Network File Editor (NFE)

A sophisticated, multi-threaded client-server file management system that implements four distinct concurrency control models for secure, collaborative file access. This system allows multiple clients to view, edit, upload, download, and manage files in a shared directory with configurable access policies, ensuring data integrity and preventing conflicts through advanced locking mechanisms.

Table of Contents

• Key Features
• Concurrency Models
• Available Commands
• Prerequisites
• Installation & Compilation
• Running the System
• Usage Examples
• Troubleshooting
• Project Structure
• Contributing
• License

Key Features

• Four Concurrency Models: Implements EREW, CREW, ERCW, and CRCW models for flexible access control.
• Real-Time Lock Status: Detailed reporting of file lock states, including lock type (READ/WRITE) and active users.
• Robust Server Architecture: Handles abrupt client disconnections gracefully, with automatic cleanup of stale locks.
• External Editor Integration: Seamless integration with nano or vim for remote file editing via the dedicated client.
• Thread-Safe Logging: Comprehensive logging with timestamps, user tracking, and color-coded console output for easy monitoring.
• Multi-Threaded Design: Efficiently manages multiple concurrent clients using C++ threads and mutexes.
• Cross-Platform Compatibility: Designed for Linux/Unix systems with C++17 support.
• Security Features: Username authentication, input validation, and access control based on concurrency models.
• File Operations: Full CRUD (Create, Read, Update, Delete) support for files and directories.
• Automatic Directory Creation: Server auto-creates the shared directory if it doesn't exist.

Concurrency Models

The system supports four classical concurrency control models, each balancing safety and performance differently:

1. EREW (Exclusive Read Exclusive Write):

   • Only one user can access a file at a time (read or write).
   • Maximum safety, minimum concurrency.
   • Ideal for critical files requiring strict serialization.

2. CREW (Concurrent Read Exclusive Write):

   • Multiple users can read simultaneously.
   • Only one user can write at a time, blocking all reads during writing.
   • Balances safety and performance for read-heavy workloads.

3. ERCW (Exclusive Read Concurrent Write):

   • Only one user can read at a time.
   • Multiple users can write simultaneously.
   • Suitable for write-heavy scenarios with occasional reads.

4. CRCW (Concurrent Read Concurrent Write):

   • Maximum concurrency: multiple users can read and write simultaneously.
   • Minimal restrictions, highest performance.
   • Best for collaborative environments with low conflict risk.

Available Commands

Command	Syntax	Description
LIST / LS	LIST	Display all files in the shared directory with details (size, permissions, owner, modified time).
INFO / EXIFTOOL	INFO <filename>	Show detailed file metadata (size, permissions, owner, timestamps, lock status).
VIEW / CAT / SHOW	VIEW <filename>	Display the complete contents of a file.
EDIT / WRITE / NANO	EDIT <filename>	Open an external editor (nano/vim) to modify a file (client-side only).
UPLOAD / PUT	UPLOAD <local_file> <remote_file>	Upload a local file to the shared directory.
DOWNLOAD / GET	DOWNLOAD <remote_file> <local_file>	Download a file from the shared directory to local machine.
DELETE / RM / DEL	DELETE <filename>	Remove a file from the shared directory.
MKDIR / MKD	MKDIR <dirname>	Create a new directory in the shared directory.
RMDIR / RMD	RMDIR <dirname>	Remove an empty directory from the shared directory.
TOUCH / CREATE	TOUCH <filename>	Create a new empty file.
LOCKWRITE / LOCK	LOCKWRITE <filename>	Acquire an exclusive write lock on a file.
UNLOCKWRITE / UNLOCK	UNLOCKWRITE <filename>	Release the write lock on a file.
LOCKSTATUS / FILESTATUS	LOCKSTATUS <filename>	Check the current lock status and access permissions for a file.
HELP	HELP	Display the command reference menu.
EXIT / QUIT	EXIT	Disconnect from the server.

