12. Utilities¶

The AMPS C++ client includes a set of utilities and helper classes to make working with AMPS easier.

Composite Message Types¶

The client provides a pair of classes for creating and parsing composite message types.

CompositeMessageBuilder allows you to assemble the parts of a composite message and then serialize them in a format suitable for AMPS.
CompositeMessageParser extracts the individual parts of a composite message type

For more information regarding composite message types, refer to Chapter 4.3.

Building Composite Messages¶

To build a composite message, create an instance of CompositeMessageBuilder, and populate the parts. The CompositeMessageBuilder copies the parts provided, in order, to the underlying message. The builder simply writes to an internal buffer with the appropriate formatting, and does not allow you to update or change the individual parts of a message once they’ve been added to the builder.

The snippet below shows how to build a composite message that includes a JSON part, constructed as a string, and a binary part consisting of the bytes from a standard vector.

std::string json_part("{\"data\":\"sample\"}");

std::vector<double> data;
/* populate data */
...

/* Create the payload for the composite message. */
AMPS::CompositeMessageBuilder builder;

builder.append(json_part.str());
builder.append(reinterpret_cast<const char*>(data.data()),
                   data.size() * sizeof(double));

/* send the message */
std::string topic("messages");
ampsClient.publish(topic.c_str(), topic.length(), builder.data(), builder.length());

Parsing Composite Messages¶

To parse a composite message, create an instance of CompositeMessageParser, then use the parse() method to parse the message provided by the AMPS client. The CompositeMessageParser gives you access to each part of the message as a sequence of bytes.

For example, the following snippet parses and prints messages that contain a JSON part and a binary part that contains an array of doubles.

for (auto message : ampsClient.subscribe("messages")) {

    parser.parse(message);

    /* first part is JSON */
    std::string json_part = std::string(parser.getPart(0));

    /* Second part is the raw bytes for a vector<double> */
    AMPS::Field binary = parser.getPart(1);

    std::vector<double> vec;
    double *array_start = (double*)binary.data();
    double *array_end = array_start + (binary.len() / sizeof(double));

    vec.insert(vec.end(), array_start, array_end);

    /* Print the contents of the message */
    std::cout << "Received message with " << parser.size() << " parts"
              << std::endl
              << "\t" << json_part
              << std::endl;

    for (auto d : vec)
        std::cout << d << " ";

    std::cout << std::endl;
}

Notice that the receiving application is written with explicit knowledge of the structure and content of the composite message type.

Composite Message Builder and Composite Message Parser Samples¶

The C++ client distribution contains the following samples to demonstrate CompositeMessageBuilder and CompositeMessageParser.

Sample Name	Demonstrates
`amps_publish_composite.cpp`	Creating and publishing a composite message using `CompositeMessageBuilder`
`amps_subscribe_composite.cpp`	Receiving and parsing a composite message using `CompositeMessageParser`

NVFIX Messages¶

The client provides a pair of classes for creating and parsing NVFIX message types.

NVFIXBuilder allows you to assemble an NVFIX message and then serialize them in a format suitable for AMPS.
FIXShredder extracts the individual fields of a NVFIX message type

Building NVFIX Messages¶

To build a NVFIX message, create an instance of NVFIXBuilder, then add the fields of the message using append(). NVFIXBuilder copies the fields provided, in order, to the underlying message. The builder simply writes to an internal buffer with the appropriate formatting, and does not allow you to update or change the individual fields of a message once they’ve been added to the builder.

The snippet below shows how to build a NVFIX message and publish it to the AMPS client.

/* Construct a client with the name "NVFIXPublisher". */
AMPS::Client ampsClient("NVFIXPublisher");

/* Construct a simple NVFIX message. */
AMPS::NVFIXBuilder builder;

/* Add data to the builder */
builder.append("Test", "data");
builder.append("More", "stuff");

/* Display the data */
std::cout << builder.getString() << std::endl;

try
{
    /* Connect to the server and log on */
    ampsClient.connect(uri);
    ampsClient.logon();

    /* Publish message to the topic messages */
    std::string topic("messages");
    ampsClient.publish(topic, builder.getString());
}
catch (const AMPS::AMPSException& e)
{
    std::cerr << e.what() << std::endl;
    exit(1);
}

Parsing NVFIX Messages¶

To parse a NVFIX message, create an instance of FIXShredder, then use the toMap() method to parse the message provided by the AMPS client. The FIXShredder gives you access to each field of the message in a map.

