feat(host/input): headless KDE input via org_kde_kwin_fake_input

Desktop-mode (KWin) streaming had no input: the path was libei via the
RemoteDesktop portal, which (a) isn't reachable from the host service env
and (b) requires a human to approve "Allow remote control?" — a
non-starter on a headless box. KWin's own headless RDP server (krdpserver)
solves this with org_kde_kwin_fake_input, authorized by the exact same
.desktop X-KDE-Wayland-Interfaces grant we already ship
(org_kde_kwin_fake_input is listed alongside zkde_screencast_unstable_v1).

Add a fake_input injector: vendor the protocol XML, bind the global as an
ordinary Wayland client, authenticate (auto-accepted for an
interface-authorized client — no dialog), and translate pointer (rel/abs),
button, scroll, keyboard (raw evdev keycodes resolved by KWin's own keymap)
and touch. Select it for KWin (compositor=="kwin" or XDG_CURRENT_DESKTOP
KDE); GNOME stays on libei (it has neither fake_input nor the wlr
protocols). PUNKTFUNK_INPUT_BACKEND=kwin forces it.

cargo check + clippy + fmt green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/protocols/fake-input.xml

@@ -0,0 +1,73 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="fake_input">
+  <copyright>
+    SPDX-FileCopyrightText: 2015 Martin Gräßlin
+    SPDX-License-Identifier: LGPL-2.1-or-later
+  </copyright>
+  <interface name="org_kde_kwin_fake_input" version="4">
+    <description summary="Fake input manager">
+      This interface allows other processes to provide fake input events.
+      Purpose is on the one hand side to provide testing facilities like XTest
+      on X11, but also to support use cases like remote control (a remote
+      desktop server). The compositor gates the interface: it is only exposed
+      to clients authorized through their .desktop X-KDE-Wayland-Interfaces, so
+      binding it is the authorization — no per-event confirmation dialog.
+    </description>
+    <request name="authenticate">
+      <description summary="Information about the application requesting fake input">
+        A FakeInput is required to authenticate itself by providing the
+        application name and the reason for fake input. The compositor may use
+        this information to decide whether to allow or deny the request.
+      </description>
+      <arg name="application" type="string" summary="user visible name of the application requesting fake input"/>
+      <arg name="reason" type="string" summary="reason of why fake input is requested"/>
+    </request>
+    <request name="pointer_motion">
+      <description summary="pointer motion event"/>
+      <arg name="delta_x" type="fixed" summary="X delta of the relative pointer motion"/>
+      <arg name="delta_y" type="fixed" summary="Y delta of the relative pointer motion"/>
+    </request>
+    <request name="button">
+      <description summary="pointer button event"/>
+      <arg name="button" type="uint" summary="evdev button code"/>
+      <arg name="state" type="uint" summary="button state, 0 released, 1 pressed"/>
+    </request>
+    <request name="axis">
+      <description summary="pointer axis (scroll) event"/>
+      <arg name="axis" type="uint" summary="wl_pointer.axis (0 vertical, 1 horizontal)"/>
+      <arg name="value" type="fixed" summary="axis value"/>
+    </request>
+    <request name="touch_down" since="2">
+      <description summary="touch down event"/>
+      <arg name="id" type="uint" summary="unique id of this touch point; must not be reused until up"/>
+      <arg name="x" type="fixed" summary="x coordinate in global compositor space"/>
+      <arg name="y" type="fixed" summary="y coordinate in global compositor space"/>
+    </request>
+    <request name="touch_motion" since="2">
+      <description summary="touch motion event"/>
+      <arg name="id" type="uint" summary="unique id of an existing touch point"/>
+      <arg name="x" type="fixed" summary="x coordinate in global compositor space"/>
+      <arg name="y" type="fixed" summary="y coordinate in global compositor space"/>
+    </request>
+    <request name="touch_up" since="2">
+      <description summary="touch up event"/>
+      <arg name="id" type="uint" summary="unique id of an existing touch point"/>
+    </request>
+    <request name="touch_cancel" since="2">
+      <description summary="cancel all current touch points"/>
+    </request>
+    <request name="touch_frame" since="2">
+      <description summary="end a set of touch events (atomic frame)"/>
+    </request>
+    <request name="pointer_motion_absolute" since="3">
+      <description summary="absolute pointer motion event"/>
+      <arg name="x" type="fixed" summary="x coordinate in global compositor space"/>
+      <arg name="y" type="fixed" summary="y coordinate in global compositor space"/>
+    </request>
+    <request name="keyboard_key" since="4">
+      <description summary="keyboard key event"/>
+      <arg name="button" type="uint" summary="evdev key code"/>
+      <arg name="state" type="uint" summary="key state, 0 released, 1 pressed"/>
+    </request>
+  </interface>
+</protocol>

