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docs(network): document the connection-filter seam and the UInt128 IP wart

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Writes up IConnectionFilter for content authors: the accept-path contract
(allocation-free, non-blocking, side effects owned by the filter), registration
order and short-circuiting, the unregister-on-throw policy, and why this must
not be routed through EventSink.InvokeSocketConnect.

Also records the IPAddress <-> UInt128 normalization quirk. Addresses are
normalized to IPv6 form, so a v4 address round-tripped through UInt128 can come
back as InterNetworkV6 with IsIPv4MappedToIPv6 set. That is what the seemingly
redundant clause in ToUInt128 is defending, not a stray condition. Noted as a
follow-up rather than churned mid-feature: the normalization would read better
as an explicit "to canonical v6 bits" step that never needs the family check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Kamron Batman 2026-07-25 01:03:46 -07:00
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7
Projects/Server/Utilities/IPAddressUtility.cs
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@ -28,7 +28,12 @@ namespace Server;
/// </summary>
public static class IPAddressUtility
{
// Converts an IPAddress to a UInt128 in IPv6 format
// Converts an IPAddress to a UInt128 in IPv6 format.
// The IsIPv4MappedToIPv6 clause below looks redundant (the BCL only ever sets it on InterNetworkV6),
// but it guards the v4 -> UInt128 -> IPAddress round-trip, which can return a mapped v6 address for
// what is really a v4 one.
//TODO Rework as an explicit "to canonical v6 bits" step that needs no family check
// (see dev-docs/networking-packets.md, "IP Address Normalization")
public static UInt128 ToUInt128(this IPAddress ip)
{
if (ip.AddressFamily == AddressFamily.InterNetwork && !ip.IsIPv4MappedToIPv6)