Delphi source code:

program RPCServer;

{$APPTYPE CONSOLE}

uses
  BTCommAdapterIndy, BTJMSConnection, BTJMSInterfaces,
  SysUtils;

procedure FibServer;
var
  Conn: IConnection;
  Session: ISession;
  RequestQueue: IDestination;
  ResponseQueue: IDestination;
  Producer: IMessageProducer;
  Consumer: IMessageConsumer;
  Request, Response: IMessage;
  Input, Output: Integer;

  function fib(n: Integer): Integer;
  begin
    if n=0 then begin Result := 0; Exit; end;
    if n=1 then begin Result := 1; Exit; end;
    Result := fib(n-1) + fib(n-2);
  end;
begin
  Conn := TBTJMSConnection.MakeConnection;
  try
    try
      Conn.Start;

      // create the session
      Session := Conn.CreateSession(False, amAutoAcknowledge);

      // prepare the reply queue
      RequestQueue := Session.CreateQueue('/amq/queue/rpc_queue');

      // wait for messages
      Consumer := Session.CreateConsumer(RequestQueue);
      while True do
      begin
        Request := Consumer.Receive;

        Input := StrToInt((Request as ITextMessage).Text);

        Output := fib(Input);

        WriteLn(' [.] fib(' + IntToStr(Input) + ')');

        // prepare and send the response
        Response := Session.CreateTextMessage(IntToStr(Output));
        Response.JMSCorrelationID := Request.JMSCorrelationID;
        Producer := Session.CreateProducer(Request.JMSReplyTo);
        Producer.Send(Response);
      end;

    except
      on E: Exception do
      begin
        WriteLn(E.Message);
        ReadLn;
      end;
    end;
  finally
    Conn.Close;
  end;
end;

begin
  ReportMemoryLeaksOnShutdown := True;

  Writeln('[*] Awaiting RPC requests');
  FibServer;
end.

A small change is needed in the Java client to support STOMP text messages:

        BasicProperties props = new BasicProperties.Builder()
                .correlationId(corrId)
                .replyTo(replyQueueName)
                .contentType("text/plain")
                .build();

But access to the RPC server process is not limited to Java applications – Delphi and Free Pascal applications using the Habari Client for RabbitMQ library can invoke the server process method too.

This article shows the code for a Delphi client which sends a RPC call message to the inbound RabbitMQ request queue, and receives the response message over a temporary queue, which exists only for the duration of the connection.

This architecture has key differences between a traditional client/server based RPC architecture and a message broker based architecture:

• the RPC client does not have to know where the RPC server is running (RPC client and RPC server only communicate with the message broker, not with each other)
• the RPC client can send requests even if the RPC server is not running
• additional computing power can be provided by running more RPC server processes (load balancing is “built-in” by design)

Delphi source code:

program RPCClient;

{$APPTYPE CONSOLE}

uses
  BTCommAdapterIndy, BTJMSConnection, BTJMSInterfaces,
  SysUtils;

function Fib(const Arg: Integer): Integer;
var
  Conn: IConnection;
  Session: ISession;
  ReplyQueue: IDestination;
  Producer: IMessageProducer;
  Consumer: IMessageConsumer;
  Request, Response: IMessage;
begin
  Result := -1;
  Conn := TBTJMSConnection.MakeConnection;
  try
    try
      Conn.Start;

      // create the session
      Session := Conn.CreateSession(False, amAutoAcknowledge);

      // prepare the reply queue
      ReplyQueue := Session.CreateTemporaryQueue;

      // prepare and send the request
      Producer := Session.CreateProducer(Session.CreateQueue('/amq/queue/rpc_queue'));
      Request := Session.CreateTextMessage(IntToStr(Arg));
      Request.JMSReplyTo := ReplyQueue;
      Request.JMSCorrelationID := FloatToStr(Now);
      Producer.Send(Request);

      // prepare and receive the response from the temp queue
      Consumer := Session.CreateConsumer(ReplyQueue);
      Response := Consumer.Receive(10000);
      if Response <> nil then
      begin
        Result := StrToInt((Response as ITextMessage).Text);
        Assert(Request.JMSCorrelationID = Response.JMSCorrelationID);
      end else begin
        WriteLn('No reply received');
      end;

    except
      on E: Exception do
      begin
        WriteLn(E.Message);
      end;
    end;
  finally
    Conn.Close;
  end;
end;

var
  Input, Output: Integer;

begin
  ReportMemoryLeaksOnShutdown := True;

  Input := 21;
  Writeln('[.] fib(' + IntToStr(Input) + ')');

  Output := Fib(Input);
  Writeln('[.] Result: ' + IntToStr(Output));

  ReadLn;
end.