crates/punktfunk-host/src/inject.rs

@@ -24,6 +24,9 @@ pub trait InputInjector {
 pub enum Backend {
     /// wlroots virtual pointer + keyboard Wayland protocols — the headless-Sway path.
     WlrVirtual,
+    /// KWin `org_kde_kwin_fake_input` — direct injection, no RemoteDesktop portal / approval dialog
+    /// (authorized by the host's `.desktop`). The headless KDE-Desktop path; what krdpserver uses.
+    KwinFakeInput,
     /// libei via `reis` — Wayland-native (RemoteDesktop portal). Not yet implemented.
     Libei,
     /// libei directly against gamescope's own EIS socket (no portal): input lands in the
@@ -47,6 +50,16 @@ pub fn open(backend: Backend) -> Result<Box<dyn InputInjector>> {
                 anyhow::bail!("wlroots virtual input requires Linux + a Wayland compositor")
             }
         }
+        Backend::KwinFakeInput => {
+            #[cfg(target_os = "linux")]
+            {
+                Ok(Box::new(kwin_fake_input::KwinFakeInjector::open()?))
+            }
+            #[cfg(not(target_os = "linux"))]
+            {
+                anyhow::bail!("KWin fake_input requires Linux + a KWin Wayland session")
+            }
+        }
         Backend::Libei => {
             #[cfg(target_os = "linux")]
             {
@@ -90,12 +103,18 @@ pub fn open(backend: Backend) -> Result<Box<dyn InputInjector>> {
 /// Pick the injection backend for the current session. gamescope hosts its own EIS server (no
 /// portal), so a gamescope session injects directly into it. wlroots/Sway only implements the
 /// ScreenCast portal (no RemoteDesktop), so libei can't run there — use the wlr virtual-input
-/// protocols. KWin and GNOME implement RemoteDesktop but not the wlr protocols, so use libei.
+/// protocols. **KWin** exposes `org_kde_kwin_fake_input` (direct injection, no portal / approval
-/// `PUNKTFUNK_INPUT_BACKEND=wlr|libei|gamescope|uinput` overrides the auto-detection.
+/// dialog — the only headless-capable path; what krdpserver uses), so prefer it there. **GNOME**
+/// has neither fake_input nor the wlr protocols, so it uses libei via the RemoteDesktop portal
+/// (which needs a user to approve, or a pre-seeded grant — not truly headless).
+/// `PUNKTFUNK_INPUT_BACKEND=wlr|kwin|libei|gamescope|uinput` overrides the auto-detection.
 pub fn default_backend() -> Backend {
     if let Ok(v) = std::env::var("PUNKTFUNK_INPUT_BACKEND") {
         match v.trim().to_ascii_lowercase().as_str() {
             "wlr" | "wlroots" | "wlrvirtual" => return Backend::WlrVirtual,
+            "kwin" | "fakeinput" | "fake_input" | "kwin-fake-input" => {
+                return Backend::KwinFakeInput
+            }
             "libei" | "ei" | "portal" => return Backend::Libei,
             "gamescope" | "gamescope-ei" => return Backend::GamescopeEi,
             "uinput" => return Backend::Uinput,
@@ -112,16 +131,26 @@ pub fn default_backend() -> Backend {
     }
     #[cfg(not(target_os = "windows"))]
     {
-        if crate::config::config()
+        // An explicit compositor pick (set per connect / mid-stream) is the strongest signal.
-            .compositor
+        let compositor = crate::config::config().compositor.clone();
-            .as_deref()
+        if let Some(c) = compositor.as_deref() {
-            .is_some_and(|v| v.trim().eq_ignore_ascii_case("gamescope"))
+            let c = c.trim();
-        {
+            if c.eq_ignore_ascii_case("gamescope") {
-            return Backend::GamescopeEi;
+                return Backend::GamescopeEi;
+            }
+            if c.eq_ignore_ascii_case("kwin") {
+                return Backend::KwinFakeInput;
+            }
+            if c.eq_ignore_ascii_case("wlroots") || c.eq_ignore_ascii_case("sway") {
+                return Backend::WlrVirtual;
+            }
+            // mutter (GNOME) falls through to the XDG_CURRENT_DESKTOP check below.
         }
         let desktop = std::env::var("XDG_CURRENT_DESKTOP").unwrap_or_default();
         let d = desktop.to_ascii_uppercase();
-        if d.contains("KDE") || d.contains("GNOME") {
+        if d.contains("KDE") {
+            Backend::KwinFakeInput
+        } else if d.contains("GNOME") {
             Backend::Libei
         } else {
             Backend::WlrVirtual
@@ -478,6 +507,9 @@ pub mod gamepad {
     }
 }
 #[cfg(target_os = "linux")]
+#[path = "inject/linux/kwin_fake_input.rs"]
+mod kwin_fake_input;
+#[cfg(target_os = "linux")]
 #[path = "inject/linux/libei.rs"]
 mod libei;
 #[cfg(target_os = "windows")]

