kohlivarun5 / geth-experiments

Experiments with geth and solc

geth-experiments

Experiments with geth and solc

Install geth and solc

• geth: https://github.com/ethereum/go-ethereum/wiki/geth
• solc: https://solidity.readthedocs.io/en/develop/

Run a private net (Reference)

• Start a network: geth --rpc --rpcaddr 127.0.0.1 --rpcport 8545 --dev --datadir privchain

Leave this window open. We will refer to this as the node-window

Create accounts and mine

• Attach console to network: geth attach ipc://Users/$USER/privchain/geth.ipc

We will refer to this as the console-window

In the console-window:

• Create account: personal.newAccount('')
• Set this as default account: web3.eth.defaultAccount = eth.accounts[0]
• Do some mining: miner.start(), wait for a bit.
• In the node-window, you will see mining activity. miner.stop() to finish mining
• Check balance: web3.eth.getBalance(eth.accounts[0])

Transfer some coin

In the console-window:

• Create account: personal.newAccount('')
• Transfer coin: web3.eth.sendTransaction({to:eth.accounts[1],value:1000})
• You might need to unlock account using personal.unlockAccount(eth.accounts[0],'')
• miner.start() then miner.stop()
• Check balance: web3.eth.getBalance(eth.accounts[1])

Complete API reference: https://github.com/ethereum/wiki/wiki/JavaScript-API#web3ethsendtransaction

Deploy a smart contract

• First get solc using npm install -g solc solc-cli
• Create multiply.solc:

pragma solidity ^0.4.15;

contract test {
  function multiply(uint a) returns(uint d){
    return a * 7;
  }
}

• Compile using solc multiply.solc

• Files would be output into ./contracts/*abi ./contracts/*.bin

• Create contract using abi: MyContract = web3.eth.contract(<Copy as is from ./contracts/multiply*.abi>)

• Load bytecode: bytecode = "0x<Copy as is from ./contracts/multiply*.bin>"

• Make sure bytecode is good using web3.eth.estimateGas({data: bytecode})

• Create contract:

contractInstance = MyContract.new({
    data: bytecode, gas: 1000000, from: account1
  }, function(e, contract){
    if(!e){
      if(!contract.address){
        console.log(
        "Contract transaction send: Transaction Hash: "+contract.transactionHash+
        " waiting to be mined...");
      } else {
        console.log("Contract mined! Address: "+contract.address);
        console.log(contract);
      }
    } else {
      console.log(e)
    }
  })

• Mine the contract using miner.start() then miner.stop()

Next steps

• Build a web UI for looking into the blockchain: http://hypernephelist.com/2016/06/21/a-simple-smart-contract-ui-web3.html
• Integrate into existing backends using python, such as http://web3py.readthedocs.io/en/latest/quickstart.html