTOKEN";
            ebx.Topic  = "NYSE";

            Console.WriteLine("Log on");
            if (!invokeEBX(function_logon, option_none))
                return; // logon failed

            Console.WriteLine("Subscribe");
            if (!invokeEBX(function_subscribe, option_none))
                subscribe_error = true; // subscribe failed

            if (!subscribe_error) 
            {
                ebx.PublicationID = "NEW";
                ebx.ReceiveBufferLength = 2048;
                ebx.Wait = "60s";
                // loop until all messages of the publication have been received.
                do 
                {
                    Console.WriteLine("Receive Publication");
                    if (!invokeEBX(function_receive_publication, option_none)) 
                    {
                        receive_error = true;   // receive failed
                        break;          // cancel the while loop
                    }
                    else
                    {
                        // work with the received publication.
                        Console.WriteLine(ebx.GetReceiveData());
                    }
                } while ((ebx.UOWStatus != uowstatus_receive_only) && 
                       (ebx.UOWStatus != uowstatus_receive_last));

                if (!receive_error) 
                {
                    Console.WriteLine("Control Publication");
                    invokeEBX(function_control_publication, option_commit);
                    // the publication status should be 5 (= processed)
                    Console.WriteLine("Publication status = " + ebx.UOWStatus);
                }
                Console.WriteLine("Unsubscribe");
                invokeEBX(function_unsubscribe, option_none);
            }
            Console.WriteLine("Log off");
            invokeEBX(function_logoff, option_none);
        }
    }
}

Writing Publisher Applications

The publisher sends publications to subscribers. Publications will fail if there is no subscriber for this topic. See Writing Applications: Publish and Subscribe for a list of the valid topics.

The methods, functions, properties and steps required to operate as Publisher are described below.

Methods

Functions

These will be set in the Function property. For all function calls, the UserID, Password (if secure Broker), Token and Topic properties must be set.

Properties

Important:
Please check the Error Status regularly; at least after every InvokeBrokerFunction.

To operate as publisher

1. Set the APIVersion property to 8, the publish-and-subscribe functionality is only available with API version 8 or above.

2. Set the BrokerID property for your EntireX Broker.

3. Set the UserID, Password (if required), Token and Topic properties.

4. Set the Option property to 0 (None).

5. Set the Function property to 9 (Logon). You must log on to use the publish-and-subscribe functionality.

6. Call the method InvokeBrokerFunction to perform the Logon function.

   The application has now been logged on to the EntireX Broker.

7. Set the Option property to 10 (Commit).

8. Set the Function property to 17 (Send Publication).

9. Set the Wait property to NO.

10. Set the PublicationID property to NEW.

11. Call the method SetSendData or SetSendDataLong to set the publication data.

12. Call the method InvokeBrokerFunction to send the publication.

13. Get the UOWstatus property and check this. It should be 2 (Accepted).

    A publication has now been sent. Please note that the publication will fail if there are no subscribers to this topic. If your publication has more than one message, the steps beginning with Set the Option property to 10 (Commit) will change. See Concepts of Persistent Messaging.

14. Set the Option property to 0 (None).

15. Set the Function property to 10 (Logoff).

16. Call the method InvokeBrokerFunction to log off.

    The application has now been logged off from the EntireX Broker.

C# Example with a simple Publisher who Sends only one (single-message) Publication

using System;
// add the "EntireX Broker ActiveX Control" in COM references
using BrokerLib;

namespace Pubsub
{
    class Class1
    {
        static BrokerClass ebx;
        // EntireX Broker ACI definitions
        const int function_logon = 9;
        const int function_logoff = 10;
        const int function_send_publication = 17;
        const int function_control_publication = 21;
        const int option_none = 0;
        const int option_commit = 10;
    
        // procedure to invoke an entirex broker function call
        static bool invokeEBX(short function, short option)
        {
            bool rc = true;
            ebx.Option = option;
            ebx.Function = function;
            ebx.InvokeBrokerFunction();
            if (ebx.ErrorCode != "00000000") 
            {
                Console.WriteLine(ebx.ErrorMsg);
                rc = false;
            }
            return rc;
        }

        [STAThread]
        static void Main(string[] args)
        {
            ebx = new BrokerClass();
            String s = "A small c# publisher example with EntireX Broker ActiveX Control.";

            ebx.APIVersion = 8;
            ebx.BrokerID = "localhost";
            ebx.UserID = "EBXUSER";
            ebx.Token  = "EBXTOKEN";
            ebx.Topic  = "NYSE";

            Console.WriteLine("Log on");
            if (!invokeEBX(function_logon, option_none))
                return; // logon failed

            ebx.Wait = "NO";            // set to NO because we cannot receive data
            ebx.PublicationID = "NEW";
            ebx.SetSendDataLong(s, s.Length);   // set the sent data

            Console.WriteLine("Send Publication");
            invokeEBX(function_send_publication, option_commit);
            // Check the status of the UOW. It should be 2 (= Accepted).
            Console.WriteLine("Publication status = " + ebx.UOWStatus);
            
            Console.WriteLine("Log off");
            invokeEBX(function_logoff, option_none);
        }
    }
}

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