`DeflateStream/GZipStream/BrotliStream .BaseStream` when instance is disposed

[skyoxZ]

runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

Line 121 in 90d0d5c

public Stream BaseStream => _stream;

runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/GZipStream.cs

Line 185 in 90d0d5c

public Stream BaseStream => _deflateStream?.BaseStream!;

runtime/src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliStream.cs

Lines 138 to 141 in 90d0d5c

	/// <summary>Gets a reference to the underlying stream.</summary>
	/// <value>A stream object that represents the underlying stream.</value>
	/// <exception cref="System.ObjectDisposedException">The underlying stream is closed.</exception>
	public Stream BaseStream => _stream;

https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.deflatestream.basestream?view=net-7.0
https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.gzipstream.basestream?view=net-7.0
https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.brotlistream.basestream?view=net-7.0

The document says that getting BaseStream throws ObjectDisposedException when the underlying stream is closed. I believe the document is incorrect and current implement doesn't check the status of underlying stream. What I want to discuss here is what should BaseStream return if the compressionStream itself is disposed:
a. Null. This is current behavior. If so, the property should be nullable.
b. Throws ObjectDisposedException.
c. The original underlying stream.
d. Undefined.

Some related facts:
The comments of BrotliStream.BaseStream is backported from its document and the document is copied from GZipStream/DeflateStream's document.

[stephentoub]

a. Null. This is current behavior. If so, the property should be nullable.

Use of an object after it's been disposed is erroneous and results in undefined behavior. We don't degrade the nullability annotations to include nulls that could possibly result with such usage.

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Issue Details

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runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/DeflateStream.cs

Line 121 in 90d0d5c

public Stream BaseStream => _stream;

runtime/src/libraries/System.IO.Compression/src/System/IO/Compression/GZipStream.cs

Line 185 in 90d0d5c

public Stream BaseStream => _deflateStream?.BaseStream!;

runtime/src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliStream.cs

Lines 138 to 141 in 90d0d5c

	/// <summary>Gets a reference to the underlying stream.</summary>
	/// <value>A stream object that represents the underlying stream.</value>
	/// <exception cref="System.ObjectDisposedException">The underlying stream is closed.</exception>
	public Stream BaseStream => _stream;

https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.deflatestream.basestream?view=net-7.0
https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.gzipstream.basestream?view=net-7.0
https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.brotlistream.basestream?view=net-7.0

The document says that getting BaseStream throws ObjectDisposedException when the underlying stream is closed. I believe the document is incorrect and current implement doesn't check the status of underlying stream. What I want to discuss here is what should BaseStream return if the compressionStream itself is disposed:
a. Null. This is current behavior. If so, the property should be nullable.
b. Throws ObjectDisposedException.
c. The original underlying stream.
d. Undefined.

Some related facts:
The comments of BrotliStream.BaseStream is backported from its document and the document is copied from GZipStream/DeflateStream's document.

Author:	skyoxZ
Assignees:	-
Labels:	area-System.IO.Compression, untriaged
Milestone:	-