Sockets Repository

Contains Socket, SocketListener, and SocketConnector classes

Quick Status

Code functions correctly

no known defects

Demonstration code

yes

Documentation

yes

Test cases

no, but planned

Static library

no, but planned

Build requires

C++17 option, Windows

Planned design changes

May eventually replace
with Boost::Asio

1.0 Concept

Fig 1. Sockets Model

Sockets are an operating system facility for sending streams of bytes through the tcp stack to another process or another machine. Their behavior is affected by buffers owned by each socket receiver.

If the sender sends N bytes, then:

if the receiver's buffer has space for the N bytes, then all are sent. The send function returns N signalling that all bytes were transfered.
if the receiving buffer has M < N bytes available, then M bytes are sent and the send function returns M signalling that N-M bytes were not sent.
if the receiving buffer is full, then the sender blocks until some space becomes available in the buffer.

Sockets don't know about any data structure other than streams of bytes. So to send a message you must frame its bytes with some additional decoration so the receiver can detect when an entire message has been received.

Also, since both sending and receiving are allowed on the same socket connection, some talk protocol is needed. Without that, both ends may send, eventually resulting in deadlock. Similarly, if both receive then buffers on both ends will empty, resulting again in deadlock.

The socket library provided in this repository provides means to simplify handling both problems. See the Resources listed below for ways to fully handle them.

2.0 Design

Fig 2. Sockets Class Diagram

Sockets-Windows provides four classes: Socket, SocketConnecter, SocketListener, and SocketSystem. An instance of Socket is created by the SocketListener when it establishes a connection. Listener creates a thread, passing it a client handler object and the new socket. Clients use SocketConnecter to establish a connection with a listener and to communicate with the remote socket.

Each program that uses Sockets must declare an instance of SocketSystem that loads the windows socket library on construction and unloads on destruction.

3.0 Resources

Win32Sockets.pdf

Discusses how Win32 Sockets operate.

CommunicationChannel.pdf

This document describes how sockets are used to build a reliable message-based asynchronous communication channel.

CppCommWithFileXfer

This repository holds code that uses these techniques.