ethereum for go developers

a.k.a. hacking the blockchain

8 Mar 2018

Tags: Ethereum, Solidity, Smart Contracts, Golang, Gophercon India

Dave Appleton

Lead blockchain developer, HelloGold

https://hellogold.com

@AppletonDave

* My aims for this workshop

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- To try to present the material in a reasonably sensible manner

- Not to look TOO stupid

- To convey new, interesting, useful information

- Take each of you to a point that you have sufficient momentum to go forth alone

- To finish the material in roughly the alotted time

* Todays Agenda

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- Introduction (me)

- The Blockchain in five minutes

- ethereum and smart Contracts

- geth and the go-ethereum code base

- Native Dapp bindings for smart contracts

- ABI and ABIGEN under the hood

- A little project

* Things to do

- please join telegram group : Gophercon.in.2018

- get this repo from github.com/DaveAppleton/Gophercon_in.git

- read the readme

* Introduction (me)

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- Englishman living in Southeast Asia for 36 years

- Programming since 1968

- background in instrumentation, machine vision

- Happiest languages : Pascal, Modula-2, Go, Solidity

- Blockchain dev since 2014

- Lead blockchain developer at HelloGold, Malaysia

- Blockchain Consultant

* The blockchain in five minutes

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* What is a blockchain ?

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- signed transactions

- Put into signed blocks

- Which are added to a chain (list) by a signed link

- in a manner such that all the independant nodes that operate the network agree the whole thing to be valid (consensus)

* Transactions ?

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- Anything that can change the state of something.

- A transfer of value or data

{

From : Dave

To : Alice

Value : 100

Data : "Happy Birthday Alice. Buy yourself something nice"

}

Web analogy:

.code demo_code.txt /start REST OMIT/,/end REST OMIT/

Current state = sum of all previous transactions

* Thought of the day....

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"Young man, in mathematics you don't understand things. You just get used to them."

.caption John von Neumann.

* Digital Signatures

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- a small change in the content causes a huge change in the result.

.play hashBaby.go /start main OMIT/,/end main OMIT/

- now encrypt the hash value using public key encryption....

* Public Key encryption in 20 seconds

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- create a truly random a private key

- public key (address) derived from private key

- something encrypted by private key can be read with public key

- encrypting the hash, ensures that the hash, thus the document is unchanged

- and ensures that the signer is who they say they are.

.code demo_code.txt /start RESTx OMIT/,/end RESTx OMIT/

* signing

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* Into blocks

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* In a manner that everybody agrees (Consensus)

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- not terribly relevent in our context except

- design of consensus algorithm ensures that no one node makes all the decisions

- makes it virtually impossible for anybody to modify the past records in the chain

- means that each node has an identical copy of the state of the blockchain

* Etherscan

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- have a look at https://etherscan.io

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* Etherscan

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- the Google of the blockchain

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* Wallets

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* Types of wallet

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- Private Keys

4ca8d6c2e6bf5209f953e9b8e2461c85bec9a29ac8c26199cedd94ea76433102

- JSON files (encrypted)

.code UTC--2018-03-03T18-22-00.825Z--794d7f1192e703b934cc92746c55a3d159f781fe

- Managed wallets (BIP39)

e.g. MetaMask

- Hardware wallets (BIP39)

e.g. Nano Ledger

* Easy ways to access your wallet?

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Something that *performs* *one* *or* *more* *of*

- managing keys

- creating transactions

- signing transactions

is often called a Wallet. (but it isn't)

* MetaMask

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Implemented in Javascript uses browser memory, BIP39

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Who did not get Metamask set up before the workshop?

Who did not get test ether from faucet.rinkeby.io

* MyCrypto

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* First Exercise

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- Using either MyEtherWallet or MyCrypto create a json wallet

- give it a simple password like `gopher` or `password`

- promise to NEVER use it with real ethereum

- send rinkeby test ether to it from MetaMask

- view the transaction on Etherscan

- Check your balance on MEW / MyCrypto

* Reading the key in go

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.code go/openKeyDemo/openKeyDemo.go /^func getOwnerTx/,/^}/

.play go/openKeyDemo/openKeyDemo.go /^func main/,/^}/

* maybe some security

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.code go/openKey/openKey.go /^// getPassword/,/^}/

.code go/openKey/openKey.go /^func main/,/END OMIT/

* Ethereum & smartcontracts

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* Ethereum and smart contracts

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- remember the "data" field?

- a way to give certain blocks of byte code an address...

- compilers

- byte-codes

- virtual machines....

- function routing...

- state variables...

Running on thousands of nodes

* What are smart contracts

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* The reference ethereum node implementation is.....

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* Writing your first smart contract

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https://remix.ethereum.org

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* Launch the contract

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* See the public interface

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* interact with the contract

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* Deploy the contract (live)

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- Set your Metamask to Rinkeby test network

- Set the Environment to Injected Web3

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* Waiting for mining

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- Create contract again

- Watch it get Mined

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* Get the details

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- and interact with it on the blockchain

- Notice that you and interact with the top 3 buttons

- If you click HitMe, MetaMask pops up asking you to pay in (testnet) ether

* Gas and Gas Price

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Asking for information:

- Since every node has the same data, you can ask ANY node.

