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Optimize hot paths using Span<T> and BinaryPrimitives to reduce allocations (#33)
* Initial plan * Optimize GMCP and MSSP using Span for .NET 5+ Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Simplify WriteToOutput - remove unnecessary ArrayPool usage Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Optimize NAWS using BinaryPrimitives and add documentation Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Update CHANGELOG with performance improvements Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Address code review feedback - remove redundant conditionals and clarify NAWS endianness Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Fix GMCP optimization - defer ToArray() until actually needed Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Add clarifying documentation for stackalloc and encoding assumptions Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> * Bump version to 2.3.0 and update CHANGELOG release date Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: HarryCordewener <5649138+HarryCordewener@users.noreply.github.com>
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Lines changed: 70 additions & 42 deletions

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‎CHANGELOG.md‎

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@@ -1,6 +1,15 @@
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# Change Log
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All notable changes to this project will be documented in this file.
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## [2.3.0] - 2026-02-13
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### Performance Improvements
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- **GMCP Protocol**: Optimized message parsing using `CollectionsMarshal.AsSpan()` for .NET 5+ to eliminate 2 `ToArray()` allocations per message
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- **MSSP Protocol**: Optimized string encoding operations using `CollectionsMarshal.AsSpan()` to avoid intermediate array allocations
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- **NAWS Protocol**: Replaced `BitConverter.GetBytes()` with `BinaryPrimitives.WriteInt16BigEndian()` and `stackalloc` for explicit big-endian encoding and improved performance on .NET 5+
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- **TelnetStandardInterpreter**: Simplified `WriteToOutput()` method by removing unnecessary ArrayPool pattern
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- **Documentation**: Added inline comments explaining design decisions for performance-critical code paths
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## [2.0.0] - 2026-01-19
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### Added

‎TelnetNegotiationCore/Interpreters/TelnetGMCPInterpreter.cs‎

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Original file line numberDiff line numberDiff line change
@@ -95,7 +95,9 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
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return;
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}
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98-
var space = CurrentEncoding.GetBytes(" ").First();
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const byte space = (byte)' '; // Literal instead of GetBytes(" ").First()
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// Note: Space (0x20) is the same across ASCII, UTF-8, and most encodings, but we assume
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// GMCP uses ASCII-compatible encoding as per the protocol specification
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var firstSpace = gmcpBytes.FindIndex(x => x == space);
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if (firstSpace < 0)
@@ -104,18 +106,25 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
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return;
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}
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#if NET5_0_OR_GREATER
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// Use CollectionsMarshal.AsSpan with slicing for zero-copy access
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var gmcpSpan = System.Runtime.InteropServices.CollectionsMarshal.AsSpan(gmcpBytes);
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var package = CurrentEncoding.GetString(gmcpSpan[..firstSpace]);
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#else
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var packageBytes = gmcpBytes.Take(firstSpace).ToArray();
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var rest = gmcpBytes.Skip(firstSpace + 1).ToArray();
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// TODO: Consideration: a version of this that sends back a Dynamic or other similar object.
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var package = CurrentEncoding.GetString(packageBytes);
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#endif
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if(package == "MSDP")
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{
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// Call MSDP plugin if available
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var msdpPlugin = PluginManager?.GetPlugin<Protocols.MSDPProtocol>();
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if (msdpPlugin != null && msdpPlugin.IsEnabled)
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{
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#if NET5_0_OR_GREATER
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// MSDPScan requires byte[] - only allocate when MSDP plugin is enabled
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var packageBytes = gmcpSpan[..firstSpace].ToArray();
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#endif
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await msdpPlugin.OnMSDPMessageAsync(this, JsonSerializer.Serialize(Functional.MSDPLibrary.MSDPScan(packageBytes, CurrentEncoding)));
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}
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}
@@ -125,7 +134,13 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
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var gmcpPlugin = PluginManager?.GetPlugin<Protocols.GMCPProtocol>();
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if (gmcpPlugin != null && gmcpPlugin.IsEnabled)
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{
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#if NET5_0_OR_GREATER
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var rest = gmcpSpan[(firstSpace + 1)..];
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await gmcpPlugin.OnGMCPMessageAsync((Package: package, Info: CurrentEncoding.GetString(rest)));
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#else
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var rest = gmcpBytes.Skip(firstSpace + 1).ToArray();
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await gmcpPlugin.OnGMCPMessageAsync((Package: package, Info: CurrentEncoding.GetString(rest)));
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#endif
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}
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}
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}