The snippet below shows how to parse and print an NVFIX message.

/* Create a client with the name "NVFIXSubscriber" */
AMPS::Client ampsClient("NVFIXSubscriber");

try
{
    /* Connect to the server and log on */
    ampsClient.connect(uri);
    ampsClient.logon();

    /* Subscribe to the messages topic
     *
     * This overload of the subscribe method returns a MessageStream
     * that can be iterated over.  When the MessageStream destructor
     * runs, the destructor unsubscribes.
     */

    /* Set up the shredder */
    AMPS::FIXShredder shredder;

    for (auto message : ampsClient.subscribe("messages")) {
        /* Shred the data to a map */
        auto subscription = shredder.toMap(message.getData());

        /* Display the data */
        for (auto iterator = subscription.begin(); iterator != subscription.end(); ++iterator) {
            std::cout << iterator->first << " " << iterator->second << std::endl;
        }
    }
}
catch (const AMPS::AMPSException& e)
{
    std::cerr << e.what() << std::endl;
    exit(1);
}

NVFIX Builder and Shredder Samples¶

The C++ client distribution contains the following samples to demonstrate NVFIXBuilder and NVFIXShredder.

Sample Name	Demonstrates
`amps_nvfix_builder_publisher.cpp`	Creating and publishing a message using `NVFIXBuilder`
`amps_nvfix_builder_subscriber.cpp`	Receiving a message and parsing it using `NVFIXShredder`

FIX Messages¶

The client provides a pair of classes for creating and parsing FIX messages.

FIXBuilder allows you to assemble a FIX message and then serialize them in a format suitable for AMPS.
FIXShredder extracts the individual fields of a FIX message.

Building FIX Messages¶

To build a FIX message, create an instance of FIXBuilder, then add the fields of the message using append(). FIXBuilder copies the fields provided, in order, to the underlying message. The builder simply writes to an internal buffer with the appropriate formatting, and does not allow you to update or change the individual fields of a message once they’ve been added to the builder.

The snippet below shows how to build a FIX message and publish it to the AMPS client.

/* Construct a client with the name "FIXPublisher". */
AMPS::Client ampsClient("FIXPublisher");

/* Construct a simple FIX message. */
AMPS::FIXBuilder builder;

/* Add data to the builder */
builder.append(0, "123");

/* Display the data */
std::cout << builder.getString() << std::endl;

try
{
    /* connect to the server and log on */
    ampsClient.connect(uri);
    ampsClient.logon();

    /* publish message to the messages topic */
    std::string topic("messages");
    ampsClient.publish(topic, builder.getString());

}
catch (const AMPS::AMPSException& e)
{
    std::cerr << e.what() << std::endl;
    exit(1);
}

Parsing FIX Messages¶

To parse a FIX message, create an instance of FIXShredder, then use the toMap() method to parse the message provided by the AMPS client. The FIXShredder gives you access to each field of the message in a map.

The snippet below shows how to parse and print a FIX message.

/* Create a client with the name "NVFIXSubscriber" */
AMPS::Client ampsClient("NVFIXSubscriber");

try
{
    /* Connect to the server and log on */
    ampsClient.connect(uri);
    ampsClient.logon();

    /* Subscribe to the messages topic
     *
     * This overload of the subscribe method returns a MessageStream
     * that can be iterated over.  When the MessageStream destructor
     * runs, the destructor unsubscribes.
     */

    /* Set up the shredder */
    AMPS::FIXShredder shredder;

    for (auto message : ampsClient.subscribe("messages"))
    {
        // Shred the data to a map
        auto subscription = shredder.toMap(message.getData());

        // Display the data
        for (auto iterator = subscription.begin(); iterator != subscription.end(); ++iterator)
        {
            std::cout << iterator->first << " " << iterator->second << std::endl;
        }
    }
}
catch (const AMPS::AMPSException& e)
{
    std::cerr << e.what() << std::endl;
    exit(1);
}

FIX Builder and Shredder Samples¶