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Using the AMQ C++ Client

Red Hat AMQ 7.6

For Use with AMQ Clients 2.7

Abstract

This guide describes how to install and configure the client, run hands-on examples, and use your client with other AMQ components.

Chapter 1. Overview

AMQ C++ is a library for developing messaging applications. It enables you to write C++ applications that send and receive AMQP messages.

AMQ C++ is part of AMQ Clients, a suite of messaging libraries supporting multiple languages and platforms. For an overview of the clients, see AMQ Clients Overview. For information about this release, see AMQ Clients 2.7 Release Notes.

AMQ C++ is based on the Proton API from Apache Qpid. For detailed API documentation, see the AMQ C++ API reference.

1.1. Key features

  • An event-driven API that simplifies integration with existing applications
  • SSL/TLS for secure communication
  • Flexible SASL authentication
  • Automatic reconnect and failover
  • Seamless conversion between AMQP and language-native data types
  • Access to all the features and capabilities of AMQP 1.0

1.2. Supported standards and protocols

AMQ C++ supports the following industry-recognized standards and network protocols:

1.3. Supported configurations

AMQ C++ supports the OS and language versions listed below. For more information, see Red Hat AMQ 7 Supported Configurations.

  • Red Hat Enterprise Linux 6 with GNU C++, compiling as C++03 or C++0x (partial C++11 support)
  • Red Hat Enterprise Linux 7 and 8 with GNU C++, compiling as C++03 or C++11
  • Microsoft Windows 10 Pro with Microsoft Visual Studio 2015 or newer
  • Microsoft Windows Server 2012 R2 and 2016 with Microsoft Visual Studio 2015 or newer

AMQ C++ is supported in combination with the following AMQ components and versions:

  • All versions of AMQ Broker
  • All versions of AMQ Interconnect
  • All versions of AMQ Online
  • A-MQ 6 versions 6.2.1 and newer

1.4. Terms and concepts

This section introduces the core API entities and describes how they operate together.

Table 1.1. API terms

EntityDescription

Container

A top-level container of connections.

Connection

A channel for communication between two peers on a network. It contains sessions.

Session

A context for sending and receiving messages. It contains senders and receivers.

Sender

A channel for sending messages to a target. It has a target.

Receiver

A channel for receiving messages from a source. It has a source.

Source

A named point of origin for messages.

Target

A named destination for messages.

Message

An application-specific piece of information.

Delivery

A message transfer.

AMQ C++ sends and receives messages. Messages are transferred between connected peers over senders and receivers. Senders and receivers are established over sessions. Sessions are established over connections. Connections are established between two uniquely identified containers. Though a connection can have multiple sessions, often this is not needed. The API allows you to ignore sessions unless you require them.

A sending peer creates a sender to send messages. The sender has a target that identifies a queue or topic at the remote peer. A receiving peer creates a receiver to receive messages. The receiver has a source that identifies a queue or topic at the remote peer.

The sending of a message is called a delivery. The message is the content sent, including all metadata such as headers and annotations. The delivery is the protocol exchange associated with the transfer of that content.

To indicate that a delivery is complete, either the sender or the receiver settles it. When the other side learns that it has been settled, it will no longer communicate about that delivery. The receiver can also indicate whether it accepts or rejects the message.

1.5. Document conventions

The sudo command

In this document, sudo is used for any command that requires root privileges. Exercise caution when using sudo because any changes can affect the entire system. For more information about sudo, see Using the sudo command.

File paths

In this document, all file paths are valid for Linux, UNIX, and similar operating systems (for example, /home/andrea). On Microsoft Windows, you must use the equivalent Windows paths (for example, C:\Users\andrea).

Variable text

This document contains code blocks with variables that you must replace with values specific to your environment. Variable text is enclosed in arrow braces and styled as italic monospace. For example, in the following command, replace <project-dir> with the value for your environment:

$ cd <project-dir>

Chapter 2. Installation

This chapter guides you through the steps to install AMQ C++ in your environment.

2.1. Prerequisites

  • To build programs using AMQ C++ on Red Hat Enterprise Linux, you must install the gcc-c++, cmake, and make packages.
  • To build programs using AMQ C++ on Microsoft Windows, you must install Visual Studio.

2.2. Installing on Red Hat Enterprise Linux

Procedure

  1. Use the subscription-manager command to subscribe to the required package repositories. If necessary, replace <variant> with the value for your variant of Red Hat Enterprise Linux (for example, server or workstation).

    Red Hat Enterprise Linux 6

    $ sudo subscription-manager repos --enable=amq-clients-2-for-rhel-6-<variant>-rpms

    Red Hat Enterprise Linux 7

    $ sudo subscription-manager repos --enable=amq-clients-2-for-rhel-7-<variant>-rpms

    Red Hat Enterprise Linux 8

    $ sudo subscription-manager repos --enable=amq-clients-2-for-rhel-8-x86_64-rpms

  2. Use the yum command to install the qpid-proton-cpp-devel and qpid-proton-cpp-docs packages.

    $ sudo yum install qpid-proton-cpp-devel qpid-proton-cpp-docs

For more information about using packages, see Appendix B, Using Red Hat Enterprise Linux packages.

2.3. Installing on Microsoft Windows

Procedure

  1. Open a browser and log in to the Red Hat Customer Portal Product Downloads page at access.redhat.com/downloads.
  2. Locate the Red Hat AMQ Clients entry in the INTEGRATION AND AUTOMATION category.
  3. Click Red Hat AMQ Clients. The Software Downloads page opens.
  4. Download the AMQ Clients 2.7.0 C++ .zip file.
  5. Extract the file contents into a directory of your choosing by right-clicking on the zip file and selecting Extract All.

