Read sliced Stream or PipeReader

The Stream.ReadSlice(long) and PipeReader.ReadSlice(long) extension methods returns a Stream or PipeReader instance that will only read up to a fixed set of bytes from the underlying source. This allows you, for example, to pass a Stream or PipeReader to a deserializer that will read to the end of the stream, even though your larger stream has more than your deserializer should see.

Sample

In the following example, ReadSlice is used to allow access to just 10 bytes of a larger stream:

var largeStream = new MemoryStream(new byte[20]);
var sliceStream = largeStream.ReadSlice(10);

// Creating the nested stream does NOT read from or buffer the underlying stream.
Assert.Equal(0, largeStream.Position);

// Attempting to read more bytes from the nested stream than are allowed results in just the allowed bytes.
int bytesRead = sliceStream.Read(new byte[20], 0, 20);
Assert.Equal(10, bytesRead);

// Attempting to read further produces 0 bytes, signaling the end of the (nested) stream.
bytesRead = sliceStream.Read(new byte[20], 0, 20);
Assert.Equal(0, bytesRead);

// The underlying stream is positioned just after the nested stream.
Assert.Equal(10, largeStream.Position);