Smart Contracts with Solidity hands-on training session
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Get hands-on experience developing smart contracts for Ethereum using Solidity programming language and ApiDapp framework
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Smart Contracts with Solidity hands-on training session
- 1. SMART CONTRACTS HANDS-ON Writing smart contracts in Solidity
- 2. BLOCKCHAIN CONCEPTS • Accounts • Contracts • Messages
- 3. TWO TYPES OF ACCOUNTS Account StorageBalance Code <> Externally Owned Account StorageBalance Account StorageBalance Code <> Contract StorageBalance Code <>
- 4. 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
- 5. CALLS AND MESSAGES Contract A Contract B Message Call • Source • Target • Data Payload • Ether • Gas • Return Data Externally owned account Message CallSend Transaction Call
- 6. 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); • } • }
- 7. GET TEST ETHER Navigate to Ropsten faucet https://faucet.ropsten.be/ Enter your public key
- 9. 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;
- 10. 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;
- 11. 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; } } }
- 12. PRACTICE • Create account on apidapp • Get Test Ether • Hello World!
- 13. HELLO WORLD CONTRACT pragma solidity ^0.5.0; contract HelloWorld { function getMessage() public view returns(string memory){ return("Hello, blockchain meetup!"); } }
- 14. PUBLISHING SMART CONTRACTS WITH APIDAPP Write Code Create and fund wallet Publish Contract
- 18. CHECK YOUR TEST ETHER https://www.apidapp.com/account/?blockchain=ropsten&account={your_ac count_id_here}
- 21. CHECK THE CONTRACT IN BLOCKCHAIN EXPLORERhttps://ropsten.etherscan.io/address/{contract- address}
- 22. CALL CONTRACT Install Postman Install ApiDapp API Collection Make a call to contract
- 24. INSTALL APIDAPP API COLLECTION https://www.getpostman.com/collections/3e9b6746316696d1b
- 25. CONFIGURE CALL CONTRACT ENTER CONTRACT ADDRESS
- 26. CONFIGURE CALL CONTRACT CHECK FUNCTION NAME
- 27. MAKE A CALL TO CONTRACT
- 28. MORE COMPLEX CODE EXAMPLE, ERC20 contract Erc20Token constructor totalSupply() balanceOf() transfer() transferFrom() approve() allowance()
- 29. VERY SIMPLE ERC20 CONTRACT pragma solidity >=0.4.22 <0.6.0; contract MyToken { mapping (address => uint256) public balanceOf; constructor() public { balanceOf[msg.sender] = 10000; // Give the creator all initial tokens } function transfer(address _to, uint256 _value) public returns (bool success) { require(balanceOf[msg.sender] >= _value); // Check if the sender has enough require(balanceOf[_to] + _value >= balanceOf[_to]); // Check for overflows balanceOf[msg.sender] -= _value; // Subtract from the sender balanceOf[_to] += _value; // Add the same to the recipient return true; } }
- 30. EVEN MORE COMPLEX CODE EXAMPLE, VOTING contract Ballot Voter Voter Voter Voter Proposal Proposal Proposal Proposal Chairperson constructor giveRightToVote() delegate() vote() winningProposal() winnerName()
- 31. QUESTIONS
- 32. STAY IN TOUCH Gene Leybzon https://www.linkedin.com/in/leybzon/ https://www.meetup.com/members/90744 20/ https://www.leybzon.com
Notas do Editor
- Every account has a persistent key-value store mapping 256-bit words to 256-bit words called storage Accounts can be externally owned or contracts
- Message: This is contract-to-contract. These are not delayed by mining because they are part of the transaction execution. Transaction: Like a message, but originates with an externally owned account. It's always a transaction that gets things started, but multiple messages may be fired off to complete the action. Ethereum also has two modes of execution. These modes are indifferent to the syntax or vernacular in the client that summoned the contract. So, the important things are to know which one is appropriate, and how to select it in your client of choice. sendTransaction: Transaction is sent to the network and verified by miners. Sender gets a transaction hash initially since no results are available until after the transaction is mined. These are potentially state-changing. call: Transaction is executed locally on the user's local machine which alone evaluates the result. These are read-only and fast. They can't change the blockchain in any way because they are never sent to the network. Most languages/platforms don't have this idea of running the code in either "read-only/dry run/practice" mode and "read-write/real world/sticky" mode. (https://ethereum.stackexchange.com/questions/12065/what-is-the-difference-between-a-call-message-call-and-a-message)
- https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI
- https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI
- https://ethereum.stackexchange.com/questions/19380/external-vs-public-best-practices
- http://leybzon.blogspot.com/2018/01/hello-world-from-solidity.html
- https://www.apidapp.com/register-2/
- https://www.apidapp.com/wallet/?blockchain=ropsten https://faucet.ropsten.be/
- https://www.apidapp.com/account/?blockchain=ropsten&account={your_account_id_here}
- https://www.apidap.com/smart-contract/?blockchain=ropsten&account={your-account-id-here}
- https://www.getpostman.com/collections/3e9b6746316696d1b7f7 In Postman: Import ->Import from link->Enter link->[Import Button]
- https://en.wikipedia.org/wiki/ERC-20
- Auction https://solidity.readthedocs.io/en/v0.5.3/solidity-by-example.html