Iterative client-server

Background

Developed for Advanced C Programming (CS 591) in Fall 2017, each lab represents a step towards the "ultimate" client-server.

Description

The functionality revolves around creating an ssh client-server which sets bash up for a connecting client on the server. However, this can easily be swapped for any other function; such as a web server (nginx). The labs crescendo into a much more sophisticated implementation using epoll and a thread pool to handle all processing. It also handles DDOS attacks and malicious clients.

Additionally, each folder has a makefile which can be used to make each client and server. More details for each particular implementation can be found in the particular folder:

• Lab 1
• Lab 2
• Lab 3
• Lab 4
• Lab 5

The code was written with Linux in mind and doesn't necessarily conform to POSIX standards. Verify code before reuse.

Features

Feature	Lab 1	Lab 2	Lab 3	Lab 4 (ThrPool)	Lab 5
Processes Created*	1	3	1	-	1
Threads Created	0	0	2	-	8 (Num_Cores)
Concurrent Server	YES	YES	YES	-	YES
Three-way Handshake	YES	YES	YES	-	YES
IO Type	Blocking	Blocking	Blocking	-	Non-blocking
Debug Mode	NO	YES	YES	YES	YES
Signal Handler	NO	YES	YES	NO	YES
Handles Malicious Clients	NO	NO	YES**	-	YES
Handles Partial Writes	NO	NO	NO	-	YES
Thread Pool	NO	NO	NO	YES	YES
Epoll	NO	NO	YES	-	YES

*^{_{It is important to note that there will be at least 1 process created for bash.}}

**^{_{Lab 3 handles malicious clients by using timers whereas Lab5 uses timerfd with its own epoll unit.}}

Usage

First start by running the server:

./server

Then connect a client (or more) using the server IP:

./client 127.0.0.1

Auxiliary Scripts

The following scripts can be used to test or debug the server:

• Broken Clients Test
• Concurrent Clients Test
• Flood Server Test
• Flood Server Hybrid Test
• Pwrite
• Show Server
• Show Clients
• Show Sockets
• All Broken Clients

Future

I plan on implementing a logger to record and report what happens during server runtime such as:

• Server creation
• Client connection
• Client destruction
• Client errors
• Server errors