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[release/11.0-preview6] Add Stream wrappers for memory and text-based types - #129811
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jozkee merged 1 commit intoJun 25, 2026
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Fixesdotnet#82801 Introduces standardized stream wrappers for text and memory types as public sealed classes (`StringStream`, `ReadOnlyMemoryStream`, `WritableMemoryStream`, and `ReadOnlySequenceStream` ) as approved in [API review](dotnet#82801 (comment)) ([video](https://www.youtube.com/watch?v=T7xc7rARCEw&t=0h9m41s)). ### What's included - `StringStream` (`System.IO`, CoreLib): non-seekable, read-only stream that encodes `string` or `ReadOnlyMemory<char>` on-the-fly. Encoding is required (no default). Never emits BOMs. - `ReadOnlyMemoryStream` (`System.IO`, CoreLib): seekable, read-only stream over `ReadOnlyMemory<byte>` - `WritableMemoryStream` (`System.IO`, CoreLib): seekable, read-write stream over `Memory<byte>` with fixed capacity - `ReadOnlySequenceStream` (`System.Buffers`, System.Memory): seekable, read-only stream over `ReadOnlySequence<byte>` - Ref assembly updates for `System.Runtime` and `System.Memory` - Updated 3 internal call sites (`ReadOnlyMemoryContent`, `XmlPreloadedResolver`, `JsonXmlDataContract`) to use the new types - Conformance and behavioral tests for all 4 types ### Implementation notes - All types are `public sealed` with direct constructors: the review moved away from factory methods on `Stream` to avoid derived-type IntelliSense noise - `StringStream` encodes directly into the caller's buffer in `Read()` rather than using an internal byte buffer - `ReadOnlyMemoryStream` and `WritableMemoryStream` derive from `MemoryStream`. - `TryGetBuffer` returns false and `GetBuffer` throws on the memory stream types (no `publiclyVisible` support for now) ### Limitations - The internal [shared-source](https://github.com/dotnet/runtime/blob/main/src/libraries/Common/src/System/IO/ReadOnlyMemoryStream.cs) `ReadOnlyMemoryStream` in `Common/` cannot be fully replaced: - `System.Memory.Data` multi-targets `netstandard2.0` where the new public type doesn't exist. - `System.Net.Http` (net11.0 only) can adopt it directly. ### Follow-up work - `IBufferWriter<byte>` → `Stream` wrapper (separate proposal per [dotnet#100434](dotnet#100434)) --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This backport introduces new public stream wrapper types for text and memory-backed data (StringStream, ReadOnlyMemoryStream, WritableMemoryStream, ReadOnlySequenceStream) and wires them into the appropriate libraries (CoreLib / System.Runtime and System.Memory), along with conformance + behavioral tests and a few call-site updates to use the new APIs.
Changes:
- Added new public stream wrapper implementations in CoreLib (
System.IO) and System.Memory (System.Buffers), plus updated ref assemblies. - Added conformance/behavioral tests for the new stream wrappers.
- Updated call sites and shared-source usage (including removing the internal Common
ReadOnlyMemoryStreamfornet11.0+and updating System.Net.Http to use the public type).
