3991bcc653
Audit Md11 (part 1 of 2). Replace unbounded HashSet<long> _seen with a WindowSize=256 ring (HashSet + Queue, LRU eviction). The stale-below-window guard (pubSeq <= HighWaterMark - WindowSize) prevents window eviction from re-admitting old seqs as novel — the load-bearing invariant. pubSeq is client-monotonic and SIO retransmit horizons are seconds-scale, so 256 covers realistic retries by a wide margin. HighWaterMark semantics preserved (Gungnir still reports it). Tests: 5 new InboundTrackerTests covering below-window guard, evicted-seq rejection, within-window dedup after eviction, memory bound, and watermark monotonicity. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
58 lines
2.1 KiB
C#
58 lines
2.1 KiB
C#
namespace SVSim.BattleNode.Reliability;
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/// <summary>
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/// Per-session inbound-emit ledger. Dedupes the client's pubSeq so we never dispatch
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/// a retransmitted emit twice; ack-echo (via SIO callback) is the caller's job.
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/// </summary>
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/// <remarks>
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/// State is bounded: the ledger keeps the most recent <see cref="WindowSize"/>
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/// pubSeqs in an LRU ring. Seqs below <c>HighWaterMark - WindowSize</c> are
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/// treated as stale-below-window and rejected without recording — this is what
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/// prevents window eviction from re-admitting an old seq as novel. The pubSeq is
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/// client-assigned monotonically; the bound is sized well above the realistic
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/// Socket.IO retransmit horizon, so legitimate retransmits always fall inside.
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/// </remarks>
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public sealed class InboundTracker
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{
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/// <summary>Sliding-window size. Anything below <c>HighWaterMark - WindowSize</c> is dropped.</summary>
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public const int WindowSize = 256;
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private readonly HashSet<long> _seen = new(WindowSize);
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private readonly Queue<long> _order = new(WindowSize);
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/// <summary>Highest pubSeq observed so far. Reported via Gungnir for diagnostics.</summary>
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public long HighWaterMark { get; private set; }
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/// <summary>Record an incoming pubSeq. Returns true if the caller should dispatch the envelope, false on duplicate or stale-below-window.</summary>
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public bool Observe(long pubSeq)
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{
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// Stale-below-window guard. Required AFTER HighWaterMark is past the window,
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// otherwise an evicted ring entry would re-admit as novel.
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if (HighWaterMark > 0 && pubSeq <= HighWaterMark - WindowSize)
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return false;
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if (pubSeq > HighWaterMark)
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{
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HighWaterMark = pubSeq;
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Record(pubSeq);
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return true;
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}
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if (_seen.Contains(pubSeq))
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return false;
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Record(pubSeq);
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return true;
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}
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private void Record(long pubSeq)
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{
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if (_order.Count >= WindowSize)
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{
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var evicted = _order.Dequeue();
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_seen.Remove(evicted);
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}
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_order.Enqueue(pubSeq);
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_seen.Add(pubSeq);
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}
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}
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