aiocoap-pubsub-broker

This is a simple CoAP broker implemented in Python using the aiocoap library. The broker creates and manages resources for storing data by implementing various Resource classes provided by aiocoap. The script follows publish-subscribe architecture for the Constrained Application Protocol (CoAP) defined at draft-ietf-core-coap-pubsub.

Requirements

• Python 3.7 or higher
• aiocoap library

Installation

You need to install the latest development version of aiocoap, which supports iPATCH.

pip3 install --upgrade "git+https://github.com/chrysn/aiocoap#egg=aiocoap[all]"

Usage

Run the CoAP broker (I recommend hupper if you are developing in python):

hupper -m broker

The broker will start listening on 127.0.0.1:5683.

Create Topic

Any client can create a topic-configuration as "admin":

./client.py -m POST coap://127.0.0.1:5683/ps --payload "{\"topic-name\": \"Room Temperature Sensor\", \"resource-type\": \"core.ps.conf\", \"media-type\": \"application/json\", \"topic-type\": \"temperature\", \"expiration-date\": \"2023-04-05T23:59:59Z\", \"max-subscribers\": 200, \"observer-check\": 86400}"

Response arrived from different address; base URI is coap://127.0.0.1/ps
Location options indicate new resource: /ps/e99889
JSON re-formated and indented
{
    "topic-name": "Room Temperature Sensor",
    "topic-data": "ps/data/08dd75d",
    "resource-type": "core.ps.conf",
    "media-type": "application/json",
    "topic-type": "temperature",
    "expiration-date": "2023-04-05T23:59:59Z",
    "max-subscribers": 200,
    "observer-check": 86400
}

The broker will create the resource paths for both the topic-configuration and topic-data resources.

Discover

Discover topics either via .well-known/core or by querying the collection resource ps.

You may discover the following resource types:

• core.ps.coll - the topic collection resource.
• core.ps.conf - the topic-configuration resource.
• core.ps.data - the topic-data resource.

❯ ./client.py -m GET coap://127.0.0.1/ps
<ps/4fb3de>;rt="core.ps.conf"

or

./client.py -m GET coap://127.0.0.1/.well-known/core

application/link-format content was re-formatted
</.well-known/core>; ct=40,
</ps>; rt=core.ps.coll,
</ps/4fb3de>; ct=application/link-format; rt=core.ps.conf; obs,
</ps/data/a08b18d>; rt=core.ps.data; obs,
<https://christian.amsuess.com/tools/aiocoap/#version-0.4.4.post0>; rel=impl-info

or by rt

./client.py -m GET 'coap://127.0.0.1/.well-known/core?rt=core.ps.conf'

application/link-format content was re-formatted
</ps/dd4494>; ct=None; rt=core.ps.conf; obs,
</ps/cdc49a>; ct=application/json; rt=core.ps.conf; obs

or

./client.py -m GET 'coap://127.0.0.1/.well-known/core?rt=core.ps.coll'

application/link-format content was re-formatted
</ps>; rt=core.ps.coll

Retrieve a topic-configuration

Any topic-configuration can be retrieved via its corresponding URI.

./client.py -m GET 'coap://127.0.0.1/ps/e99889'

{"topic-name": "Room Temperature Sensor", "topic-data": "ps/data/08dd75d", "resource-type": "core.ps.conf", "media-type": "application/json", "topic-type": "temperature", "expiration-date": "2023-04-05T23:59:59Z", "max-subscribers": 200, "observer-check": 86400}

From it, the associated topic-data can be interacted with providing it is FULLY created. For that a publisher needs to publish.

Update a topic-configuration with PUT

Properties of a topic-configuration can be updated on its corresponding URI.

./client.py -m PUT coap://127.0.0.1:5683/ps/b616a3 --payload "{\"max-subscribers\": 200}"

Response arrived from different address; base URI is coap://127.0.0.1/ps/b616a3
JSON re-formated and indented
{
    "topic-name": "Room Temperature Sensor",
    "topic-data": "ps/data/957d7fd",
    "resource-type": "core.ps.conf",
    "media-type": "application/json",
    "topic-type": "temperature",
    "expiration-date": "2023-04-05T23:59:59Z",
    "max-subscribers": 200,
    "observer-check": 86400
}

Update a topic-configuration with iPATCH

Properties of a topic-configuration can be updated on its corresponding URI.

./client.py -m iPATCH coap://127.0.0.1/ps/e99889 --payload "{\"max-subscribers\": 300}"

JSON re-formated and indented
{
    "topic-name": "Room Temperature Sensor",
    "topic-data": "ps/data/08dd75d",
    "resource-type": "core.ps.conf",
    "media-type": "application/json",
    "topic-type": "temperature",
    "expiration-date": "2023-04-05T23:59:59Z",
    "max-subscribers": 300,
    "observer-check": 86400
}

FETCH a topic-configurations by Properties

A client can filter a collection of topics with a topic filter in a FETCH request to the topic collection URI.

./client.py -m FETCH 'coap://127.0.0.1/ps' --content-format 'application/cbor' --payload '{"max-subscribers": 300}'

application/link-format content was re-formatted
<ps/e99889>; rt=core.ps.conf

Publish

A CoAP client can act as publisher by sending a CoAP PUT to a topic-data resource. This initializes the resource into FULLY CREATED state:

./client.py -m PUT coap://127.0.0.1:5683/ps/data/08dd75d --payload "{"n": "temperature","u": "Cel","t": 1621452122,"v": 21.3}"

Response arrived from different address; base URI is coap://127.0.0.1/ps/data/08dd75d
{n: temperature,u: Cel,t: 1621452122,v: 21.3}

Subscribe

Subscribe to a topic by using CoAP Observe:

./client.py -m GET --observe coap://127.0.0.1:5683/ps/data/08dd75d

Response arrived from different address; base URI is coap://127.0.0.1/ps/data/08dd75d
{n: temperature,u: Cel,t: 1621452122,v: 21.3}
---
{n: temperature,u: Cel,t: 1621452122,v: 21.3}

Resource Classes

The broker implements the following resource classes:

• CollectionResource: The collection resource /ps for storing topics.
• TopicResource: A resource for topic-configurations.
• TopicDataResource: A resource for topic-data and for the publish-subscribe interactions over CoAP.

Supported operations

• Discovery
  • GET /.well-known/core to discover collection
    • Well known discovery with rt
    • Topic Collection discovery
    • Update to current list of Topic Properties on draft
    • GET topic to discover topic configuration
    • GET /ps to retrieve all topics
    • FETCH
    • multicast
• Configuration
  • POST topic to create topic
  • PUT to update topic configuration
  • iPATCH to partially update topic configuration
  • DELETE topic to delete topic
  • Client defined topic-data url
• Topic Data
  • PUT on topic-data to publish
  • GET + observe on topic-data to Subscribe
  • GET on topic-data to get last measurement
  • Delete to delete topic-data
• Other
  • Improve Broker Logic
  • Fix Scripts

Disclaimer: There is lots of hardcoded stuff, as this was quickly developed during the IETF116 nad IETF118 hackathons.