Smart contracts on Ethereum Getting started

DappsMedia Tomoaki Sato

June 2015

Main source: https://github.com/ethereum/wiki/wiki/Ethereum-Development-Tutorial

~From blockchain installation to make tokenContract ~

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What are smart contracts on Ethereum blockchain?

Source: https://github.com/ethereum/wiki/wiki/White-Paper

Original idea derived from Nick Szabo’s paper in1997.

http://szabo.best.vwh.net/smart_contracts_idea.html and going to be live by Stateful blockchain with Ethereum virtual machine

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What kind of application needs smart contracts ?

Source: Source

1.Vending machine 2.Asset automated transfer system

• Token Systems• Financial derivatives• Identity and Reputation Systems• Decentralized File Storage• Decentralized Autonomous

Organizations• See also

https://docs.google.com/spreadsheets/u/1/d/1VdRMFENPzjL2V-vZhcc_aa5-ysf243t5vXlxC2b054g/edit

After blockchain age

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Smart contract 4 purposes

Smart contract

1. Maintain a data store contract.

2. Forwarding contract which has access policy, and some conditions to send messages.

3. Ongoing contract such as escrow, crowdfunding.

4.Library type contract which provides functions to other contracts.

Process objectives

Ethereum contracts objectives

Source: https://github.com/ethereum/wiki/wiki/Ethereum-Development-Tutorial

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1.Maintain a data store contractMost simple type can be used by Embark (more about the later)

Source: http://jorisbontje.github.io/sleth/#/

# app/contracts/simple_storage.solcontract SimpleStorage { uint storedData; function set(uint x) { storedData = x * x * x; } function get() constant returns (uint retVal) { return storedData; }}

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2.Forwarding contractSleth is the decentralized slot machine application using forwarding type smart contract.

Currently I can not find the forwarding type contract which can be run on testnet. If you know please comment on.

Source: https://github.com/ethereum/wiki/wiki/Ethereum-Development-Tutorial

When Bob wants to finalize the bet, the following steps happen:

1. A transaction is sent, triggering a message from Bob's EOA to Bob's forwarding contract.

2. Bob's forwarding contract sends the hash of the message and the Lamport signature to a contract which functions as a Lamport signature verification library.

3. The Lamport signature verification library sees that Bob wants a SHA256-based Lamport sig, so it calls the SHA256 library many times as needed to verify the signature.

4. Once the Lamport signature verification library returns 1, signifying that the signature has been verified, it sends a message to the contract representing the bet.

5. The bet contract checks the contract providing the San Francisco temperature to see what the temperature is.

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3.Ongoing contract

Source: https://github.com/WeiFund/WeiFund/blob/master/WeiFund.sol

Most smart contracts are ongoing type contracts, such as crowdfunding is ongoing contract.

// WeiFund System// Start, donate, payout and refund crowdfunding campaigns// @authors:// Nick Dodson <thenickdodson@gmail.com>// If goal is not reached and campaign is expired, contributers can get their donation refunded individually// If goal is reached by alloted time, contributions can still be madecontract WeiFundConfig { function onContribute(uint cid, address addr, uint amount){} function onRefund(uint cid, address addr, uint amount){} function onPayout(uint cid, uint amount){}}

contract WeiFund { struct User { uint numCampaigns; mapping(uint => uint) campaigns; } struct Funder { address addr; uint amount; }...

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4. Library contract

Source: https://github.com/ethereum/wiki/wiki/Ethereum-Development-Tutorial

Smart contract which provides utility functions.

In the case below, Lamport sig verifier contract is Library type contracts.The contract will provide a set of function

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Structuring every type of smart contractYou can make structure by combining different contracts

Source: https://github.com/ethereum/wiki/wiki/Ethereum-Development-Tutorial

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LET’S ENJOY ETHEREUMNext

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Our goal today

Download blockchain, writing smart contracts, publish contract on blockchain, send message to contracts.