When you extract the contents of the .zip file, a directory named amq-clients-2.7.0-cpp-win is created. This is the top-level directory of the installation and is referred to as <install-dir> throughout this document.

Chapter 3. Getting started

This chapter guides you through the steps to set up your environment and run a simple messaging program.

3.1. Prerequisites

  • You must complete the installation procedure for your environment.
  • You must have an AMQP 1.0 message broker listening for connections on interface localhost and port 5672. It must have anonymous access enabled. For more information, see Starting the broker.
  • You must have a queue named examples. For more information, see Creating a queue.

3.2. Running Hello World on Red Hat Enterprise Linux

The Hello World example creates a connection to the broker, sends a message containing a greeting to the examples queue, and receives it back. On success, it prints the received message to the console.

Procedure

  1. Copy the examples to a location of your choosing.

    $ cp -r /usr/share/proton/examples/cpp cpp-examples
  2. Create a build directory and change to that directory:

    $ mkdir cpp-examples/bld
    $ cd cpp-examples/bld
  3. Use cmake to configure the build and use make to compile the examples.

    $ cmake ..
    $ make
  4. Run the helloworld program.

    $ ./helloworld
    Hello World!

Chapter 4. Examples

This chapter demonstrates the use of AMQ C++ through example programs.

For more examples, see the AMQ C++ example suite.

Note

The code presented in this guide uses C++11 features. AMQ C++ is also compatible with C++03, but the code requires minor modifications.

4.1. Sending messages

This client program connects to a server using <connection-url>, creates a sender for target <address>, sends a message containing <message-body>, closes the connection, and exits.

Example: Sending messages

#include <proton/connection.hpp>
#include <proton/container.hpp>
#include <proton/message.hpp>
#include <proton/messaging_handler.hpp>
#include <proton/sender.hpp>
#include <proton/target.hpp>

#include <iostream>
#include <string>

struct send_handler : public proton::messaging_handler {
    std::string conn_url_ {};
    std::string address_ {};
    std::string message_body_ {};

    void on_container_start(proton::container& cont) override {
        cont.connect(conn_url_);

        // To connect with a user and password:
        //
        // proton::connection_options opts {};
        // opts.user("<user>");
        // opts.password("<password>");
        //
        // cont.connect(conn_url_, opts);
    }

    void on_connection_open(proton::connection& conn) override {
        conn.open_sender(address_);
    }

    void on_sender_open(proton::sender& snd) override {
        std::cout << "SEND: Opened sender for target address '"
                  << snd.target().address() << "'\n";
    }

    void on_sendable(proton::sender& snd) override {
        proton::message msg {message_body_};
        snd.send(msg);

        std::cout << "SEND: Sent message '" << msg.body() << "'\n";

        snd.close();
        snd.connection().close();
    }
};

int main(int argc, char** argv) {
    if (argc != 4) {
        std::cerr << "Usage: send <connection-url> <address> <message-body>\n";
        return 1;
    }

    send_handler handler {};
    handler.conn_url_ = argv[1];
    handler.address_ = argv[2];
    handler.message_body_ = argv[3];

    proton::container cont {handler};

    try {
        cont.run();
    } catch (const std::exception& e) {
        std::cerr << e.what() << "\n";
        return 1;
    }

    return 0;
}

Running the example

To run the example program, copy it to a local file, compile it, and execute it from the command line.

$ g++ send.cpp -o send -std=c++11 -lstdc++ -lqpid-proton-cpp
$ ./send amqp://localhost queue1 hello

4.2. Receiving messages

This client program connects to a server using <connection-url>, creates a receiver for source <address>, and receives messages until it is terminated or it reaches <count> messages.

Example: Receiving messages

#include <proton/connection.hpp>
#include <proton/container.hpp>
#include <proton/delivery.hpp>
#include <proton/message.hpp>
#include <proton/messaging_handler.hpp>
#include <proton/receiver.hpp>
#include <proton/source.hpp>

#include <iostream>
#include <string>

struct receive_handler : public proton::messaging_handler {
    std::string conn_url_ {};
    std::string address_ {};
    int desired_ {0};
    int received_ {0};

    void on_container_start(proton::container& cont) override {
        cont.connect(conn_url_);

        // To connect with a user and password:
        //
        // proton::connection_options opts {};
        // opts.user("<user>");
        // opts.password("<password>");
        //
        // cont.connect(conn_url_, opts);
    }

    void on_connection_open(proton::connection& conn) override {
        conn.open_receiver(address_);
    }

    void on_receiver_open(proton::receiver& rcv) override {
        std::cout << "RECEIVE: Opened receiver for source address '"
                  << rcv.source().address() << "'\n";
    }

    void on_message(proton::delivery& dlv, proton::message& msg) override {
        std::cout << "RECEIVE: Received message '" << msg.body() << "'\n";

        received_++;

        if (received_ == desired_) {
            dlv.receiver().close();
            dlv.connection().close();
        }
    }
};

int main(int argc, char** argv) {
    if (argc != 3 && argc != 4) {
        std::cerr << "Usage: receive <connection-url> <address> [<message-count>]\n";
        return 1;
    }

    receive_handler handler {};
    handler.conn_url_ = argv[1];
    handler.address_ = argv[2];

    if (argc == 4) {
        handler.desired_ = std::stoi(argv[3]);
    }

    proton::container cont {handler};

    try {
        cont.run();
    } catch (const std::exception& e) {
        std::cerr << e.what() << "\n";
        return 1;
    }

    return 0;
}

Running the example

To run the example program, copy it to a local file, compile it, and execute it from the command line.

