Add stream wrappers for memory and text based types#562
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SimonCropp merged 3 commits intoJun 24, 2026
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Polyfills StringStream, ReadOnlyMemoryStream, WritableMemoryStream and ReadOnlySequenceStream from dotnet/runtime#126669. These types are approved for net11 but are not in the current net11 preview, so they are gated on `#if FeatureMemory` and remain active on net11. When a net11 SDK ships the real types, ApiBuilderTests.StreamWrapperBclDetectionTests fails with the exact change to make in each file: flip the guard to `#if FeatureMemory && !NET11_0_OR_GREATER` and add a TypeForwardedTo under `#if NET11_0_OR_GREATER`. The same steps are documented atop each source file. - ReadOnlyMemoryStream/WritableMemoryStream derive from MemoryStream and delegate to the MemoryStream(byte[],int,int,bool,bool) constructor, giving read-only / fixed-capacity semantics with GetBuffer throwing and TryGetBuffer returning false, without relying on MemoryStream internals unavailable on older TFMs. - StringStream (non-seekable, never emits a BOM) and ReadOnlySequenceStream (seekable) derive from Stream. Tests run on every framework where FeatureMemory is available; verified compiling across all 22 TFMs and passing on net11.0 and net48.
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…562) (#563) * Align stream wrappers with the dotnet 11 implementation (follow-up to #562) StringStream and ReadOnlySequenceStream diverged from dotnet/runtime#126669 in ways that hurt performance on the cases those types exist for. Bring them in line and port the PR's tests. StringStream - Encode incrementally via a stateful Encoder (fast-path single-shot, spillover buffer for sub-scalar reads, final flush) instead of encoding the whole text into one buffer on first read. Peak memory is now bounded by the caller's read buffer rather than the full encoded length, matching the BCL. - Span-based Encoder.Convert/Encoding.GetBytes on net core 2.1 / netstandard 2.1+, array-based equivalents on older TFMs. ReadOnlySequenceStream - Track a SequencePosition cursor alongside the absolute position so Read/ReadByte advance from the current segment instead of re-slicing from the start every call (was O(segments^2) for multi-segment sequences). Seek/Position reposition the cursor forward from the current spot, walking from the start only for back jumps. - Override CopyTo/CopyToAsync to write segments directly to the destination. CopyTo is gated to net core 2.1 / netstandard 2.1+ (Stream.CopyTo(Stream, int) is not virtual on older TFMs); CopyToAsync applies everywhere. ReadOnlyMemoryStream / WritableMemoryStream are unchanged: they are already at parity for array-backed memory, and matching the BCL for native (non-array) memory would require MemoryStream internals unavailable outside CoreLib. Tests - Port the explicit unit tests from the PR (StringStream encodings, surrogate pairs, chunk boundaries, GetMaxByteCount overflow guard, memory-slice/char-array ctors; WritableMemoryStream capacity/seek/overwrite cases) into the TUnit suite, plus ReadOnlySequenceStream CopyTo/CopyToAsync coverage. Regenerated Split + assemblySize; public API surface unchanged. Verified across all 22 TFMs (Consume) and passing on net10.0 and net48. * Update Directory.Build.props
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