TCP/IP Chat Application

There is no such thing as a "simple" TCP/IP application, but this is pretty close. This repository is a minimal correct implementation.

Minimal Correct Implementation

Each socket connection is two unidirectional streams of bytes. A minimal correct implementation consists of:

Message framing, to translate the streams of bytes to streams of messages.
Error handling:
- Always Be Reading - this lets you detect errors as quickly as possible.
- Asynchronous APIs - so we don't need multiple threads per socket.
- Close both streams for a connection at the same time - so that both sides can detect errors as long as data is still being transferred.
Keepalives, to detect the half-open scenario.

PipelineSocket - kind of like NetworkStream but using System.IO.Pipelines instead of Stream. PipelineSocket provides two unidirectional pipelines of bytes.
ChatConnection:
- Serializes chat protocol messages to/from bytes. ChatConnection provides two unidirectional channels of messages.
- Handles keepalives:
  - Periodically sends keepalive messages.
  - Ignores incoming keepalive messages.
- Handles request/response logic:
  - Has a collection of outstanding requests.
  - Handles response messages by completing their matching request.

Security
- Encryption. This protocol is a plain-text protocol.
- Server/client authentication.
- Misbehaving clients/servers. This app assumes correctly formed packets.
- Denial of service. E.g., really large length prefixes, sending data too slowly, etc.
- Reflection attacks. E.g., broadcast huge message at a high rate.
Higher-level state machine. E.g., when connection is lost, retry connection after some timeout.
- Consider a Desired State pattern: the user indicates the desired state, and your application performs whatever connection and messages are necessary to achieve that state.

Process Monitor to trace socket APIs called by an application.
TcpView to show the state of TCP/IP sockets.
Clumsy for simulating network black holes.
Wireshark for monitoring network traffic.
- Template for custom TCP protocol extension for Wireshark to teach Wireshark how to understand your TCP/IP protocol.