File Integrity Checker and Transfer System

A simple client/server system that transfers files over TCP sockets and verifies their integrity using SHA-256 hashes.

How it works

• Upload: the client sends a file to the server. The server saves it under storage/, calculates its SHA-256 hash, and stores that hash in hashes.json.
• Download: the client requests a file back. The server re-calculates the hash of the stored file and reports whether it still matches the hash recorded at upload time (MATCH / MISMATCH). The client then calculates its own hash of the downloaded copy and confirms it matches what the server sent (VALID / CORRUPTED).
• Threading: the server spawns one thread per connected client (threading.Thread), so multiple uploads/downloads can happen at the same time without blocking each other.

Run it

Terminal 1 (start the server):

cd file_integrity_system
python server.py

Terminal 2 (client commands):

cd file_integrity_system
python client.py upload path/to/some_file.txt
python client.py list
python client.py download some_file.txt

No external dependencies — everything uses the Python standard library (socket, threading, hashlib, json).

Files

• server.py — FileServer (accepts connections) and HashStore (thread-safe hash database).
• client.py — FileClient (upload / download / list).
• common.py — shared SHA-256 helper functions.

Ideas to extend it

• Add a tkinter GUI with a drag-and-drop upload area and a progress bar.
• Add TLS (ssl module) to encrypt the connection itself.
• Add resumable/chunked transfer for very large files.