Notes from Ethereum and Solidity Training Course

Bitcoin History

• October 31, 2008
  • A white paper describing peer to peer payments without a financial itermediary like banks was released
  • It cited transaction reversals as an issue with online commerce - the ability of customers to charge back a purchase
  • Satoshi Nakamoto released the white paper though the identity of this person or group is unknown
  • Whitepaper: https://bitcoin.org/bitcoin.pdf

Ethereum History

• Vitalik Buterin(Russian) created Ethereum late 2013
  • Uses 'smart contract' which is code that lives in the Ethereum block chain. These contracts are at the core of what Ethereum is.
  • Uses the concept of DAC(decentralized autonomous corporations)
    • Basically a corporation split into sub-corporations where decisions are made based on votes from shareholders. Shareholders who own more Ethereum have more voting power.
  • Whitepaper: http://web.archive.org/web/20131228111141/http://vbuterin.com/ethereum.html

Ethereum Tools

• For Developers to connect:
  • Web3.js
• For Consumers to connect:
  • Metamask(chrome extension)
  • Mist Browser
• Test sending ether to metamask rinkeby test server: http://rinkeby-faucet.com/
  • Another(where you have to make a social media post only containing your rinkeby account address to get the ether): faucet.rinkeby.io

Solidity Smart Contracts

• Written in solidity language(.sol files)
  • Strongly Typed
  • Similar to Javascript(sort of)
  • Gets compiled before deployment
  • Application Binary Interface(ABI)
    • Translates Solidity smart contract byte code to a usable data format for Javascript to use the smart contract
  • Doesn't require long development time
    • More time is invested in writing applications around the Solidity smart contracts that interact with the smart contracts
  • Solidity online editor: ---> REMIX ONLINE CONTRACT EDITOR!!!!!! ---> http://remix.ethereum.org/
    • Remix can be used to test contracts by compiling to bytecode and sending contract to a fake ethereum network and create an instance of your contract on that fake network
      • You can write a contract, press run, select javascript VM environment(which is the in-browser virtual ethereum network),then configure the settings as needed, and then you can hit the run/play button
    • Once

General Transaction

• Transaction properties:
  • nonce(stands for nonsense): how many times the sender has sent a transaction
  • to: address of account this money is going to
  • value: amount of 'wei' to send to the target address
  • gasPrice: amount of wei the sender is willing to pay per unit of gas to get this transaction processed
  • startGas/gaslimit: units of gas that this transaction can consume
  • v/r/s: cryptographic pieces of data that can be used to generate the senders account address. Generated from the sender's private key

External Account to create Contract Transaction

• Transaction properties:
  • nonce(stands for nonsense): how many times the sender has sent a transaction
  • to: if this is left blank, the user is attempting to create a new contract
  • data: compiled bytecode of the contract
  • value: amount of 'wei' to send to the target address
  • gasPrice: amount of wei the sender is willing to pay per unit of gas to get this transaction processed
  • startGas/gaslimit: units of gas that this transaction can consume
  • v/r/s: cryptographic pieces of data that can be used to generate the senders account address. Generated from the sender's private key

Solidity Gotchas:

• Whenever a transaction is submitted, it takes time to be mined via a proof of work algorithm in order to reach consensus as to whether or not your transaction is valid.
• If you make a function with the same name as your contract within your contract, that will be treated as a constructor function and invoked whenever the contract gets invoked/instantiated.
• A function that will be used in a transaction such as setMessage in the inbox contract cannot return values. If you try you won't get an error, but because that function will be used in a transaction, which is asynchronous, only a transaction hash will be returned from that function when the transaction is completed, despite what you code it to return.
• Sending a transaction to a function within a smart contract costs money. (Gas, which is some amount of ether) Gas is used as a price for a miner to charge for completing your transaction for you.
• Test networks have very quick/sometimes instant block times, so the transactions are asynchronous but the test networks are just much quicker than the real ethereum network.
• 1 Ether is 1,000,000,000,000,000,000 'Wei'(wei is always rounded to the nearest whole number, no decimals) converter: https://etherconverter.online/

MetaMask

• Allows for users to transfer Ether within different Ethereum networks in the browser through a Chrome extension
• You can create as many accounts as you'd like(for example: spending, savings, business, etc)
• Each account has an address, public, and private key
• Creates 12 word mnemonic phrases as a type of password to secure your account keys/tokens/hexadecimal hashes. Each mnemonic phrase is per metamask extension per browser for all accounts on that extension. To get a new phrase, uninstall/reinstall metamask.
• Side Note: Mnemonic means a series of easy to memorize words.
• Mnemonic Code Converter(to see how your mnemonic phrase converts into account addresses/public and private keys): https://iancoleman.io/bip39/

Truffle

• Command line tool that can aid in contract creation, local contract testing, and contract deployment for example to the Rinkeby network
• Undergoing rapid development(some features are not perfect or completed at this point(01/24/2018))
• Library can change and old code can become deprecated quickly

Web3

• Can be used to deploy contracts to an ethereum network
• Can be used to get access to existing contracts on an ethereum network(requires having the address of the deployed contract you're targeting)
• The Sole interface between nodejs and an ethereum network

Solidity with NodeJS

• Install npm package: "solc" to compile your solidity code in Node
  • Example in: ./inbox_node_project/compile.js
• Deployment of contract bytecode can be done with Ganache(previously known as TestRPC). Ganache creates a local Ethereum test network for you to use for development(production code would take some time to complete, but Ganache completes transactions almost instantaneously).
• Web3 is used to interact with the Ethereum network and your deployed contracts
  • Currently going through a rewrite, code in this repo is 1.0.0-beta.26.

Infura API

• Allows for an easy connection to the Rinkeby network
• An alternative would be to run an ethereum node locally and have that node communicate to Rinkeby, but that would be much more work

Etherscan

• https://rinkeby.etherscan.io/
• https://etherscan.io/ (main network)
• Reads all contracts on main ethereum networks including main and test networks
• Contract addresses can be searched in the top right search bar(the contract address will be returned after deploying a contract with web3 in your code)