Overview

A robust client-server file backup and retrieval system implementing a stateless protocol over TCP/IP. The system consists of a C++ server component and a Python client that communicate via a custom binary protocol.

Components

Server (C++)

• Language: C++17
• Architecture: Stateless, thread-based concurrency
• Dependencies: Boost 1.88.0 (ASIO for networking)
• Design Pattern: Object-oriented with RAII principles

Client (Python)

• Language: Python 3.9+
• Architecture: Object-oriented design
• Dependencies: Standard libraries only (socket, struct)

Protocol Specification

Binary Format

All data is transmitted in little-endian format with unsigned numeric values.

Request Structure

Field	Size	Description
user_id	4 bytes	Client unique identifier
version	1 byte	Protocol version
op	1 byte	Operation code
name_len	2 bytes	Length of filename
filename	Variable	ASCII filename
size	4 bytes	Size of payload
payload	Variable	Binary file content

Request Operation Codes

Code	Operation	Description	Fields Used
100	FILE_BACKUP	Store file on server	All fields
200	FILE_RESTORE	Retrieve file from server	All except size and payload
201	FILE_REMOVE	Delete file from server	All except size and payload
202	FILE_DIR	List client's files	Only user_id, version, op

Response Structure

Field	Size	Description
version	1 byte	Server version
status	2 bytes	Status code
name_len	2 bytes	Length of filename
filename	Variable	ASCII filename
size	4 bytes	Size of payload
payload	Variable	Binary file content

Response Status Codes

Code	Status	Description	Fields Used
210	SUCCESS_RESTORE	File successfully restored	All fields
211	SUCCESS_DIR	File list successfully returned	All fields
212	SUCCESS_BACKUP_DELETE	File backed up or deleted successfully	All except size and payload
1001	ERROR_NOT_EXIST	File does not exist	All except size and payload
1002	ERROR_NO_FILES	Client has no files	Only version and status
1003	ERROR_GENERIC	Generic server error	Only version and status

Server Implementation Details

File Storage Structure

c:\backupsvr\[CLIENT_ID]\[FILENAME]

Features

• Thread-safe user handling with atomic locks
• Efficient memory management with RAII principles
• Secure random string generation
• Robust error handling
• Support for large file transfers

Client Implementation Details

Configuration Files

• server.info: Contains server IP and port in format IP:PORT
• backup.info: Contains list of files to backup (one per line)

Features

• Unique client ID generation
• Automatic file operations sequence
• Robust error handling
• Type-safe implementation

Installation and Setup

Server (C++)

Prerequisites

• Visual Studio 2019 or newer
• Boost Library 1.88.0
• Windows 10 or newer

Boost Setup

1. Download Boost 1.88.0 from boost.org
2. Extract to a location of your choice (e.g., C:\boost_1_88_0)
3. Open Visual Studio Developer Command Prompt
4. Navigate to the Boost directory:

   cd C:\boost_1_88_0
   

5. Build Boost libraries:

   bootstrap.bat
   b2 --toolset=msvc-14.2 address-model=64 --build-type=complete
   

Project Configuration

1. Open the solution in Visual Studio

2. Right-click on the project and select Properties

3. Configure the following settings:

   C/C++ → General → Additional Include Directories:

   C:\boost_1_88_0
   

   Linker → General → Additional Library Directories:

   C:\boost_1_88_0\stage\lib
   

   C/C++ → Preprocessor → Preprocessor Definitions:

   WIN32_WINNT=0x0A00
   

   C/C++ → Language → C++ Language Standard:

   C++17 (/std:c++17)
   

4. Disable Precompiled Headers:

   • Navigate to C/C++ → Precompiled Headers
   • Set "Precompiled Header" to "Not Using Precompiled Headers"

Building the Server

1. Build the solution in Visual Studio (Release configuration recommended for production)
2. The executable will be generated in the output directory

Client (Python)

Prerequisites

• Python 3.9 or newer

Setup

1. Place the client files in a directory
2. Create or update server.info with the server's IP and port:

   127.0.0.1:1234
   

3. Create or update backup.info with the files to backup:

   file1.txt
   file2.pdf
   

4. Ensure the files listed in backup.info exist in the same directory

Running the System

Starting the Server

1. Run the server executable:

   BackupServer.exe
   

2. The server will start listening for connections on the default port (1234)

Running the Client

1. Open a command prompt in the client directory
2. Run the client script:

   python client.py
   

3. The client will automatically execute the required sequence of operations:
   • Request file list
   • Backup two files
   • Request updated file list
   • Restore a file to 'tmp'
   • Delete a file
   • Attempt to restore the deleted file

Security Considerations

• Input validation on both client and server
• Memory safety with RAII and smart pointers
• Secure random number generation
• Proper error handling and logging
• Protection against buffer overflows

Error Handling

• Network errors are gracefully handled
• File system errors are properly reported
• Invalid requests are rejected with appropriate status codes
• Resource cleanup is guaranteed even in error conditions

Development Notes

• All numeric fields use little-endian byte ordering
• The protocol is binary for efficiency
• The server is designed to be stateless
• Thread safety is maintained for concurrent client connections
• Large file transfers are handled efficiently with chunking

Performance Considerations

• Memory usage is optimized with appropriate buffer sizes
• File operations use efficient streaming
• Network operations are non-blocking where appropriate
• Thread pool management for concurrent connections

Author

Natanel Fishman - Defensive Programming Course, 2025

License

This project is for educational purposes only.