test generate hash

hash.sol

pragma solidity ^0.4.21;

contract TestHash {

    bytes32 public result;

    constructor() public {}

    function generate(bytes input) public {
        result = keccak256(input);
    }
}

test.go

package main

import (
	"context"
	"crypto/rand"
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/accounts/abi/bind"
	"github.com/ethereum/go-ethereum/accounts/abi/bind/backends"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/crypto"
)

func main() {
	first, _ := crypto.GenerateKey()
	faddr := crypto.PubkeyToAddress(first.PublicKey)
	genesis := core.GenesisAlloc{
		faddr: {Balance: big.NewInt(10000000000000)},
	}
	b := backends.NewSimulatedBackend(genesis)
	b.Commit()
	fopts := bind.NewKeyedTransactor(first)
	_, _, c, err := DeployTestHash(fopts, b)
	must(err)
	b.Commit()
	input := make([]byte, 50*1024)
	_, err = rand.Read(input)
	must(err)
	tx, err := c.Generate(fopts, input)
	must(err)
	b.Commit()
	receipt, err := bind.WaitMined(context.TODO(), b, tx)
	must(err)
	hash, err := c.Result(nil)
	must(err)
	fmt.Printf("Hash %x costs %d\n", hash, receipt.GasUsed)
}

func must(err error) {
	if err != nil {
		panic(err)
	}
}