Source: http://jorisbontje.github.io/sleth/#/ http://ethereum.gitbooks.io/frontier-guide/content/contract_coin.html http://meteor-dapp-cosmo.meteor.com/

Cool!

1. Install Ethereum blockchain 2.writing smart contract

3.Publish contract on blockchain 4.Send message to contracts & check the result

tokenInstance.getBalance.call(eth.accounts[1])

tokenInstance.sendToken.sendTransaction(eth.accounts[1], 100, {from: eth.accounts[0]})

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1. Install Ethereum blockchain

3 ways to install...

Source: http://jorisbontje.github.io/sleth/#/

1. Live Testnet chain https://stats.ethdev.com/2. Private chain 3. Private chain with framework (Embark framework)

https://github.com/iurimatias/embark-framework

Cool!

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1. Install Ethereum blockchain

Source: http://jorisbontje.github.io/sleth/#/

1. Live Testnet chain we will install this chain. https://stats.ethdev.com/

Cool!

CPP

O △ ☓

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1. Install Ethereum blockchain

Source:

1.Live Testnet chain we will install this chain. https://stats.ethdev.com/

June, 2015

Go-Ethereum = Geth !

1. installation of geth https://github.com/ethereum/go-ethereum/releases/tag/v0.9.20

2. geth account new  http://ethereum.gitbooks.io/frontier-guide/content/creating_accounts.html

3. Do mining & should wait until the Blocknumber on stats (roughly 4 ~6 hours )https://stats.ethdev.com/

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1. Install Ethereum blockchain

2.Private chain is private blockchain just for you. No network, your own blockchain.

Source: https://github.com/ethereum/go-ethereum/wiki/Setting-up-private-network-or-local-cluster

Currently Ethereum using blockchain,

You can run multiple chains locally to do this, 1. Each instance has separate data dir2. Each instance runs on a different port ( both eth and rpc. )3. The instances know about each other

You can run multiple chains locally 1st chain// create dir for blockchain$ mkdir /tmp/eth/60/01 // run private chain$ geth –datadir=“/tmp/eth/60/01” –verbosity 6 –port 30301 –rpcport 8101 console 2>> /tmp/eth/60/01.log

// mining start $ admin.miner.start()

You can run multiple chains locally 2nd chain but for my env doesn’t work.// create dir for blockchain$ mkdir /tmp/eth/61/01 // run private chain$ geth –datadir=“/tmp/eth/61/01” –verbosity 6 –port 30302 –rpcport 8102 console 2>> /tmp/eth/61/01.log

// mining start $ admin.miner.start()

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1. Install Ethereum blockchain

3. Embark Framework for Ethereum DApps. https://iurimatias.github.io/embark-framework/

Source: https://iurimatias.github.io/embark-framework/

I feel 1. Easy to upload contracts you write to private blockchain2. If you don’t know about How to use 3. Fast demo – Simple storage application using private chain is buildin demo.

$ npm install -g embark-framework grunt-cli$ embark demo$ cd embark_demo$ embark blockchain$ embark run

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2. Write smart contract after $ geth console

1. Write Token contract you can publish your own token. After $ geth console

### coin contract from console var tokenSource = 'contract token { mapping (address => uint) balances; function token() { balances[msg.sender] = 10000; } function sendToken(address receiver, uint amount) returns(bool sufficient) { if (balances[msg.sender] < amount) return false; balances[msg.sender] -= amount; balances[receiver] += amount; return true; } function getBalance(address account) returns(uint balance){ return balances[account]; } }'var tokenCompiled = eth.compile.solidity(tokenSource).tokenvar tokenAddress = eth.sendTransaction({data: tokenCompiled.code, from: eth.accounts[0], gas:1000000});admin.miner.start()admin.miner.stop()eth.getCode(tokenAddress)tokenContract = eth.contract(tokenCompiled.info.abiDefinition)tokenInstance = tokenContract.at(tokenAddress);> tokenInstance{ address: '0xf95ff51f532bd6821b98f312e876e1e2213f3e36', sendToken: [Function], getBalance: [Function]}tokenInstance.getBalance.call(eth.accounts[0])tokenInstance.sendToken.sendTransaction(eth.accounts[1], 100, {from: eth.accounts[0]})admin.miner.start()admin.miner.stop()tokenInstance.getBalance.call(eth.accounts[0])> tokenInstance.getBalance.call(eth.accounts[0])'9900'

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3.Publish contract

This phrase is uploading the contract onto blockchain.

