Introduction to programming Ethereum smart contacts using Solidity

1. BLOCKCHAIN AND SMART
CONTRACTS SESSION 2
Hands-on introduction for
Software Developers and
Architects

2. PLAN FOR TODAY
Understand basis Etherium concepts
Selenium Language
Install Etherium Test Network
Install truffle code development environment
Create your first contract
Compile
Test

3. CONCEPTS
• Accounts
• Contracts
• Messages

4. TWO TYPES OF ACCOUNTS
Account
StorageBalance Code
<>
Externally Owned Account
StorageBalance
Account
StorageBalance Code
<>
Contract
StorageBalance Code
<>

5. CONTRACTS
Contracts are accounts that contain code
Store the state
• Example:
keeps account
balance
Source of notifications
(events)
• Example: messaging
service that forwards
only messages when
certain conditions are
met
Mapping - relationship
between users
• Example: mapping
real-world financial
contract to Etherium
contract
Act like a software
library
• Example:
return calculated
value based on
message arguments

6. CALLS AND MESSAGES
Contract A Contract B
Message Call
• Source
• Target
• Data Payload
• Ether
• Gas
• Return Data
Externally
owned
account
Message CallSend Transaction
Call

7. WHAT CONTRACT CAN DO?
Read internal state
• contract
ReadStateDemo {
• uint public state;
• function read() {
• console.log(“State:
"+state);
• }
• }
Modify internal State
• contract
ModStateDemo {
• uint public state;
• function update() {
• state=state+1;
• }
• }
Consume message
• contract
ReadStateDemo {
• uint public state;
• function hi() {
• console.log(“Hello
from: “ "+msg.sender
+ “ to “ + msg.
receiver);
• }
• }
Trigger execution of
another contract
• contract CallDemo {
• function send(address
receiver, uint amount)
public {
• Sent(msg.sender,
receiver, amount);
• }
• }

8. CONTRACT LANGUAGES
Solidit
y
Serpent
LL
L
Bytecodes
Etherium
Virtual Machine
(EVM)

9. REGISTRARS (ETHEREUM NAME
SERVICE, ENS)
1. Send ether to an address in Metamask
(soon: MEW, Mist, Bitfinex)
2. Use it inside your own contracts to
resolve names of other contracts and
addresses
3. Store contract ABIs for easy lookup
using the ethereum-ens library
4. Address of a Swarm site
Use Cases
Registry
Regista
r
Resolve
r

10. ETHER
• Wei: 1
• Ada: 1000
• Fentoether: 1000
• Kwei: 1,000
• Mwei: 1,000,000
• Babbage:
1,000,000
• Pictoether: 1,000,000
• Shannon:
1,000,000,000
• Gwei: 1,000,000,000
• Nano: 1,000,000,000
• Szabo:
1,000,000,000,000
• Micro:
1,000,000,000,000
• Microether:
1,000,000,000,000
• Finney:
1,000,000,000,000,000
• Milli: 1,000,000,000,000,000
• Milliether:
1,000,000,000,000,000
• Ether:
1,000,000,000,000,000,000
Wei = 10-18
Ether

11. GAS
step 1 Default amount of gas to pay for an execution
cycle
stop 0 Nothing paid for the STOP operation
suicide 0 Nothing paid for the SUICIDE operation
sha3 20 Paid for a SHA3 operation
sload 30 Paid for a SLOAD operation
sstore 100 Paid for a normal SSTORE operation
(doubled or waived sometimes)
balance 20 Paid for a BALANCE operation
create 100 Paid for a CREATE operation
call 20 Paid for a CALL operation
memory 1 Paid for every additional word when
expanding memory
txdata 5 Paid for every byte of data or code for a
transaction
transaction 500 Paid for every transaction
Example:
300 CPU cycles = 300 gas units = 0.000006 ETH =
$0.00553
(as of 2/20/2018)
Cost of Gas as in 2018