$ g++ receive.cpp -o receive -std=c++11 -lstdc++ -lqpid-proton-cpp
$ ./receive amqp://localhost queue1

Chapter 5. Using the API

For more information, see the AMQ C++ API reference and AMQ C++ example suite.

5.1. Handling messaging events

AMQ C++ is an asynchronous event-driven API. To define how the application handles events, the user implements callback methods on the messaging_handler class. These methods are then called as network activity or timers trigger new events.

Example: Handling messaging events

struct example_handler : public proton::messaging_handler {
    void on_container_start(proton::container& cont) override {
        std::cout << "The container has started\n";
    }

    void on_sendable(proton::sender& snd) override {
        std::cout << "A message can be sent\n";
    }

    void on_message(proton::delivery& dlv, proton::message& msg) override {
        std::cout << "A message is received\n";
    }
};

These are only a few common-case events. The full set is documented in the API reference.

5.2. Creating a container

The container is the top-level API object. It is the entry point for creating connections, and it is responsible for running the main event loop. It is often constructed with a global event handler.

Example: Creating a container

int main() {
    example_handler handler {};
    proton::container cont {handler};
    cont.run();
}

5.3. Setting the container identity

Each container instance has a unique identity called the container ID. When AMQ C++ makes a connection, it sends the container ID to the remote peer. To set the container ID, pass it to the proton::container constructor.

Example: Setting the container identity

proton::container cont {handler, "job-processor-3"};

If the user does not set the ID, the library will generate a UUID when the container is constucted.

Chapter 6. Network connections

6.1. Connection URLs

Connection URLs encode the information used to establish new connections.

Connection URL syntax

scheme://host[:port]

  • Scheme - The connection transport, either amqp for unencrypted TCP or amqps for TCP with SSL/TLS encryption.
  • Host - The remote network host. The value can be a hostname or a numeric IP address. IPv6 addresses must be enclosed in square brackets.
  • Port - The remote network port. This value is optional. The default value is 5672 for the amqp scheme and 5671 for the amqps scheme.

Connection URL examples

amqps://example.com
amqps://example.net:56720
amqp://127.0.0.1
amqp://[::1]:2000

6.2. Creating outgoing connections

To connect to a remote server, call the container::connect() method with a connection URL. This is typically done inside the messaging_handler::on_container_start() method.

Example: Creating outgoing connections

class example_handler : public proton::messaging_handler {
    void on_container_start(proton::container& cont) override {
        cont.connect("amqp://example.com");
    }

    void on_connection_open(proton::connection& conn) override {
        std::cout << "The connection is open\n";
    }
};

See the Chapter 7, Security section for information about creating secure connections.

6.3. Configuring reconnect

Reconnect allows a client to recover from lost connections. It is used to ensure that the components in a distributed system reestablish communication after temporary network or component failures.

AMQ C++ disables reconnect by default. To enable it, set the reconnect connection option to an instance of the reconnect_options class.

Example: Enabling reconnect

proton::connection_options opts {};
proton::reconnect_options ropts {};

opts.reconnect(ropts);

container.connect("amqp://example.com", opts);

With reconnect enabled, if a connection is lost or a connection attempt fails, the client will try again after a brief delay. The delay increases exponentially for each new attempt.

To control the delays between connection attempts, set the delay, delay_multiplier, and max_delay options. All durations are specified in milliseconds.

To limit the number of reconnect attempts, set the max_attempts option. Setting it to 0 removes any limit.

Example: Configuring reconnect

proton::connection_options opts {};
proton::reconnect_options ropts {};

ropts.delay(proton::duration(10));
ropts.delay_multiplier(2.0);
ropts.max_delay(proton::duration::FOREVER);
ropts.max_attempts(0);

opts.reconnect(ropts);

container.connect("amqp://example.com", opts);

6.4. Configuring failover

AMQ C++ allows you to configure multiple connection endpoints. If connecting to one fails, the client attempts to connect to the next in the list. If the list is exhausted, the process starts over.

To specify alternate connection endpoints, set the failover_urls reconnect option to a list of connection URLs.

Example: Configuring failover

std::vector<std::string> failover_urls = {
    "amqp://backup1.example.com",
    "amqp://backup2.example.com"
};

proton::connection_options opts {};
proton::reconnect_options ropts {};

opts.reconnect(ropts);
ropts.failover_urls(failover_urls);

container.connect("amqp://primary.example.com", opts);

6.5. Accepting incoming connections

AMQ C++ can accept inbound network connections, enabling you to build custom messaging servers.

To start listening for connections, use the proton::container::listen() method with a URL containing the local host address and port to listen on.

Example: Accepting incoming connections

class example_handler : public proton::messaging_handler {
    void on_container_start(proton::container& cont) override {
        cont.listen("0.0.0.0");
    }

    void on_connection_open(proton::connection& conn) override {
        std::cout << "New incoming connection\n";
    }
};

The special IP address 0.0.0.0 listens on all available IPv4 interfaces. To listen on all IPv6 interfaces, use [::0].

For more information, see the server receive.cpp example.

Chapter 7. Security

7.1. Securing connections with SSL/TLS

AMQ C++ uses SSL/TLS to encrypt communication between clients and servers.

To connect to a remote server with SSL/TLS, set the ssl_client_options connection option and use a connection URL with the amqps scheme. The ssl_client_options constructor takes the filename, directory, or database ID of a CA certificate.

