Oracles

ORACLES
Role of blockchain oracles
Oracle demo
5/7/2020

DEFINITION
Blockchain Oracles are third-party services that
provide smart contracts with external information.
They serve as bridges between blockchains and
the outside world.

WHAT ORACLES DO?
Provide information to the smart contracts on the blockchain
Translate information from outside platforms
Trigger smart contracts
Deliver information from smart contracts to outside world

ORACLES ON ETHEREUM
Ethereum
Network
Stock
Market
Data
Currency
Exchange
Rates
Bank
payments
Other
blockchains
Web API
IOT Events

MANY TYPES OF ORACLES
Software
Oracles
Inbound
Oracles
Hardware
Oracles
Outbound
Oracles
Consensus-
based Oracles

DEMO
Use case
Create oracle contract and
deploy to blockchain
Configure event listener
on IoT device

USE CASES
Seller
Put treasure is safe
Lock safe
Set unlock price in
smart contract
Pay on blockchain to
smart contract
Open safe
Get treasure
Buyer

ARCHITECTURE
User Interface Blockchain Raspberry Pi Safe

CREATE SMART CONTRACT IN
REMIX

OPEN SESAME SMART
CONTRCT
Oracle

SMART CONTRACT
pragma solidity >=0.4.22 <0.6.0;
contract OpenSesame{
enum State { Locked, Unlocked }
State public state;
uint public value; //value to unlock
address payable public seller;
event Unlock();
event Lock();
…

SMART CONTRACT (UNLOCK AND
LOCK FUNCTIONS)
function unlock()
public
inState(State.Locked)
condition(msg.value >
value)
payable
{
state = State.Unlocked;
emit Unlock();
}
function lock(uint _value)
public
onlySeller
inState(State.Unlocked)
{
value = _value;
state = State.Locked;
emit Lock();
}

REQUEST PUBLISHING THE
CONTRACT TO ROPSTEN TEST
NETWORK

AND “PAY” FOR PUBLISHING THE
CONTRACT

WAIT FOR THE CONTRACT TO BE
PUBLISHED

CONFIRM SENDING TRANSACTION
TO UNLOCK

CONFIRM ON ETHERSCAN THAT
EVENT WAS CREATED

LOCK AND SET UNLOCK FEE TO
10,000 WEI

CHECK THAT THE STATE IS 0
(LOCKED) AND VALUE IS SET TO
10,OOO (WEI)

RASPBERRY PI • Raspbian OS
• NodeJS
• Web3JS Node module
• Onoff Node module

GET BALANCE ON SESAME
CONTRACT
const Web3 = require("web3")
const web3 = new Web3(new
Web3.providers.HttpProvider("https://ropsten.infura.io/v3/edb1d45f792244bfa97c13d84
a809090"))
web3.eth.getBalance("0x126A01a11b7fD2a4C7c62887af21D2C69FB29bd5", function(err,
result) {
if (err) {
console.log(err);
} else {
console.log("Account balance: " + result + " [WEI]");
}
})

LISTEN TO SESAME’S EVENTS
const Web3 = require("web3");
const fs = require('fs’);
const contractAddress =
"0x032D472C05ff870cf800dbaD
4B14A50c031432aB";
Web3.providers.WebsocketProvid
er("wss://ropsten.infura.io/ws/v
3/edb1d45f792244bfa97c13d84
a809090"))
var myContract = new
web3.eth.Contract(JSON.parse(ab
i), contractAddress);
console.log("Listening for events
on", contractAddress);
myContract.events.allEvents()
.on('data', (event) => {
console.log(event);
})
.on('error', console.error);

STAY IN TOUCH
Gene Leybzon https://www.linkedin.com/in/leybzon/
https://www.meetup.com/members/90744
20/
https://www.leybzon.com

CODE FOR THE EVENT LISTENER
1/3const Web3 = require("web3");
const fs = require('fs');
var Gpio = require('onoff').Gpio; //include onoff to interact with the GPIO
var LED = new Gpio(23, 'out'); //use GPIO pin 18, and specify that it is output
var blinkInterval = setInterval(blinkLED, 250); //run the blinkLED function every 250ms
const contractAddress = "0x032D472C05ff870cf800dbaD4B14A50c031432aB";
function blinkLED() { //function to start blinking
if (LED.readSync() === 0) { //check the pin state, if the state is 0 (or off)
LED.writeSync(1); //set pin state to 1 (turn LED on)
} else {
LED.writeSync(0); //set pin state to 0 (turn LED off)
}
}

2/3function endBlink() { //function to stop blinking
clearInterval(blinkInterval); // Stop blink intervals
LED.writeSync(0); // Turn LED off
//LED.unexport(); // Unexport GPIO to free resources
}
endBlink();
var abi = fs.readFileSync('OpenSesame_sol_OpenSesame.abi', 'utf8');
//console.log("ABI", abi);
Web3.providers.WebsocketProvider("wss://ropsten.infura.io/ws/v3/edb1d45f792244bfa97c13d84
a809090"))
var myContract = new web3.eth.Contract(JSON.parse(abi), contractAddress);
console.log("Listening for events on", contractAddress);

3/3myContract.events.allEvents()
.on('data', (event) => {
console.log("Event:", event);
console.log("Event Type:", event.event);
if (event.event == "Unlock") {
console.log("Will unlock the safe");
blinkLED();
}
if (event.event == "Lock") {
console.log("Will lock the safe");
endBlink();
}
})
.on('error', console.error);

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