Publisher-Subscriber

Implementation of a Publisher Subscriber model using blockchain. This project was done under the course: Blockchain Technology and Applications(CS731A).

Instruction to Run

Firstly we need the blockchain up, before we can get the other servers running.

Start ganache, use the truffle-config.js file found in the directory to setup the workspace.

Run the following command in the terminal (base working directory,i.e., publisher-subscriber)

truffle migrate

This compiles the contracts and prints their metadata, which also contains their deployed contract address. Copy the contract addresses and paste(replace) them into listener.go(present in the ./scripts/ directory) at lines mentioned below:

• Pub address goes in line 51
• Sub address goes in line 52
• Event address goes in line 53

Now execute the following commands to complete the setup:

Server setup commands

Our implementation requires 2 servers running simultaneously. To setup run the following commands (make sure docker is setup on your system):

cd kakfa-event-queue
docker compose up -d
go run *.go

If docker compose up -d gives permission error, run it with sudo.

This sets up the gin-server which is used by the scripts and event-queue to communicate.

In a separate terminal, navigate to the scripts directory and get the scripts running:

cd scripts
go run *.go

Instructions to run the relay-server

Navigate to the relay-server directory, run the commands:

npm install
node relay.js

This will start a server listening on port 3000. After the API is called and the data is sent back to the contract, the first event is also printed on the console (just as a sanity check).

Testing Guidelines

Note: If you want to use any other method (say js scripts) to call the functions, please refer to /contracts/README.md for all the function specifications and calling conventions.

For testing in truffle:

truffle console

This connects to ganache chain if it is running in the background, and opens up it's own console. To test and call functions, you can use the following in the truffle console:

Getting accounts:

var accounts;
> 
web3.eth.getAccounts(function(err,res){accounts=res;});
> 

This displays all the account addresses from the chain truffle is connected to. These addresses can be used for testing.

Note: > indicates output of the respective command

Get objects of deployed contracts:

Events.deployed().then(function (i){eve=i})
>
Pub.deployed().then(function (i){pub=i})
>
Sub.deployed().then(function (i){sub=i})
>

These objects can be used to call the respective functions present in the smart contract.

Create Publisher:

pub.create_publisher('publisher_address')
>

Create Subscriber:

sub.create_subscriber('subscriber_address')
>

Create new event stream:

eve.add_topic()
>

Add Publisher to event stream:

pub.add_publisher(stream_id, 'publisher_address')
>

stream_id is the unique stream identifier that is returned when you call eve.add_topic().

Add Subscriber to event stream:

sub.subscribe_to_event(stream_id, 'subscriber_address')
>

Publish a message to event stream:

pub.publish_to_eventstream("msg", stream_id, 'publisher_address')
>

Get events from event stream

You need to make two sequential calls to get the events. The second call's return object contains the relevant events. You might want to refer to /contracts/README.md on how to unpack the events.

sub.call_for_events(stream_id, 'subscriber_address')
>
sub.get_back_events('subscriber_address')
>