Example: Enabling SSL/TLS

proton::ssl_client_options sopts {"/etc/pki/ca-trust"};
proton::connection_options opts {};

opts.ssl_client_options(sopts);

container.connect("amqps://example.com", opts);

7.2. Connecting with a user and password

AMQ C++ can authenticate connections with a user and password.

To specify the credentials used for authentication, set the user and password options on the connect method.

Example: Connecting with a user and password

proton::connection_options opts {};

opts.user("alice");
opts.password("secret");

container.connect("amqps://example.com", opts);

7.3. Configuring SASL authentication

AMQ C++ uses the SASL protocol to perform authentication. SASL can use a number of different authentication mechanisms. When two network peers connect, they exchange their allowed mechanisms, and the strongest mechanism allowed by both is selected.

Note

The client uses Cyrus SASL to perform authentication. Cyrus SASL uses plug-ins to support specific SASL mechanisms. Before you can use a particular SASL mechanism, the relevant plug-in must be installed. For example, you need the cyrus-sasl-plain plug-in in order to use SASL PLAIN authentication.

To see a list of Cyrus SASL plug-ins in Red Hat Enterprise Linux, use the yum search cyrus-sasl command. To install a Cyrus SASL plug-in, use the yum install PLUG-IN command.

By default, AMQ C++ allows all of the mechanisms supported by the local SASL library configuration. To restrict the allowed mechanisms and thereby control what mechanisms can be negotiated, use the sasl_allowed_mechs connection option. This option accepts a string containing a space-separated list of mechanism names.

Example: Configuring SASL authentication

proton::connection_options opts {};

opts.sasl_allowed_mechs("ANONYMOUS");

container.connect("amqps://example.com", opts);

This example forces the connection to authenticate using the ANONYMOUS mechanism even if the server we connect to offers other options. Valid mechanisms include ANONYMOUS, PLAIN, SCRAM-SHA-256, SCRAM-SHA-1, GSSAPI, and EXTERNAL.

AMQ C++ enables SASL by default. To disable it, set the sasl_enabled connection option to false.

Example: Disabling SASL

proton::connection_options opts {};

opts.sasl_enabled(false);

container.connect("amqps://example.com", opts);

7.4. Authenticating using Kerberos

Kerberos is a network protocol for centrally managed authentication based on the exchange of encrypted tickets. See Using Kerberos for more information.

  1. Configure Kerberos in your operating system. See Configuring Kerberos to set up Kerberos on Red Hat Enterprise Linux.
  2. Enable the GSSAPI SASL mechanism in your client application.

    proton::connection_options opts {};
    
    opts.sasl_allowed_mechs("GSSAPI");
    
    container.connect("amqps://example.com", opts);
  3. Use the kinit command to authenticate your user credentials and store the resulting Kerberos ticket.

    $ kinit USER@REALM
  4. Run the client program.

Chapter 8. Senders and receivers

The client uses sender and receiver links to represent channels for delivering messages. Senders and receivers are unidirectional, with a source end for the message origin, and a target end for the message destination.

Source and targets often point to queues or topics on a message broker. Sources are also used to represent subscriptions.

8.1. Creating queues and topics on demand

Some message servers support on-demand creation of queues and topics. When a sender or receiver is attached, the server uses the sender target address or the receiver source address to create a queue or topic with a name matching the address.

The message server typically defaults to creating either a queue (for one-to-one message delivery) or a topic (for one-to-many message delivery). The client can indicate which it prefers by setting the queue or topic capability on the source or target.

To select queue or topic semantics, follow these steps:

  1. Configure your message server for automatic creation of queues and topics. This is often the default configuration.
  2. Set either the queue or topic capability on your sender target or receiver source, as in the examples below.

Example: Sending to a queue created on demand

void on_container_start(proton::container& cont) override {
    proton::connection conn = cont.connect("amqp://example.com");
    proton::sender_options opts {};
    proton::target_options topts {};

    topts.capabilities(std::vector<proton::symbol> { "queue" });
    opts.target(topts);

    conn.open_sender("jobs", opts);
}

Example: Receiving from a topic created on demand

void on_container_start(proton::container& cont) override {
    proton::connection conn = cont.connect("amqp://example.com");
    proton::receiver_options opts {};
    proton::source_options sopts {};

    sopts.capabilities(std::vector<proton::symbol> { "topic" });
    opts.source(sopts);

    conn.open_receiver("notifications", opts);
}

For more details, see the following examples:

8.2. Creating durable subscriptions

A durable subscription is a piece of state on the remote server representing a message receiver. Ordinarily, message receivers are discarded when a client closes. However, because durable subscriptions are persistent, clients can detach from them and then re-attach later. Any messages received while detached are available when the client re-attaches.

Durable subscriptions are uniquely identified by combining the client container ID and receiver name to form a subscription ID. These must have stable values so that the subscription can be recovered.

To create a durable subscription, follow these steps:

  1. Set the connection container ID to a stable value, such as client-1:

    proton::container cont {handler, "client-1"};
  2. Create a receiver with a stable name, such as sub-1, and configure the receiver source for durability by setting the durability_mode and expiry_policy options:

    void on_container_start(proton::container& cont) override {
        proton::connection conn = cont.connect("amqp://example.com");
        proton::receiver_options opts {};
        proton::source_options sopts {};
    
        opts.name("sub-1");
        sopts.durability_mode(proton::source::UNSETTLED_STATE);
        sopts.expiry_policy(proton::source::NEVER);
    
        opts.source(sopts);
    
        conn.open_receiver("notifications", opts);
    }

To detach from a subscription, use the proton::receiver::detach() method. To terminate the subscription, use the proton::receiver::close() method.

