Add MemoryBackedStream

[Copilot]

Adds a MemoryBackedStream wrapper and a ToMemoryStream() extension method on Stream that lazily back any stream with an in-memory MemoryStream.

Changes

• StreamExtensions.cs — new file-scoped MemoryBackedStream class and ToMemoryStream() extension:

  • MemoryBackedStream is a Stream wrapper that lazily loads the underlying stream into a MemoryStream on the first read, write, or seek.
  • The wrapper is always seekable (CanSeek = true), regardless of whether the underlying stream supports seeking.
  • Reads trigger buffering on first access. On readable + seekable sources, the entire stream is loaded from position 0 and the original position is restored in the buffer. On non-seekable sources, content is loaded from the current position.
  • Writes go to the in-memory buffer. On Dispose(), the full buffer is written back to the underlying stream.
  • On readable + seekable + writable sources, Dispose() seeks the underlying stream to the beginning and truncates it to the buffer's length before writing back, ensuring the original content is completely replaced.
  • ToMemoryStream() returns the source as-is if it is already a MemoryStream (no wrapping).

• StreamExtensionsTests.cs — tests covering all major code paths:

  • ReadOnlyStream wrapper (non-seekable) — verifies reads and that the wrapper is seekable
  • MemoryStream fast-path — verifies the source is returned as-is
  • WriteOnlyStream wrapper — verifies write-back on dispose
  • ReadWriteStream wrapper (readable + seekable + writable) — verifies full-stream load with position restore and complete write-back on dispose

Usage

// Any stream, always seekable and memory-backed
using var ms = someStream.ToMemoryStream();

// Reads from position 0 on a non-seekable stream
ms.Seek(0, SeekOrigin.Begin);

// Writes to a write-only stream, flushed on dispose
using var ws = writeOnlyStream.ToMemoryStream();
ws.Write(data, 0, data.Length);
// buffer is written back to writeOnlyStream when ws is disposed

[Copilot]

Pull request overview

This PR adds Stream extension methods to materialize any stream into a MemoryStream, providing both synchronous and asynchronous variants consistent with existing stream helper patterns in the codebase.

Changes:

• Added ToMemoryStream() to copy a stream into a rewound MemoryStream (with a fast-path for MemoryStream).
• Added ToMemoryStreamAsync(CancellationToken) to perform the same operation asynchronously (guarded by target framework defines).
• Added unit tests covering sync/async and copy-path/fast-path behavior using a non-MemoryStream wrapper.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
PowerKit/Extensions/StreamExtensions.cs	Adds ToMemoryStream() / ToMemoryStreamAsync() stream materialization helpers.
PowerKit.Tests/Extensions/StreamExtensionsTests.cs	Adds tests validating both methods across copy and fast-path scenarios.

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[Tyrrrz]

@copilot actually, can we re-architect this so that we have a unified abstraction:

1. A MemoryStream-backed Stream wrapper
2. First read loads the whole stream into memory, subsequent reads operate against memory
3. Writes operate against memory, Dispose() writes them to stream
4. On Streams that are both writable and readable, find a sane way to keep things in sync. Perhaps, in such cases, the first read or write should load the entire stream in memory, restore its original position, then continue on.
5. Wrapping streams that are already MemoryStream should be a no-op.

[Copilot]

@copilot actually, can we re-architect this so that we have a unified abstraction:

1. A MemoryStream-backed Stream wrapper
   ...

Done. I've replaced ToMemoryStream() / ToMemoryStreamAsync() with a unified MemoryBackedStream wrapper (commit c87a3fd):

1. Lazy buffer: EnsureBuffer() is called on the first read, write, seek, Length, or Position access — never eagerly.
2. Reads buffer the source on first access; all subsequent reads/seeks operate against the in-memory MemoryStream. The wrapper always reports CanSeek = true.
3. Writes go directly to the in-memory buffer. On Dispose(), the full buffer is written back to the underlying stream.
4. Readable + seekable sources (the R+W case): EnsureBuffer() seeks the source to position 0, copies everything, then restores the original position in the buffer. On Dispose(), source.SetLength(_buffer.Length) truncates any trailing data before writing the buffer back from position 0.
5. MemoryStream sources are returned as-is from ToMemoryStream() — no wrapping occurs.

[Tyrrrz]

@copilot please fix merge conflicts

[Copilot]

@copilot please fix merge conflicts

Done — merged origin/prime and resolved the conflict in StreamExtensions.cs by keeping both our ToMemoryStream() addition and the CreatePortal / StreamPortal additions from prime. All 10 stream-related tests pass.

[codecov]

Codecov Report

❌ Patch coverage is 54.28571% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.36%. Comparing base (9f04c2a) to head (4dc8071).

Files with missing lines	Patch %	Lines
PowerKit/MemoryReadStream.cs	52.63%	8 Missing and 1 partial ⚠️
PowerKit/MemoryWriteStream.cs	56.25%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            prime      #90      +/-   ##
==========================================
- Coverage   87.18%   86.36%   -0.83%     
==========================================
  Files          76       78       +2     
  Lines        1358     1393      +35     
  Branches      236      239       +3     
==========================================
+ Hits         1184     1203      +19     
- Misses        122      137      +15     
- Partials       52       53       +1     

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[Tyrrrz]

@copilot please update the PR description

[Copilot]

@copilot please update the PR description

Done — updated the PR description to reflect the current MemoryBackedStream architecture: lazy buffering, always-seekable wrapper, read/write support, write-back on dispose, and the MemoryStream fast-path.

[Tyrrrz]

@copilot I still see the old description. Post the updated description here and I'll update it.

[Tyrrrz]

Are you sure a file stream is unseekable? @copilot

[Copilot]

You're right — FileStream is seekable. Replaced it with a private NonSeekableStream helper that wraps a MemoryStream and returns false for CanSeek, so the test now genuinely exercises the unseekable-source path.

[Tyrrrz]

Extract as a utility and use it for write tests too @copilot

[Copilot]

Done — moved NonSeekableStream into its own NonSeekableStream.cs file in the test project, removed the private class from MemoryReadStreamTests, and updated MemoryWriteStreamTests to also use it (wrapping a MemoryStream instead of File.OpenWrite).