Ethereum and Solidity

Tooling

• Remix
• npm / Node.js

web3j web3.js

Introduction to Smart Contracts

Solidity 是 Ethereum 上智能合约实现的主要语言之一。 运行在 EVM 上。

• static typing
• variadic return types
• Complex member variables for contracts including arbitrarily hierarchical mappings and structs
• Contracts support inheritance, including multiple inheritance with C3 linearization.
• An application binary interface (ABI) facilitating multiple type-safe functions within a single contract was also introduced (and later supported by Serpent).
• A documentation system for specifying a user-centric description of the ramifications of a method-call was also included in the proposal, known as “Natural Language Specification”.
• on EVM
• compile to bytecode
• designed around ECMAScript

Blockchain Basics

• Transactions
• Blocks
• EVM
  • Accounts: external accounts controlled by public private key pairs
  • contract accounts controlled by the code stored together with the account.
  • Every account has a persistent key-value store mapping 256-bit words to 256-bit words called storage.
• Storage:a key-value store that maps 256-bit words to 256-bit words. It is not possible to enumerate storage from within a contract and it is comparatively costly to read and even more so, to modify storage. A contract can neither read nor write to any storage apart from its own.
• Memory: a contract obtains a freshly cleared instance for each message call. Memory is linear and can be addressed at byte level, but reads are limited to a width of 256 bits, while writes can be either 8 bits or 256 bits wide. Memory is expanded by a word (256-bit), when accessing (either reading or writing) a previously untouched memory word (ie. any offset within a word). At the time of expansion, the cost in gas must be paid. Memory is more costly the larger it grows (it scales quadratically).
• Stack
• Instruction Set
• Message Calls
• Delegatecall / Callcode and Libraries
• Logs
• Create
• self-destruct

Installing the Solidity Compiler

Solidity by Example

Solidity in Depth

Security Considerations

Using the compiler

Contract Metadata

Application Binary Interface Specification

Joyfully Universal Language for (Inline) Assembly

Style Guide

Common Patterns

List of Known Bugs

Contributing

Frequently Asked Questions

##

Gloabal variable

Ether Units

• wei,
• finney,
• szabo or
• ether

Time Units

• 1 == 1 seconds
• 1 minutes == 60 seconds
• 1 hours == 60 minutes
• 1 days == 24 hours
• 1 weeks == 7 days
• 1 years == 365 days

Globals

• block.blockhash(uint blockNumber) returns (bytes32): hash of the given block - only works for 256 most recent blocks excluding current
• block.coinbase (address): current block miner’s address
• block.difficulty (uint): current block difficulty
• block.gaslimit (uint): current block gaslimit
• block.number (uint): current block number
• block.timestamp (uint): current block timestamp as seconds since unix epoch
• gasleft() returns (uint256): remaining gas
• msg.data (bytes): complete calldata
• msg.gas (uint): remaining gas - deprecated in version 0.4.21 and to be replaced by gasleft()
• msg.sender (address): sender of the message (current call)
• msg.sig (bytes4): first four bytes of the calldata (i.e. function identifier)
• msg.value (uint): number of wei sent with the message
• now (uint): current block timestamp (alias for block.timestamp)
• tx.gasprice (uint): gas price of the transaction
• tx.origin (address): sender of the transaction (full call chain)

Error Handling

• assert(bool condition): throws if the condition is not met - to be used for internal errors.
• require(bool condition): throws if the condition is not met - to be used for errors in inputs or external components.
• revert(): abort execution and revert state changes

Mathematical and Cryptographic Functions

• addmod(uint x, uint y, uint k) returns (uint):
• mulmod(uint x, uint y, uint k) returns (uint):
• keccak256(…) returns (bytes32):
• sha256(…) returns (bytes32):
• sha3(…) returns (bytes32):
• ripemd160(…) returns (bytes20):
• ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address):

Adddress Related

• <address>.balance (uint256):
• <address>.transfer(uint256 amount):
• <address>.send(uint256 amount) returns (bool):
• <address>.call(...) returns (bool):
• <address>.callcode(...) returns (bool):
• <address>.delegatecall(...) returns (bool):

Contract Related

• this
• selfdestruct(address recipient)
• suicide(address recipient)

Doxity: Documentation Generator for Solidity.

