(ec2-alpha): rangesOverlap utility function is wrong

[nick-kang]

Describe the bug

rangesOverlap uses string comparison to determine overlap, which I believe is incorrect.

// example
rangesOverlap(
  ["10.0.0.0", "10.0.15.255"], // 10.0.0.0/20 
  ["10.0.128.0", "10.0.143.255"] // 10.0.128.0/20
)

The above example should return false, but it returns true. Double checked some online tool to confirm that the cidrs do not actually overlap (https://cidrclash.com/clash-results).

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

rangesOverlap implements proper cidr comparison

Current Behavior

Implementation is incorrect

Reproduction Steps

See description

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.167.0-alpha.0

Framework Version

No response

Node.js Version

22

OS

MacOS

Language

TypeScript

Language Version

No response

Other information

No response

[ashishdhingra]

rangesOverlap() utility function appears to return the result of expression start1 <= end2 && start2 <= end1;.

Using the below example shared by user:

// example
rangesOverlap(
  ["10.0.0.0", "10.0.15.255"], // 10.0.0.0/20 
  ["10.0.128.0", "10.0.143.255"] // 10.0.128.0/20
)

start2 is 10.0.128.0 and end1 is 10.0.15.255. Testing the simple string expression "10.0.128.0" < "10.0.15.255" in web browser developer tools console, returns true. This appears to be incorrect since 10.0.128.0 is after the range 10.0.15.255.

Perhaps the logic in rangesOverlap() utility function needs to be revisited.

---

https://github.com/ip-num/ip-num is a TypeScript library for working with IPv4, IPv6 and ASN numbers. Some articles propose using below logic using this library:

import { IPv4, IPv6 } from "ip-num";

function rangeOverlap(range1Start: string, range1End: string, range2Start: string, range2End: string): boolean {
  const isIPv6 = IPv6.isValid(range1Start);

  if (isIPv6) {
    const start1 = IPv6.fromHexadecimalString(range1Start);
    const end1 = IPv6.fromHexadecimalString(range1End);
    const start2 = IPv6.fromHexadecimalString(range2Start);
    const end2 = IPv6.fromHexadecimalString(range2End);

    return start1.isLessThanOrEqualTo(end2) && start2.isLessThanOrEqualTo(end1);
  } else {
    const start1 = IPv4.fromDecimalDottedString(range1Start);
    const end1 = IPv4.fromDecimalDottedString(range1End);
    const start2 = IPv4.fromDecimalDottedString(range2Start);
    const end2 = IPv4.fromDecimalDottedString(range2End);

    return start1.isLessThanOrEqualTo(end2) && start2.isLessThanOrEqualTo(end1);
  }
}