For more information, see the durable-subscribe.cpp example.

8.3. Creating shared subscriptions

A shared subscription is a piece of state on the remote server representing one or more message receivers. Because it is shared, multiple clients can consume from the same stream of messages.

The client configures a shared subscription by setting the shared capability on the receiver source.

Shared subscriptions are uniquely identified by combining the client container ID and receiver name to form a subscription ID. These must have stable values so that multiple client processes can locate the same subscription. If the global capability is set in addition to shared, the receiver name alone is used to identify the subscription.

To create a durable subscription, follow these steps:

  1. Set the connection container ID to a stable value, such as client-1:

    proton::container cont {handler, "client-1"};
  2. Create a receiver with a stable name, such as sub-1, and configure the receiver source for sharing by setting the shared capability:

    void on_container_start(proton::container& cont) override {
        proton::connection conn = cont.connect("amqp://example.com");
        proton::receiver_options opts {};
        proton::source_options sopts {};
    
        opts.name("sub-1");
        sopts.capabilities(std::vector<proton::symbol> { "shared" });
    
        opts.source(sopts);
    
        conn.open_receiver("notifications", opts);
    }

To detach from a subscription, use the proton::receiver::detach() method. To terminate the subscription, use the proton::receiver::close() method.

For more information, see the shared-subscribe.cpp example.

Chapter 9. Message delivery

9.1. Sending messages

To send a message, override the on_sendable event handler and call the sender::send() method. The sendable event fires when the proton::sender has enough credit to send at least one message.

Example: Sending messages

struct example_handler : public proton::messaging_handler {
    void on_container_start(proton::container& cont) override {
        proton::connection conn = cont.connect("amqp://example.com");
        conn.open_sender("jobs");
    }

    void on_sendable(proton::sender& snd) override {
        proton::message msg {"job-1"};
        snd.send(msg);
    }
};

9.2. Tracking sent messages

When a message is sent, the sender can keep a reference to the tracker object representing the transfer. The receiver accepts or rejects each message that is delivered. The sender is notified of the outcome for each tracked delivery.

To monitor the outcome of a sent message, override the on_tracker_accept and on_tracker_reject event handlers and map the delivery state update to the tracker returned from send().

Example: Tracking sent messages

void on_sendable(proton::sender& snd) override {
    proton::message msg {"job-1"};
    proton::tracker trk = snd.send(msg);
}

void on_tracker_accept(proton::tracker& trk) override {
    std::cout << "Delivery for " << trk << " is accepted\n";
}

void on_tracker_reject(proton::tracker& trk) override {
    std::cout << "Delivery for " << trk << " is rejected\n";
}

9.3. Receiving messages

To receive messages, create a receiver and override the on_message event handler.

Example: Receiving messages

struct example_handler : public proton::messaging_handler {
    void on_container_start(proton::container& cont) override {
        proton::connection conn = cont.connect("amqp://example.com");
        conn.open_receiver("jobs");
    }

    void on_message(proton::delivery& dlv, proton::message& msg) override {
        std::cout << "Received message '" << msg.body() << "'\n";
    }
};

9.4. Acknowledging received messages

To explicitly accept or reject a delivery, use the delivery::accept() or delivery::reject() methods in the on_message event handler.

Example: Acknowledging received messages

void on_message(proton::delivery& dlv, proton::message& msg) override {
    try {
        process_message(msg);
        dlv.accept();
    } catch (std::exception& e) {
        dlv.reject();
    }
}

By default, if you do not explicity acknowledge a delivery, then the library accepts it after on_message returns. To disable this behavior, set the auto_accept receiver option to false.

Chapter 10. Error handling

Errors in AMQ C++ can be handled in two different ways:

  • Catching exceptions
  • Overriding virtual functions to handle AMQP protocol or connection errors

Catching exceptions is the most basic, but least granular, way to handle errors. If an error is not handled using an override in a handler routine, an exception is thrown and can be caught and handled.

10.1. Handling exceptions

If an error is not handled using an override in a handler routine, an exception is thrown by the container’s run method.

All of the exceptions that AMQ C++ throws inherit from the proton::error class, which in turn inherits from the std::runtime_error and std::exception classes.

The following example illustrates how to catch any exception thrown from AMQ C++:

Example: API-Specific exception handling

try {
    // Something that might throw an exception
} catch (proton::error& e) {
    // Handle Proton-specific problems here
} catch (std::exception& e) {
    // Handle more general problems here
}

If you do not require API-specific exception handling, you only need to catch std::exception, since proton::error inherits from it.

Example: General exception handling

int main() {
    try {
        // Something that might throw an exception
    } catch (std::exception& e) {
        std::cerr << "Caught exception: " << e.what() << std::endl;
    }
}

Note

Because all exceptions in a C++ program inherit from std::exception, you can write a code block to wrap your main method and display information about any std::exception errors.

10.2. Handling connection and protocol errors

You can handle protocol-level errors by overriding the following messaging_handler methods:

  • on_transport_error(proton::transport&)
  • on_connection_error(proton::connection&)
  • on_session_error(proton::session&)
  • on_receiver_error(proton::receiver&)
  • on_sender_error(proton::sender&)

These event handling routines are called whenever there is an error condition with the specific object that is in the event. After calling the error handler, the appropriate close handler is also called.

If not overridden, the default error handler will be called with an indication of the error condition that occurred.

