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Issue #29, Phase 4 - Resolver Lookups
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Lines changed: 560 additions & 70 deletions

‎BenchmarkDotNet.Artifacts/results/DnsBench.CacheLookupBenchmarks-report-github.md‎

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```
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BenchmarkDotNet v0.14.0, macOS 26.1 (25B78) [Darwin 25.1.0]
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Apple M1 Max, 1 CPU, 10 logical and 10 physical cores
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.NET SDK 8.0.104
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[Host] : .NET 8.0.4 (8.0.424.16909), Arm64 RyuJIT AdvSIMD
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Job-RDUOPE : .NET 8.0.4 (8.0.424.16909), Arm64 RyuJIT AdvSIMD
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IterationCount=5 WarmupCount=2
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```
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| Method | Mean | Error | StdDev | Gen0 | Allocated |
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|-------------------------------------- |----------:|---------:|---------:|-------:|----------:|
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| 'Zone Lookup: Dictionary<string>' | 102.18 ns | 1.732 ns | 0.268 ns | 0.0255 | 160 B |
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| 'Zone Lookup: Dictionary<struct>' | 44.19 ns | 0.750 ns | 0.116 ns | - | - |
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| 'Zone Lookup: ConcurrentDict<string>' | 102.22 ns | 1.065 ns | 0.276 ns | 0.0255 | 160 B |
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| 'Zone Lookup: ConcurrentDict<struct>' | 41.82 ns | 0.905 ns | 0.235 ns | - | - |
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| 'Zone Lookup: FrozenDict<struct>' | 44.88 ns | 5.114 ns | 1.328 ns | - | - |

‎BenchmarkDotNet.Artifacts/results/DnsBench.CacheLookupBenchmarks-report.csv‎

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Method,Job,AnalyzeLaunchVariance,EvaluateOverhead,MaxAbsoluteError,MaxRelativeError,MinInvokeCount,MinIterationTime,OutlierMode,Affinity,EnvironmentVariables,Jit,LargeAddressAware,Platform,PowerPlanMode,Runtime,AllowVeryLargeObjects,Concurrent,CpuGroups,Force,HeapAffinitizeMask,HeapCount,NoAffinitize,RetainVm,Server,Arguments,BuildConfiguration,Clock,EngineFactory,NuGetReferences,Toolchain,IsMutator,InvocationCount,IterationCount,IterationTime,LaunchCount,MaxIterationCount,MaxWarmupIterationCount,MemoryRandomization,MinIterationCount,MinWarmupIterationCount,RunStrategy,UnrollFactor,WarmupCount,Mean,Error,StdDev,Gen0,Allocated
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'Zone Lookup: Dictionary<string>',Job-RDUOPE,False,Default,Default,Default,Default,Default,Default,0000000000,Empty,RyuJit,Default,Arm64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,5,Default,Default,Default,Default,Default,Default,Default,Default,16,2,102.18 ns,1.732 ns,0.268 ns,0.0255,160 B
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'Zone Lookup: Dictionary<struct>',Job-RDUOPE,False,Default,Default,Default,Default,Default,Default,0000000000,Empty,RyuJit,Default,Arm64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,5,Default,Default,Default,Default,Default,Default,Default,Default,16,2,44.19 ns,0.750 ns,0.116 ns,0.0000,0 B
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'Zone Lookup: ConcurrentDict<string>',Job-RDUOPE,False,Default,Default,Default,Default,Default,Default,0000000000,Empty,RyuJit,Default,Arm64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,5,Default,Default,Default,Default,Default,Default,Default,Default,16,2,102.22 ns,1.065 ns,0.276 ns,0.0255,160 B
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'Zone Lookup: ConcurrentDict<struct>',Job-RDUOPE,False,Default,Default,Default,Default,Default,Default,0000000000,Empty,RyuJit,Default,Arm64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,5,Default,Default,Default,Default,Default,Default,Default,Default,16,2,41.82 ns,0.905 ns,0.235 ns,0.0000,0 B
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'Zone Lookup: FrozenDict<struct>',Job-RDUOPE,False,Default,Default,Default,Default,Default,Default,0000000000,Empty,RyuJit,Default,Arm64,8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c,.NET 8.0,False,True,False,True,Default,Default,False,False,False,Default,Default,Default,Default,Default,Default,Default,Default,5,Default,Default,Default,Default,Default,Default,Default,Default,16,2,44.88 ns,5.114 ns,1.328 ns,0.0000,0 B

