// zero-copy BinaryData creation from MemoryStream

var stream = new MemoryStream();
stream.Write([1, 2, 3]); // some data is written to the memory stream
stream.Flush();

// this requires a memory copy
var dataViaStreamCopy = BinaryData.FromStream(stream);

// this does not require a memory copy
var dataViaBufferAccess = new BinaryData(stream.GetBuffer().AsMemory(0, (int)stream.Position)); 

// what BinaryData does internally is the same:
// https://github.com/dotnet/dotnet/blob/main/src/runtime/src/libraries/System.Memory.Data/src/System/BinaryData.cs#L305