Prerequisites

• Operating System: Linux/Unix-based system (tested on Kali Linux, Ubuntu, Debian).
• Compiler: C++17 compatible compiler (e.g., g++ 7.0+).
• Build Tools: make utility.
• Libraries: POSIX threads (pthread), readline library (libreadline-dev).
• Editors: nano or vim for file editing (auto-detected by client).
• Network Tools: netcat (optional, for basic client connections).
• Enhanced CLI: rlwrap (recommended for better interactive experience with netcat).

Install prerequisites on Debian/Ubuntu/Kali:

sudo apt-get update
sudo apt-get install -y build-essential libpthread-stubs0-dev libreadline-dev libc6-dev make nano vim rlwrap

Installation & Compilation

Build Instructions

1. Clone or download the project:

   git clone https://github.com/TheLeopard65/Network-File-Editor.git
   cd Network-File-Editor

2. Compile the project:

   make clean
   make

3. Verify compilation:

   ls -la nfe_server nfe_client

   • nfe_server: The server executable.
   • nfe_client: The client executable with editor integration.

Build Options

• Debug Build (default): make - Includes debug symbols and no optimizations.
• Release Build: make release - Optimized for performance, no debug symbols.
• Clean Build: make clean - Removes all compiled binaries and logs.

Running the System

Starting the Server

The server can be started with default settings or customized via command-line arguments.

# Basic usage (defaults: port 2121, EREW model, ./share/ directory)
./nfe_server
# Custom configuration
./nfe_server -p 3333 -d /path/to/shared/dir -m CREW
# Command-line options:# -p, --port PORT Server port (default: 2121)# -d, --directory DIR Shared directory path (default: ./share/)# -m, --model MODEL Concurrency model: EREW, CREW, ERCW, CRCW (default: EREW)# -h, --help Display help message

Server Logs: All server activity is logged to NFE-Server.log with timestamps and user tracking.

Connecting Clients

Method 1: Dedicated Client (Recommended)

./nfe_client [server_ip] [port]
# Examples:
./nfe_client # Connect to localhost:2121
./nfe_client 192.168.1.100 3333 # Connect to specific IP/port
./nfe_client -h # Show client help

Method 2: Using netcat (Basic)

nc localhost 2121

Method 3: Using netcat with rlwrap (Enhanced Interactive Experience)

rlwrap nc localhost 2121

Note: rlwrap provides arrow key support, command history, and tab completion for a much better CLI experience.

Authentication

Upon connection, clients must provide a username (alphanumeric, underscores, hyphens only, max 50 characters). The server then displays the active concurrency model and available commands.

Usage Examples

Basic File Operations

# List files
LIST
# View file contents
VIEW example.txt
# Get file information
INFO example.txt
# Create a new file
TOUCH newfile.txt
# Create a directory
MKDIR myfolder
# Upload a local file
UPLOAD /local/path/file.txt remote_file.txt
# Download a file
DOWNLOAD remote_file.txt /local/path/file.txt

Editing Files

# Edit with external editor
EDIT example.txt

Note: This acquires a write lock, downloads the file, opens it in nano/vim, uploads changes, and releases the lock automatically.

Lock Management

# Check lock status
LOCKSTATUS example.txt
# Manual lock acquisition (for advanced users)
LOCKWRITE example.txt
# Manual lock release
UNLOCKWRITE example.txt

Lock Status Examples

Unlocked File:

[+] Current File Lock Status:
>>> UNLOCKED
>>> You can acquire WRITE lock
>>> You can acquire READ lock

File Locked for Writing (EREW/CREW):

[+] Current File Lock Status:
>>> LOCKED for WRITE Access by User: leopard
>>> WRITE access is currently restricted
>>> READ access is currently restricted

File Locked for Reading (CREW):

[+] Current File Lock Status:
>>> LOCKED for READ Access by User: alex, kali
>>> WRITE access is currently restricted
>>> You can acquire READ lock

File Locked for Concurrent Writing (ERCW):

[+] Current File Lock Status:
>>> LOCKED for CONCURRENT WRITE Access by User: leopard, alex (Total: 2)
>>> You can acquire WRITE lock
>>> READ access is currently restricted

Multi-User Collaboration Example

1. User 1 (leopard) starts editing:

   EDIT document.txt

   File is locked for writing.

