PikaTopic - a convenience layer atop Pika for use with RabbitMQ topic exhanges

Pika is a good general purpose library for interacting with a RabbitMQ server. PikaTopic is a simpler, limited interface which can be used when you just need to send or receive messages using a topic exchange.

Additionally, PikaTopic will handle json conversion when sending and receiving data.

Quickstart

pip install pikatopic

A RabbitMQ service ( https://www.rabbitmq.com/ ) must be running.

Run this, it will listen for new messages and not exit unless you kill it.

$ ./examples/recv.py

In another window, run this:

$ ./examples/send.py

You should see output from recv.py.

If your rabbit server is running on a different machine, you can set the PIKATOPIC_HOST environment variable. For example:

$ PIKATOPIC_HOST=172.17.0.2 ./examples/recv.py

$ PIKATOPIC_HOST=172.17.0.2 ./examples/send.py

Configuration

You will probably need to set the host name to connect to your RabbitMQ server. The username, password and exchange are all set to defaults which work for a generic server install.

Default values:

• host is localhost OR the PIKATOPIC_HOST envariable if that is set
• username is guest OR the PIKATOPIC_USERNAME envariable if that is set
• password is guest OR the PIKATOPIC_PASSWORD envariable if that is set
• exchange is amq.topic OR the PIKATOPIC_EXCHANGE envariable if that is set

These may be overridden by passing any of these arguments to the PikaTopic class initialiser or you can change them at the module level by:

import pikatopic

pikatopic.DEFAULT_USERNAME = 'otheruser'
pikatopic.DEFAULT_PASSWORD = 'secrt'
pikatopic.DEFAULT_HOST = '172.17.0.2'
pikatopic.DEFAULT_EXCHANGE = 'monster'

Pika Library

Pikatopic depends on the pika libary.

• http://pika.readthedocs.io/

$ pip install pika

Examples

from pikatopic import PikaTopic

with PikaTopic(host='172.17.0.2') as pt:
    pt.sendData(
        "project.new",
        {
        'project_id':"12345-12345",
        'name':"The Amazing Adventures of Sausage Farts The Dog",
        'creator_id':"676867-45657",
        },
    )

from pikatopic import PikaTopic

def handler(routing_key, message, message_data):
    if message_data:
        print("%r data=%r" % (routing_key, message_data))
    else:
        print("%r text=%r" % (routing_key, message))
    return True


with PikaTopic(host='172.17.0.2') as pt:
    pt.listen(handler, ['#'])

Reference

This library provides a class, PikaTopic which can be used for sending and receiving messages.

Unless using the with construct as in the examples above, you must call open() and close() before and after the send...() and listen() functions.

Sending

sendText(routing_key (string), message (string))

sendData(routing_key (string), message (dict or list))

The sendData method converts the message to a json string and sets the message content_type property to application/json.

Receiving

listen(handler (function), binding_keys (list of strings))

The listen method enters an event loop which normally does not return.

It accepts a handler function which is called for each message received.

handler(routing_key, message_text, message_data)

message_text contains the raw text of the message. If the message is json encoded then message_data contains the decoded dict otherwise it is set to None.

If the handler returns a false value, the listen() loop will return.

Serverless Testing

Pass no_rabbit_server=True to the class initialiser to run without connecting to a server.

This might be useful for testing or transition.

You may want to also set verbose=True

Verbose

Pass verbose=True to the class initialiser to get messages sent to stdout by the listen() and send...() functions.

Thanks, Artella!

This work was funded by Artella ( https://www.artella.com/ ).