A small change is needed in the tutorial code to support STOMP text messages:

                BasicProperties replyProps = new BasicProperties.Builder()
                        .correlationId(props.getCorrelationId())
                        .contentType("text/plain")
                        .build();

Server output:

run:
 [x] Awaiting RPC requests
 [.] fib(21)

Client output:

[.] fib(21)
[.] Result: 10946

SOAP and REST – Using GZip with Delphi client.

The library uses JSON serialization to and from Delphi objects and supports Generics. This allows to perform complex REST commands with little code, for example a GET which retrieves a TPerson object list:

var
  vList : TList<TPerson>;
begin
  vList := RestClient.Resource('http://localhost:8080/java-rest-server/rest/persons')
                     .Accept(RestUtils.MediaType_Json)
                     .Get<TList<TPerson>>();

This is the first alpha of release 2.5, which introduces support for
Indy 10.6 and has been tested with build 14 of Open MQ 5.0, the
next-generation message broker version which implements JMS 2.0
(introduced with the new Java EE 7.0 specification).

Home page:
http://www.habarisoft.com/habari_openmq.html

API documentation (HTML):
http://www.habarisoft.com/habari_openmq/2.4/docs/api/index.html

Demo and documentation download (2.4 release):
http://www.habarisoft.com/download/HabariOpenMQ-demo.zip

Demo and documentation download (2.5a1 release):
http://cc.embarcadero.com/Item/26810

All registered users can download the 2.5a1 development snapshot now.

For Delphi and Free Pascal, Habarisoft offers a client library for RabbitMQ 2.8.7 and newer.

A STOMP based Delphi and Free Pascal client library for HornetQ is available from Habarisoft.

• new: exception stack trace logging
  • exceptions during request execution (Service method) will be logged with stack trace and do not stop the application
  • the stack trace will also be shown as web page content
  • this feature requires madExcept (Delphi only)
• new: example class TdjNCSALogHandler implements the standardized NCSA log format
• new: example project which shows how web resources can be protected using HTTP Basic Authentication, by adding a simple subclass of TdjHandlerWrapper to the request handler chain
• changed: if an unhandled exception occurs during execution of a web components Service method, the HTTP response code will be set to 500 Internal Server Error
• updated: demo applications updated to use jQuery 1.9.1 and Twitter Bootstrap 2.3.1
• fixed: duplication of logger names in Log4D trace level log messages
• fixed: Ajax request statistics demo – fixed hang on some browser caused by caching of JSON responses
• experimental code for RESTful applications has been removed
• experimental code for WebSocket applications has been removed

Exception stack trace in logging output

Spring Discount

Single Developer Licenses for Habari Web Components, the easy to use web application framework for Delphi and Free Pascal, are now available with a 40 Euro discount. To receive this discount, please use coupon code ‘web40′ in the order form.

Habari Web Components provide a simple framework for small web applications, which run embedded in an existing Delphi or Free Pascal application, or as a stand-alone HTTP server. If you like to see it in action, download and run the off-line demo applications, try out the on-line demo or install the demo client app for Android. Need more information? Browse the on-line API documentation, or the comprehensive Getting Started document.

Quick facts

• supports Delphi 2009 and Free Pascal 2.6.0 or newer with Internet Direct (Indy) 10.5.9
• supports the open source logging framework Log4D
• no external libraries (DLL), compiles into the executable
• full source code included, with DUnit tests and example applications using Twitter Bootstrap and jQuery mobile
• redistribution with your application does not require any additional fees
• free minor and major updates for one year