# Apache Qpid: Open Source AMQP Messaging - .NET User Guide

## Tutorial

This tutorial consists of a series of examples using the three most commonly used exchange types - Direct, Fanout and Topic exchanges. These examples show how to write applications that use the most common messaging paradigms.

- direct

  In the direct examples, a message producer writes to the direct exchange, specifying a routing key. A message consumer reads messages from a named queue. This illustrates clean separation of concerns - message producers need to know only the exchange and the routing key, message consumers need to know only which queue to use on the broker.

- fanout

  The fanout examples use a fanout exchange and do not use routing keys. Each binding specifies that all messages for a given exchange should be delivered to a given queue.

- pub-sub

  In the publish/subscribe examples, a publisher application writes messages to an exchange, specifying a multi-part key. A subscriber application subscribes to messages that match the relevant parts of these keys, using a private queue for each subscription.

- request-response

  In the request/response examples, a simple service accepts requests from clients and sends responses back to them. Clients create their own private queues and corresponding routing keys. When a client sends a request to the server, it specifies its own routing key in the reply-to field of the request. The server uses the client's reply-to field as the routing key for the response.

### Running the Examples

Before running the examples, you need to unzip the file Qpid.NET-net-2.0-M4.zip, the following tree is created:

    <home>
      |-qpid
         |-lib (contains the required dlls)
         |-examples
              |- direct
              |    |-example-direct-Listener.exe
              |    |-example-direct-Producer.exe
              |- fanout
              |    |-example-fanout-Listener.exe
              |    |-example-fanout-Producer.exe
              |- pub-sub
              |    |-example-pub-sub-Listener.exe
              |    |-example-pub-sub-Publisher.exe
              |- request-response
                   |-example-request-response-Client.exe
                   |-example-request-response-Server.exe

Make sure your PATH contains the directory <home>/qpid/lib The examples can be run by executing the provided exe files:

    $ cd <home>/qpid/examples/examplefolder
    $ example-...-.exe [hostname] [portnumber]

where [hostname] is the qpid broker host name (default is localhost) and [portnumber] is the port number on which the qpid broker is accepting connection (default is 5672).

### Creating and Closing Sessions

All of the examples have been written using the Apache Qpid .NEt 0.10 API. The examples use the same skeleton code to initialize the program, create a session, and clean up before exiting:

    using System;
    using System.IO;
    using System.Text;
    using System.Threading;
    using org.apache.qpid.client;
    using org.apache.qpid.transport;

    ...

            private static void Main(string[] args)
            {
                string host = args.Length > 0 ? args[0] : "localhost";
                int port = args.Length > 1 ? Convert.ToInt32(args[1]) : 5672;
                Client connection = new Client();
                try
                {
                    connection.connect(host, port, "test", "guest", "guest");
                    ClientSession session = connection.createSession(50000);

                    //--------- Main body of program --------------------------------------------

                    connection.close();
                }
                catch (Exception e)
                {
                    Console.WriteLine("Error: \n" + e.StackTrace);
                }
            }
    ...

### Writing Direct Applications

This section describes two programs that implement direct messaging using a Direct exchange: • org.apache.qpid.example.direct.Producer (from example-direct-producer) publishes messages to the amq.direct exchange, using the routing key routing_key. •org.apache.qpid.example.direct.Listener (from example-direct-Listener) uses a message listener to receive messages from the queue named message_queue.

#### Running the Direct Examples

1) Make sure your PATH contains the directory <home>/qpid/lib

2) Make sure that a qpid broker is running:

    $ ps -eaf | grep qpidd

If a broker is running, you should see the qpidd process in the output of the above command.

3) Read the messages from the message queue using direct listener, as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-direct-Listener.exe [hostname] [portnumber]

or with mono:

    $ mono ./example-direct-Listener.exe [hostname] [portnumber]

This program is waiting for messages to be published, see next step:

4) Publish a series of messages to the amq.direct exchange by running direct producer, as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-direct-Producer.exe  [hostname] [portnumber]

or with mono:

    $ mono ./example-direct-Producer.exe [hostname] [portnumber]

This program has no output; the messages are routed to the message queue, as instructed by the binding.

5) Go to the windows where you are running your listener. You should see the following output:

    Message: Message 0
    Message: Message 1
    Message: Message 2
    Message: Message 3
    Message: Message 4
    Message: Message 5
    Message: Message 6
    Message: Message 7
    Message: Message 8
    Message: Message 9
    Message: That's all, folks!

Now we will examine the code for each of these programs. In each section, we will discuss only the code that must be added to the skeleton shown in Section "Creating and Closing Sessions".

