p2p-chat (Linux, C++20, Boost.Asio)

Two small terminal programs:

• rendezvous_server: presence/discovery server (never relays chat content)
• p2p_chat_gui: Qt6 desktop chat client (friends list + chat pane)

Build (Ubuntu/Debian)

Suggested packages:

sudo apt-get update
sudo apt-get install -y build-essential pkg-config libboost-system-dev libssl-dev

Notes:

• JSON uses a vendored nlohmann/json.hpp in third_party/nlohmann/json.hpp (no system package required).

Build:

make -j

-march=native:

• Enabled by default for local make builds.
• Auto-disabled on GitHub Actions (GITHUB_ACTIONS=true).
• Override with make NATIVE_ARCH=0 -j (disable) or make NATIVE_ARCH=1 -j (enable).

Qt GUI build (Qt6 Widgets):

sudo apt-get install -y qt6-base-dev qt6-base-dev-tools qt6-multimedia-dev libopus-dev
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/p2p_chat_gui

CMake also enables -march=native by default for local non-CI, non-cross builds. Override with -DP2PCHAT_ENABLE_MARCH_NATIVE=OFF.

Cross-compile to Windows (from Linux)

Most reliable: build on Windows (or CI Windows runner). Cross-compiling from Linux works best with MXE (MinGW + Qt).

High-level MXE steps:

1. Build MXE toolchain + deps (Qt6, OpenSSL, Boost).
2. Configure this project with MXE’s mxe-conf.cmake.
3. Build p2p_chat_gui.exe (and optionally rendezvous_server.exe).
4. Bundle Qt DLLs via windeployqt (from the same Qt toolchain).

Example (MXE, 64-bit, shared):

git clone https://github.com/mxe/mxe.git ~/mxe
cd ~/mxe
make MXE_TARGETS='x86_64-w64-mingw32.shared' qt6-qtbase openssl boost

cd /path/to/p2p-chat
cmake -S . -B build-win \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=~/mxe/usr/x86_64-w64-mingw32.shared/share/cmake/mxe-conf.cmake
cmake --build build-win -j

After build, run MXE’s windeployqt on p2p_chat_gui.exe to collect required Qt DLLs into a distributable folder (zip that folder to send to friends).

Build on Windows (MSYS2)

This is often simpler than cross-compiling:

1. Install MSYS2, open MSYS2 MinGW x64 shell
2. Install deps:

pacman -Syu
pacman -S --needed \
  mingw-w64-x86_64-gcc mingw-w64-x86_64-cmake mingw-w64-x86_64-ninja \
  mingw-w64-x86_64-qt6-base mingw-w64-x86_64-qt6-multimedia mingw-w64-x86_64-opus \
  mingw-w64-x86_64-boost mingw-w64-x86_64-openssl \
  mingw-w64-x86_64-pkgconf

3. Build + bundle:

cmake -S . -B build-win -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build-win
mkdir dist
cp build-win/p2p_chat_gui.exe dist/
windeployqt --release --no-translations dist/p2p_chat_gui.exe

Run

Server (public VPS):

./rendezvous_server 0.0.0.0 5555

Clients:

./build/p2p_chat_gui
# or force runtime debug logs
P2PCHAT_DEBUG=1 ./build/p2p_chat_gui
# or
./build/p2p_chat_gui --debug

Profiles:

• On startup, the GUI shows a profile picker (qTox-style): select existing profile or create a new one.
• New profiles can be created with optional password protection (encrypts identity.pem at rest).
• Legacy single-profile data in ~/.config/p2p-chat is auto-migrated to ~/.config/p2p-chat/profiles/<name>/.
• Headless migration only:

QT_QPA_PLATFORM=offscreen ./build/p2p_chat_gui --migrate-profiles

CLI profile selection:

./build/p2p_chat --profile default
./build/p2p_chat --profile secure --profile-password 'your-password'

Both GUI and CLI read profile data from the same profile directory and therefore share the same ID/key for that profile.

Voice calls:

• Requires Qt6 Multimedia + Opus.
• Use the top-right Call button in a chat; configure devices/bitrate via Options -> Audio Settings....

IDs and names:

• Each user has a cryptographic shareable ID (Your ID:) derived from their Ed25519 public key.
• Each profile stores its identity key as identity.pem in its own profile directory.
• Your name is only shared with peers after they accept your friend request and you establish a direct P2P connection.

Encryption:

• P2P traffic is end-to-end encrypted and authenticated (X25519 + HKDF-SHA256 + ChaCha20-Poly1305), with peer authentication via Ed25519 signatures (your ID).
• The rendezvous server channel is not encrypted (it never relays chat content, only discovery + requests).

Discovery / UDP:

• Clients publish their current UDP endpoint to rendezvous and connect peer-to-peer via UDP hole punching.
• Rendezvous stores observed address + UDP mapping only; it does not maintain a TCP reachability flag.