Reviewed changes
Copilot reviewed 28 out of 29 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| src/libraries/System.Private.CoreLib/src/System/IO/StringStream.cs | Implements StringStream (read-only, non-seekable, on-the-fly encoding). |
| src/libraries/System.Private.CoreLib/src/System/IO/ReadOnlyMemoryStream.cs | Implements ReadOnlyMemoryStream over ReadOnlyMemory<byte>. |
| src/libraries/System.Private.CoreLib/src/System/IO/WritableMemoryStream.cs | Implements WritableMemoryStream over Memory<byte> with fixed capacity. |
| src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs | Exposes selected MemoryStream fields as private protected to support in-assembly derived wrappers. |
| src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems | Includes new CoreLib stream wrapper sources; switches CachedCompletedInt32Task to Common-linked source. |
| src/libraries/System.Runtime/ref/System.Runtime.cs | Adds ref-surface for StringStream, ReadOnlyMemoryStream, WritableMemoryStream. |
| src/libraries/System.Runtime/tests/System.IO.Tests/System.IO.Tests.csproj | Includes new test files for the added stream wrapper types. |
| src/libraries/System.Runtime/tests/System.IO.Tests/StringStream/StringStreamTestBase.cs | Shared test harness for validating StringStream behaviors across read APIs. |
| src/libraries/System.Runtime/tests/System.IO.Tests/StringStream/StringStreamTests_String.cs | StringStream(string, Encoding) tests across sync/async read APIs and misc behaviors. |
| src/libraries/System.Runtime/tests/System.IO.Tests/StringStream/StringStreamTests_Memory.cs | StringStream(ReadOnlyMemory<char>, Encoding) tests including slicing and surrogate edge cases. |
| src/libraries/System.Runtime/tests/System.IO.Tests/StringStream/StringStreamConformanceTests.cs | Conformance test coverage for StringStream using an identity encoding for arbitrary bytes. |
| src/libraries/System.Runtime/tests/System.IO.Tests/ReadOnlyMemoryStream/ReadOnlyMemoryStreamTests.cs | Behavioral tests for ReadOnlyMemoryStream. |
| src/libraries/System.Runtime/tests/System.IO.Tests/ReadOnlyMemoryStream/ReadOnlyMemoryStreamConformanceTests.cs | Stream conformance coverage for ReadOnlyMemoryStream. |
| src/libraries/System.Runtime/tests/System.IO.Tests/WritableMemoryStream/WritableMemoryStreamTests.cs | Behavioral tests for WritableMemoryStream, especially capacity semantics. |
| src/libraries/System.Runtime/tests/System.IO.Tests/WritableMemoryStream/WritableMemoryStreamConformanceTests.cs | Stream conformance coverage for WritableMemoryStream. |
| src/libraries/System.Memory/src/System/Buffers/ReadOnlySequenceStream.cs | Implements ReadOnlySequenceStream over ReadOnlySequence<byte>. |
| src/libraries/System.Memory/src/System.Memory.csproj | Includes ReadOnlySequenceStream and links CachedCompletedInt32Task from Common. |
| src/libraries/System.Memory/src/Resources/Strings.resx | Adds SR strings needed for ReadOnlySequenceStream exceptions. |
| src/libraries/System.Memory/ref/System.Memory.cs | Adds ref-surface for ReadOnlySequenceStream. |
| src/libraries/System.Memory/tests/System.Memory.Tests.csproj | Adds conformance test sources and references StreamConformanceTests for the new stream wrapper. |
| src/libraries/System.Memory/tests/ReadOnlyBuffer/ReadOnlySequenceStream.ConformanceTests.cs | Conformance coverage for ReadOnlySequenceStream across single/multi/fragmented sequences. |
| src/libraries/System.Memory/tests/ReadOnlyBuffer/NativeMemoryOwningStream.cs | Test helper to own/dispose unmanaged buffers used by native-memory conformance tests. |
| src/libraries/System.Memory/tests/ReadOnlyBuffer/NativeReadOnlyMemoryStream.ConformanceTests.cs | Conformance coverage for ReadOnlyMemoryStream over unmanaged-backed memory. |
| src/libraries/System.Memory/tests/ReadOnlyBuffer/NativeWritableMemoryStream.ConformanceTests.cs | Conformance coverage for WritableMemoryStream over unmanaged-backed memory. |
| src/libraries/System.Memory.Data/tests/BinaryDataTests.cs | Adjusts exception expectations to align with updated seek/OD behavior. |
| src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/Json/JsonXmlDataContract.cs | Uses StringStream instead of allocating a UTF-8 byte[] + MemoryStream. |
| src/libraries/System.Net.Http/src/System.Net.Http.csproj | Stops linking the internal Common ReadOnlyMemoryStream (uses public CoreLib type for net11+). |
| src/libraries/Common/src/System/IO/ReadOnlyMemoryStream.cs | Excludes internal Common ReadOnlyMemoryStream on net11.0+ (public CoreLib type supersedes it). |
| src/libraries/Common/src/System/Threading/Tasks/CachedCompletedInt32Task.cs | Introduces Common-linked cached task helper used by stream implementations. |
jozkee
approved these changes
Jun 24, 2026
jeffhandley
approved these changes
Jun 24, 2026
jeffhandley
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Great to get this into Preview 6. Has my support!
This was referenced Jun 24, 2026
jozkee
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Jun 25, 2026
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/ba-g known errors only and 2 legs show as unfinished but they are cancelled. |
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Backport of #126669 to release/11.0-preview6. See that PR for full details.
Adds new public stream wrapper APIs (
StringStream,ReadOnlyMemoryStream,WritableMemoryStream,ReadOnlySequenceStream).Fixes#82801.