C2Hat

C2Hat is an experimental TCP chat system (server and clients) written in C. The goal of the project is to refresh and improve my C/C++ skills, therefore there is no commitment to have a production-grade system at the moment.

This is experimental software, use it at your own risk.

Current features

The current release of C2hat server:

• implements its own simple chat protocol over TCP/IP;
• is multi-threaded;
• can be started either as a system service or a user-space program;
• can be started in the background and controlled by a frontend command;
• can be started as a foreground process and embedded into a Docker container;
• can send and receives Unicode messages with emojis;
• can receive some / commands from the users;
• uses the TLS protocol.

The current C2Hat client:

• is a command line ncurses-based application;
• runs on Linux/macOS/FreeBSD;
• provides TLS certificate verification for non-localhost servers;

Features in progress

• Send and receive end-to-end encrypted messages
• Implement some user authentication plugins
• Implement /admin commands for admin users
• Graphical cross-platform client based on wxWidgets

Build and Install

To compile the server you need a macOS or Linux machine with:

• standard build tools (GCC, Clang, Make, etc)
• OpenSSL (dev and static package)
• Mozilla CA certificates for TSL certificate handling and verification
• Valgrind (optional) for testing

To compile the client you need the above plus:

• ncurses (dev, static and terminfo packages)

Build

$ make [server|client]

Run tests

$ make test

Important: run make clean after running tests before (re)running make or make install to clean some debug leftovers.

Install

After a successful build you can run both the client and the server from the bin directory. If you want to install the binaries to the default location (/usr/local) run

$ [sudo] make install

To install the binaries to a custom location instead, run

$ [sudo] make install -e PREFIX=/custom/path

Usage

Start the server

To start the server with the default configuration (localhost:10000, max 5 connections):

$ c2hat-server start \
  --ssl-cert=</path/to/cert.pem> \
  --ssk-key=</path/to/key.pem>

Starting background server on localhost:10000 with locale 'en_GB.UTF-8' and PID 12345

Start the command line client

$ c2hat-cli localhost 10000 --capath=</path/to/ca/certs>

where capath is a directory containing CA certificates, for example /etc/ssl/certs on Linux.

You can also use a singe CA certificate file with the cacert option

$ c2hat-cli localhost 10000 --cacert=</path/to/ca/certificate.pem>

Check the server's status

$ c2hat-server status

The server is running with the following configuration:
         PID: 12345
 Config file: /home/someuser/.config/c2hat/server.conf
    Log file: /home/someuser/.local/state/c2hat/server.log
    PID file: /home/someuser/.local/run/c2hat.pid
        Host: localhost
        Port: 10000
    SSL cert: /home/someuser/.config/c2hat/ssl/cert.pem
     SSL key: /home/someuser/.config/c2hat/ssl/key.pem
      Locale: en_GB.UTF-8
 Max Clients: 5
 Working Dir: /home/someuser/.local/state/c2hat

Stop the server

$ c2hat-server stop

The server is running with PID 12345
The server with PID 12345 has been successfully stopped

Documentation

• Client Commands
• Server Configuration
• TLS Configuration
• C2hat Protocol
• Unicode Support
• Docker Support

License

C2Hat is licensed under GPL-3.0. C2Hat also includes external libraries that are available under a variety of licenses. Please refer to the LICENSE file for detailed information.

Intellectual Property Considerations

The author asserts no intellectual property rights over the protocols and algorithms used, and is not aware of any other such claims.