‎BenchmarkDotNet.Artifacts/results/DnsBench.CacheLookupBenchmarks-report.html‎

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<!DOCTYPE html>
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<html lang='en'>
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<head>
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<meta charset='utf-8' />
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<title>DnsBench.CacheLookupBenchmarks-20251126-010234</title>
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<style type="text/css">
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table { border-collapse: collapse; display: block; width: 100%; overflow: auto; }
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td, th { padding: 6px 13px; border: 1px solid #ddd; text-align: right; }
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tr { background-color: #fff; border-top: 1px solid #ccc; }
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tr:nth-child(even) { background: #f8f8f8; }
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</style>
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</head>
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<body>
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<pre><code>
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BenchmarkDotNet v0.14.0, macOS 26.1 (25B78) [Darwin 25.1.0]
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Apple M1 Max, 1 CPU, 10 logical and 10 physical cores
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.NET SDK 8.0.104
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[Host] : .NET 8.0.4 (8.0.424.16909), Arm64 RyuJIT AdvSIMD
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Job-RDUOPE : .NET 8.0.4 (8.0.424.16909), Arm64 RyuJIT AdvSIMD
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</code></pre>
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<pre><code>IterationCount=5 WarmupCount=2
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</code></pre>
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<table>
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<thead><tr><th>Method </th><th>Mean</th><th>Error</th><th>StdDev</th><th>Gen0</th><th>Allocated</th>
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</tr>
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</thead><tbody><tr><td>&#39;Zone Lookup: Dictionary&lt;string&gt;&#39;</td><td>102.18 ns</td><td>1.732 ns</td><td>0.268 ns</td><td>0.0255</td><td>160 B</td>
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</tr><tr><td>&#39;Zone Lookup: Dictionary&lt;struct&gt;&#39;</td><td>44.19 ns</td><td>0.750 ns</td><td>0.116 ns</td><td>-</td><td>-</td>
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</tr><tr><td>&#39;Zone Lookup: ConcurrentDict&lt;string&gt;&#39;</td><td>102.22 ns</td><td>1.065 ns</td><td>0.276 ns</td><td>0.0255</td><td>160 B</td>
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</tr><tr><td>&#39;Zone Lookup: ConcurrentDict&lt;struct&gt;&#39;</td><td>41.82 ns</td><td>0.905 ns</td><td>0.235 ns</td><td>-</td><td>-</td>
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</tr><tr><td>&#39;Zone Lookup: FrozenDict&lt;struct&gt;&#39;</td><td>44.88 ns</td><td>5.114 ns</td><td>1.328 ns</td><td>-</td><td>-</td>
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</tr></tbody></table>
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</body>
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</html>

