How to interact with smart contract in GO

Question

I’m modifying go-ethereum for a particular function in my application. I am writing a contract to give rewards to miners if a certain condition is met. For this, I need to change the go-ethereum to call a function that gives out reward to miners.  So I wanted to know how to build a Raw transaction in Go to call the reward function.  Can someone help me out with this?

Answer 1

I am providing an example. Modify it according to your requirement.

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"

}