Reliable UDP

Goal

• Implement a reliable file transfer system over UDP using custom logic to handle:
  • Packet loss
  • Reordering
  • Duplicate suppression

Stretch Goal

• Develop a simple web-based or desktop UI to improve usability and allow file transfers via a graphical interface.

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TODO

Core Functionality

• Set up basic UDP client and server
• Implement file reading and sending logic on the client
• Implement file writing logic on the server
• Add packet sequence numbering
• Implement basic ACK system
• Add retransmission mechanism with timeouts
• Define and document end-of-file signaling

Testing and Validation

• Test file transfers under normal conditions
• Simulate packet loss and validate reliability
• Log transfer statistics (e.g., number of packets sent, retransmissions)

🧰 Stretch Features

• Basic CLI interface to choose file and mode
• Web-based or desktop GUI for file selection and status display
• Dockerize for isolated testing

Handshake protocol

Compact alternating 3‑way handshake (packet, seq, and state changes):

• Sender (IDLE → SYN_SENT): sends SYN (seq=0); waits for SYN-ACK (retry on timeout - not implemented yet).
• Receiver (IDLE → SYN_RECV → ACK_SENT): receives SYN (seq=0), verifies seq; sends SYN-ACK (seq=1); waits for ACK.
• Sender (SYN_SENT → SYN_ACK → ACK_SENT → CONNECTED): receives SYN-ACK (seq=1), verifies seq; sends ACK (seq=1) and transitions to CONNECTED.
• Receiver (ACK_SENT → CONNECTED): receives ACK (seq=1), verifies seq; transitions to CONNECTED (ready to transfer).

Notes: retries/timeouts and seq verification are applied at each wait step; mismatches trigger retries or aborts.