Fixes System.Drawing.Image.FromStream(...) throws "Parameter is not valid." when Stream.Read does not return full file length

[ricardobossan]

Fixes #14064

Proposed changes

• Fix ComManagedStream.Read (the COM IStream wrapper used when a managed Stream is handed to GDI+) to keep reading until the requested buffer is filled or the stream reaches EOF, instead of issuing a single Stream.Read.
• This repairs Image.FromStream / Bitmap.FromStream / new Bitmap(stream) / Metafile(stream) for any stream that legally returns fewer bytes than requested (chunked / network / zip-wrapped), which GDI+ was rejecting with Parameter is not valid.
• Add regression tests for the short-read case and the read-past-EOF case.
• Loading images through System.Drawing from a stream that returns partial reads now succeeds instead of throwing ArgumentException: Parameter is not valid. (Also reported in System.Drawing.Bitmap.FromStream fails when called with ZipWrappingStream #8824).
• No change for streams that already returned full reads (FileStream, MemoryStream, ...); those keep working exactly as before.

Regression?

• No. The single-read behavior was ported verbatim from the legacy GPStream (git blame) and predates that; System.Drawing.Bitmap.FromStream fails when called with ZipWrappingStream #8824 shows the same failure on .NET Core 3.1 / System.Drawing.Common 4.7.0.

Risk

• Low. The change is confined to one method and only adds a fill loop: it returns identical results for full-read streams and the correct total for short-read streams. The COM IStream::Read contract explicitly allows satisfying a request across multiple source reads.

Screenshots

Before

After

Test methodology

• New unit tests in ComManagedStreamTests call IStream::Read directly against a stream that caps every read: one asserts the buffer is filled across chunks, the other asserts a request past EOF returns only the available bytes without throwing.
• Manual end-to-end check using the attached Program.cs (extract and paste it into src/test/integration/ScratchProject/Program.cs and run): it decodes an in-memory PNG through a 32-byte-per-read stream via Image.FromStream and shows the loaded image. Throws Parameter is not valid. before the fix, loads after.
• Full System.Private.Windows.Core.Tests suite.

Test environment(s)

• 11.0.100-preview.5.26302.115

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR fixes System.Drawing stream decoding failures by improving the COM IStream wrapper (ComManagedStream) so it can satisfy a single read request across multiple underlying Stream.Read calls (handling “short reads” correctly), and adds regression tests to cover the scenario.

Changes:

• Update ComManagedStream’s ISequentialStream::Read implementation to keep reading until the requested buffer is filled or EOF is reached.
• Add unit tests that exercise short-read streams and reads that request more bytes than remain.

Reviewed changes

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

File	Description
src/System.Private.Windows.Core/src/Windows/Win32/System/Com/ComManagedStream.cs	Implements a fill-loop in Read to handle short reads from managed streams passed to native consumers (e.g., GDI+).
src/System.Private.Windows.Core/tests/System.Private.Windows.Core.Tests/Windows/Win32/System/Com/ComManagedStreamTests.cs	Adds regression coverage for chunked/short-read behavior and read-past-EOF behavior via direct IStream::Read calls.

Comments suppressed due to low confidence (1)

src/System.Private.Windows.Core/src/Windows/Win32/System/Com/ComManagedStream.cs:143

• ISequentialStream::Read should return S_FALSE when fewer than cb bytes are read due to end-of-stream. Returning S_OK even on short reads diverges from the COM contract and makes it harder for callers to distinguish a complete read from EOF.

        if (pcbRead is not null)
            *pcbRead = (uint)read;

        return HRESULT.S_OK;

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