### coin contract from console var tokenSource = 'contract token { mapping (address => uint) balances; function token() { balances[msg.sender] = 10000; } function sendToken(address receiver, uint amount) returns(bool sufficient) { if (balances[msg.sender] < amount) return false; balances[msg.sender] -= amount; balances[receiver] += amount; return true; } function getBalance(address account) returns(uint balance){ return balances[account]; } }'var tokenCompiled = eth.compile.solidity(tokenSource).token

var tokenAddress = eth.sendTransaction({data: tokenCompiled.code, from: eth.accounts[0], gas:1000000});admin.miner.start()admin.miner.stop()eth.getCode(tokenAddress)tokenContract = eth.contract(tokenCompiled.info.abiDefinition)tokenInstance = tokenContract.at(tokenAddress);> tokenInstance{ address: '0xf95ff51f532bd6821b98f312e876e1e2213f3e36', sendToken: [Function], getBalance: [Function]}tokenInstance.getBalance.call(eth.accounts[0])tokenInstance.sendToken.sendTransaction(eth.accounts[1], 100, {from: eth.accounts[0]})admin.miner.start()admin.miner.stop()tokenInstance.getBalance.call(eth.accounts[0])> tokenInstance.getBalance.call(eth.accounts[0])'9900'

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4.Send message to the contract and check the result

This phrase is sending message to the contract on blockchain.

### coin contract from console var tokenSource = 'contract token { mapping (address => uint) balances; function token() { balances[msg.sender] = 10000; } function sendToken(address receiver, uint amount) returns(bool sufficient) { if (balances[msg.sender] < amount) return false; balances[msg.sender] -= amount; balances[receiver] += amount; return true; } function getBalance(address account) returns(uint balance){ return balances[account]; } }'var tokenCompiled = eth.compile.solidity(tokenSource).tokenvar tokenAddress = eth.sendTransaction({data: tokenCompiled.code, from: eth.accounts[0], gas:1000000});admin.miner.start()admin.miner.stop()eth.getCode(tokenAddress)tokenContract = eth.contract(tokenCompiled.info.abiDefinition)tokenInstance = tokenContract.at(tokenAddress);> tokenInstance{ address: '0xf95ff51f532bd6821b98f312e876e1e2213f3e36', sendToken: [Function], getBalance: [Function]}

tokenInstance.getBalance.call(eth.accounts[0])tokenInstance.sendToken.sendTransaction(eth.accounts[1], 100, {from: eth.accounts[0]})admin.miner.start()admin.miner.stop()tokenInstance.getBalance.call(eth.accounts[0])> tokenInstance.getBalance.call(eth.accounts[0])'9900'

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Miscellaneous

Ethereum frontier guide

Solidty online compilerhttps://chriseth.github.io/cpp-ethereum/

Geth(go-ethereum) https://github.com/ethereum/go-ethereum/releases/tag/v0.9.20

State of the DApps spreadsheethttps://docs.google.com/spreadsheets/d/1VdRMFENPzjL2V-vZhcc_aa5-ysf243t5vXlxC2b054g/edit#gid=0

Ethereum forumhttps://forum.ethereum.org/categories/services-and-decentralized-applications

Solidity presentationhttps://www.youtube.com/watch?v=DIqGDNPO5YM

http://ethereum.gitbooks.io/frontier-guide/content/creating_accounts.html

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