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])