This requires reference types that can be null to be annotated by a ? operator, similar to value types.
This gives the advantage that the compiler can warn against any null dereference exceptions, of which this commits elimits a few.
To make the underlying protocol implementation not any more complicated and to eliminate existing problems, and not that precise error reporting, I replaced some return null statements with explicit Exceptions. This lead to the assumption that those core protocoll functions always return non-null objects if they do not throw, making the PLC code simpler.
Adjust some NotConnected tests to look for explicit PlcException instead of NullReferenceException.
Note: This keeps the old methods to be backward compatible.
Note: Unforntunatly a lot of whitespace fixes, refactoring and other trivial stuff is
included. It was to hard to split of in a seperate commit.
Note: Async methods does not use exactly the same structure/signature as the
existing methods. "Out" parameters like ReadClass and ReadStruct instead
returns the struct in tuple. Async methods also rely on exceptions
instead of ErrorCodes to communicate exception states to calling client.
* Use TcpClient and use Async methods (ReadAsync/WriteAsync)
* Implemnt async methods for all existing methods
* Implemnt existing methods using tcpclient.
* Split Plc.cs in more files. (Common, Async, Sync, Helpers)
* Mark old methods as Obsolete
* Split tests in two files
* Implement Async tests