12. 2 MINUTE INTRODUCTION
TO SOLIDITY
Data Types
Functions

13. ELEMENTARY DATA TYPES
Data Type Example
uint<M> , M=1,2,4, …, 256
int<M>, uint, int
Unsigned/signed integer uint256 counter = 1;
address 160-bit value that does not
allow any arithmetic
operations. It is suitable for
storing addresses of
contracts or keypairs
belonging to external
persons
address owner =
msg.sender;
bool Same as uint8 but values are
0 or 1
Bool b = 0;
fixed<M>x<N>
ufixed<M>x<N>
Signed fixed-point decimal
number of M bits
fixed128x19 f = 1.1;
bytes<M>, M=1..32 Binary of M bytes bytes32 n=123;
function Same as bytes24 Function f;

14. ARRAYS
Data Type Example
<type>[M] fixed-length array of fixed-
length type
byte[100]
<type>[] variable-length array of
fixed-length type
byte[]
bytes dynamic sized byte sequence bytes ab;
string dynamic sized Unicode
string
String s = “String”;
fixed<M>x<N>
ufixed<M>x<N>
Signed fixed-point decimal
number of M bits
fixed128x19 f = 1.1;

15. FUNCTIONS
Functions
Constant
Transactional
Function Visibility
External Can be called via
transactions
Public Can be called via
messages or locally
Internal Only locally called or
from derived contracts
Private Locally called
pragma solidity^0.4.12;
contract Test {
function test(uint[20] a) public returns (uint){
return a[10]*2;
}
function test2(uint[20] a) external returns (uint){
return a[10]*2; }
}
}

16. HANDS-ON Code time

17. PREREQUISITES

18. INSTALL TRUFFLE FRAMEWORK
•$ sudo npm install -g truffle
•$ mkdir solidity-experiments
•$ cd solidity-experiments/
•$ truffle init
Truffle
Framework

19. INSTALL AND START LOCAL TEST
NETWORK
•$ npm install -g
ganache-cli
•$ ganache-cli &
Etherium
test
network

20. CONFIGURE TRUFFLE
• module.exports = {
• networks: {
• development: {
• host: "localhost",
• port: 8545,
• network_id: "*"
• }
• }
• }
Update
truffle.js

21. DEVELOPING SMART CONTRACT
WITH TRUFFLE
Write Code
Create
deployment
script
Migrate/Deploy

22. HELLO WORLD CONTRACT
(SOLIDITY CODE)
pragma solidity ^0.4.4;
contract Hello {
function Hello() public {
// constructor
}
function sayHello() public pure returns
(string) {
//console.log("sayHello() function
called...");
return 'Hello World!';
}
}

23. DEPLOYMENT SCRIPT
var Hello1 =
artifacts.require("./Hello.sol");
module.exports =
function(deployer) {
deployer.deploy(Hello1);
};

24. DEPLOY CONTRACT TO THE TEST
NETWORK$ truffle console
truffle(development)> truffle migrate --reset
Using network 'development'.
Running migration: 1_initial_migration.js
Deploying Migrations...
...
0xb6bbeaaf3649ecb38d548cba96f681682dad9e0225726924fbee3ce3
6eff94e3
Migrations: 0xc08c46796ba0edc0bebbbd0d90868c010055cb0e
Saving successful migration to network...
...
0x16fe364b9f2c3e8f07fa1ebd6b84b8ad9b4e750d8698a7e920d824eb
d019dd80
Saving artifacts...
Running migration: 2_deploy_contracts.js
Deploying Hello...
...
0xfe120836b2d7395bd988104feff018fe352f93555f71003bbf1a6467
1cca9ba1
Hello: 0x2b649a87d20ce1ac3b6a0218e911165fa0f095f0
Saving successful migration to network...
...
0x1a09073a3b3f7996f3d63a81a99d8cd09198ad7b467f35f7ddc500a
4291332b9
Saving artifacts...
truffle(development)>

25. TEST CONTRACT
truffle(development)> var he =
Hello.at(Hello.address)
Undefined
truffle(development)> he.sayHello()
'Hello World!'

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