LEFT: Large Efficient Flexible and Trusty File Sharing System

A lightweight Python socket–based file sharing system supporting:

• Automatic file & folder detection
• Large file transmission (tested up to 500MB)
• Breakpoint retransmission (resume after interruption)
• File synchronization between two devices

This project was originally developed as part of the Introduction to Networking course.

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Features

1. Automatic File Detection

The program scans the share/ directory to detect:

• newly added files (any format, any size)
• newly added folders containing multiple files

2. File Transmission Protocol

A custom application-layer protocol over TCP ensures:

• reliable transmission
• correct MD5 integrity verification
• compatibility between Linux virtual instances

3. Breakpoint Retransmission

If the receiver is interrupted:

• the partially received file is saved as .temp
• after restart, the program continues transmission from where it stopped

4. File Synchronization

The system compares file modification time (or MD5) to determine whether synchronization is required, ensuring both devices stay consistent.

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Project Structure

main.py # entry point, argument parsing & coordination
server.py # sender-side logic (traverse, compute md5, send files)
client.py # receiver-side logic (create dirs, receive & restore files)
share/ # directory being monitored for syncing

How to Run

1. Start two PCs / virtual machines
2. Clone this repository on both devices
3. In each device, run:

python3 main.py --ip <peer_ipv4_address>

Files in each share/ folder will be automatically compared, transmitted, resumed, or synchronized.

Testing Summary

The system was tested using:

• PyCharm 2021.1.2, Python 3.9

• VirtualBox Linux instances (two VMs)

Key tests included:

• Sending a single 10MB file ✔️

• Sending a 500MB file + folder of 50 files ✔️

• Breakpoint retransmission after forced interruption ✔️

• Synchronization after file update ✔️

All test cases passed successfully. (Details documented in the original coursework report.)

Implementation Techniques

• Python Socket programming (TCP)

• Threading & OOP design

• MD5 checksum for data integrity

• Directory traversal & file monitoring

• Error handling for port conflicts and incomplete transfers

Future Improvements

Planned extensions include:

• File encryption (AES/DES)

• File compression before transmission

• More robust synchronization mechanisms