lowlat

Stream your Linux desktop to any Parsec client.

lowlat is an ultra-low-latency remote desktop host that speaks the Parsec protocol. Unmodified Parsec clients connect to it on every platform they already run on, with no plugin, no forked client, and no patched binary on the other end.

It targets Linux first. Unattended operation, headless operation, and running as a system service are design inputs rather than afterthoughts.

Design complete, implementation starting. The protocol, IO shell, and host pipeline are specified in docs/; no code has landed yet. The phase plan and its verification gates are in docs/impl-plan.md.

This README describes what lowlat is being built to do. Nothing here is a claim that it currently does it.

Parsec has never officially supported hosting on Linux. The client ships for Linux and always has, so a Linux machine can connect out to a host. The reverse has never been available: a Linux machine cannot be connected to. lowlat closes that asymmetry, and it does so on the existing protocol, so the clients people already have keep working unchanged.

The wider Linux picture has the same shape. Existing remote desktop tools fall into two groups. Some capture only X11, which is a dead end on Wayland-default distributions and cannot inject input below the display server. Others are session-bound, so they cannot serve a machine you are not already logged into.

lowlat is built for the case where the host is a machine you connect back to: it runs as a system service, injects through the kernel rather than through a display server, and is designed so that the tray application is a convenience rather than a dependency. Close the tray, log out, and the stream keeps running.

1. Ultra low latency, before everything else. Capture to present is budgeted per stage and measured, not estimated.
2. Never display corruption. Loss shows as a bounded micro-freeze of about one round trip, never as gray, torn, or smeared frames.
3. Unmodified clients. If a stock client cannot connect and stream, the feature is not done.
4. A real Linux host. Not a port of a Windows product.

lowlat-common    clock, futex wait, SPSC rings, byteorder, sequence arithmetic, log
lowlat-core      no_std sans-IO: wire, channels, rings, crypto, recovery, NAT, ICE, STUN, TURN
lowlat-net       IO shell: sockets, threads, timers, wakeups
lowlat-sim       deterministic simulator and network namespace fixtures
lowlat-capture   frame source trait and backends
lowlat-encode    NVENC, FFmpeg software, VAAPI
lowlat-inject    uinput
lowlat-host      orchestration and the C ABI shared library
lowlat-kessel    signaling client
lowlatd          system service
lowlat-tray      user session client

The protocol core is no_std and sans-IO: no sockets, no threads, no clock reads, no random number generator, and no allocation. Time is a parameter and I/O is bytes in and bytes out. That makes the transport and connectivity state machines fully deterministic, which is what allows loss, reordering, and NAT topologies to be tested as reproducible unit tests rather than as soak runs.

The SDK owns all of its threads and contains no async runtime, no TLS, and no JSON. Signaling lives outside it, so an application can bring its own.

Capture backends and their privilege requirements are covered in docs/07-platforms.md.

The public surface is a stable C ABI: opaque handles, versioned plain structs, stable-numbered enums, and poll-based calls. It is consumable from C, C++, C#, Rust, and anything else that speaks C. The API shape follows the established host SDK, so porting an existing integration is close to mechanical, but struct layouts are lowlat's own and binary drop-in compatibility is not offered. Exported symbols carry a lowlat_ prefix so a layout mismatch is a link error rather than silent memory corruption.

See docs/06-api.md.

Requires a stable Rust toolchain, Rust 2024 edition.

cargo build --release
cargo test
cargo clippy --all-targets -- -D warnings

Hardware encoding requires an NVIDIA GPU with NVENC and a current driver. Software encoding loads FFmpeg at runtime and is used where hardware encoding is unavailable, and in continuous integration where no GPU is present.

The daemon needs access to /dev/uinput for input injection and to the display or GPU devices for capture. Privilege requirements per capture backend, along with the udev rules and the systemd unit, are documented in docs/07-platforms.md.

MIT. See LICENSE.

Third-party components retain their own licenses. FFmpeg is loaded dynamically at runtime and is never linked, so GPL-licensed codec libraries stay out of lowlat's link graph.

lowlat is an independent implementation and is not affiliated with, endorsed by, or supported by Parsec or Unity. "Parsec" is used only to identify the protocol that lowlat interoperates with.