File Transfer System

A peer-to-peer file transfer application built in Python with a Tkinter GUI. Allows users to send files directly to another machine over a TCP socket connection without relying on cloud storage or third-party services.

---

Why this was built

Most file sharing solutions route data through a central cloud server — adding latency, storage costs, and privacy concerns. This project eliminates the middleman by establishing a direct TCP connection between the sender and receiver, keeping transfers fast, local, and private.

---

Tech Stack

Technology	Why it was chosen
Python	Cross-platform, built-in socket and threading libraries — no external dependencies for core functionality
TCP Sockets	Reliable, ordered byte-stream delivery — critical for file integrity. UDP would risk data loss without added complexity
Tkinter	Ships with Python's standard library, zero install friction for a lightweight GUI
Threading	Keeps the UI responsive while the server listens for incoming connections in the background

---

Architecture

The project follows a Client-Server model within a P2P setup. Each peer runs both sides — one machine acts as the server (receiver), the other as the client (sender). The roles can be swapped.

Peer2Peer_FT/
├── Client/
│   └── client_code.py   # GUI + sender logic
└── Server/
    └── server_code.py   # Receiver/server logic

---

How it works

Server (server_code.py)

1. Binds a TCP socket to 127.0.0.1:8000 and starts listening for incoming connections
2. On connection, reads the incoming byte stream in this order:
   • First 4 bytes → length of the username (big-endian int)
   • Next N bytes → username string
   • Next 4 bytes → length of the filename
   • Next M bytes → filename string
   • Remaining bytes → raw file data (read in 1024-byte chunks)
3. Reconstructs the file and saves it to a local uploads/ folder (auto-created if missing)

Client (client_code.py)

1. User enters a username and clicks Choose File — opens a native file picker dialog
2. Establishes a TCP connection to the server
3. Sends data in the same structured format the server expects — 4-byte length prefix → username → 4-byte length prefix → filename → raw file bytes
4. A background thread simultaneously runs a listener so the same peer can receive files while the UI stays active
5. Received files are announced via a popup and logged in an on-screen listbox

Why length-prefixed framing?

TCP is a stream protocol — it has no concept of message boundaries. Sending a raw filename followed by raw file data would make it impossible to know where the filename ends and the file begins. The 4-byte big-endian length prefix before each field tells the receiver exactly how many bytes to read, making the protocol self-describing and unambiguous.

---

Running locally

Start the server (receiver machine):

cd Peer2Peer_FT/Server
python server_code.py

Start the client (sender machine):

cd Peer2Peer_FT/Client
python client_code.py

1. Enter your username in the GUI
2. Click Choose File and select any file
3. File is sent to the server and saved in uploads/

To transfer across machines on the same network, update HOST in both files to the receiver's actual IP address.

---

Tech

Python · TCP Sockets · Tkinter · Threading · Client-Server Architecture