Chatty Chat Chat, a Java Chat App

COSC 150 - Advanced Programming

• Goals
• Description
• Specification and requirements
• Provided files
• Grading rubric

Goals

In order to complete this assignment, I needed to:

• Understand how to model network connections using sequence diagrams
  • Describe the operations required for a complete network interaction.
  • Model the communications between client and server processes, and between the threads supporting those processes.
• Understand how to use Java sockets to create and sustain network connnections.
  • Create a server that accepts multiple simultaneous connections.
  • Implement a design to handle interactions with many clients at once.
• Understand how to use Java threads to allow for nondeterministic execution.
  • Allow for both client and server processes to handle multiple simultaneous tasks.
  • Use proper object locks and/or wait-notify signaling to collaborate on a shared object.

Description

In this assignment, I implemented my very own internet chat protocol -- the ChattyChatChat protocol (CCC). The protocol governs how a single ChattyChatChat server mediates connections between any number of ChattyChatChat clients as they communicate with each other.

Implementing this protocol required that I create at least two Java classes:

• The ChattyChatChatServer, which is run on a single computer at a specified port and receives connections from clients.
• The ChattyChatChatClient, which is run by each client computer and connects to the server.

Boring Historical Context

The idea of text-based messaging has been around (almost) as long as networked computers have, with early bullitin board servers (BBS) and Usenet protocols allowing threaded discussion. The first widely-used real-time chat protocol was Internet Relay Chat (IRC), which was developed in 1988 and standardized in 1993.

Specification and requirements

ChattyChatChatServer

The server program is a class named ChattyChatChatServer; this program accepts a single command-line argument describing the port for the server to listen on. For example, to start the server and have it listen to port 9876, the command-line invocation would be:

java ChattyChatChatServer 9876

A single instance of the ChattyChatChat server serves as the common point of connection for all clients wanting to interact with the chat server.

ChattyChatChatClient

The client program is a class named ChattyChatChatClient; this program accepts two command-line arguments describing the server name and port to connect to. For example, to start a client and connect to a server running on port 9876 on cs-class, the command-line invocation would be:

java ChattyChatChatClient cs-class.uis.georgetown.edu 9876

Note that the server must be running in order for any client to successfully connect.

Chat protocol and commands

The communication protocol for the chat clients and server obeys the following rules:

• A "normal" message is text sent by one client to the server; this message should be relayed to all other clients, who will print it to standard out (e.g., using System.out.println()) upon receipt.
• The CCC protocol also provides the following chat commands which should be interpreted by the server to perform a special task:
  • /nick <name> : Set this client's nickname to be the string <name>. For example:

  /nick cosc150student
  

  would set the user's nickname to cosc150student.
  • The nickname command may be used more than once per session by any user; the current nickname is retained unless/until a subsequent /nick command is received.
  • Nicknames do not need to be unique on the server.
  • Nicknames are single-words and do not contain spaces.
  • Any additional characters beyond the first word may be ignored; that is, the above and below commands would have identical effect:

  /nick cosc150student these words may be discarded
  

  • /dm <name> <msg> : Send a message to user(s) with the specified nickname. For example:

  /dm cosc150student This is a "secret" message
  

  should deliver the message "This is a "secret" message" only to user(s) who have the nickname "cosc150student".
  • Only clients with the correct nickname should receive this message; nothing should be sent to any other clients.
  • If no client has the specified nickname, this message may be ignored.
  • If multiple clients have the specified nickname, all of them should receive the message.
  • /quit : Disconnect from the server and end the client program.
    • When a client enters this message, it is still be sent to the server as a notice that the client will disconnect; the server then safely closes this socket connection and clean-up details related to the client.
    • The client program disconnects, cleans up, and ends when this string is entered.
    • Any additional characters after the /quit are safely ignored.
• Any other input (including one beginning with a slash, but not exactly matching the above) is considered a regular message.

Other Files

The following files related to project logistics are present in the repository:

• README.md which provides this specification.
• .gitignore which specifies files git should NOT track.