Blockchain Oracles with code examples on Solidity and JavaScript

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

2. CONSULTING THE ORACLE

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

4. 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

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

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

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

8. OPEN SESAME!

9. 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

10. ARCHITECTURE
User Interface Blockchain Raspberry Pi Safe

11. CREATE SMART CONTRACT IN
REMIX

12. OPEN SESAME SMART
CONTRCT
Oracle

13. 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();
…

14. 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();
}

15. DEPLOY TO TEST
NETWORK

16. GENERATE MNEMONIC

17. LOG IN TO METAMASK

18. CONNECT REMIX TO METAMASK

19. GET SOME TEST ETHER (1ETH)

20. COMPILE THE CONTRACT

21. REQUEST PUBLISHING THE
CONTRACT TO ROPSTEN TEST
NETWORK

22. AND “PAY” FOR PUBLISHING THE
CONTRACT

23. WAIT FOR THE CONTRACT TO BE
PUBLISHED

24. PAY >1000 WEI TO UNLOCK

25. CONFIRM SENDING TRANSACTION
TO UNLOCK

26. CONFIRM ON ETHERSCAN THAT
EVENT WAS CREATED

27. LOCK AND SET UNLOCK FEE TO
10,000 WEI

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

29. IOT SIDE Raspberry PI

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

31. SCHEMATICS AND REALITY

32. 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]");
}
})

33. LISTEN TO SESAME’S EVENTS
const Web3 = require("web3");
const fs = require('fs’);
const contractAddress =
"0x032D472C05ff870cf800dbaD
4B14A50c031432aB";
const web3 = new Web3(new
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);

34. UNLOCK EVENT

35. LOCK EVENT

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

37. 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)
}
}

38. CODE FOR THE EVENT LISTENER
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);
const web3 = new Web3(new
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);

39. CODE FOR THE EVENT LISTENER
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);