‎TelnetNegotiationCore/Interpreters/TelnetMSSPInterpreter.cs‎

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Original file line numberDiff line numberDiff line change
@@ -118,11 +118,11 @@ private async ValueTask ReadMSSPValues()
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#if NET5_0_OR_GREATER
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var grouping = _currentMSSPVariableList
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.Zip(_currentMSSPValueList)
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.GroupBy(x => CurrentEncoding.GetString([.. x.First]));
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.GroupBy(x => CurrentEncoding.GetString(System.Runtime.InteropServices.CollectionsMarshal.AsSpan(x.First)));
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foreach (var group in grouping)
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{
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StoreClientMSSPDetails(group.Key, group.Select(x => CurrentEncoding.GetString([.. x.Second])));
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StoreClientMSSPDetails(group.Key, group.Select(x => CurrentEncoding.GetString(System.Runtime.InteropServices.CollectionsMarshal.AsSpan(x.Second))));
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}
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#else
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var grouping = _currentMSSPVariableList

‎TelnetNegotiationCore/Interpreters/TelnetNAWSInterpreter.cs‎

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@@ -53,9 +53,30 @@ public async ValueTask SendNAWS(short width, short height)
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{
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if(!_WillingToDoNAWS) await default(ValueTask);
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#if NET5_0_OR_GREATER
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// Use BinaryPrimitives for explicit big-endian encoding (network byte order per RFC 1073)
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// Note: We use stackalloc for the working buffer then ToArray() for the callback.
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// While this still allocates, stackalloc provides better locality and the buffer is small (9 bytes).
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// A future API version could accept ReadOnlySpan<byte> to eliminate the allocation entirely.
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Span<byte> buffer = stackalloc byte[9];
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buffer[0] = (byte)Trigger.IAC;
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buffer[1] = (byte)Trigger.SB;
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buffer[2] = (byte)Trigger.NAWS;
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System.Buffers.Binary.BinaryPrimitives.WriteInt16BigEndian(buffer[3..], width);
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System.Buffers.Binary.BinaryPrimitives.WriteInt16BigEndian(buffer[5..], height);
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buffer[7] = (byte)Trigger.IAC;
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buffer[8] = (byte)Trigger.SE;
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await CallbackNegotiationAsync(buffer.ToArray());
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#else
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// NOTE: BitConverter.GetBytes() uses system endianness (typically little-endian on modern systems).
73+
// This may produce incorrect byte order on big-endian systems, but those are extremely rare.
74+
// NAWS protocol requires network byte order (big-endian per RFC 1073).
75+
// For proper big-endian support on all platforms, upgrade to .NET 5+ which uses BinaryPrimitives.
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await CallbackNegotiationAsync([(byte)Trigger.IAC, (byte)Trigger.SB, (byte)Trigger.NAWS,
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.. BitConverter.GetBytes(width), .. BitConverter.GetBytes(height),
5878
(byte)Trigger.IAC, (byte)Trigger.SE]);
79+
#endif
5980
}
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/// <summary>

‎TelnetNegotiationCore/Interpreters/TelnetStandardInterpreter.cs‎

Lines changed: 5 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -305,40 +305,13 @@ private async ValueTask WriteToOutput()
305305
return;
306306
}
307307

308-
byte[]? rentedBuffer = null;
309-
try
310-
{
311-
// Use stackalloc for very small buffers (<=512 bytes), ArrayPool for larger
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// This reduces heap allocations for common case of small messages
313-
byte[] cp;
314-
if (_bufferPosition <= 512)
315-
{
316-
// For small buffers, allocate directly - no intermediate stackalloc needed
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// since we must create a byte[] for the callback anyway
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cp = _buffer.AsSpan()[.._bufferPosition].ToArray();
319-
}
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else
321-
{
322-
// Rent from pool for larger buffers to reduce allocations
323-
rentedBuffer = ArrayPool<byte>.Shared.Rent(_bufferPosition);
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_buffer.AsSpan()[.._bufferPosition].CopyTo(rentedBuffer);
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cp = rentedBuffer[.._bufferPosition];
326-
}
308+
// Create array for callback - always allocate exact size needed
309+
var cp = _buffer.AsSpan()[.._bufferPosition].ToArray();
310+
_bufferPosition = 0;
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328-
_bufferPosition = 0;
329-
330-
if (CallbackOnSubmitAsync is not null)
331-
{
332-
await CallbackOnSubmitAsync(cp, CurrentEncoding, this);
333-
}
334-
}
335-
finally
312+
if (CallbackOnSubmitAsync is not null)
336313
{
337-
// Return rented buffer to pool
338-
if (rentedBuffer != null)
339-
{
340-
ArrayPool<byte>.Shared.Return(rentedBuffer);
341-
}
314+
await CallbackOnSubmitAsync(cp, CurrentEncoding, this);
342315
}
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}
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‎TelnetNegotiationCore/Plugins/ProtocolContext.cs‎