#### Reading Messages from the Queue

The program , listener.cs, is a message listener that receives messages from a queue.

First it creates a queue named message_queue, then binds it to the amq.direct exchange using the binding key routing_key.

    //--------- Main body of program --------------------------------------------
    // Create a queue named "message_queue", and route all messages whose
    // routing key is "routing_key" to this newly created queue.
    session.queueDeclare("message_queue");
    session.exchangeBind("message_queue", "amq.direct", "routing_key");

The queue created by this program continues to exist after the program exits, and any message whose routing key matches the key specified in the binding will be routed to the corresponding queue by the broker. Note that the queue could have been be deleted using the following code:

    session.queueDelete("message_queue");

To create a message listener, create a class derived from IMessageListener, and override the messageTransfer method, providing the code that should be executed when a message is received.

    public class MessageListener : IMessageListener
    {
      ......
      public void messageTransfer(IMessage m)
      {
      .....
    }

The main body of the program creates a listener for the subscription; attaches the listener to a message queue; and subscribe to the queue to receive messages from the queue.

    lock (session)
    {
      // Create a listener and subscribe it to the queue named "message_queue"
      IMessageListener listener = new MessageListener(session);
      session.attachMessageListener(listener, "message_queue");
      session.messageSubscribe("message_queue");
      // Receive messages until all messages are received
      Monitor.Wait(session);
    }

The MessageListener's messageTransfer() function is called whenever a message is received. In this example the message is printed and tested to see if it is the final message. Once the final message is received, the messages are acknowledged.

    BinaryReader reader = new BinaryReader(m.Body, Encoding.UTF8);
    byte[] body = new byte[m.Body.Length - m.Body.Position];
    reader.Read(body, 0, body.Length);
    ASCIIEncoding enc = new ASCIIEncoding();
    string message = enc.GetString(body);
     Console.WriteLine("Message: " + message);
    // Add this message to the list of message to be acknowledged
    _range.add(m.Id);
    if( message.Equals("That's all, folks!") )
    {
      // Acknowledge all the received messages
      _session.messageAccept(_range);
      lock(_session)
      {
          Monitor.Pulse(_session);
      }
    }

#### Publishing Messages to a Direct Exchange

The second program in the direct example, Producer.cs, publishes messages to the amq.direct exchange using the routing key routing_key.

First, create a message and set a routing key. The same routing key will be used for each message we send, so you only need to set this property once.

    IMessage message = new Message();
    // The routing key is a message property. We will use the same
    // routing key for each message, so we'll set this property
    // just once. (In most simple cases, there is no need to set
    // other message properties.)
    message.DeliveryProperties.setRoutingKey("routing_key");

Now send some messages:

    // Asynchronous transfer sends messages as quickly as
    // possible without waiting for confirmation.
    for (int i = 0; i < 10; i++)
    {
      message.clearData();
      message.appendData(Encoding.UTF8.GetBytes("Message " + i));
      session.messageTransfer("amq.direct", message);
    }

Send a final synchronous message to indicate termination:

    // And send a syncrhonous final message to indicate termination.
    message.clearData();
    message.appendData(Encoding.UTF8.GetBytes("That's all, folks!"));
    session.messageTransfer("amq.direct", "routing_key", message);
    session.sync();

### Writing Fanout Applications

This section describes two programs that illustrate the use of a Fanout exchange.

- Listener.cs makes a unique queue private for each instance of the listener, and binds that queue to the fanout exchange. All messages sent to the fanout exchange are delivered to each listener's queue.

- Producer.cs publishes messages to the fanout exchange. It does not use a routing key, which is not needed by the fanout exchange.

#### Running the Fanout Examples

1) Make sure your PATH contains the directory <home>/qpid/lib

2) Make sure that a qpid broker is running:

    $ ps -eaf | grep qpidd

If a broker is running, you should see the qpidd process in the output of the above command.

3) In separate windows, start one or more fanout listeners as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-fanout-Listener.exe [hostname] [portnumber]

or with mono:

    $ mono ./example-fanout-Listener.exe [hostname] [portnumber]

The listener creates a private queue, binds it to the amq.fanout exchange, and waits for messages to arrive on the queue. When the listener starts, you will see the following message:

    Listening

This program is waiting for messages to be published, see next step:

4) In a separate window, publish a series of messages to the amq.fanout exchange by running fanout producer, as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-fanout-Producer.exe  [hostname] [portnumber]

or with mono:

    $ mono ./example-fanout-Producer.exe [hostname] [portnumber]

This program has no output; the messages are routed to the message queue, as prescribed by the binding.

