feat: add eth_addr_checksum validation, update eth_addr (#1080)

rationale:

- ethereum addresses are derived from a public key (the last 20 bytes). The network accepts any case insensitive address as long as it is a 40 char alphanumeric (When the last 20 bytes are converted to hex). It is 0x prefixed so that it becomes 42 in length, hence the current eth_addr implementation is modified to reflect this.
- Checksum-ing is optional on ethereum and is a way of typo checking the address hence this is introduced as a new validation i.e. eth_addr_checksum.

refs:

- https://github.com/ethereum/go-ethereum/blob/master/crypto/crypto.go#L275
- https://goethereumbook.org/en/wallet-generate/
- https://goethereumbook.org/en/address-check/

baked_in.go

@@ -140,6 +140,7 @@ var (
 		"isbn10":                        isISBN10,
 		"isbn13":                        isISBN13,
 		"eth_addr":                      isEthereumAddress,
+		"eth_addr_checksum":             isEthereumAddressChecksum,
 		"btc_addr":                      isBitcoinAddress,
 		"btc_addr_bech32":               isBitcoinBech32Address,
 		"uuid":                          isUUID,
@@ -613,14 +614,16 @@ func isISBN10(fl FieldLevel) bool {
 func isEthereumAddress(fl FieldLevel) bool {
 	address := fl.Field().String()
 
+	return ethAddressRegex.MatchString(address)
+}
+
+// isEthereumAddressChecksum is the validation function for validating if the field's value is a valid checksumed Ethereum address.
+func isEthereumAddressChecksum(fl FieldLevel) bool {
+	address := fl.Field().String()
+
 	if !ethAddressRegex.MatchString(address) {
 		return false
 	}
-
-	if ethAddressRegexUpper.MatchString(address) || ethAddressRegexLower.MatchString(address) {
-		return true
-	}
-
 	// Checksum validation. Reference: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-55.md
 	address = address[2:] // Skip "0x" prefix.
 	h := sha3.NewLegacyKeccak256()

regexes.go

@@ -118,8 +118,6 @@ var (
 	btcUpperAddressRegexBech32 = regexp.MustCompile(btcAddressUpperRegexStringBech32)
 	btcLowerAddressRegexBech32 = regexp.MustCompile(btcAddressLowerRegexStringBech32)
 	ethAddressRegex            = regexp.MustCompile(ethAddressRegexString)
-	ethAddressRegexUpper       = regexp.MustCompile(ethAddressUpperRegexString)
-	ethAddressRegexLower       = regexp.MustCompile(ethAddressLowerRegexString)
 	uRLEncodedRegex            = regexp.MustCompile(uRLEncodedRegexString)
 	hTMLEncodedRegex           = regexp.MustCompile(hTMLEncodedRegexString)
 	hTMLRegex                  = regexp.MustCompile(hTMLRegexString)

validator_test.go

@@ -5672,7 +5672,7 @@ func TestEthereumAddressValidation(t *testing.T) {
 		{"0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359", true},
 		{"0xdbF03B407c01E7cD3CBea99509d93f8DDDC8C6FB", true},
 		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDb", true},
-		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDB", false}, // Invalid checksum.
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDB", true}, // Invalid checksum, but valid address.
 
 		// Other.
 		{"", false},
@@ -5703,6 +5703,56 @@ func TestEthereumAddressValidation(t *testing.T) {
 	}
 }
 
+func TestEthereumAddressChecksumValidation(t *testing.T) {
+	validate := New()
+
+	tests := []struct {
+		param    string
+		expected bool
+	}{
+		// All caps.
+		{"0x52908400098527886E0F7030069857D2E4169EE7", true},
+		{"0x8617E340B3D01FA5F11F306F4090FD50E238070D", true},
+
+		// All lower.
+		{"0x27b1fdb04752bbc536007a920d24acb045561c26", true},
+		{"0x123f681646d4a755815f9cb19e1acc8565a0c2ac", false},
+
+		// Mixed case: runs checksum validation.
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDb", true},
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDB", false}, // Invalid checksum.
+		{"0x000000000000000000000000000000000000dead", false}, // Invalid checksum.
+		{"0x000000000000000000000000000000000000dEaD", true},  // Valid checksum.
+
+		// Other.
+		{"", false},
+		{"D1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDb", false},    // Missing "0x" prefix.
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDbc", false}, // More than 40 hex digits.
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aD", false},   // Less than 40 hex digits.
+		{"0xD1220A0cf47c7B9Be7A2E6BA89F429762e7b9aDw", false},  // Invalid hex digit "w".
+	}
+
+	for i, test := range tests {
+
+		errs := validate.Var(test.param, "eth_addr_checksum")
+
+		if test.expected {
+			if !IsEqual(errs, nil) {
+				t.Fatalf("Index: %d eth_addr_checksum failed Error: %s", i, errs)
+			}
+		} else {
+			if IsEqual(errs, nil) {
+				t.Fatalf("Index: %d eth_addr_checksum failed Error: %s", i, errs)
+			} else {
+				val := getError(errs, "", "")
+				if val.Tag() != "eth_addr_checksum" {
+					t.Fatalf("Index: %d Latitude failed Error: %s", i, errs)
+				}
+			}
+		}
+	}
+}
+
 func TestBitcoinAddressValidation(t *testing.T) {
 	validate := New()