# 11. Utilities

The AMPS Python 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 an `array.array` that contains doubles.

    json = '{"data":"sample"}'

    theData = array.array('d')
    # populate theData
    ...

    # Create the payload for the composite message.
    builder = AMPS.CompositeMessageBuilder()

    # Construct the composite
    builder.append(json)
    builder.append(theData.tostring())

    # Send the message
    client.publish("messages", builder.get_data())

### 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.

    parts = parser.parse(message)

    json = parser.get_part(0)
    theData = array.array('d')
    theData.fromstring(parser.get_part(1))

    print ("Received message with %d parts." % parts)
    print (json)
    datastring = ""
    for d in theData:
        datastring += "%f " % d
    print (datastring)

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

## NVFIX Messages

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

- `nvfixbuilder` allows you to assemble a NVFIX message and then serialize it in a format suitable for AMPS.
- `nvfixshredder` 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 FIX message and publish it to the AMPS client.

    # create the payload for the NVFIX Message
    builder = AMPS.NVFIXBuilder()

    # construct the NVFIX message
    builder.append("sample","data")
    builder.append("even", "more data")
    ...

    # display the data
    print (builder.get_string())

    # publish the message
    client.publish("messages-sow", builder.get_string())

### Parsing NVFIX Messages

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

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

    # create the shredder for the message and subscribe to the topic
    shredder = AMPS.NVFIXShredder()
    message = client.subscribe(topic="messages-sow", timeout=5000)

    # shred the message to a map
    message_map = shredder.to_map(message.next().getData())

    # display the values of the message
    for key in message_map :
        print (key + " " + message_map[key])

## 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 it 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.

    # create the payload for the FIX Message
    builder = AMPS.FIXBuilder()

    # construct the FIX message
    builder.append(0,"data")
    builder.append(1, "more data")
    ...

    # display the data
    print (builder.get_string())

    # publish the message
    client.publish("messages-sow", builder.get_string())

### Parsing FIX Messages

To parse a FIX message, create an instance of `fixShredder`, then use the `to_Map()` 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 the shredder for the message and subscribe to the topic
    shredder = AMPS.FIXShredder()
    message = client.subscribe(topic="messages-sow", timeout=5000)

    # shred the message to a map
    message_map = shredder.to_map(message.next().getData())

    # display the values of the message
    for key in message_map :
        print (str(key) + " " + message_map[key])