How to compress IPV6 address using javascript?

Question

I have seen the code to compress IPV6 in java. The link specifies the same. Below is the code in Java . String resultString = subjectString.replaceAll("((?::0\\b){2,}):?(?!\\S*\\b\\1:0\\b)(\\S*)", "::$2"); But in Javascript I am confused as how can I get the regex expression to match the same . Can you share some pointers here?

Example : fe80:00:00:00:8e3:a11a:2a49:1148 Result : fe80::8e3:a11a:2a49:1148

Do not use the tag `pattern-matching` for regular expression questions. — PeterMader, Jun 08 '17 at 09:45
Replace `\b(?:0+:){2,}` with `:`. [Check it out at regex101](https://regex101.com/r/Bb7U4H/2). — SamWhan, Jun 08 '17 at 09:50
@ClasG you mean subjectString.replace("::?(?!\\S*\\b\\1:0\\b)(\\S*)", "::$2") ? . Tried but no luck — karthik339, Jun 08 '17 at 09:55
`subjectString.replace(/(^|:)0+(?!(?::|$))/g, "$1").replace(/(:(?:0:){2,})(?!\S*(?:\1)0:)/, "::")` I'll have to explain it later — Thomas, Jun 08 '17 at 10:26
@Thomas this might handle with the condition having leading 0. The below regex was able to handle that /((?:(?:^|:)0+\b){2,}):?(?!\S*\b\1:0+\b)(\S*)/ — karthik339, Jun 09 '17 at 03:37

score 4 · Answer 1 · answered Dec 30 '17 at 06:59

There's a couple problems with the other answer by @ClasG:

If the repeating zeroes are at the beginning of the IPv6 address or it's all zeroes, only 1 colon is replaced.
If the repeating zeroes are at the end, they're not replaced.

I suggest using the regex \b:?(?:0+:?){2,} and have it replaced with :: (two colons)

Regex101 tests

JavaScript example:

var ips = [
'2001:0db8:ac10:0000:0000:0000:0000:ffff',
'2001:0db8:ac10:0000:0000:0000:0000:0000',
'0:0:0:0:0:2001:0db8:ac10',
'2001:0db8:ac10:aaaa:0000:bbbb:cccc:ffff',
'2001:0db8:ac10:0000:0000:bbbb:00:00' 
];

for (var i = 0; i < ips.length; i++) {
document.write(ips[i].replace(/\b:?(?:0+:?){2,}/, '::') + "<br>"); 
}

Note: The Regex101 tests replace multiple repeating groups of zeroes. In XYZ programming language, you'll have to limit the number of replacements to 1. In JavaScript, you omit the global flag. In PHP, you set the $limit for preg_replace to 1.

This is not correct. Your code produces the wrong output for '2001:0db0:0000:0001:0000:0000:1428:57ab' — themaninthewoods, Mar 21 '23 at 23:35

score 3 · Accepted Answer · answered Jun 08 '17 at 09:56

3

You can do it by replacing

\b(?:0+:){2,}

with

function compIPV6(input) {
  return input.replace(/\b(?:0+:){2,}/, ':');
}

document.write(compIPV6('2001:db8:0:0:0:0:2:1') + '<br/>');
document.write(compIPV6('fe80:00:00:00:8e3:a11a:2a49:1148' + '<br/>'));

Check it out at regex101.

answered Jun 08 '17 at 09:56

SamWhan

8,296
1
18
45

2

this answer does not remove leading 0s – user3167654 Dec 15 '17 at 22:47

Tostti · Answer 3 · 2022-11-18T18:48:29.027

You can use a function that considers all of the needed cases:

const compressIPV6 = (ip) => {
  //First remove the leading 0s of the octets. If it's '0000', replace with '0'
  let output = ip.split(':').map(terms => terms.replace(/\b0+/g, '') || '0').join(":");

  //Then search for all occurrences of continuous '0' octets
  let zeros = [...output.matchAll(/\b:?(?:0+:?){2,}/g)];

  //If there are occurences, see which is the longest one and replace it with '::'
  if (zeros.length > 0) {
    let max = '';
    zeros.forEach(item => {
      if (item[0].replaceAll(':', '').length > max.replaceAll(':', '').length) {
        max = item[0];
      }
    })
    output = output.replace(max, '::');
  }
  return output;
}

document.write(compressIPV6('38c1:3db8:0000:0000:0000:0000:0043:000a') + '<br/>');
document.write(compressIPV6('0000:0000:0000:0000:38c1:3db8:0043:000a') + '<br/>');
document.write(compressIPV6('38c1:3db8:0000:0043:000a:0000:0000:0000') + '<br/>');
document.write(compressIPV6('38c1:0000:0000:3db8:0000:0000:0000:12ab') + '<br/>');

If there's more than one occurrence of consecutive '0' octets of the same length, it will only replace the first one. This will work regardless if the repeating zeroes are at the beginning, at the middle or at the end.

Finally, an answer that works, as long as the input is fully expanded. It does not handle some valid IPs if they have already been compressed, so you must expand them first. For example, '2001::1:0:0:1428:57ab' becomes '2001:0:1::1428:57ab' and '2001:0:0:1::1428:57ab' becomes '2001::1:0:1428:57ab' when run through this function. These aren't even the same addresses, so be careful! It should be '2001::1:0:0:1428:57ab' by RFC5952 recommendations. — themaninthewoods, Mar 22 '23 at 16:03

Gie · Answer 4 · 2019-10-29T10:38:45.133

1

You can use this method in order to compress IPv6 AND remove leading 0s:

   

function compressIPV6(input) {
 var formatted = input.replace(/\b(?:0+:){2,}/, ':');
 var finalAddress = formatted.split(':')
  .map(function(octet) {
   return  octet.replace(/\b0+/g, '');
  }).join(':');
 return finalAddress;
}
document.write(compressIPV6('2001:0db8:0000:0000:0000:0000:1428:57ab') );

edited Oct 29 '19 at 10:38

answered Jul 25 '19 at 14:42

Gie

222
3
5

Welcom to SO. Please be so kind and write small introductory paragraph, putting your code into context (of the question). – B--rian Jul 25 '19 at 15:17
This is not correct. If you change 2 characters in the example address to '2001:0db0:0000:1:0000:0000:1428:57ab' this code produces '2001:db0::1::1428:57ab' which is wrong because it replaced a single '0000' with '::' and it has two '::'. Also, try '2001:0000:0000:1:0000:0000:1428:57ab' and it returns '2001::1:::1428:57ab'. Not only does it have two '::' in it (not allowed), but the second one is actually ':::'. – themaninthewoods Mar 21 '23 at 23:25

How to compress IPV6 address using javascript?

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