Qpid C++ API Reference

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Qpid C++ API Reference

## Messaging Client API classes

- Qpid C++ Client API

- Qpid Management Framework C++ API

## Code for common tasks

### Includes and Namespaces

     #include <qpid/messaging/Connection.h>
     #include <qpid/messaging/Message.h>
     #include <qpid/messaging/Receiver.h>
     #include <qpid/messaging/Sender.h>
     #include <qpid/messaging/Session.h>

     #include <iostream>

     using namespace qpid::messaging;

### Opening Sessions and Connections

     int main(int argc, char** argv) {
         std::string broker = argc > 1 ? argv[1] : "localhost:5672";
         std::string address = argc > 2 ? argv[2] : "amq.topic";
         Connection connection(broker);
         try {
             connection.open();
             Session session = connection.createSession();

     	// ### Your Code Here ###

             connection.close();
             return 0;
         } catch(const std::exception& error) {
             std::cerr << error.what() << std::endl;
             connection.close();
             return 1;
         }
     }

### Creating and Sending a Message

     Sender sender = session.createSender(address);
     sender.send(Message("Hello world!"));

### Setting Message Content

     Message message;
     message.setContent("Hello world!");

     // In some applications, you should also set the content type,
     // which is a MIME type
     message.setContentType("text/plain");

### Receiving a Message

     Receiver receiver = session.createReceiver(address);
     Message message = receiver.fetch(Duration::SECOND * 1); // timeout is optional
     session.acknowledge(); // acknowledge message receipt
     std::cout << message.getContent() << std::endl;

### Receiving Messages from Multiple Sources

To receive messages from multiple sources, create a receiver for each source, and use session.nextReceiver().fetch() to fetch messages. session.nextReceiver() is guaranteed to return the receiver responsible for the first available message on the session.

     Receiver receiver1 = session.createReceiver(address1);
     Receiver receiver2 = session.createReceiver(address2);

     Message message =  session.nextReceiver().fetch();
     session.acknowledge(); // acknowledge message receipt
     std::cout << message.getContent() << std::endl;

### Replying to a message:

     // Server creates a service queue and waits for messages
     // If it gets a request, it sends a response to the reply to address

     Receiver receiver = session.createReceiver("service_queue; {create: always}");
     Message request = receiver.fetch();
     const Address& address = request.getReplyTo(); // Get "reply-to" from request ...
     if (address) {
       Sender sender = session.createSender(address); // ... send response to "reply-to"
       Message response("pong!");
       sender.send(response);
       session.acknowledge();
     }

     // Client creates a private response queue - the # gets converted
     // to a unique string for the response queue name. Client uses the
     // name of this queue as its reply-to.

     Sender sender = session.createSender("service_queue");
     Address responseQueue("#response-queue; {create:always, delete:always}");
     Receiver receiver = session.createReceiver(responseQueue);

     Message request;
     request.setReplyTo(responseQueue);
     request.setContent("ping");
     sender.send(request);
     Message response = receiver.fetch();
     std::cout << request.getContent() << " -> " << response.getContent() << std::endl;

### Getting and Setting Standard Message Properties

This shows some of the most commonly used message properties, it is not complete.

     Message message("Hello world!");
     message.setContentType("text/plain");
     message.setSubject("greeting");
     message.setReplyTo("response-queue");
     message.setTtl(100); // milliseconds
     message.setDurable(1);

     std::cout << "Content: " << message.getContent() << std::endl
               << "Content Type: " << message.getContentType()
               << "Subject: " << message.getSubject()
     	  << "ReplyTo: " << message.getReplyTo()
     	  << "Time To Live (in milliseconds) " << message.getTtl()
     	  << "Durability: " << message.getDurable();

### Getting and Setting Application-Defined Message Properties

     std::string name = "weekday";
     std::string value = "Thursday";
     message.getProperties()[name] = value;

     std:string s = message.getProperties()["weekday"];

### Transparent Failover

If a connection opened using the reconnect option, it will transparently reconnect if the connection is lost.

     Connection connection(broker);
     connection.setOption("reconnect", true);
     try {
         connection.open();
         ....

### Maps

Maps provide a simple way to exchange binary data portably, across languages and platforms. Maps can contain simple types, lists, or maps.

     // Sender

     Variant::Map content;
     content["id"] = 987654321;
     content["name"] = "Widget";
     content["probability"] = 0.43;
     Variant::List colours;
     colours.push_back(Variant("red"));
     colours.push_back(Variant("green"));
     colours.push_back(Variant("white"));
     content["colours"] = colours;
     content["uuid"] = Uuid(true);

     Message message;
     encode(content, message);

     sender.send(message);

     // Receiver

     Variant::Map content;
     decode(receiver.fetch(), content);

### Guaranteed Delivery

If a queue is durable, the queue survives a messaging broker crash, as well as any durable messages that have been placed on the queue. These messages will be delivered when the messaging broker is restarted. Delivery is not guaranteed unless both the message and the queue are durable.

     Sender sender = session.createSender("durable-queue");

     Message message("Hello world!");
     message.setDurable(1);

     sender.send(Message("Hello world!"));

### Transactions

Transactions cover enqueues and dequeues.

When sending messages, a transaction tracks enqueues without actually delivering the messages, a commit places messages on their queues, and a rollback discards the enqueues.

When receiving messages, a transaction tracks dequeues without actually removing acknowledged messages, a commit removes all acknowledged messages, and a rollback discards acknowledgements. A rollback does not release the message, it must be explicitly released to return it to the queue.

     Connection connection(broker);
     Session session =  connection.createTransactionalSession();
     ...
     if (looksOk)
        session.commit();
     else
        session.rollback();

### Exceptions

All exceptions for the messaging API have MessagingException as their base class.

A common class of exception are those related to processing addresses used to create senders and/or receivers. These all have AddressError as their base class.

Where there is a syntax error in the address itself, a MalformedAddress will be thrown. Where the address is valid, but there is an error in interpreting (i.e. resolving) it, a ResolutionError - or a sub-class of it - will be thrown. If the address has assertions enabled for a given context and the asserted node properties are not in fact correct then AssertionFailed will be thrown. If the node is not found, NotFound will be thrown.

The loss of the underlying connection (e.g. the TCP connection) results in TransportFailure being thrown. If automatic reconnect is enabled, this will be caught be the library which will then try to reconnect. If reconnection - as configured by the connection options - fails, then TransportFailure will be thrown. This can occur on any call to the messaging API.

Sending a message may also result in an exception (e.g. TargetCapacityExceeded if a queue to which the message is delivered cannot enqueue it due to lack of capacity). For asynchronous send the exception may not be thrown on the send invocation that actually triggers it, but on a subsequent method call on the API.

Certain exceptions may render the session invalid; once these occur, subsequent calls on the session will throw the same class of exception. This is not an intrinsic property of the class of exception, but is a result of the current mapping of the API to the underlying AMQP 0-10 protocol. You can test whether the session is valid at any time using the hasError() and/or checkError() methods on Session.

### Logging

The Qpidd broker and C++ clients can both use environment variables to enable logging. Use QPID_LOG_ENABLE to set the level of logging you are interested in (trace, debug, info, notice, warning, error, or critical):

     export QPID_LOG_ENABLE="warning+"

Use QPID_LOG_OUTPUT to determine where logging output should be sent. This is either a file name or the special values stderr, stdout, or syslog:

     export QPID_LOG_TO_FILE="/tmp/myclient.out"