Golang IsEIP55

is_eip55.go

package main

import (
	"fmt"
	"strings"
	"testing"
	"golang.org/x/crypto/sha3"
)

// IsEIP55 checks if the given Ethereum address is EIP-55 compliant.
// It does this by hashing the lowercase address and then checking if each character in the original address is correctly cased according to the EIP-55 specification.
// If the address is EIP-55 compliant, the function returns nil. Otherwise, it returns an error that provides more information about why the address is not compliant.
func IsEIP55(address string) error {
	// Check if the address has a '0x' prefix
	if !strings.HasPrefix(address, "0x") {
		return fmt.Errorf("address does not start with '0x'")
	}

	// Remove '0x' prefix
	address = address[2:]

	// Check if the address is the correct length
	if len(address) != 40 {
		return fmt.Errorf("address is not the correct length")
	}

	// Hash the lowercase address
	hash := sha3.NewLegacyKeccak256()
	hash.Write([]byte(strings.ToLower(address)))
	hashedAddress := hash.Sum(nil)

	// Iterate over each character in the address
	for i := 0; i < len(address); i++ {
		if address[i] >= '0' && address[i] <= '9' {
			// We can't upper-case the decimal digits
			continue
		}

		// Check if the corresponding hex digit (nibble) in the hash is 8 or higher
		hashedValue := hashedAddress[i/2] >> uint(4*(1-i%2)) & 0xf
		if hashedValue >= 8 {
			if address[i] < 'A' || address[i] > 'F' {
				// The character is not upper-case
				return fmt.Errorf("character at position %d should be upper-case", i)
			}
		} else {
			if address[i] < 'a' || address[i] > 'f' {
				// The character is not lower-case
				return fmt.Errorf("character at position %d should be lower-case", i)
			}
		}
	}

	return nil
}

func TestIsEIP55(t *testing.T) {
	// Define test cases
	testCases := []struct {
		name    string
		address string
		wantErr bool
	}{
		{
			name:    "Valid EIP55 address",
			address: "0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed",
			wantErr: false,
		},
		{
			name:    "Invalid EIP55 address",
			address: "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed",
			wantErr: true,
		},
		{
			name:    "Address without 0x prefix",
			address: "5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed",
			wantErr: true,
		},
		{
			name:    "Address of incorrect length",
			address: "0x5aAeb6053F3E94C9b9A09f33669435E7Ef1Be",
			wantErr: true,
		},
	}

	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			err := isEIP55(tc.address)
			if (err != nil) != tc.wantErr {
				t.Errorf("isEIP55() error = %v, wantErr %v", err, tc.wantErr)
			}
		})
	}
}

func main() {
	fmt.Println(IsEIP55("0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed")) // Should print: <nil>
	fmt.Println(IsEIP55("0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed")) // Should print: character at position 1 should be upper-case
}