This GitHub repo contains the solution for Project 1 for the Computer Networks course taught by Professor Yasir Zaki at NYU Abu Dhabi. Here, we implement a simple file transfer protocol designed to handle multiple concurrent client connections and file transfers. The team members for this project are Avinash Gyawali and Aadim Nepal.

To run the code in your terminal, please follow these steps:

1. Clone the Repository:

   git clone https://github.com/Tauke190/ComputerNetworksHW1.git

2. Navigate to the Server and Client Directories:

   Inspect the directories closely. The server directory contains:

   • Three subdirectories: Bob, Harry, and Ron
   • A text file: users.txt

   The subdirectories Bob, Harry, and Ron are for the authenticated users stored on the server. The users.txt file contains usernames and passwords that the server authenticates before running the program.

1. Open Four Terminals:

   • One for the server
   • Three for the clients: Bob, Harry, and Ron

2. Run the Server Code:

   • Navigate to the server directory:

     cd server

   • Compile the makefile.

3. Run the Client Code:

   • In each client terminal, navigate to the client directory:

     cd client

   • Compile the makefile for all three clients.

4. Start Authenticating:

   • Follow the procedures displayed by the terminal. Typically, you will input:
     • USER <username>
     • PASS <password>
     • Commands like RETR <filename>, STOR <filename>, CWD <directory>, !CWD <directory>, LIST <directory>, !LIST <directory>, QUIT

The code should handle concurrent connections smoothly.

• Directory Changes:

  • Once the client changes the server directory, it cannot revert.
  • Once you change the client directory, you cannot revert.

• File Overwrites:

  • If the client attempts to send a filename that already exists, the new file overwrites the existing file.

• Users.txt Format:

  • The users.txt file should have a delimiter at the end ("-------") for ease of loading into the code.
  • Each username and password pair should be on one line, separated by a space, with a delimiter at the end of the file. Example:

    Aadim Nepal
    Avinash Gyawali
    ----------------
    

• Port Selection:

  • We used port 9002 instead of the default ports 21 and 20 due to availability issues on MacOS.
  • If you encounter a "cannot bind to address" error, change the port by navigating to:

    #DEFINE CMD_PORT 9002

    • You can try different port numbers if necessary.

• Implementation of PORT Command:

  • The client sends a PORT command to the server before initiating a new TCP connection for file transfer.
  • We use a random free port provided by the OS instead of implementing N+i.
  • This approach was discussed and approved by both the professor and the TA.