5) Go to the windows where you are running listeners. You should see the following output for each listener:

    Message: Message 0
    Message: Message 1
    Message: Message 2
    Message: Message 3
    Message: Message 4
    Message: Message 5
    Message: Message 6
    Message: Message 7
    Message: Message 8
    Message: Message 9
    Message: That's all, folks!

Now we will examine the code for each of these programs. In each section, we will discuss only the code that must be added to the skeleton shown in Section "Creating and Closing Sessions".

### Consuming from a Fanout Exchange

The first program in the fanout example, Listener.cs, creates a private queue, binds it to the amq.fanout exchange, and waits for messages to arrive on the queue, printing them out as they arrive. It uses a Listener that is identical to the one used in the direct example:

      public class MessageListener : IMessageListener
        {
            private readonly ClientSession _session;
            private readonly RangeSet _range = new RangeSet();
            public MessageListener(ClientSession session)
            {
                _session = session;
            }

            public void messageTransfer(IMessage m)
            {
                BinaryReader reader = new BinaryReader(m.Body, Encoding.UTF8);
                byte[] body = new byte[m.Body.Length - m.Body.Position];
                reader.Read(body, 0, body.Length);
                ASCIIEncoding enc = new ASCIIEncoding();
                string message = enc.GetString(body);
                Console.WriteLine("Message: " + message);
                // Add this message to the list of message to be acknowledged
                _range.add(m.Id);
                if (message.Equals("That's all, folks!"))
                {
                    // Acknowledge all the received messages
                    _session.messageAccept(_range);
                    lock (_session)
                    {
                        Monitor.Pulse(_session);
                    }
                }
            }
        }

The listener creates a private queue to receive its messages and binds it to the fanout exchange:

    string myQueue = session.Name;
    session.queueDeclare(myQueue, Option.EXCLUSIVE, Option.AUTO_DELETE);
    session.exchangeBind(myQueue, "amq.fanout", "my-key");

Now we create a listener and subscribe it to the queue:

    lock (session)
    {
       Console.WriteLine("Listening");
       // Create a listener and subscribe it to my queue.
       IMessageListener listener = new MessageListener(session);
       session.attachMessageListener(listener, myQueue);
       session.messageSubscribe(myQueue);
       // Receive messages until all messages are received
       Monitor.Wait(session);
    }

#### Publishing Messages to the Fanout Exchange

The second program in this example, Producer.cs, writes messages to the fanout queue.

    // Unlike topic exchanges and direct exchanges, a fanout
    // exchange need not set a routing key.
    IMessage message = new Message();
    // Asynchronous transfer sends messages as quickly as
    // possible without waiting for confirmation.
    for (int i = 0; i < 10; i++)
    {
        message.clearData();
        message.appendData(Encoding.UTF8.GetBytes("Message " + i));
        session.messageTransfer("amq.fanout", message);
    }

    // And send a syncrhonous final message to indicate termination.
    message.clearData();
    message.appendData(Encoding.UTF8.GetBytes("That's all, folks!"));
    session.messageTransfer("amq.fanout", message);
    session.sync();

### Writing Publish/Subscribe Applications

This section describes two programs that implement Publish/Subscribe messaging using a topic exchange.

• Publisher.cS sends messages to the amq.topic exchange, using the multipart routing keys usa.news, usa.weather, europe.news, and europe.weather. • Listener.cs creates private queues for news, weather, usa, and europe, binding them to the amq.topic exchange using bindings that match the corresponding parts of the multipart routing keys.

In this example, the publisher creates messages for topics like news, weather, and sports that happen in regions like Europe, Asia, or the United States. A given consumer may be interested in all weather messages, regardless of region, or it may be interested in news and weather for the United States, but uninterested in items for other regions. In this example, each consumer sets up its own private queues, which receive precisely the messages that particular consumer is interested in.

#### Running the Publish-Subscribe Examples

1) Make sure your PATH contains the directory <home>/qpid/lib

2) Make sure that a qpid broker is running:

    $ ps -eaf | grep qpidd

If a broker is running, you should see the qpidd process in the output of the above command.

3) In separate windows, start one or more topic subscribers as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-pub-sub--Listener.exe [hostname] [portnumber]

or with mono:

    $ mono ./example-pub-sub-Listener.exe [hostname] [portnumber]

You will see output similar to this:

    Listening for messages ...
    Declaring queue: usa
    Declaring queue: europe
    Declaring queue: news
    Declaring queue: weather

Each topic consumer creates a set of private queues, and binds each queue to the amq.topic exchange together with a binding that indicates which messages should be routed to the queue.