2. User 2 (alex) checks status:

   LOCKSTATUS document.txt

   Shows locked by leopard.

3. User 2 tries to edit:

   EDIT document.txt

   Access denied based on concurrency model.

4. User 1 finishes editing: Lock automatically released after upload.

5. User 2 can now edit:

   EDIT document.txt

Troubleshooting

Issue	Symptom	Solution
Compilation fails	g++: command not found	Install build-essential: sudo apt-get install build-essential
Linker errors	undefined reference to readline	Install libreadline-dev: sudo apt-get install libreadline-dev
Server won't start	Bind failed	Check if port is in use: netstat -tlnp | grep :2121
Client can't connect	Connection refused	Ensure server is running and IP/port are correct
Arrow keys show ^[[D	Using nc without wrapper	Use rlwrap nc localhost 2121
File permissions	Permission denied	Check shared directory permissions on server
Editor not found	Failed to execute editor	Install nano or vim: sudo apt-get install nano vim
Stale locks	Files remain locked after crash	Server auto-cleans locks after 5 minutes (configurable)
High CPU usage	Many concurrent clients	Reduce client connections or increase server resources
Log file grows large	NFE-Server.log too big	Rotate logs manually or implement log rotation

Common Error Messages

• [-] ERROR: Cannot read file - Access denied!: File is locked by another user in a restrictive model.
• [-] ERROR: Cannot acquire write lock for <file>: Another user holds an incompatible lock.
• [-] ERROR: Username contains invalid characters: Use only alphanumeric, underscore, hyphen.
• [-] ERROR: Failed to execute editor: Install nano or vim.

Performance Tuning

• Server: Increase ulimit -n for more open file descriptors if handling many clients.
• Client: For large files, increase socket buffer sizes in client.cpp if needed.
• Models: Use CRCW for maximum performance, EREW for maximum safety.

Project Structure

Network-File-Editor/
├── LICENSE # MIT License file
├── Makefile # Build configuration and rules
├── README.md # This documentation
├── requirements.txt # List of system dependencies
├── share/ # Default shared directory (auto-created)
│ ├── code.cpp # Sample C++ file
│ ├── info.txt # Sample text file
│ └── script.sh # Sample shell script
├── source/ # Source code directory
│ ├── client/ # Client-side code
│ │ ├── client.cpp # Main client implementation
│ │ ├── client.hpp # Client header
│ │ └── main_client.cpp # Client entry point
│ ├── common/ # Shared utilities
│ │ ├── concurrency.cpp # Concurrency model implementations
│ │ ├── concurrency.hpp # Concurrency headers
│ │ ├── config.hpp # Configuration management
│ │ ├── logger.cpp # Logging system
│ │ └── logger.hpp # Logger headers
│ └── server/ # Server-side code
│ ├── client_handler.cpp # Client connection handling
│ ├── client_handler.hpp # Handler headers
│ ├── file_manager.cpp # File operations
│ ├── file_manager.hpp # File manager headers
│ ├── main_server.cpp # Server entry point
│ ├── server.cpp # Main server logic
│ └── server.hpp # Server headers
└── NFE-Server.log # Server activity log (auto-generated)

Contributing

1. Fork the repository.
2. Create a feature branch: git checkout -b feature-name
3. Make changes and test thoroughly.
4. Ensure code follows C++17 standards and includes proper error handling.
5. Update documentation if adding new features.
6. Submit a pull request with a clear description of changes.

Development Guidelines

• Use C++17 features consistently.
• Follow RAII principles for resource management.
• Add comprehensive logging for new features.
• Test with all four concurrency models.
• Handle edge cases (file not found, permission denied, network errors).
• Update the README for any new commands or features.

License

This project is licensed under the MIT License. See the LICENSE file for complete details.