Updating information:

- that data has to be mined into blocks and sent to every node to the network.

The Ethereum Network charges you based on

Gas Used

- the amount of code executed

- the amount of long term storage used

Gas Price

- What you offer to pay (and if anybody is willing to take it)

* Others can access it too!

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- Get the ABI

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* Interact with it on MyCrypto (0x7F3A19eDC1fFBd3fC2b4fc978b0d8f8C19316186)

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* A blockchain is about trust

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Verified contract on Etherscan

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* accessible data

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* Log Entries

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- there should be TWO of these contracts listed

- call hitMe on each

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* Well that was fun but what has that to do with Go?

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* Remember the log event "Thump" ?

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- make a filter

.code go/gophercon/gophercon.go /^func makeFilter/,/^}/

- To = nil => 'latest' block

- signature has function name & data types not return or names

* filter blockchain : from start to latest for "Thump"

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.play go/gophercon/gophercon.go /^func main/,/^}/

.link https://rinkeby.etherscan.io/tx/0xb381155e74b859b216a09ee6c6e343eced07dd1ad8baf50ae4740a07620840f4 etherscan

* ABI Encoding

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In that example we had these lines :

address := common.BytesToAddress(log.Data[12:32])

count, _ := strconv.ParseInt(common.Bytes2Hex(log.Data[32:]), 16, 64)

All data and function signatures etc use ABI encoding which can be pretty painful.

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* ABI for function calls

header = 1st 4 bytes of keccak256 of signature

.play go/ABI/main.go /start main/,/end main/

* Making it easier.... ABIGEN

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- ABIGEN creates a wrapper around your contract to make interaction easier

.code go/src/wrapper/wrapper.go /^// Code generated/,/^package wrapper/

...

.code go/src/wrapper/wrapper.go /^const GopherConABI/,/^ parsed/

* ABIGEN is a wrapper to

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- get data and call the functions of the contract

- monitor the events

for _, log := range logs {

address := common.BytesToAddress(log.Data[12:32])

count, _ := strconv.ParseInt(common.Bytes2Hex(log.Data[32:]), 16, 64)

fmt.Println(log.BlockNumber, " : Thump(", address.Hex(), ",", count, ")")

}

becomes

.code go/gopherconRead/gopherconRead.go /start OMIT/,/end OMIT/

* Viewing past events using ABIGEN

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.play go/gopherconRead/gopherconRead.go /long OMIT/,/end OMIT/

* Reading the contract's status using ABIGEN

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.play go/reader/reader.go /start OMIT/,/end OMIT/

* Sending a transaction to the contract using ABIGEN

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.play go/hitMe/hitme.go /start OMIT/,/end OMIT/

:-)

* Types of connection to ethereum nodes

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- local RPC connection e.g. `http://localhost:8545`

- IPC connection e.g. `/Users/daveappleton/Library/Ethereum/rinkeby/geth.ipc`

- remote hosts e.g. Infura or QuikNode

Infura

- free to use

- limited range of services available (no logs)

QuikNode

- paid service

- flexible choice of chains and clients

- all services except accounts

* Event subscription using ABIGEN

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.play go/gopherconMonitor/monitor.go /start OMIT/,/end OMIT/

* github.com/DaveAppleton/ether_go

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- Q & D library to create and use public keys

- accounts (Keys)

- transactions

- connection (now uses ethclient)

account := ethKeys.NewKey("adminKeys/" + job)

if err := transactorAcc.RestoreOrCreate(); err != nil {

log.Println(err)

}

account.GetKey() // private key

account.PublicKey() // address

account.PublicKeyAsHexString()

* keys - utility library used here

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.code go/src/keys/keys.go /^func KeyTx/,/^}/

.code go/src/keys/keys.go /^func Role/,/^}/

.code go/src/keys/keys.go /^func RoleKey/,/^}/

* Simulated Backend

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- Connect to a local one-step blockchain - i.e a chain with no history

- excellent for testing purposes (a lot faster)

.code go/simulateandtest/test.go /startClient OMIT/,/endClient OMIT/

- uses the same back EVM as geth

* simulated mining

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.code go/simulateandtest/test.go /startMine OMIT/,/endMine OMIT/

* A test

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.play go/simulateandtest/test.go /startCode OMIT/,/endCode OMIT/

* Solidity Stuff

- require / assert / revert

- modifiers

- send / transfer

- cross contract calls

- fallback function

- block time (now)

- msg.sender, msg.value etc

solidity.readthedocs.io

* There's something special about ethereum

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- ethereum has attracted its fair share of scams / money grabs / etc

- it has also provided a platform for transparency in projects

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* Project Ideas I

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design a contract where you can submit a transaction

function submitTransaction(address dest, bytes data)

that forwards the data to the given address.

* Project Ideas II

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Design go code to encode transactions to be sent to project I

(this would also be useful for Multisigs)

MultiSignature wallet contracts are great at sending ether but terrible at any other transaction because you submit transactions to them in the following format

{

To : 0x1234...

Value : 42

Data : 0x98765....

}

Can you design code to read an ABI, ask for the correct parameters and encode it correctly?