Love Letter Protocol Client Server

The Lover Letter Protocol Client Server is designed to be an education example of the client-server model taught for A-Level computer science.

The project implements a fictional "Love Letter" Application Layer protocol, which operates over the Transmission Control Protocol (TCP).

The user can use an ASCII client (such as telnet or PuTTY Telnet) and communicate with the server, using the defined protocol.

Students are encouraged to run the code locally and experiment with how it works, there are snippets throughout the codebase where improvements could be made. Submit a Pull Request for new additions.

Getting Started

To get started, run main.py within python 3.8 or greater, the server should start.

$ python3.8 main.py 
root - INFO - Starting listening on port 8888
root - INFO - Listening for connections
root - INFO - 172.19.0.1

Then connect with your telnet client to the IP listed and port 8888.

$ telnet 127.0.0.1 8888
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
> OK - Welcome to the Love Letter Server
Supported commands are: LOGIN, LOGOUT, LIST, MESSAGE


LOGIN olivia
> OK - Hello olivia

Refer to this document for commands you can use. You can also launch multiple clients from the same machine. Use the LIST command to see connected users and ports in use!

Love Letter Protocol

Introduction

The objectives of LLP are 1) promote love while learning about networking and protocols, 2) send messages between clients, 3) highlight the concepts of the client-server model. LLP, though usable using an ASCII terminal, can be implemented into a graphical interface or used by other programs.

The LLP protocol is designed to be easily used by a simple ASCII TCP client, such as telnet or PuTTY Telnet).

The TCP/IP Layer when using LLP is as follows:

Application Layer - Love Letter Protocol (LLP) - defined by this document
Transport Layer - Transmission Control protocol (TCP)
Network Layer - Internet Protocol V4 (IPV4)

Response Codes

Upon processing a message, the server will return one of the following status codes followed by a descriptive message.

ERROR
OK

For example:

> OK - Hello user

Server Model

llp_server.py - Run's a socket server which listens for connections. Spawns a ClientProcessor in a new Thread upon a new connection.
client_processor.py - Handles the income LLP messages from the clients text based terminal, parsing the message and making calls to the CoreServer.
core_server.py - Maintains the central state of the server, allows clients to message each other by maintaining a map of clients.

Client Commands

The following table shows a list of commands which can be used. Further details for each command are documented below.

Command	Description
`LOGIN <username>`	Used to attach a username to the opened TCP/IP session.
`LIST`	Used to list all clients which are connected to the server.
`MESSAGE <username>`	Sends a message to another user on the server.
`XOXOXO`	Indicates the end of a message.

LOGIN

Used to attach a username to the opened TCP/IP session. Usernames must be between 3-15 characters. Valid characters: a-z A-Z 0-9

LOGIN bob
> OK - Hello bob

LOGIN %^&
> ERROR - Invalid username, try again

LIST

Outputs all the clients logged into the server.

LIST
> OK - Data Available...
192.168.69.165:58628 | bob
127.0.0.1:55430 | olivia

Use this command to discover usernames to send messages to.

MESSAGE

Used to send a message to a user

MESSAGE bob
> OK - Send Message, end with XOXOXO
hello, happy valentines
XOXOXO

It will be displayed in the recipients console like

> OK - Hello mms
> INBOUND MESSAGE - SENDER: olivia
> RECIPIENT: bob
> hello, happy valentines
> XOXOXO

Learning?

New to opensource? Try opening a Pull-Request and improve the codebase? There is lots that can be done!

Better/full test coverage
Unified error messages/handling
BLOCK functionality
BROADCAST functionality to send a message to everyone on the server

martysweet/llp-server