‎Dns/DnsLookupKey.cs‎

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// //-------------------------------------------------------------------------------------------------
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// // <copyright file="DnsLookupKey.cs" company="stephbu">
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// // Copyright (c) Steve Butler. All rights reserved.
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// // </copyright>
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// //-------------------------------------------------------------------------------------------------
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namespace Dns
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{
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using System;
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/// <summary>
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/// Value-type key for DNS request/response tracking.
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/// Eliminates string allocation (~80 bytes) per lookup by using struct with precomputed hash.
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/// </summary>
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/// <remarks>
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/// Phase 4 optimization: replaces string.Format("{id}|{class}|{type}|{name}") with zero-allocation struct.
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/// Used in DnsServer._requestResponseMap to correlate forwarded queries with their originators.
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/// </remarks>
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public readonly struct DnsRequestKey : IEquatable<DnsRequestKey>
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{
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public readonly ushort QueryId;
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public readonly ResourceClass Class;
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public readonly ResourceType Type;
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public readonly string Name;
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private readonly int _hashCode;
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public DnsRequestKey(ushort queryId, ResourceClass resClass, ResourceType resType, string name)
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{
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QueryId = queryId;
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Class = resClass;
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Type = resType;
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Name = name ?? string.Empty;
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// Precompute hash for fast dictionary lookups
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_hashCode = HashCode.Combine(QueryId, Class, Type, StringComparer.OrdinalIgnoreCase.GetHashCode(Name));
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}
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public DnsRequestKey(DnsMessage message)
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: this(
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message.QueryIdentifier,
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message.QuestionCount > 0 ? message.Questions[0].Class : ResourceClass.IN,
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message.QuestionCount > 0 ? message.Questions[0].Type : ResourceType.A,
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message.QuestionCount > 0 ? message.Questions[0].Name : string.Empty)
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{
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}
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public bool Equals(DnsRequestKey other)
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{
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return QueryId == other.QueryId
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&& Class == other.Class
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&& Type == other.Type
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&& string.Equals(Name, other.Name, StringComparison.OrdinalIgnoreCase);
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}
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public override bool Equals(object obj) => obj is DnsRequestKey other && Equals(other);
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public override int GetHashCode() => _hashCode;
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public static bool operator ==(DnsRequestKey left, DnsRequestKey right) => left.Equals(right);
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public static bool operator !=(DnsRequestKey left, DnsRequestKey right) => !left.Equals(right);
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public override string ToString() => $"{QueryId}|{Class}|{Type}|{Name}";
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}
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/// <summary>
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/// Value-type key for DNS zone lookups.
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/// Eliminates string allocation for zone map key generation.
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/// </summary>
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/// <remarks>
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/// Phase 4 optimization: replaces string.Format("{host}|{class}|{type}") with zero-allocation struct.
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/// Used in SmartZoneResolver._zoneMap for hostname resolution.
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/// </remarks>
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public readonly struct DnsZoneLookupKey : IEquatable<DnsZoneLookupKey>
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{
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public readonly ResourceClass Class;
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public readonly ResourceType Type;
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public readonly string Host;
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private readonly int _hashCode;
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public DnsZoneLookupKey(string host, ResourceClass resClass, ResourceType resType)
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{
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Host = host ?? string.Empty;
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Class = resClass;
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Type = resType;
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// Precompute hash for fast dictionary lookups (case-insensitive for DNS)
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_hashCode = HashCode.Combine(
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StringComparer.OrdinalIgnoreCase.GetHashCode(Host),
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Class,
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Type);
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}
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public bool Equals(DnsZoneLookupKey other)
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{
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return Class == other.Class
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&& Type == other.Type
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&& string.Equals(Host, other.Host, StringComparison.OrdinalIgnoreCase);
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}
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public override bool Equals(object obj) => obj is DnsZoneLookupKey other && Equals(other);
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public override int GetHashCode() => _hashCode;
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public static bool operator ==(DnsZoneLookupKey left, DnsZoneLookupKey right) => left.Equals(right);
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public static bool operator !=(DnsZoneLookupKey left, DnsZoneLookupKey right) => !left.Equals(right);
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public override string ToString() => $"{Host}|{Class}|{Type}";
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}
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}

