Warning: this software is currently in an experimental phase. You will find stable releases in the github releases section, as soon as they are ready.

libpubsub-cpp

libpubsub-cpp is a topic based publish/subscribe framework for C++. It uses JSON-RPC on top of HTTP as transport layer to deliver topic notifications.

Overview

• Topic based Publish/Subscribe framework on top of JSON-RPC notifications
• UDP Broadcast connectors for peer detection
• JSON-RPC Client/Server for subscription management
• JSON-RPC Client/Server for application specific notifications (topics)
• pubsubstub: tool to generate peer stubs based on specification

Overlay network / Subscription management

• Each peer is a JSON-RPC server and client.
• If a peer wants to publish a new topic type, it broadcasts it through the network (pubsub.topics).
• If a peer wants to subscribe for a new topic, it broadcasts its intent through the network (pubsub.interest).
• Broadcasted intents for subscription/publishment are immediately answered by all affected peers with topic offers (pubsub.offertopic).
• Subscription: call pubsub.subscribe, which returns a subscription id.
• Revocation: call pubsub.unsubscribe with subscription id.

So the interface each peer offers for subscription management can be described using the libjson-rpc-cpp IDL:

[
	{
		"name": "pubsub.interest",
		"params": {"ip": "192.168.13.1", "topic": "sometopic"}
	},
	{
		"name": "pubsub.topics",
		"params": {"ip": "192.168.13.1", "topics": ["sometopic", "sometopic2"]}
	},
	{
		"name": "pubsub.offertopic",
		"params": {"ip": "192.168.13.1", "topics": ["sometopic", "sometopic2"]}
	},
	{
		"name": "pubsub.subscribe",
		"params": {"ip": "192.168.13.1", "notification": "sometopic"},
		"returns": "b65dc7fa-a1ac-4a17-ac12-c693da8131f5"
	},
	{
		"name": "pubsub.unsubscribe",
		"params": {"notificationId": "b65dc7fa-a1ac-4a17-ac12-c693da8131f5"},
		"returns": true
	}
]

By implementing these JSON-RPC methods via Broadcast and HTTP for each peer as client and server, also other languages can be used to join the Publish/Subscribe network of libpubsub-cpp.

Specification Syntax

It is a JSON file containing 2 sections:

• List of topics (containing parameter information)
  • name: name of the topic
  • params: can be ommmited, otherwhise contains parameter names + types
• List of peers (containing publish/subscribe information)
  • name: name of the peer class to be generated
  • publish: list of topics, the peer can publish (can be ommited)
  • subscribe: list of topic, the peer can subscribe (can be ommited)

{
	"topics": [
		{
			"name": "tempChanged",
			"params": {"temp": 23.4}
		},
		{
			"name": "humidityChanged",
			"params": {"humidity": 0.65}
		},
		{
			"name": "airspeedChanged",
			"params": {"speeed": 45.3}
		},
		{
			"name": "shutterChanged",
			"params": {"open": false}
		}
	],
	"peers": [
		{
			"name": "TempSensor",
			"publish": ["tempChanged"]
		},
		{
			"name": "AirspeedSensor",
			"publish": ["airspeedChanged"]
		},
		{
			"name": "HumiditySensor",
			"publish": ["humidityChanged"]
		},
		{
			"name": "Shutter",
			"publish": ["shutterChanged"],
			"subscribe": ["airspeedChanged"]
		},
		{
			"name": "Monitor",
			"subscribe": ["tempChanged", "humidityChanged", 
					"airspeedChanged", "shutterChanged"]
		}
	]
}

Example

1. Call pubsubstub with above topic specification file

Build from source

The framework currently only supports UNIX based environments.

1. Install the dependencies

The framework has libjson-rpc-cpp as major dependency. By installing it, all further dependencies will be installed.

See here how to install libjson-rpc-cpp on UNIX environments.

2. Compile libpubsub-cpp

git clone https://github.com/cinemast/libpubsub-cpp.git
cd libpubsub-cpp
mkdir -p build
cd build
cmake ..
make
sudo make install
sudo ldconfig