ZipHelper.ReadBytes throws an unreachable exception

[carlossanlop]

In this method:

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

Lines 39 to 46 in abf8e94

	internal static void ReadBytes(Stream stream, byte[] buffer, int bytesToRead)
	{
	int bytesRead = stream.ReadAtLeast(buffer.AsSpan(0, bytesToRead), bytesToRead, throwOnEndOfStream: false);
	if (bytesRead < bytesToRead)
	{
	throw new IOException(SR.UnexpectedEndOfStream);
	}
	}

We would never throw the IOException because Stream.ReadAtLeast is expected to throw when the specified minimum number of bytes is not read. So we should refactor/simplify this code.

Important: We should refactor this after we merge #103153 as that PR is making changes around that method.

The docs on top of ReadBytes might also have to be changed, because ReadAtALeast will read an equal or larger number of bytes from the stream, which depends on the size of the buffer too.

We could consider getting rid of ReadBytes altogether and always directly use Stream.ReadAtLeast.

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[stephentoub]

We would never throw the IOException because Stream.ReadAtLeast is expected to throw when the specified minimum number of bytes is not read.

It's not unreachable. See the last parameter:
throwOnEndOfStream: false
So this may return fewer than the requested minimum if it his EOF.

The code could be simplified if instead throwOnEndOfStream is set to true, which is also the default. The resulting exception will be of a derived type.