Stream Extensions

System.IO.Stream is an abstraction over many kinds of streams, and not every stream supports every operation. A NetworkStream cannot seek, so its Length and Position throw a NotSupportedException; a MemoryStream cannot time out, so ReadTimeout throws an InvalidOperationException. The BCL's answer is a set of Can… flags you are expected to check before touching the property.

Funcky folds the flag and the property into one Option-returning call:

Option<long> GetLengthOrNone(this Stream stream)
Option<long> GetPositionOrNone(this Stream stream)
Option<int> GetReadTimeoutOrNone(this Stream stream)
Option<int> GetWriteTimeoutOrNone(this Stream stream)
Option<byte> ReadByteOrNone(this Stream stream)

The first four are implemented by catching the specific exception the BCL documents for the unsupported case. Other exceptions, such as ObjectDisposedException on a closed stream or an IOException, are not caught and still propagate.

ReadByteOrNone removes the -1 sentinel from ReadByte, which returns an int only so that it can signal the end of the stream. The result is a real byte.

Example

string DescribeProgress(Stream stream)
    => (from position in stream.GetPositionOrNone()
        from length in stream.GetLengthOrNone()
        select $"{position} of {length} bytes")
        .GetOrElse("position unknown");

IEnumerable<byte> Bytes(Stream stream)
    => Sequence.Successors(stream.ReadByteOrNone(), _ => stream.ReadByteOrNone());

See The TryVerb-pattern for the same idea across the rest of the BCL.