How to call an Ethereum contract from Go?

Question

I've tried to follow the go-ethereum guide for this but it seems out of date. I've tried looking around for a web3 library in Go but everything tries to point back to "use geth."

From Go, how do I call a contract in the Ethereum block chain? How different would it be if I'm targeting testnet or testrpc?

Uncial

You may find this helpful ethereum.stackexchange.com/questions/3514/… . Depends on what kind of things you are wanting to do with Go and Ethereum. – Wivern

Answer 1

Here's a simple example of how you can interact with a smart contract in Go. Assuming you have solc and abigen installed.

solc --abi Store.sol > Store.abi
solc --bin Store.sol > Store.bin
abigen --bin=Store.bin --abi=Store.abi --pkg=store --out=Store.go

Store.sol

pragma solidity ^0.4.24;

contract Store {
  event ItemSet(bytes32 key, bytes32 value);

  string public version;
  mapping (bytes32 => bytes32) public items;

  constructor(string _version) public {
    version = _version;
  }

  function setItem(bytes32 key, bytes32 value) external {
    items[key] = value;
    emit ItemSet(key, value);
  }
}

main.go

package main

import (
    "context"
    "crypto/ecdsa"
    "fmt"
    "log"
    "math/big"

    "github.com/ethereum/go-ethereum/accounts/abi/bind"
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/ethclient"

    store "./contracts" // for demo
)

func main() {
    client, err := ethclient.Dial("https://rinkeby.infura.io")
    if err != nil {
        log.Fatal(err)
    }

    privateKey, err := crypto.HexToECDSA("fad9c8855b740a0b7ed4c221dbad0f33a83a49cad6b3fe8d5817ac83d38b6a19")
    if err != nil {
        log.Fatal(err)
    }

    publicKey := privateKey.Public()
    publicKeyECDSA, ok := publicKey.(*ecdsa.PublicKey)
    if !ok {
        log.Fatal("error casting public key to ECDSA")
    }

    fromAddress := crypto.PubkeyToAddress(*publicKeyECDSA)
    nonce, err := client.PendingNonceAt(context.Background(), fromAddress)
    if err != nil {
        log.Fatal(err)
    }

    gasPrice, err := client.SuggestGasPrice(context.Background())
    if err != nil {
        log.Fatal(err)
    }

    auth := bind.NewKeyedTransactor(privateKey)
    auth.Nonce = big.NewInt(int64(nonce))
    auth.Value = big.NewInt(0)     // in wei
    auth.GasLimit = uint64(300000) // in units
    auth.GasPrice = gasPrice

    address := common.HexToAddress("0x147B8eb97fD247D06C4006D269c90C1908Fb5D54")
    instance, err := store.NewStore(address, client)
    if err != nil {
        log.Fatal(err)
    }

    key := [32]byte{}
    value := [32]byte{}
    copy(key[:], []byte("foo"))
    copy(value[:], []byte("bar"))

    tx, err := instance.SetItem(auth, key, value)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("tx sent: %s", tx.Hash().Hex()) // tx sent: 0x8d490e535678e9a24360e955d75b27ad307bdfb97a1dca51d0f3035dcee3e870

    result, err := instance.Items(&bind.CallOpts{}, key)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(result[:])) // "bar"
}

For more examples, check out the Ethereum Development with Go book.

European

is it possible to access the smart contract without building the ABI generation steps. Like how we access the contract instance in web3.js or web3.py ? – Kauffman

@SushantKumar yes you don't have to use the abi helper package and you can send raw transactions to read or write data but you'll need to construct the encoded arguments manually – European