Ask Dr. Broker: Developer FAQ

• Can I distribute my applications royalty-free?
• Is source code provided for the RPC Broker client software?
• What software needs to be running on my workstation for development?
• Once I set the TRPCBroker property "Connected" to True, is there any way to verify that a true connection has been established, since setting properties do not have a return value?
• Is there a mechanism to view TRPCBroker property settings at runtime?
• Can multiple connections be established by a single program (e.g., multiple RpcCreate ())?
• Is it possible to call an RPC without passing parameters?
• What if I want to pass more than one array through the Broker? (It looks as if the Mult field of the Param property only supports one array.)
• When should I set the TRPCBroker Connected property to True or False? Does the Call method automatically make a connection if none exists?
• What is the difference between the Call, lstCall, and strCall methods?
• If an M error occurs during processing of an RPC on the server side, is the error trapped? Is my client application notified?
• How do I make an existing M API available for use by a Broker client application?
• What strategies do you recommend for returning disparate data (i.e., data that probably was stored in different arrays on the M side)?
• What does the Tag property do? Does it override Tag in the Remote Procedure file's entry?
• I'm creating a GUI version of an existing application that uses the Broker. If I turn my existing roll-and-scroll options into Broker-type "B"-type options, can my existing roll-and-scroll users and my new Broker users both run the same options?

• Q: Can I distribute my applications royalty-free?

  Dr. Broker: The executables (i.e., EXEs) you develop using Delphi and the RPC Broker are royalty and license free.

  
  
• Q: Is source code provided for the RPC Broker client software?

  Dr. Broker: Source code for the the RPC Broker client is not distributed for security reasons.

  
  
• Q: What software needs to be running on my workstation for development?

  Dr. Broker: Your workstation must have:

  1. One of the following 32 bit operating systems:
     • Microsoft Windows 95
     • Microsoft Windows NT Workstation V. 3.51 or later
  2. TCP/IP networking. It is recommended that you connect to your development server through a local area network (LAN) using a network interface card and TCP/IP protocol.Currently only Winsock compliant TCP/IP protocol is supported on the LAN or remotely as Point-to-Point Protocol (PPP) or Serial Line Internet Protocol (SLIP).
  3. Borland Delphi V. 2.0 or higher.
  4. The Broker Development Kit (BDK), installed in Delphi.
  
  
• Q: Once I set the TRPCBroker property "Connected" to True, is there any way to verify that a true connection has been established, since setting properties do not have a return value?

  Dr. Broker: Use RpcbPropGet to querry the Connected property. Even though the application may try to set it to True, it remains False until an actual connection has been established and the user is authenticated.

  
  
• Q: Is there a mechanism to view TRPCBroker property settings at runtime?

  Dr. Broker: Use RpcbPropGet to obtain property values at run time.

  
  
• Q: Can multiple connections be established by a single program (e.g., multiple RpcCreate ())?

  Dr. Broker: A single program may create as many Broker components as it needs. These Broker components may be used to establish multiple connections to different IP-ports at the same time. However, only one circuit is created for each unique IP-port and will be shared by all Broker components that "point" to it.

  
  
• Q: Is it possible to call an RPC without passing parameters?

  Dr. Broker: Yes.This version of the Broker (i.e., Broker V. 1.1) no longer requires you to pass one "dummy" parameter with the PType field of the Mult subproperty set to null.

  
  
• Q: How can I pass more than one array through the Broker? (It looks as if the Mult field of the Param property only supports one array.)

  Dr. Broker: The Broker uses a function call approach, only one value or array is returned. The Param property is an array of parameters. Use one Param element per parameter. If your aim is to pass two arrays to an RPC, use Param[0] and Param[1], and set their PType fields to list.
  
  Examples using the Param property:

  RPCBroker1.Param[0].Value := '10/31/95'; RPCBroker1.Param[0].PType := literal; RPCBroker1.Param[1].Mult['"NAME"'] := 'SMITH, JOHN'; RPCBroker1.Param[1].Mult['"SSN"'] := '123-45-6789'; RPCBroker1.Param[1].PType := list;

  
  
• Q: When should I set the TRPCBroker Connected property to True or False? Does the Call method automatically make a connection if none exists?

  Dr. Broker: The Connected property gives you full control in connecting and disconnecting from the server. It can also be used to tell if the TRPCBroker component is currently connected or not. The Broker also automatically connects when any call method (Call, lstCall, strCall) is executed. The connection is maintained until the Connected property is set to False or until the TRPCBroker component is destroyed.

  You should call the Broker's GetServerInfo function before any part of your code that establishes a connection can execute. GetServerInfo reads this information from the workstation, providing the appropriate Server and ListenerPort the TRPCBroker component should connect to. A good place to call GetServerInfo is your form's OnCreate event. Then, whether connection is established by setting Connected to True, or by executing a Call method, the TRPCBroker component knows the appropriate server to connect to.

  
  
• Q: What is the difference between the Call, lstCall, and strCall methods?

  Dr. Broker: The Broker uses three methods to invoke RPCs on a server:

  1. Call
  2. lstCall
  3. strCall

  All three methods rely on the Param property for the parameters. There are two main differences between these methods. The first difference is that the Call method is more versatile then strCall or lstCall. strCall can only be used to return one string. lstCall can only return a list of strings. The Call method can return either. The other difference is where the results of the calls are placed.
  
  The Call method uses the Results property for the return values. The strCall method works like a function which can be assigned to some string-typed variable. For example:
  
  

       Patient.Name := strCall

  lstCall puts the results of the call into the passed TStrings-typed variable:

  
  
  

       lstCall(MyListBox.Items)

  strCall and lstCall do not affect the Results property.

  
  
• Q: If an M error occurs during processing of an RPC on the server side, is the error trapped? Is my client application notified?

  Dr. Broker: It is trapped using Kernel. The client is notified of the error via a popup window.

  
  
• Q: How do I make an existing M API available for use by a Broker client application?

  Dr. Broker: An M API has defined input and output values/parameters that are passed via the standard M invoking methods. An RPC, however, needs to do the following:

  • Pass data to an API
  • Receive values back
  • Accept input from the Broker (i.e., passing data/parameters from the client application)
  • Pass API output back through the Broker

  Thus, the RPC can be thought of as a wrapper placed around an API for use with client applications.

  
  
• Q: What strategies do you recommend for returning disparate data (i.e., data that probably was stored in different arrays on the M side)?

  Dr. Broker: One strategy may be to label sections of the returning array as illustrated below:

  Results[0] := '[[DATA]]' Results[1] := 'Some data' Results[2] := 'Some more data' Results[3] := '[[Errors]]' Results[4] := 'Error message'

  You loop through the array looking for your labels to indicate what data follows the label.

  
  
• Q: What does the Tag property do? Does it override Tag in the Remote Procedure file's entry?

  Dr. Broker: The Tag property is inherited from Delphi's TComponent. The Tag property stores an integer value as a scratch value for use by a component. While the Tag property has no meaning to Delphi, your application can use this property to store a value for its special needs.
  
  It is not related to the Tag field in the REMOTE PROCEDURE file (#8994).

  
  
• Q: I'm creating a GUI version of an existing application that uses the Broker. If I turn my existing roll-and-scroll options into Broker-type "B"-type options, can my existing roll-and-scroll users and my new Broker users both run the same options?

  Dr. Broker: A Broker "B" type option can not be run from the menu system. You should instead build a new option for the Broker version of the application.