Reliable-File-Transfer-over-UDP-using-custom-protocol

This project implements a simple yet reliable file transfer system over the UDP protocol. UDP by nature is fast but unreliable — it doesn't guarantee delivery, order, or integrity. This system builds a custom protocol on top of UDP to ensure reliable, ordered, and complete file transfer between two peers using batching, part tracking, timeouts, and retransmission logic.

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📦 Features

• Custom protocol messages: SENDING, SENDBATCH, DATA, RESENDPARTS
• File split into batches and parts for scalable transfer
• Bitmap-based tracking of received parts
• Automatic retransmission of lost or delayed packets
• Adaptive part size negotiation between sender and receiver
• Timers for reliable retry handling
• Command-line interface for sending and receiving files

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🗂️ Project Structure

├── main.c # Entry point; command parsing and socket setup ├── sender.c # Handles sending file parts and retransmissions ├── receiver.c # Handles receiving file parts and managing requests ├── timer.c # Provides timeout and timer utilities ├── part.c # Manages bitmap data structure to track parts ├── helper.c # Utility functions (file I/O, byte ops, etc.) ├── Makefile # Compilation script ├── intr/ # Header files and protocol constants │ ├── consts.h │ ├── helper.h │ ├── main.h │ ├── ops.h │ ├── part.h │ ├── receiver.h │ ├── sender.h │ └── timer.h └── README.md

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🔧 How to Build

Prerequisites

• GCC or any modern C compiler
• Linux environment (uses clock_gettime, arpa/inet, etc.)

Compilation

Use the included Makefile for compilation:

make

🕹️ How to Use

On Receiver Side
./file_transfer <your_port> <sender_port>
Then, type:
receive
On Sender Side (in another terminal or machine)
./file_transfer <your_port> <receiver_port>
Then, type:
send <filename>

The system automatically:
-Splits the file into parts
-Sends them in batches
-Retransmits any lost parts
-Reconstructs the file on the receiving end

✅ Received files are saved in the recv/ directory.

💡 Protocol Design
Message Types
Message Type	     Description
SENDING	File       Metadata and part size info
SENDBATCH	         Request for a batch of parts
DATA	             A specific part of a batch
RESENDPARTS	       Request to resend missing parts

File Splitting Strategy
-File is split into batches
-Each batch consists of multiple fixed-size parts (partsize)
-Each part is tracked using a bitmap
-If a batch is incomplete, the receiver sends a RESENDPARTS request

📂 Example
On Terminal 1 (Receiver):

Copy
Edit
./file_transfer 5001 5000
receive
On Terminal 2 (Sender):

Copy
Edit
./file_transfer 5000 5001
send myfile.txt

🛡️ Reliability Features
-Timeout and exponential backoff on message retries
-Bitmap-based tracking of received parts
-Retransmission of only missing parts
-Sender adapts partsize based on receiver capability

🙏 Acknowledgments
Built to understand and explore:
-Network reliability
-Custom protocol design
-UDP challenges and strategies for mitigation