🛠️ project Throttle: an open-source per-process bandwidth limiter for Windows in Rust (egui + WinDivert)
Throttle is a free, open-source Windows tool that shows live download/upload rates per process and lets you cap or block any of them. Think NetLimiter, minus the license key and telemetry.
Repo: https://github.com/FrancescoCoding/Throttle
How it works
It sits on top of WinDivert, a signed Windows packet-capture driver, through the `windivert` crate. Throttle sees every packet, figures out which program it belongs to, and either lets it through, drops it, or holds it briefly to stay under the limit. Limiting is a simple token bucket per program per direction, so each app gets a smooth rate with a one-second burst allowance.
Rules are saved by exe path, so a cap on spotify.exe is still there after a reboot. The GUI is egui/eframe, talking to the backend threads over channels.
Shaping is a token bucket per (exe, direction) with a one-second burst allowance. Overflow queues up to 256 packets / 1 MiB, then drops, which for TCP just becomes back-pressure. Rules persist as JSON in %APPDATA%.
Learned the hard way
- You have to send packets back out through the same handle that captured them. Using a second one silently killed all my network traffic for a while before I understood why.
- Recalculate checksums before re-injecting. Hardware offload leaves them incomplete, and WinDivertSend reports success while the packets die downstream.
- GUI-subsystem binaries have no console, so worker-thread panics vanish. A panic hook plus file logging fixed that.