📁 TFTP — Trivial File Transfer Protocol in C

A client-server file transfer application written in C, built over UDP sockets, following the TFTP protocol. Supports uploading and downloading files between client and server with multiple transfer modes and block-level acknowledgment.

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🔍 How It Works

Client                          Server
  │                               │
  │──── RRQ / WRQ (filename) ────►│
  │◄─── SUCCESS / FAILURE ────────│
  │                               │
  │◄─── DATA (block 1) ──────────►│  ← send_file() / receive_file()
  │──── ACK  (block 1) ──────────►│
  │         ...                   │
  │──── DATA (block N, 0 bytes) ──│  ← EOF signal

Both send_file() and receive_file() are shared between client and server via tftp.c and tftp.h.

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✨ Features

• 📤 PUT — upload a file from client to server (WRQ)
• 📥 GET — download a file from server to client (RRQ)
• 🔁 Block-wise transfer — 512 bytes per block with ACK after each block
• 🔄 Retransmission — automatically resends on ACK mismatch
• 🗂️ Transfer modes — Default (512 B), Octet (1 B), NetASCII
• ✅ IP & port validation — checked before connecting
• 📡 UDP sockets — connectionless, lightweight communication
• 🖼️ Binary file support — tested with .txt, .c, .jpg files

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🗂️ Project Structure

TFTP_project/
├── TFTP_client/
│   ├── tftp_client.c     # Client main — menu, connect, put, get
│   ├── tftp_client.h     # tftp_client_t struct and function declarations
│   ├── tftp.c            # Shared — send_file() and receive_file()
│   └── tftp.h            # Shared — packet structs, opcodes, constants
│
└── TFTP_server/
    ├── tftp_server.c     # Server main — bind, listen, handle_client()
    ├── tftp.c            # Shared — send_file() and receive_file()
    └── tftp.h            # Shared — packet structs, opcodes, constants

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🚀 Build & Run

Compile

# Terminal 1 — Server
cd TFTP_server
gcc tftp.c tftp_server.c -o server

# Terminal 2 — Client
cd TFTP_client
gcc tftp.c tftp_client.c -o client

Run

# Start server first
./server

# Then start client
./client

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📖 Usage

Step 1 — Connect to server

......................Menu....................
1. Connect
2. Put
3. Get
4. Mode
5. Exit
Enter your option from menu: 1
Enter Server IP Address: 127.0.0.1
Enter Server Port Number: 6969
Connected to IP address 127.0.0.1 and port 6969

Step 2 — Upload a file (PUT)

Enter your option from menu: 2
Enter the filename: file1.txt

# Server output:
Request received: operation = 2
Request received: filename = file1.txt
Started receiving file: file1.txt
File transfer completed...

Step 3 — Download a file (GET)

Enter your option from menu: 3
Enter filename: file1.txt
File receive completed...

Step 4 — Change transfer mode

Enter your option from menu: 4

Select Mode
0. Default (512 bytes)
1. Octet   (1 byte)
2. NetASCII
Enter mode: 1

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📦 TFTP Packet Types

Opcode	Type	Description
1	RRQ	Read request — client wants to download
2	WRQ	Write request — client wants to upload
3	DATA	Data block with block number
4	ACK	Acknowledgment for received block
5	ERROR	Error notification

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⚙️ Transfer Modes

Mode	Block Size	Use Case
Default	512 bytes	General file transfer
Octet	1 byte	Precise / binary transfer
NetASCII	512 bytes	Text with \n → \r conversion

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🧠 Key Concepts Used

Concept	Purpose
socket() + bind()	Create and bind UDP socket on server
sendto() + recvfrom()	Send/receive packets without a connection
htons() / ntohs()	Convert between host and network byte order
fork() / open() / read() / write()	File handling during transfer
struct sockaddr_in	Store IP address and port information
Block numbering + ACK loop	Reliable transfer over unreliable UDP

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👤 Author

Amar C M — Embedded Systems Engineer

· amarcm1502@gmail.com

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📜 License

MIT License — free to use and modify with attribution.