Function capnp::serialize::try_read_message

pub fn try_read_message<R>(
    read: R, 
    options: ReaderOptions
) -> Result<Option<Reader<OwnedSegments>>> where
    R: Read, 

Like read_message(), but returns None instead of an error if there are zero bytes left in read. This is useful for reading a message stream of unknown length -- you call this function until it returns None.