[duplicate-code] Duplicate Code: BaseSerializer.cs Dual #if NETCOREAPP / #else Primitive Read/Write Implementations

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Summary

src/Platform/Microsoft.Testing.Platform/IPC/Serializers/BaseSerializer.cs implements every read/write primitive twice — once under #if NETCOREAPP using Span<byte>, ArrayPool<byte>, and ReadExactly, and once under #else using heap-allocated byte[] and stream.Read. The two implementations are structurally identical; the only differences are the allocation strategy and the ReadExactly vs manual-read pattern. The codebase already ships polyfills for these exact APIs in src/Polyfills/.

Duplication Details

Pattern: Dual #if NETCOREAPP / #else primitive read/write implementations

• Severity: Medium
• Occurrences: 12 methods duplicated (~87 #else lines mirroring ~140 #if NETCOREAPP lines)
• Location: src/Platform/Microsoft.Testing.Platform/IPC/Serializers/BaseSerializer.cs (lines 30–257)

Method	#if NETCOREAPP lines	#else lines
ReadString	31–46	172–181
ReadStringValue	48–60	183–188
WriteString	62–83	191–197
WriteSize<T>	85–97	199–205
WriteInt	99–106	207–211
ReadInt	108–113	213–218
WriteLong	115–121	220–224
ReadLong	123–128	232–237
WriteUShort	130–136	226–230
ReadUShort	138–143	239–244
WriteBool	145–151	246–250
ReadBool	153–168	252–257

Example — WriteInt (signatures are 100% identical; only the body differs):

#if NETCOREAPP (stack-allocated Span<byte>):

protected static void WriteInt(Stream stream, int value)
{
    Span<byte> bytes = stackalloc byte[sizeof(int)];
    if (!BitConverter.TryWriteBytes(bytes, value))
    {
        throw Unreachable();
    }
    stream.Write(bytes);
}

#else (heap-allocated byte[]):

protected static void WriteInt(Stream stream, int value)
{
    byte[] bytes = BitConverter.GetBytes(value);
    stream.Write(bytes, 0, bytes.Length);
}

Example — ReadString:

#if NETCOREAPP uses ArrayPool<byte>.Shared.Rent/Return + stream.ReadExactly.
#else uses new byte[length] + stream.Read(bytes, 0, bytes.Length).

Impact Analysis

• Maintainability: Adding a new primitive (e.g., ReadUInt, WriteFloat) requires writing it twice. Any bug in a read/write primitive must be fixed in both branches.
• Bug Risk: The #else branch's stream.Read calls do not assert/retry on short reads, while ReadExactly in #if NETCOREAPP does — a subtle behavioral divergence that could surface as data corruption on .NET Framework in low-level scenarios.
• Code Bloat: ~87 lines of duplicated code in the #else branch alone.

Refactoring Recommendations

1. Use existing polyfills: The src/Polyfills/ directory already contains shims for Span<byte> and related APIs. Add or verify polyfills for:

   • Stream.ReadExactly(Span<byte>) — already shimmable via ReadExactly(byte[], int, int) plus a loop
   • BitConverter.TryWriteBytes(Span<byte>, int) — can be shimmed with BitConverter.GetBytes + Array.Copy
   • stream.Write(ReadOnlySpan<byte>) — can be shimmed with stream.Write(byte[], 0, length)

2. Collapse to a single implementation once the polyfills are in place, retaining the #if NETCOREAPP performance-optimized path as optional (or removing the #else branch entirely if .NET Framework is no longer a supported target for this assembly).

3. Fix the stream.Read short-read risk in the #else branch as a priority independent of the above, since it can produce silent data corruption.

Implementation Checklist

• Review duplication findings
• Check which TFMs Microsoft.Testing.Platform must support on .NET Framework
• Add/verify polyfill shims for ReadExactly, BitConverter.TryWriteBytes, Span<T> write
• Collapse BaseSerializer.cs to a single implementation using polyfills
• Verify all IPC/serializer tests pass under all target frameworks
• Fix the stream.Read short-read issue in the #else branch as an independent safety fix if the branch must remain

Analysis Metadata

• Analyzed Files: 1 (BaseSerializer.cs)
• Detection Method: Semantic code analysis
• Analysis Date: 2026-07-09

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• expires on Jul 11, 2026, 5:42 AM UTC