description: Tutorial on how to check if an address is a smart contract or an account with Go.

Address Check

This section will describe how to validate an address and determine if it’s a smart contract address.

Check if Address is Valid

We can use a simple regular expression to check if the ethereum address is valid:

  1. re := regexp.MustCompile("^0x[0-9a-fA-F]{40}$")
  3. fmt.Printf("is valid: %v\n", re.MatchString("0x323b5d4c32345ced77393b3530b1eed0f346429d")) // is valid: true
  4. fmt.Printf("is valid: %v\n", re.MatchString("0xZYXb5d4c32345ced77393b3530b1eed0f346429d")) // is valid: false

Check if Address is an Account or a Smart Contract

We can determine if an address is a smart contract if there’s bytecode stored at that address. Here’s an example where we fetch the code for a token smart contract and check the length to verify that it’s a smart contract:

  1. // 0x Protocol Token (ZRX) smart contract address
  2. address := common.HexToAddress("0xe41d2489571d322189246dafa5ebde1f4699f498")
  3. bytecode, err := client.CodeAt(context.Background(), address, nil) // nil is latest block
  4. if err != nil {
  5.   log.Fatal(err)
  6. }
  8. isContract := len(bytecode) > 0
  10. fmt.Printf("is contract: %v\n", isContract) // is contract: true

When there’s no bytecode at the address then we know that it’s not a smart contract and it’s a standard ethereum account:

  1. // a random user account address
  2. address := common.HexToAddress("0x8e215d06ea7ec1fdb4fc5fd21768f4b34ee92ef4")
  3. bytecode, err := client.CodeAt(context.Background(), address, nil) // nil is latest block
  4. if err != nil {
  5.   log.Fatal(err)
  6. }
  8. isContract = len(bytecode) > 0
  10. fmt.Printf("is contract: %v\n", isContract) // is contract: false

Full code

address_check.go

  1. package main
  3. import (
  4.     "context"
  5.     "fmt"
  6.     "log"
  7.     "regexp"
  9.     "github.com/ethereum/go-ethereum/common"
  10.     "github.com/ethereum/go-ethereum/ethclient"
  11. )
  13. func main() {
  14.     re := regexp.MustCompile("^0x[0-9a-fA-F]{40}$")
  16.     fmt.Printf("is valid: %v\n", re.MatchString("0x323b5d4c32345ced77393b3530b1eed0f346429d")) // is valid: true
  17.     fmt.Printf("is valid: %v\n", re.MatchString("0xZYXb5d4c32345ced77393b3530b1eed0f346429d")) // is valid: false
  19.     client, err := ethclient.Dial("https://mainnet.infura.io")
  20.     if err != nil {
  21.         log.Fatal(err)
  22.     }
  24.     // 0x Protocol Token (ZRX) smart contract address
  25.     address := common.HexToAddress("0xe41d2489571d322189246dafa5ebde1f4699f498")
  26.     bytecode, err := client.CodeAt(context.Background(), address, nil) // nil is latest block
  27.     if err != nil {
  28.         log.Fatal(err)
  29.     }
  31.     isContract := len(bytecode) > 0
  33.     fmt.Printf("is contract: %v\n", isContract) // is contract: true
  35.     // a random user account address
  36.     address = common.HexToAddress("0x8e215d06ea7ec1fdb4fc5fd21768f4b34ee92ef4")
  37.     bytecode, err = client.CodeAt(context.Background(), address, nil) // nil is latest block
  38.     if err != nil {
  39.         log.Fatal(err)
  40.     }
  42.     isContract = len(bytecode) > 0
  44.     fmt.Printf("is contract: %v\n", isContract) // is contract: false
  45. }