quic-rs

A from-scratch QUIC server written in Rust, built to learn the protocol from the ground up using raw syscalls (via nix) and manual packet parsing — no quinn/quiche.

What it does

quic-rs listens on UDP 0.0.0.0:3000, receives a QUIC Initial packet, and:

1. Parses the long header — version, connection IDs, token, length (RFC 9000 §17.2.2).
2. Derives the client/server Initial secrets — key, IV, and header-protection key — from the Destination Connection ID (RFC 9001 §5.2).
3. Removes header protection and recovers the packet number (RFC 9001 §5.4).
4. AEAD-decrypts the payload with AES-128-GCM, exposing the QUIC frames — the CRYPTO frame that carries the TLS 1.3 ClientHello (RFC 9001 §5.3).

It does not yet send a response or complete the handshake.

Layout

File	Responsibility
src/main.rs	Binary entry point.
src/lib.rs	Crate root and module declarations.
src/server.rs	UDP socket setup and the receive loop.
src/packet.rs	Initial long-header parsing and decryption orchestration.
src/crypto.rs	HKDF key schedule, header protection, and AEAD decryption.
src/varint.rs	QUIC variable-length integer decoding.
tests/rfc9001_vectors.rs	RFC 9001 Appendix A known-answer tests.

Build, test & run

cargo build
cargo test     # verifies key derivation + decryption against RFC 9001 Appendix A
cargo run      # listens on 0.0.0.0:3000 for one Initial packet

Credit

This project began as a restructured and extended version of datasalaryman/quic-server-from-scratch. The original key-derivation and packet-parsing bugs were fixed, the code was reorganized into focused modules, and the full Initial-packet decryption path (header protection + AEAD) was added.