4) In another window, start the topic publisher, which publishes messages to the amq.topic exchange, as follows:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-pub-sub-Producer.exe  [hostname] [portnumber]

or with mono:

    $ mono ./example-pub-sub-Producer.exe [hostname] [portnumber]

This program has no output; the messages are routed to the message queues for each topic_consumer as specified by the bindings the consumer created.

5) Go back to the window for each topic consumer. You should see output like this:

    Message: Message 0 from usa
    Message: Message 0 from news
    Message: Message 0 from weather
    Message: Message 1 from usa
    Message: Message 1 from news
    Message: Message 2 from usa
    Message: Message 2 from news
    Message: Message 3 from usa
    Message: Message 3 from news
    Message: Message 4 from usa
    Message: Message 4 from news
    Message: Message 5 from usa
    Message: Message 5 from news
    Message: Message 6 from usa
    Message: Message 6 from news
    Message: Message 7 from usa
    Message: Message 7 from news
    Message: Message 8 from usa
    Message: Message 8 from news
    Message: Message 9 from usa
    ....
    Message: That's all, folks! from weather
    Shutting down listener for control
    Message: That's all, folks! from europe
    Shutting down listener for control

Now we will examine the code for each of these programs. In each section, we will discuss only the code that must be added to the skeleton shown in Section "Creating and Closing Sessions".

#### Publishing Messages to a Topic Exchange

The first program in the publish/subscribe example, Publisher.cs, defines two new functions: one that publishes messages to the topic exchange, and one that indicates that no more messages are coming.

The publishMessages function publishes a series of five messages using the specified routing key.

    private static void publishMessages(ClientSession session, string routing_key)
    {
     IMessage message = new Message();
     // Asynchronous transfer sends messages as quickly as
     // possible without waiting for confirmation.
     for (int i = 0; i < 10; i++)
     {
        message.clearData();
        message.appendData(Encoding.UTF8.GetBytes("Message " + i));
        session.messageTransfer("amq.topic", routing_key, message);
     }
    }

The noMoreMessages function signals the end of messages using the control routing key, which is reserved for control messages.

    private static void noMoreMessages(ClientSession session)
    {
      IMessage message = new Message();
      // And send a syncrhonous final message to indicate termination.
      message.clearData();
      message.appendData(Encoding.UTF8.GetBytes("That's all, folks!"));
      session.messageTransfer("amq.topic", "control", message);
      session.sync();
    }

In the main body of the program, messages are published using four different routing keys, and then the end of messages is indicated by a message sent to a separate routing key.

    publishMessages(session, "usa.news");
    publishMessages(session, "usa.weather");
    publishMessages(session, "europe.news");
    publishMessages(session, "europe.weather");

    noMoreMessages(session);

#### Reading Messages from the Queue

The second program in the publish/subscribe example, Listener.cs, creates a local private queue, with a unique name, for each of the four binding keys it specifies: usa.#, europe.#, #.news, and #.weather, and creates a listener.

    Console.WriteLine("Listening for messages ...");
    // Create a listener
    prepareQueue("usa", "usa.#", session);
    prepareQueue("europe", "europe.#", session);
    prepareQueue("news", "#.news", session);
    prepareQueue("weather", "#.weather", session);

The prepareQueue() method creates a queue using a queue name and a routing key supplied as arguments it then attaches a listener with the session for the created queue and subscribe for this receiving messages from the queue:

    // Create a unique queue name for this consumer by concatenating
    // the queue name parameter with the Session ID.
    Console.WriteLine("Declaring queue: " + queue);
    session.queueDeclare(queue, Option.EXCLUSIVE, Option.AUTO_DELETE);

    // Route messages to the new queue if they match the routing key.
    // Also route any messages to with the "control" routing key to
    // this queue so we know when it's time to stop. A publisher sends
    // a message with the content "That's all, Folks!", using the
    // "control" routing key, when it is finished.

    session.exchangeBind(queue, "amq.topic", routing_key);
    session.exchangeBind(queue, "amq.topic", "control");

    // subscribe the listener to the queue
    IMessageListener listener = new MessageListener(session);
    session.attachMessageListener(listener, queue);
    session.messageSubscribe(queue);

### Writing Request/Response Applications

In the request/response examples, we write a server that accepts strings from clients and converts them to upper case, sending the result back to the requesting client. This example consists of two programs.

- Client.cs is a client application that sends messages to the server. • Server.cs is a service that accepts messages, converts their content to upper case, and sends the result to the amq.direct exchange, using the request's reply-to property as the routing key for the response.

