Ethereum Smart Contract Tutorial
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Tutorial on writing, using, and deploying smart contracts
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Ethereum Smart Contract Tutorial
- 1. Ethereum Developers Community Smart Contract Tutorial Arnold Pham Cofounder of Lunyr www.linkedin.com/in/arnoldpham Unless otherwise stated, these slides are licensed under the Creative Commons Attribution-NonCommercial 3.0 License (https://creativecommons.org/licenses/by-nc/3.0/us/)
- 2. High level view of web app client server architecture
- 3. High level view of Ethereum Dapp Architecture
- 4. Yikes! Downloading the whole blockchain?
- 5. EVM - Database and Code
- 6. Built in financial system
- 7. Solidity
- 8. Useful Tools - Opportunities for contribution ethereumjs-testrpc • Node.js based Ethereum client for testing and development • Simulates full client behavior • https://github.com/ethereumjs/testrpc dapple • developer multitool for managing the growing complexity of interconnected smart contract systems • https://github.com/nexusdev/dapple truffle • A development environment, testing framework and asset pipeline for Ethereum
- 10. Shows errors
- 12. What is the ABI? Application Binary Interface
- 13. Deploying a Contract with Web3
- 14. 1. Write your contract
- 15. 2. Make sure you have the Solidity compiler No Solidity compiler? Proceed to next step Download https://github.com/ethereum/solidity/releases
- 16. 3. Compile your contract with web3.eth.compile.solidity(source) to get an object with the contract and compiler info
- 17. You need the abiDefinition
- 18. Create a contract object which can be used to instantiate contracts on an address
- 19. Deploy the Contract var contractInstance = MyContract.new([contructorParam1] [, contructorParam2], {data: '0x12345...', from: myAccount, gas: 1000000}); Make sure to unlock the account first with personal.unlockAccount(eth.accounts[0])
- 20. Contract mined!
- 23. You can also check that the contract was deployed at the address with: eth.getCode(simplestorage.address) Contract Address: "0xeb2186b9f667796497f0fc3c824d0bb57a548c25"
- 24. 1. Write your contract
- 25. Retrieving Data from the simplestorage Contract instance > simplestorage.get ()
- 26. Method calls with sendTransaction contractInstance.method.sendTransaction([parameter], { from: eth.accounts[0])
- 27. Change storedData to 20. simplestorage.get() to view change > simplestorage.set.sendTransaction(20, {from: eth.accounts[0]})
- 28. Getting other people to interact with your code Requires the ABI Then they can instantiate a Javascript object which can be used to call the contract from any node on the network var newInstance = eth.contract(ABI).at(Address);
- 29. Deploying a Contract with Browser-Solidity
- 30. Write the contract in Browser-Solidity
- 31. Uses Metamask. Spend Ether to deploy it
- 33. Etherscan Block Explorer shows the contract
- 34. ERC20 Specification Token Methods: totalSupply balanceOf transfer transferFrom approve allowance
- 35. Creating a simple token contract (Warning: Very simplified Example)
- 37. Steps to deploy the contract > var tokenSource = 'contract Token{address public owner;mapping(address=>uint)balances;function Token(){owner=msg.sender;balances[owner]=100;}function transfer(address _to,uint _value)returns(bool success){if(balances[msg.sender]<_value){return false;}balances[msg.sender]-=_value;balances[_to]+=_value;return true;}function getBalance(address _user)constant returns(uint _balance){return balances[_user];}}'
- 38. > var tokenCompiled = web3.eth.compile.solidity(tokenSource)
- 39. > var tokenContract = web3.eth.contract(tokenCompiled.Token.info.abiDefinition)
- 41. Check the owner
- 42. GetBalance
- 43. Transfer tokens to another address
- 44. Thank you for watching! Stay tuned for more!
Notas do Editor
- If you are a web developer, you know how a webapp with it’s client server architecture works at a very high level. You have your web application hosted on a hosting provider like AWS, Heroku or a VPS. All the clients interact with this one central application. Clients can be a browser, another api consuming your service etc. When a client makes a request to the server, the server does it’s magic, talks to the database and/or cache, reads/writes/updates the database and serves the client. https://medium.com/@mvmurthy/ethereum-for-web-developers-890be23d1d0c#.l6ucyhvl0
- If you notice, every client (browser) communicates with it’s own instance of the application. There is no central server to which all clients connect to. This means, every person who wants to interact with a dapp (Decentralized Application) will need a full copy of the blockchain running on their computer/phone etc. That means, before you can use an application, you have to download the entire blockchain and then start using the application. This is currently changing with the continued development of “light” clients which will enable users in low-capacity environments to receive data from the network about parts of the state without downloading the blockchain in its entirety https://medium.com/@mvmurthy/ethereum-for-web-developers-890be23d1d0c#.l6ucyhvl0
- In reality, you aren’t really using all of your storage and RAM downloading the entire blockchain. There are optimizations and technical advancements within Ethereum improving the efficiency
- The Ethereum blockchain can be thought of as a world Database and Code base. The Ethereum Virtual Machine (EVM) stores your data, stores the code, and runs the code in the EVM
- A special capability of Ethereum is it has a built in financial system. You create bank accounts at a fraction of a second. These accounts store a cryptocurrency called Ether which you can send to other accounts on Ethereum
- The high-level language used in Ethereum for writing contracts. Javascript-like with strong variable types
- Useful tool
- Shows errors
- The contract are stored as bytecode in a binary form into the blockchain under a specific address. The ABI defines the structures and methods that you will use to interact with binary contract (just like the API did), only on a lower level. You can accesses the binary data in the contract through the ABI. In ethereum, the ABI is how you can encode solidity contracts for the EVM and backwards how to read the data out of transactions.
- Since we’re working inside the geth console, we don’t need to use web3.eth and can just write eth.
- Compile your contract in Browser-Solidity or use web3.eth.compile.solidity(source)
- var simpleStorageCompiled = web3.eth.compile.solidity(simpleStorageSource)
- var simpleStorageContract = web3.eth.contract(simpleStorageCompiled.SimpleStorage.info.abiDefinition) Gets you a contract object
- Deploy the contract and check if it was mined using the transactionHash
- Check Transaction Hash on Ropsten Testnet. 2 Block confirmations
- Compile your contract in Browser-Solidity or use web3.eth.compile.solidity(source)
- After calling the set method
- You can see the bytecode of the contract and the ABI. There isn’t anything to interact with in this. Write your code. Then click Create.
- Metamask will popup and ask you if you’d like to accept or reject the transaction. Ignore the Transaction Error, it’s a current bug with Browser-Solidity and metamask when confirming transactions but everything works fine. You can still compile, create the contract, and run transactions
- Get the total token supply Get the account balance of another account with address _owner Send _value amount of tokens to address _to Send _value amount of tokens from address _from to address _to Allow _spender to withdraw from your account, multiple times, up to the _value amount. If this function is called again it overwrites the current allowance with _value. Returns the amount which _spender is still allowed to withdraw from _owner