Utility Classes

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 the Message Types chapter in the AMPS User Guide.

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"}'


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


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

# Construct the composite
builder.append(json)
builder.append(data.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)
data = array.array('d')
data.fromstring(parser.get_part(1))

print("Received message with %d parts." % parts)
print(json)
datastring = ""
for d in data:
    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 an NVFIX message and then serialize it in a format suitable for AMPS.

• NVFIXShredder extracts the individual fields of an NVFIX message type.

Building NVFIX Messages

To build an 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 an NVFIX 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 an 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 an 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().get_data())

# 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().get_data())

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