#### Running the Request/Response Examples

1) Make sure your PATH contains the directory <home>/qpid/lib

2) Make sure that a qpid broker is running:

    $ ps -eaf | grep qpidd

If a broker is running, you should see the qpidd process in the output of the above command.

3) Run the server.

$ cd <home>/qpid/examples/direct

          With cygwin:

$ ./example-request-response-Server.exe [hostname] [portnumber]

          or with mono:

$ mono ./example-request-response-Server.exe [hostname] [portnumber]

          You will see output similar to this:

Waiting for requests

    4) In a separate window, start a client:

    $ cd <home>/qpid/examples/direct

With cygwin:

    $ ./example-request-response-Client.exe [hostname] [portnumber]

or with mono:

    $ mono ./example-request-response-Client.exe [hostname] [portnumber]

You will see output similar to this:

    Activating response queue listener for: clientSystem.Byte[]
    Waiting for all responses to arrive ...
    Response: TWAS BRILLIG, AND THE SLITHY TOVES
    Response: DID GIRE AND GYMBLE IN THE WABE.
    Response: ALL MIMSY WERE THE BOROGROVES,
    Response: AND THE MOME RATHS OUTGRABE.
    Shutting down listener for clientSystem.Byte[]
    Response: THAT'S ALL, FOLKS!

4) Go back to the server window, the output should be similar to this:

    Waiting for requests
    Request: Twas brillig, and the slithy toves
    Request: Did gire and gymble in the wabe.
    Request: All mimsy were the borogroves,
    Request: And the mome raths outgrabe.
    Request: That's all, folks!

Now we will examine the code for each of these programs. In each section, we will discuss only the code that must be added to the skeleton shown in Section "Creating and Closing Sessions".

#### The Client Application

The first program in the request-response example, Client.cs, sets up a private response queue to receive responses from the server, then sends messages the server, listening to the response queue for the server's responses.

    string response_queue = "client" + session.getName();
    // Use the name of the response queue as the routing key
    session.queueDeclare(response_queue);
    session.exchangeBind(response_queue, "amq.direct", response_queue);

    // Create a listener for the response queue and listen for response messages.
    Console.WriteLine("Activating response queue listener for: " + response_queue);
    IMessageListener listener = new ClientMessageListener(session);
    session.attachMessageListener(listener, response_queue);
    session.messageSubscribe(response_queue);

Set some properties that will be used for all requests. The routing key for a request is request. The reply-to property is set to the routing key for the client's private queue.

    IMessage request = new Message();
    request.DeliveryProperties.setRoutingKey("request");
    request.MessageProperties.setReplyTo(new ReplyTo("amq.direct", response_queue));

Now send some requests...

    string[] strs = {
                     "Twas brillig, and the slithy toves",
                     "Did gire and gymble in the wabe.",
                     "All mimsy were the borogroves,",
                     "And the mome raths outgrabe.",
                     "That's all, folks!"
                    };
    foreach (string s in strs)
    {
     request.clearData();
     request.appendData(Encoding.UTF8.GetBytes(s));
     session.messageTransfer("amq.direct", request);
    }

And wait for responses to arrive:

    Console.WriteLine("Waiting for all responses to arrive ...");
    Monitor.Wait(session);

#### The Server Application

The second program in the request-response example, Server.cs, uses the reply-to property as the routing key for responses.

The main body of Server.cs creates an exclusive queue for requests, then waits for messages to arrive.

    const string request_queue = "request";
    // Use the name of the request queue as the routing key
    session.queueDeclare(request_queue);
    session.exchangeBind(request_queue, "amq.direct", request_queue);

    lock (session)
    {
     // Create a listener and subscribe it to the request_queue
     IMessageListener listener = new MessageListener(session);
     session.attachMessageListener(listener, request_queue);
     session.messageSubscribe(request_queue);
     // Receive messages until all messages are received
     Console.WriteLine("Waiting for requests");
     Monitor.Wait(session);
    }

The listener's messageTransfer() method converts the request's content to upper case, then sends a response to the broker, using the request's reply-to property as the routing key for the response.

    BinaryReader reader = new BinaryReader(request.Body, Encoding.UTF8);
    byte[] body = new byte[request.Body.Length - request.Body.Position];
    reader.Read(body, 0, body.Length);
    ASCIIEncoding enc = new ASCIIEncoding();
    string message = enc.GetString(body);
    Console.WriteLine("Request: " + message);

    // Transform message content to upper case
    string responseBody = message.ToUpper();

    // Send it back to the user
    response.clearData();
    response.appendData(Encoding.UTF8.GetBytes(responseBody));
    _session.messageTransfer("amq.direct", routingKey, response);