If one of the more specific error handlers is not overridden, the default error handler is called:

  • on_error(proton::error_condition&)
Note

As the close handlers are called in the event of any error, only the error itself needs to be handled within the error handler. Resource clean up can be managed by close handlers. If there is no error handling that is specific to a particular object it is typical to use the general on_error handler and not have a more specific handler.

10.3. Logging

10.3.1. Enabling protocol logging

The client can log AMQP protocol frames to the console. This data is often critical when diagnosing problems.

To enable protocol logging, set the PN_TRACE_FRM environment variable to 1:

Example: Enabling protocol logging

$ export PN_TRACE_FRM=1
$ <your-client-program>

To disable protocol logging, unset the PN_TRACE_FRM environment variable.

Chapter 11. Threading and scheduling

AMQ C++ supports full multithreading with C++11 and later. Limited multithreading is possible with older versions of C++. See Section 11.6, “Using older versions of C++”.

11.1. The threading model

The container object can handle multiple connections concurrently. When AMQP events occur on connections, the container calls messaging_handler callback functions. Callbacks for any one connection are serialized (not called concurrently), but callbacks for different connections can be safely executed in parallel.

You can assign a handler to a connection in container::connect() or listen_handler::on_accept() using the handler connection option. It is recommended to create a separate handler for each connection so that the handler does not need locks or other synchronization to protect it against concurrent use by library threads. If any non-library threads use the handler concurrently, then you need synchronization.

11.2. Thread-safety rules

The connection, session, sender, receiver, tracker, and delivery objects are not thread-safe and are subject to the following rules.

  1. You must use them only from a messaging_handler callback or a work_queue function.
  2. You must not use objects belonging to one connection from a callback for another connection.
  3. You can store AMQ C++ objects in member variables for use in a later callback, provided you respect rule two.

The message object is a value type with the same threading constraints as a standard C++ built-in type. It cannot be concurrently modified.

11.3. Work queues

The work_queue interface provides a safe way to communicate between different connection handlers or between non-library threads and connection handlers.

  • Each connection has an associated work_queue.
  • The work queue is thread-safe (C++11 or greater). Any thread can add work.
  • A work item is a std::function, and bound arguments are called like an event callback.

When the library calls the work function, it is serialized safely so that you can treat the work function like an event callback and safely access the handler and AMQ C++ objects stored on it.

11.4. The wake primitive

The connection::wake() method allows any thread to prompt activity on a connection by triggering an on_connection_wake() callback. This is the only thread-safe method on connection.

wake() is a lightweight, low-level primitive for signaling between threads.

  • It does not carry any code or data, unlike work_queue.
  • Multiple calls to wake() might be coalesced into a single on_connection_wake().
  • Calls to on_connection_wake() can occur without any application call to wake() since the library uses wake() internally.

The semantics of wake() are similar to std::condition_variable::notify_one(). There will be a wakeup, but there must be some shared application state to determine why the wakeup occurred and what, if anything, to do about it.

Work queues are easier to use in many instances, but wake() may be useful if you already have your own external thread-safe queues and need an efficient way to wake a connection to check them for data.

11.5. Scheduling deferred work

AMQ C++ has the ability to execute code after a delay. You can use this to implement time-based behaviors in your application, such as periodically scheduled work or timeouts.

To defer work for a fixed amount of time, use the schedule method to set the delay and register a function defining the work.

Example: Sending a message after a delay

void on_sender_open(proton::sender& snd) override {
    proton::duration interval {5 * proton::duration::SECOND};
    snd.work_queue().schedule(interval, [=] { send(snd); });
}

void send(proton::sender snd) {
    if (snd.credit() > 0) {
        proton::message msg {"hello"};
        snd.send(msg);
    }
}

This example uses the schedule method on the work queue of the sender in order to establish it as the execution context for the work.

11.6. Using older versions of C++

Before C++11 there was no standard support for threading in C++. You can use AMQ C++ with threads but with the following limitations.

  • The container does not create threads. It only uses the single thread that calls container::run().
  • None of the AMQ C++ library classes are thread-safe, including container and work_queue. You need an external lock to use container in multiple threads. The only exception is connection::wake(). It is thread-safe even in older C++.

The container::schedule() and work_queue APIs accept C++11 lambda functions to define units of work. If you are using a version of C++ that does not support lambdas, you must use the make_work() function instead.

Chapter 12. File-based configuration

AMQ C++ can read the configuration options used to establish connections from a local file named connect.json. This enables you to configure connections in your application at the time of deployment.

The library attempts to read the file when the application calls the container connect method without supplying any connection options.

12.1. File locations

If set, AMQ C++ uses the value of the MESSAGING_CONNECT_FILE environment variable to locate the configuration file.

If MESSAGING_CONNECT_FILE is not set, AMQ C++ searches for a file named connect.json at the following locations and in the order shown. It stops at the first match it encounters.

On Linux:

  1. $PWD/connect.json, where $PWD is the current working directory of the client process
  2. $HOME/.config/messaging/connect.json, where $HOME is the current user home directory
  3. /etc/messaging/connect.json

On Windows:

  1. %cd%/connect.json, where %cd% is the current working directory of the client process

If no connect.json file is found, the library uses default values for all options.

12.2. The file format

The connect.json file contains JSON data, with additional support for JavaScript comments.