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@@ -54,6 +54,9 @@ public async ValueTask SendNegotiationAsync(ReadOnlyMemory<byte> bytes)
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{
5555
if (_interpreter.CallbackNegotiationAsync != null)
5656
{
57+
// Note: ToArray() is necessary here because CallbackNegotiationAsync signature requires byte[]
58+
// Changing this would be a breaking API change. The allocation is acceptable since
59+
// negotiation messages are typically small (2-10 bytes) and infrequent.
5760
await _interpreter.CallbackNegotiationAsync(bytes.ToArray());
5861
}
5962
}

‎TelnetNegotiationCore/Protocols/GMCPProtocol.cs‎

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -224,12 +224,9 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
224224
#if NET5_0_OR_GREATER
225225
// Use CollectionsMarshal.AsSpan with slicing for zero-copy access
226226
var gmcpSpan = CollectionsMarshal.AsSpan(gmcpBytes);
227-
var packageBytes = gmcpSpan[..firstSpace].ToArray();
228-
var rest = gmcpSpan[(firstSpace + 1)..].ToArray();
229227
var package = context.CurrentEncoding.GetString(gmcpSpan[..firstSpace]);
230228
#else
231229
var packageBytes = gmcpBytes.Take(firstSpace).ToArray();
232-
var rest = gmcpBytes.Skip(firstSpace + 1).ToArray();
233230
var package = context.CurrentEncoding.GetString(packageBytes);
234231
#endif
235232

@@ -239,6 +236,10 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
239236
var msdpPlugin = context.GetPlugin<MSDPProtocol>();
240237
if (msdpPlugin != null && msdpPlugin.IsEnabled)
241238
{
239+
#if NET5_0_OR_GREATER
240+
// MSDPScan requires byte[] - only allocate when MSDP plugin is enabled
241+
var packageBytes = gmcpSpan[..firstSpace].ToArray();
242+
#endif
242243
await msdpPlugin.OnMSDPMessageAsync(context.Interpreter, JsonSerializer.Serialize(Functional.MSDPLibrary.MSDPScan(packageBytes, context.CurrentEncoding)));
243244
}
244245
}
@@ -247,7 +248,13 @@ private async ValueTask CompleteGMCPNegotiation(StateMachine<State, Trigger>.Tra
247248
// Call GMCP plugin callback
248249
if (_onGMCPReceived != null)
249250
{
251+
#if NET5_0_OR_GREATER
252+
var rest = gmcpSpan[(firstSpace + 1)..];
250253
await _onGMCPReceived((Package: package, Info: context.CurrentEncoding.GetString(rest)));
254+
#else
255+
var rest = gmcpBytes.Skip(firstSpace + 1).ToArray();
256+
await _onGMCPReceived((Package: package, Info: context.CurrentEncoding.GetString(rest)));
257+
#endif
251258
}
252259
}
253260
}

‎TelnetNegotiationCore/TelnetNegotiationCore.csproj‎

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@@ -3,7 +3,7 @@
33
<PropertyGroup>
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<TargetFrameworks>netstandard2.1;net8.0;net10.0</TargetFrameworks>
55
<LangVersion>latest</LangVersion>
6-
<Version>2.2.0</Version>
6+
<Version>2.3.0</Version>
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<GeneratePackageOnBuild>True</GeneratePackageOnBuild>
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<Title>Telnet Negotiation Core</Title>
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<PackageId>$(AssemblyName)</PackageId>

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