mqtt.py

#

import sys

import codecs
import stringphone
import paho.mqtt.client as mqtt

TOPIC_NAME = "stringphone"

#

A simple convenience function to avoid repetition.

def send(client, message):

#

    client.publish(TOPIC_NAME, bytearray(codecs.encode(message, "hex")))

#

The operations to perform when connecting to MQTT.

def on_connect(client, userdata, flags, rc):

#

    print("Participant %s: Connected with id %s!" %
          (id, codecs.encode(topic.id, "hex")))
    client.subscribe(TOPIC_NAME)

#

Introduce ourselves to the channel, to hopefully get other participants to trust us.

    send(client, topic.construct_intro())

#

The operations to perform on receiving a new message.

def on_message(client, userdata, msg):

#

Decode the payload.

    payload = codecs.decode(msg.payload, "hex")
    try:

#

Try to decode the message.

        message = topic.decode(payload)
        if message:

#

Print the decoded message, if we didn't drop it.

            print(message)
    except stringphone.exceptions.IntroductionError:
        message = stringphone.Message(payload)
        print("Participant %s: New participant with ID %s joined, should I"
              " trust them? Since you can't really reply, I'll assume you"
              " said yes." %
              (id, codecs.encode(message.sender_id, "hex")))

#

Trust the participant that just introduced itself.

        topic.add_participant(message.sender_key)

#

Construct the reply that contains the topic key.

        reply = topic.construct_reply(payload)
        print("Sending reply...")
        send(client, reply)
    except stringphone.exceptions.IntroductionReplyError:

#

Decode the received introduction reply.

        print("Decoding reply...")
        topic.parse_reply(payload)
        send(client, topic.encode(bytearray("Hey guys! This is participant %s." % id, "ascii")))

#

Connect to MQTT.

def main(topic, id):

#

    client = mqtt.Client()
    client.on_connect = on_connect
    client.on_message = on_message

    client.connect("test.mosquitto.org", 1883, 60)
    client.loop_forever()


if __name__ == "__main__":
    if len(sys.argv) != 2:
        sys.exit("Usage: mqttsample.py <numeric id, starting at 1>")

    id = int(sys.argv[1])

    if id == 1:
        topic_key = stringphone.generate_topic_key()
    else:
        topic_key = None

    topic = stringphone.Topic(topic_key=topic_key)

    main(topic, id)