All of the configuration attributes are optional or have default values, so a simple example need only provide a few details:

Example: A simple connect.json file

{
    "host": "example.com",
    "user": "alice",
    "password": "secret"
}

SASL and SSL/TLS options are nested under "sasl" and "tls" namespaces:

Example: A connect.json file with SASL and SSL/TLS options

{
    "host": "example.com",
    "user": "ortega",
    "password": "secret",
    "sasl": {
        "mechanisms": ["SCRAM-SHA-1", "SCRAM-SHA-256"]
    },
    "tls": {
        "cert": "/home/ortega/cert.pem",
        "key": "/home/ortega/key.pem"
    }
}

12.3. Configuration options

The option keys containing a dot (.) represent attributes nested inside a namespace.

Table 12.1. Configuration options in connect.json

KeyValue typeDefault valueDescription

scheme

string

"amqps"

"amqp" for cleartext or "amqps" for SSL/TLS

host

string

"localhost"

The hostname or IP address of the remote host

port

string or number

"amqps"

A port number or port literal

user

string

None

The user name for authentication

password

string

None

The password for authentication

sasl.mechanisms

list or string

None (system defaults)

A JSON list of enabled SASL mechanisms. A bare string represents one mechanism. If none are specified, the client uses the default mechanisms provided by the system.

sasl.allow_insecure

boolean

false

Enable mechanisms that send cleartext passwords

tls.cert

string

None

The filename or database ID of the client certificate

tls.key

string

None

The filename or database ID of the private key for the client certificate

tls.ca

string

None

The filename, directory, or database ID of the CA certificate

tls.verify

boolean

true

Require a valid server certificate with a matching hostname

Chapter 13. Interoperability

This chapter discusses how to use AMQ C++ in combination with other AMQ components. For an overview of the compatibility of AMQ components, see the product introduction.

13.1. Interoperating with other AMQP clients

AMQP messages are composed using the AMQP type system. This common format is one of the reasons AMQP clients in different languages are able to interoperate with each other.

When sending messages, AMQ C++ automatically converts language-native types to AMQP-encoded data. When receiving messages, the reverse conversion takes place.

Note

More information about AMQP types is available at the interactive type reference maintained by the Apache Qpid project.

Table 13.1. AMQP types

AMQP typeDescription

null

An empty value

boolean

A true or false value

char

A single Unicode character

string

A sequence of Unicode characters

binary

A sequence of bytes

byte

A signed 8-bit integer

short

A signed 16-bit integer

int

A signed 32-bit integer

long

A signed 64-bit integer

ubyte

An unsigned 8-bit integer

ushort

An unsigned 16-bit integer

uint

An unsigned 32-bit integer

ulong

An unsigned 64-bit integer

float

A 32-bit floating point number

double

A 64-bit floating point number

array

A sequence of values of a single type

list

A sequence of values of variable type

map

A mapping from distinct keys to values

uuid

A universally unique identifier

symbol

A 7-bit ASCII string from a constrained domain

timestamp

An absolute point in time

Table 13.2. AMQ C++ types before encoding and after decoding

AMQP typeAMQ C++ type before encodingAMQ C++ type after decoding

null

nullptr

nullptr

boolean

bool

bool

char

wchar_t

wchar_t

string

std::string

std::string

binary

proton::binary

proton::binary

byte

int8_t

int8_t

short

int16_t

int16_t

int

int32_t

int32_t

long

int64_t

int64_t

ubyte

uint8_t

uint8_t

ushort

uint16_t

uint16_t

uint

uint32_t

uint32_t

ulong

uint64_t

uint64_t

float

float

float

double

double

double

list

std::vector

std::vector

map

std::map

std::map

uuid

proton::uuid

proton::uuid

symbol

proton::symbol

proton::symbol

timestamp

proton::timestamp

proton::timestamp

Table 13.3. AMQ C++ and other AMQ client types (1 of 2)

AMQ C++ type before encodingAMQ JavaScript typeAMQ .NET type

nullptr

null

null

bool

boolean

System.Boolean

wchar_t

number

System.Char

std::string

string

System.String

proton::binary

string

System.Byte[]

int8_t

number

System.SByte

int16_t

number

System.Int16

int32_t

number

System.Int32

int64_t

number

System.Int64

uint8_t

number

System.Byte

uint16_t

number

System.UInt16

uint32_t

number

System.UInt32

uint64_t

number

System.UInt64

float

number

System.Single

double

number

System.Double

std::vector

Array

Amqp.List

std::map

object

Amqp.Map

proton::uuid

number

System.Guid

proton::symbol

string

Amqp.Symbol

proton::timestamp

number

System.DateTime

Table 13.4. AMQ C++ and other AMQ client types (2 of 2)

AMQ C++ type before encodingAMQ Python typeAMQ Ruby type

nullptr

None

nil

bool

bool

true, false

wchar_t

unicode

String

std::string

unicode

String

proton::binary

bytes

String

int8_t

int

Integer

int16_t

int

Integer

int32_t

long

Integer

int64_t

long

Integer

uint8_t

long

Integer

uint16_t

long

Integer

uint32_t

long

Integer

uint64_t

long

Integer

float

float

Float

double

float

Float

std::vector

list

Array

std::map

dict

Hash

proton::uuid

-

-

proton::symbol

str

Symbol

proton::timestamp

long

Time

13.2. Interoperating with AMQ JMS

AMQP defines a standard mapping to the JMS messaging model. This section discusses the various aspects of that mapping. For more information, see the AMQ JMS Interoperability chapter.

JMS message types

AMQ C++ provides a single message type whose body type can vary. By contrast, the JMS API uses different message types to represent different kinds of data. The table below indicates how particular body types map to JMS message types.

For more explicit control of the resulting JMS message type, you can set the x-opt-jms-msg-type message annotation. See the AMQ JMS Interoperability chapter for more information.

