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Developer-guide.md

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About

This is the developer guide for any further implementations of this library in another programming language.

Message Format

Messages are simple dictionaries, represented in JSON format. Mandatory keys of a message are as follows:

  • sender: Array of strings. First element is creator's, rest is forwarders' id's.
  • timestamp: Unix time stamp
  • msg_id: a unique message id. practically concatenate creator_id and i where i is sequence number of message
  • payload: a dictionary, described below.

Payload is basically in {'Subject': data} format. Here are some examples:

  • To set green-led pin to True, one must send the following message:

    Python:

    msg = { 'IoMessage': { 'pin_name': 'green-led', 'val': True } }

    Javascript:

    var msg = { IoMessage: { pin_name: 'green-led', val: true } }

    LiveScript:

    msg = IoMessage: pin_name: \green-led, val: on

So, a full message should look like this:

{"sender":["5fa6c6d7-077a-4467-9bb3-1f2c2ee58d78","5e7b8786-4885-4e2d-b4c6-98dc21856ba9","3444aadc-ed01-4ce6-94bc-ae144510eb31","41dl-Gj3"],"timestamp":1440885632.49,"msg_id":"5fa6c6d7-077a-4467-9bb3-1f2c2ee58d78.147","payload":{"IoMessage":{"pin_name":"green-led","val":true}}}

C# Implementation Story

These steps are followed while implementing C# port of this library:

  1. Create an application that can send and receive strings (eg. 'Hello' and 'Hello back!') via ZeroMQ .

  2. Install aktos-dcs.

  3. Edit and set DEBUG_NETWORK_MESSAGES = True in aktos_dcs/gevent_actor.py file to see the debug messages.

  4. Run examples/ponger.py.

  5. Send following string (the_raw_msg) as is from the new implementation code and see if broker got message message is printed in ponger.py:

      "{ \"timestamp\": 1451168495.814, \"msg_id\": \"MZ9YV.6\", \"sender\": [\"MZ9YV\", \"cKsNg\"], \"payload\": {\"PongMessage\": {\"text\": \"Hello ponger, this is pinger 1!\"}}}"

Note that field strings (like timestamp or msg_id etc...) SHOULD be in double quotes (like "msg_id", not single quotes (not like 'msg_id'), else message won't be unpacked by ponger.py.

  1. Because timestamp is too old, message will be dropped. See the following message:

       dropping timeouted message (XXXXX seconds old.)
   filter process done...

  2. Update timestamp field with a current unix time value.

    Note that if you see "key name of object must be string" error, you should check the timestamp value if its decimal separator is dot(.), not comma (,).

  3. See that messages are not dropped because of they are too old, but they are dropped because they are duplicates.

  4. Append a sequence number to msg_id field value.

  5. See messages are reaching ponger.py correctly.

  6. Listen for ponger.py's answers.

  7. Move the listener (the subscriber) to a different thread (or BackgroundWorker).

  8. Create msg_ids and sender id randomly.