DCE Replacement Strategies

Chapter 9. Scenario 2: Non-secure RPC application 177

 Root contexts: Unlike a DCE CDS cell namespace, CORBA CosNaming

allows for more than one root context. (A CORBA CosNaming context can

roughly be compared with a directory in CDS.)

 Object UUIDs: CORBA CosNaming does not support DCE UUIDs. In DCE,

object UUIDs are used to distinctly identify multiple interchangeable servers

by name, for example, or to identify objects inside the server application.

 Management: Some implementations of CORBA CosNaming do not offer

management tools. However, the IBM WebSphere Application Server

implementation of CORBA offers the regimpl tool for management.

WebSphere supports the CORBA CosNaming service, which binds CORBA

objects to a public name. Clients are “bootstrapped” according to the CORBA

programming model. CORBA-compliant Interoperable Object References (IORs)

must be obtained, and server objects must be bound to the CORBA CosNaming

service. WebSphere also enables you to manage namespace bindings and

name servers through the administrative console.

For a detailed description of IBM WebSphere Application Server name server,

refer to chapter 13, “Using naming,” of the

IBM WebSphere Application Server

Enterprise, Version 5, Applications

. (See “Related publications” on page 421 to

learn how to download this document.)

9.2 DCE application

This section briefly describes the sample DCE dependent program, which makes

use of DCE RPC basic, namespace, and endpoint services without using DCE

security. The key DCE services that are used by this program are extracted and

explained. The complete source code can be found in Appendix B, “Scenario 2:

Source code listings” on page 331.

The application logic of the sample application again is simple: The application

client sends a string message to the application server in one parameter of the

remote procedure call. The application server, after writing the client’s message

to standard output, replies to the application client with another string message in

another parameter of the same call in reverse character order.

9.2.1 Configuring and running the DCE application

For the example to run, the directory /.:/servers has to exist in the DCE CDS

namespace. If it does not already exist, it can be created using the command:

cdscp create directory /.:/servers

(The issuer of this command has to be logged in to DCE as cell administrator.)

178 DCE Replacement Strategies

To build the application, the DCE IDL compiler has to process the IDL definition

of this example in order to produce a client and a server stub.

Start the application server by entering its executable name on the command

line. For the application client, the string message and the number of RPC calls

must be added to the command, separated by a blank. For example:

$ server_s2

$ client_s2 “Hello World” 5

9.2.2 Application client

The client program uses a sequence of calls to the DCE naming service API

(rpc_ns_*) to obtain a partial bound bind handle to the server. It exclusively looks

for a binding using the UDP protocol. When it finds a binding handle to the

server, it immediately invokes an RPC to that server, leaving the endpoint

resolution to the DCE RPC run time. The client sample application uses to these

key services to make a connection to the server:

 rpc_ns_binding_import_begin

When calling this API, the application client passes in the server’s entry name

and the interface handle of the interface to be imported. The service returns

an import context handle to be used in the subsequent calls.

 rpc_ns_binding_import_next

With the import context handle, created with the previous API, the application

client parses the namespace for server bindings, meeting its needs. In this

case, a binding handle to the application server is using the protocol UDP.

The application client calls this API in a loop until either no more entries are

available or a suitable binding is found. To filter out binding handles that use

UDP, the client converts the retrieved bindings into string form and performs a

string comparison.

 rpc_ns_binding_import_done

After successfully retrieving a binding handle to the server, the application

client closes the import context using rpc_ns_binding_import_done.

9.2.3 Application server

The application server uses a sequence of calls to the RPC server, RPC naming

service, and RPC endpoint API (rpc_server_*, rpc_ns_*, and rpc_ep_*,

respectively), using only the UDP protocol. It exports a partial binding to its DCE

CDS name service entry /.:/servers/greet and full bindings to the local endpoint

map. When this is accomplished, it starts listening for client calls. The server

program in this example accepts a maximum of 5 concurrent client connections.