I'm doing some testing trying to isolate some odd behavior in the libraries (.NET). When I use the Winsock API through C++ and simply call, closesocket(), I see the windows side send the FIN/ACK packet and the remote side send back an ACK packet. This is what I would call a graceful close. However, when programming in C# I'm not seeing what I would call a graceful close.
In C#, I open my socket and then, when closing it, I see windows send a FIN packet Only when first calling Socket.Shutdown(). However, regardless, when I call Socket.Close() in C#, an RST packet is sent and the connection summarily dropped. This confuses me because, from what I've read on line, the TCP closing process should be FIN/ACK -> ACK (from both sides actually but for now, I'm only concerned with "my" side); i.e. there should not be an RST packet in the mix at all. From what I've read, apparently, an RST packet is only sent when the receiver is uncertain about the connection state and wants out.
Why is this RST packet being sent on a planned shutdown in .NET and not at all in a planned shutdown from the winsock API? Is there a way to prevent the transmission of an RST packet during a graceful shutdown from .NET?
In case it's important, in both code paths, I'm reading all available data on the socket before calling the respective close() method.