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ethereum.md

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This memo explains how to compile, deploy, and run smart contracts on a local ethereum network.
It also discusses event transmission from Ethereum to SCXML processes (run by scxmlrun).

Prerequisites

Truffle (Framework for Solidity)

$ npm install -g truffle

Ganache: local ethereum network for testing

$ npm install -g ganache-cli

Compilation & Deployment

Compose a contract in Solidity, and compile & deploy it in the following manner.

$ truffle compile && truffle deploy

Testing

Compose test scripts using web3.
Then, launch a new local ethereum network (at port 7545 by default).

$ ganache-cli &

Then, run the test scripts.

$ truffle test

Connection between Ethereum and MQTT

At this moment, there is no 'off-the-shelf' tool but we are on our own.

However, in order to send events from Solidity contracts to a MQTT broker, we just need a bridge script that performs the following operations using web3.js and mqtt.js.

  • listen to events emitted by contracts using web3.eth.
  • publish them to a MQTT broker using the MQTT.Client#publish method.

Specifically, for each Solidity event Event emitted by contract, you can define a lister with a callback that looks like:

contract.Event ({...}, {fromBlock:'latest', toBlock:'latest'}, function (err, log) {  
  payload = "{\"event\":{\"name\":\"" + log.event + "\",...}}";  
  mqtt.publish (topic, payload);  
})

References