Wk 6a - Sockets

Synopsis:

This lecture introduces Win32 Sockets and a C++ Sockets library. The library encapsulates connected, stream-oriented sockets with four classes: Sockets, SocketConnecter, SocketListener, and SocketSystem.

Readings and Activities for the Week:

Glossary of Terms

Socket:
An interface for network communication provided by a low-level library. The sockets we discuss are all stream-oriented, reading and writing sequences of bytes. Stream-oriented means that sockets do not provide you with a message structure. If you need that you will have to provide it². In order to communicate these sockets have to be connected. To connect your code needs, on one end of the channel, a connecter socket and, on the other end, a socket listener, to listen for, and establish a connected channel.
Messages:
Sockets are easier to use if we endow them, through library code, with a message structure. We want to be able to construct messages and send and receive them over connected sockets channels, e.g., message-passing communication.
HTTP:
One very common message protocol is Hyper-Text Transport Protocol (HTTP). An HTTP message consists of a series of lines of text, the message header, possibly followed by a block of bytes, e.g., binary message body. The first line is a command like: GET, POST, PUT, DELETE, ... That is followed by zero or more lines of key:value attributes describing properties of the communication, like Content-Length:453, specifying that a binary body of 453 (8 bit) bytes follows the header. The Header section is separated from the body by a single blank line. In this course we will use messages that use the HTTP format, but may not use the same commands or attributes.

Projects:

Sample Project #1, Code folder
Lexical scanner
Sample Project #2. Code folder
Rule-based parser
Sample Project #3, Code folder
Parser with Abstract Syntax Tree
Sample Project #4, Code folder
Code Analyzer

Win32 and C++ Sockets

Sockets natively read and write sequences of bytes

To communicate usefully you usually have to frame messages and abide by some talk protocol, e.g., who can send and who should listen. All of this is discussed and illustrated with code, using the links on this page.

Win32 Sockets Presentation, pptx
Presentation discusses connected, stream-oriented sockets, and some of the issues in using them.
Windows Sockets Error Codes
This may occasionally be useful when debugging socket applications.
Sockets Library - ver 5.1
This is the recommended source for sockets starter code.
Beej's Guide to Network Programming (HTML pages), pdf
Quite complete discussion of sockets, with a lot of code snippets. The code is written for Linux, but most of it is applicable for Windows as well. I used a lot of the ideas presented here in the Socket Library.
C++ StringServer
Frames messages as single strings - a very simple protocol for sockets. This demo illustrates clients interacting with the server concurrently.
Message Passing Communication
Discusses a proposed structure for message-passing communication for both Sockets and WCF.
HTTP style message-passing with File Transfer
Demonstrates how to process HTTP style messages and send files. Has an HttpMessage class.

You've seen the links, below, in the last lecture on Threads. The techniques they present are needed for building responsive message-passing communication channels.

Simple callable objects demo
Callable objects are very useful for defining thread processing.
Lambda Capture
Demos for various options when capturing data with lambdas.
C++11 Concurrency
A series of basic demos that cover most of what you need to know for the midterm and projects.
Blocking Queue
Thread safe queue that blocks on dequeuing an empty queue.
Tasks and ThreadPool
Listeners for High load servers should use threadpool to run client handlers.

Tutorials:

Sockets Tutorial - rpi.edu
Intro to Sockets Programming in C
Beej's Guide to Network Programming
HTTP Tutorial - J.Marshall
Introduction to Sockets Programming - CS.Rutgers.edu
Socket-Programming - geeksforgeeks.org
Netstat - Windows docs
netstat - wikipedia

Preparation for Synchronous Discussion:

Draw a class diagram for the C++ StringServer, including the Sockets Library code it uses.
Compare the results of this analysis with the structure of the Message Passing Communication systems discussed today.

Lecture Take-aways:

The most important things we discussed are:

Week 6a - Sockets and Sockets Library

Connected, stream-oriented communication