All identifiers (contract names, function names and variable names) are restricted to the ASCII character set. It is possible to store UTF-8 encoded data in string variables.

• public: The keyword public automatically generates a function that allows you to access the current value of the state variable from outside of the contract. Without this keyword, other contracts have no way to access the variable.
• address: 160 bit value
• mapping: Mappings can be seen as hash tables which are virtually initialized such that every possible key exists and is mapped to a value whose byte-representation is all zeros.
• progma once
• Coin.balances.call(arg)

How to develop and debug?

EVM

• 256bit register stack
• e-WASM
• send()
• transfer()
• call.value()

ERC20

pragma solidity ^0.4.23;


// https://github.com/ethereum/EIPs/issues/20
interface ERC20 {
    function totalSupply() external view returns (uint supply);
    function balanceOf(address _owner) external view returns (uint balance);
    function transfer(address _to, uint _value) external returns (bool success);
    function transferFrom(address _from, address _to, uint _value) external returns (bool success);
    function approve(address _spender, uint _value) external returns (bool success);
    function allowance(address _owner, address _spender) external view returns (uint remaining);
    function decimals() external view returns(uint digits);
    event Approval(address indexed _owner, address indexed _spender, uint _value);
}

import java.util.HashMap;
import java.util.Map;

public class ERC20Coin {

    static class Address {
        private String val;
        private static final String PATTERN_ERC20_HASH = "0x[0-9A-Fa-f]{64}";

        public Address(String val) {
            assert (val.matches(PATTERN_ERC20_HASH));
            this.val = val;
        }

        public String toString() {
            return this.val;
        }

        @Override
        public boolean equals(Object obj) {
            return (obj instanceof Address)
                    && ((Address) obj).val.equals(this.val);
        }
    }

    static class TransferEvent{
        public TransferEvent(Address _from, Address _to, Integer _value){

        }
    }

    Address sender;


    String name;
    String symbol;
    long totalSupply;
    Integer demicals;

    Map<Address, Integer> balances;
    Map<Address, Map<Address, Integer>> allowances;


    public ERC20Coin(String name, String symbol, long totalSupply, Integer demicals){
        balances = new HashMap<>();
        allowances = new HashMap<>();
        this.name = name;
        this.symbol = symbol;
        this.totalSupply = totalSupply;
        this.demicals = demicals;
    }

    public Integer balanceOf(Address address) {
        return balances.get(address);
    }

    public void transfer(Address from, Address to, Integer val) {
        Integer balanceFrom = balances.getOrDefault(from, 0);
        Integer balanceTo = balances.getOrDefault(to, 0);

        Map<Address, Integer> allowance;
        if(!allowances.containsKey(from)){
            allowance = new HashMap<Address, Integer>();
        }else{
            allowance = allowances.get(from);
        }
        Integer allowed = allowance.get(sender);
        assert  (allowance.get(sender) >= val) &&
                (balanceFrom >= val);

        if(allowed < Integer.MAX_VALUE){
            allowance.put(sender, allowed - val);
            allowances.put(from, allowance);
        }

        balances.put(from, balanceFrom - val);
        balances.put(to, balanceTo + val);
    }

    public void approve(Address from, Address to, Integer val){
        Map<Address, Integer> allowance;
        if(!allowances.containsKey(from)){
            allowance = new HashMap<Address, Integer>();
        }else{
            allowance = allowances.get(from);
        }

        allowance.put(to, val);
        allowances.put(from, allowance);
    }



}

Airdrop 空投

参考: https://medium.com/bitfwd/how-to-airdrop-your-first-token-3ba187ff7cbf

空投地址列表

空投之前需要找到你需要空投地址列表。 如何找到这些地址列表呢？

1. 在 Slack 或者 telegram 等群里寻找鱼儿。
2. 扫描 Ethereum 上 balance >0 的那些有效账号地址

parity export state --chain=ropsten -no-storage -no-code -min-balance=1000 -max-balance=500000 -at=2000000 balances.json

节省 gas 费用

如何一次向多个账号send token?