TryParseReverseDomain should fail on invalid IPv4 addresses such as one octet less or more.

[zbalkan]

Solves #41:

When one ore more octets are missing the Span<byte> buffer = stackalloc byte[4]; line fills it with zeroes, therefore covers the error.

When one or more octets are extra, for (int i = 0, j = parts.Length - 3; (i < 4) && (j > -1); i++, j--) loop covers as it ignores the extras.

I added an explicit guard clause for IPv4 addresses.

[Copilot]

Pull request overview

This PR fixes a bug in the TryParseReverseDomain method where invalid IPv4 reverse DNS domains were incorrectly accepted. The issue occurred because missing octets were implicitly filled with zeros due to stackalloc initialization, and extra octets were silently ignored by the loop bounds.

Changes:

• Added explicit validation to ensure IPv4 reverse DNS domains have exactly 6 parts (4 octets + "in-addr" + "arpa")
• Added a clear comment explaining the expected format

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.