public static boolean isIPv6Address()

in sshd-common/src/main/java/org/apache/sshd/common/util/net/SshdSocketAddress.java [598:693]
77 lines of code
29 McCabe index (conditional complexity)

    public static boolean isIPv6Address(String address) {
        address = GenericUtils.trimToEmpty(address);
        if (GenericUtils.isEmpty(address)) {
            return false;
        }

        if (WELL_KNOWN_IPV6_ADDRESSES.contains(address)) {
            return true;
        }

        boolean containsCompressedZeroes = address.contains("::");
        if (containsCompressedZeroes && (address.indexOf("::") != address.lastIndexOf("::"))) {
            return false;
        }

        if (((address.indexOf(':') == 0) && (!address.startsWith("::")))
                || (address.endsWith(":") && (!address.endsWith("::")))) {
            return false;
        }

        String[] splitOctets = GenericUtils.split(address, ':');
        List<String> octetList = new ArrayList<>(Arrays.asList(splitOctets));
        if (containsCompressedZeroes) {
            if (address.endsWith("::")) {
                // String.split() drops ending empty segments
                octetList.add("");
            } else if (address.startsWith("::") && (!octetList.isEmpty())) {
                octetList.remove(0);
            }
        }

        int numOctests = octetList.size();
        if (numOctests > IPV6_MAX_HEX_GROUPS) {
            return false;
        }

        int validOctets = 0;
        int emptyOctets = 0; // consecutive empty chunks
        for (int index = 0; index < numOctests; index++) {
            String octet = octetList.get(index);
            int pos = octet.indexOf('%'); // is it a zone index
            if (pos >= 0) {
                // zone index must come last
                if (index != (numOctests - 1)) {
                    return false;
                }

                octet = (pos > 0) ? octet.substring(0, pos) : "";
            }

            int octetLength = octet.length();
            if (octetLength == 0) {
                emptyOctets++;
                if (emptyOctets > 1) {
                    return false;
                }

                validOctets++;
                continue;
            }

            emptyOctets = 0;

            // Is last chunk an IPv4 address?
            if ((index == (numOctests - 1)) && (octet.indexOf('.') > 0)) {
                if (!isIPv4Address(octet)) {
                    return false;
                }
                validOctets += 2;
                continue;
            }

            if (octetLength > IPV6_MAX_HEX_DIGITS_PER_GROUP) {
                return false;
            }

            int octetInt = 0;
            try {
                octetInt = Integer.parseInt(octet, 16);
            } catch (NumberFormatException e) {
                return false;
            }

            if ((octetInt < 0) || (octetInt > 0x000ffff)) {
                return false;
            }

            validOctets++;
        }

        if ((validOctets > IPV6_MAX_HEX_GROUPS)
                || ((validOctets < IPV6_MAX_HEX_GROUPS) && (!containsCompressedZeroes))) {
            return false;
        }
        return true;
    }