‎Dns/DnsServer.cs‎

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namespace Dns
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{
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using System;
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using System.Collections.Concurrent;
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using System.Collections.Generic;
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using System.IO;
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using System.Linq;
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private long _responses;
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private long _nacks;
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30-
private Dictionary<string, EndPoint> _requestResponseMap = new Dictionary<string, EndPoint>();
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private ReaderWriterLockSlim _requestResponseMapLock = new ReaderWriterLockSlim();
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/// <summary>
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/// Maps forwarded DNS requests to their originating endpoints.
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/// Phase 4: Uses struct key (DnsRequestKey) + ConcurrentDictionary for lock-free, allocation-free lookups.
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/// </summary>
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private readonly ConcurrentDictionary<DnsRequestKey, EndPoint> _requestResponseMap = new ConcurrentDictionary<DnsRequestKey, EndPoint>();
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private ushort port;
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//
125128
else // Referral to regular DC DNS servers
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{
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// store current IP address and Query ID.
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try
129-
{
130-
string key = GetKeyName(message);
131-
_requestResponseMapLock.EnterWriteLock();
132-
_requestResponseMap.Add(key, remoteEndPoint);
133-
}
134-
finally
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{
136-
_requestResponseMapLock.ExitWriteLock();
137-
}
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// store current IP address and Query ID using struct key (zero allocation)
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var key = new DnsRequestKey(message);
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_requestResponseMap.TryAdd(key, remoteEndPoint);
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}
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140135
using (PooledMemoryStream responseStream = BufferPool.RentMemoryStream())
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159154
}
160155
else
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{
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// message is response to a delegated query
163-
string key = GetKeyName(message);
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try
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{
166-
_requestResponseMapLock.EnterUpgradeableReadLock();
157+
// message is response to a delegated query - use struct key (zero allocation)
158+
var key = new DnsRequestKey(message);
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168-
EndPoint ep;
169-
if (_requestResponseMap.TryGetValue(key, out ep))
160+
// TryRemove atomically checks and removes - no locks needed
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if (_requestResponseMap.TryRemove(key, out EndPoint ep))
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{
163+
using (PooledMemoryStream responseStream = BufferPool.RentMemoryStream())
170164
{
171-
// first test establishes presence
172-
try
173-
{
174-
_requestResponseMapLock.EnterWriteLock();
175-
// second test within lock means exclusive access
176-
if (_requestResponseMap.TryGetValue(key, out ep))
177-
{
178-
using (PooledMemoryStream responseStream = BufferPool.RentMemoryStream())
179-
{
180-
message.WriteToStream(responseStream);
181-
Interlocked.Increment(ref _responses);
165+
message.WriteToStream(responseStream);
166+
Interlocked.Increment(ref _responses);
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183-
Console.WriteLine("{0} answered {1} {2} {3} to {4}", remoteEndPoint.ToString(), message.Questions[0].Name, message.Questions[0].Class, message.Questions[0].Type, ep.ToString());
168+
Console.WriteLine("{0} answered {1} {2} {3} to {4}", remoteEndPoint.ToString(), message.Questions[0].Name, message.Questions[0].Class, message.Questions[0].Type, ep.ToString());
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185-
SendUdp(responseStream.GetBuffer(), 0, (int)responseStream.Position, ep);
186-
}
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_requestResponseMap.Remove(key);
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}
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190-
}
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finally
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{
193-
_requestResponseMapLock.ExitWriteLock();
194-
}
195-
}
196-
else
197-
{
198-
Interlocked.Increment(ref _nacks);
170+
SendUdp(responseStream.GetBuffer(), 0, (int)responseStream.Position, ep);
199171
}
200172
}
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finally
173+
else
202174
{
203-
_requestResponseMapLock.ExitUpgradeableReadLock();
175+
Interlocked.Increment(ref _nacks);
204176
}
205177
}
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}
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180+
/// <summary>
181+
/// Creates a lookup key from a DNS message.
182+
/// Legacy method preserved for compatibility - prefer using DnsRequestKey struct directly.
183+
/// </summary>
184+
[Obsolete("Use new DnsRequestKey(message) for zero-allocation key creation")]
208185
private string GetKeyName(DnsMessage message)
209186
{
210187
if (message.QuestionCount > 0)

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