Thread: Compress Ipv6 Addresses

Hi all,

How to compress Ipv6 addresses? Are there any existing API's in Java which offer the functionality?

For example the compressed equivalent of the Ipv6 address 3ffe:0000:0000:0000:0000:0000:0000:0001
is 3ffe::1

Regards,

I took the liberty of studying the RFC for IPv6 and then I created this method.

    /**
     * This method takes an IPv6 address and compresses it according to the RFC (http://www.ietf.org/rfc/rfc2373.txt).
     *
     * @param uncompressed the uncompressed IPv6 address
     * @return a compressed IPv6 address
     */
    public static String compressIpv6(final String uncompressed) {
        if (uncompressed == null) {
            return null;
        }
 
        if (uncompressed.contains("::")) {
            return uncompressed;
        }
 
        if (uncompressed.equals("0:0:0:0:0:0:0:0")) {
            return "::";
        }
 
        int start = -1;
        int end = -1;
 
        for (int i = 0; i < uncompressed.length(); ++i) {
            final char character = uncompressed.charAt(i);
 
            if (start == -1) {
                if (character == '0' && i > 0 && uncompressed.charAt(i - 1) == ':') {
                    start = i - 1;
                } else if (character == '0' && i == 0) {
                    start = 0;
                }
            } else {
                if (character != '0' && character != ':') {
                    if (uncompressed.charAt(i - 1) == ':') {
                        end = i;
                    }
 
                    break;
                }
            }
        }
 
        if (start > -1 && end > start) {
            return uncompressed.substring(0, start) + "::" + uncompressed.substring(end, uncompressed.length());
        }
 
        return uncompressed;
    }

It might be flawed but I tested it with the following addresses:

FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
3ffe:0000:0000:0000:0000:0000:0000:0001
1080:0:0:0:8:800:200C:417A
FF01:0:0:0:0:0:0:101
0:0:0:0:0:0:0:1
0:0:0:0:0:0:0:0

Feel free to use it if you dare

// Json