Custom Message Formats

By default, the client library support encoding and decoding events and commands as json messages. To add support for your own custom message formats you can create and register implementations of wiotp.sdk.MessageCodec. MessageCodecs work for both commands and events. To Implement a MessageCodec you must support two static class methods:

Encoding

The job of the encode(data, timestamp) method is to take data (any python object) and optionally a timestamp (a datetime.datetime object) and return a String representation of the message ready to be sent over MQTT.

Decoding

The job of decode(message) is to decode an incoming MQTT message and return an instance of ibmiotf.Message

Sample Code

import yaml
import wiotp.sdk.device
import wiotp.sdk.Message
import wiotp.sdk.MessageCodec

class YamlCodec(ibmiotf.MessageCodec):

    @staticmethod
    def encode(data=None, timestamp=None):
        return yaml.dumps(data)

    @staticmethod
    def decode(message):
        try:
            data = yaml.loads(message.payload.decode("utf-8"))
        except ValueError as e:
            raise InvalidEventException("Unable to parse YAML.  payload=\"%s\" error=%s" % (message.payload, str(e)))

        timestamp = datetime.now(pytz.timezone('UTC'))

        return wiotp.sdk.Message(data, timestamp)

myConfig = ibmiotf.device.ParseConfigFile("device.yaml")
client = ibmiotf.device.Client(config=myConfig, logHandlers=None)
client.setMessageCodec("yaml", YamlCodec)
myData = { 'hello' : 'world', 'x' : 100}

# Publish the same event, in both json and yaml formats:
client.publishEvent("status", "json", myData)
client.publishEvent("status", "yaml", myData)

If you want to lookup which encoder is set for a specific message format use the getMessageEncoderModule(msgFormt). If an event is sent/received in an unknown format or if a client does not recognize the format, the client library will raise wiotp.sdk.MissingMessageEncoderException or wiotp.sdk.MissingMessageDecoderException.