Table 13.5. AMQ C++ and JMS message types

AMQ C++ body typeJMS message type

std::string

TextMessage

nullptr

TextMessage

proton::binary

BytesMessage

Any other type

ObjectMessage

13.3. Connecting to AMQ Broker

AMQ Broker is designed to interoperate with AMQP 1.0 clients. Check the following to ensure the broker is configured for AMQP messaging:

  • Port 5672 in the network firewall is open.
  • The AMQ Broker AMQP acceptor is enabled. See Default acceptor settings.
  • The necessary addresses are configured on the broker. See Addresses, Queues, and Topics.
  • The broker is configured to permit access from your client, and the client is configured to send the required credentials. See Broker Security.

13.4. Connecting to AMQ Interconnect

AMQ Interconnect works with any AMQP 1.0 client. Check the following to ensure the components are configured correctly:

  • Port 5672 in the network firewall is open.
  • The router is configured to permit access from your client, and the client is configured to send the required credentials. See Securing network connections.

Appendix A. Using your subscription

AMQ is provided through a software subscription. To manage your subscriptions, access your account at the Red Hat Customer Portal.

A.1. Accessing your account

Procedure

  1. Go to access.redhat.com.
  2. If you do not already have an account, create one.
  3. Log in to your account.

A.2. Activating a subscription

Procedure

  1. Go to access.redhat.com.
  2. Navigate to My Subscriptions.
  3. Navigate to Activate a subscription and enter your 16-digit activation number.

A.3. Downloading release files

To access .zip, .tar.gz, and other release files, use the customer portal to find the relevant files for download. If you are using RPM packages or the Red Hat Maven repository, this step is not required.

Procedure

  1. Open a browser and log in to the Red Hat Customer Portal Product Downloads page at access.redhat.com/downloads.
  2. Locate the Red Hat AMQ entries in the INTEGRATION AND AUTOMATION category.
  3. Select the desired AMQ product. The Software Downloads page opens.
  4. Click the Download link for your component.

A.4. Registering your system for packages

To install RPM packages on Red Hat Enterprise Linux, your system must be registered. If you are using downloaded release files, this step is not required.

Procedure

  1. Go to access.redhat.com.
  2. Navigate to Registration Assistant.
  3. Select your OS version and continue to the next page.
  4. Use the listed command in your system terminal to complete the registration.

For more information, see How to Register and Subscribe a System to the Red Hat Customer Portal.

Appendix B. Using Red Hat Enterprise Linux packages

This section describes how to use software delivered as RPM packages for Red Hat Enterprise Linux.

B.1. Overview

A component such as a library or server often has multiple packages associated with it. You do not have to install them all. You can install only the ones you need.

The primary package typically has the simplest name, without additional qualifiers. This package provides all the required interfaces for using the component at program run time.

Packages with names ending in -devel contain headers for C and C++ libraries. These are required at compile time to build programs that depend on this package.

Packages with names ending in -docs contain documentation and example programs for the component.

For more information about using RPM packages, see one of the following resources:

B.2. Searching for packages

To search for packages, use the yum search command. The search results include package names, which you can use as the value for <package> in the other commands listed in this section.

$ yum search <keyword>...

B.3. Installing packages

To install packages, use the yum install command.

$ sudo yum install <package>...

B.4. Querying package information

To list the packages installed in your system, use the rpm -qa command.

$ rpm -qa

To get information about a particular package, use the rpm -qi command.

$ rpm -qi <package>

To list all the files associated with a package, use the rpm -ql command.

$ rpm -ql <package>

Appendix C. Using AMQ Broker with the examples

The AMQ C++ examples require a running message broker with a queue named examples. Use the procedures below to install and start the broker and define the queue.

C.1. Installing the broker

Follow the instructions in Getting Started with AMQ Broker to install the broker and create a broker instance. Enable anonymous access.

The following procedures refer to the location of the broker instance as <broker-instance-dir>.

C.2. Starting the broker

Procedure

  1. Use the artemis run command to start the broker.

    $ <broker-instance-dir>/bin/artemis run
  2. Check the console output for any critical errors logged during startup. The broker logs Server is now live when it is ready.

    $ example-broker/bin/artemis run
               __  __  ____    ____            _
         /\   |  \/  |/ __ \  |  _ \          | |
        /  \  | \  / | |  | | | |_) |_ __ ___ | | _____ _ __
       / /\ \ | |\/| | |  | | |  _ <| '__/ _ \| |/ / _ \ '__|
      / ____ \| |  | | |__| | | |_) | | | (_) |   <  __/ |
     /_/    \_\_|  |_|\___\_\ |____/|_|  \___/|_|\_\___|_|
    
     Red Hat AMQ <version>
    
    2020-06-03 12:12:11,807 INFO  [org.apache.activemq.artemis.integration.bootstrap] AMQ101000: Starting ActiveMQ Artemis Server
    ...
    2020-06-03 12:12:12,336 INFO  [org.apache.activemq.artemis.core.server] AMQ221007: Server is now live
    ...

C.3. Creating a queue

In a new terminal, use the artemis queue command to create a queue named examples.

$ <broker-instance-dir>/bin/artemis queue create --name examples --address examples --auto-create-address --anycast

You are prompted to answer a series of yes or no questions. Answer N for no to all of them.

Once the queue is created, the broker is ready for use with the example programs.

C.4. Stopping the broker

When you are done running the examples, use the artemis stop command to stop the broker.

$ <broker-instance-dir>/bin/artemis stop

Revised on 2020-06-16 17:50:23 UTC

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