crates/punktfunk-host/src/inject/linux/kwin_fake_input.rs

@@ -0,0 +1,209 @@
+//! Headless input injection on KWin via the privileged `org_kde_kwin_fake_input` protocol — the
+//! exact path KDE's own headless RDP server (`krdpserver`) uses. KWin advertises this restricted
+//! global only to a client authorized through its installed `.desktop` `X-KDE-Wayland-Interfaces`
+//! (we ship `io.unom.Punktfunk.Host.desktop`, which lists `org_kde_kwin_fake_input` alongside
+//! `zkde_screencast_unstable_v1`). Binding the global IS the authorization, so injection needs **no
+//! RemoteDesktop portal and no "Allow remote control?" dialog** — it works with no user present,
+//! which the libei/portal path cannot. We connect as an ordinary Wayland client on the KWin session's
+//! `$WAYLAND_DISPLAY` and translate events into fake-input requests; keyboard keys are raw Linux
+//! evdev codes that KWin resolves through the session's own keymap (no keymap upload, unlike the wlr
+//! virtual-keyboard path), and absolute pointer/touch coordinates are global compositor space — which
+//! on a headless box (single per-session virtual output at the origin, scale 1) equals the streamed
+//! output's pixels.
+
+#![allow(clippy::all, dead_code, non_camel_case_types, non_snake_case, unused)]
+// Every `unsafe` block in this file carries a `// SAFETY:` proof; enforce it (unsafe-proof program).
+#![deny(clippy::undocumented_unsafe_blocks)]
+
+use super::{gs_button_to_evdev, vk_to_evdev, InputEvent, InputInjector};
+use anyhow::{Context, Result};
+use punktfunk_core::input::InputKind;
+use wayland_client::protocol::wl_registry::{self, WlRegistry};
+use wayland_client::{Connection, Dispatch, EventQueue, Proxy, QueueHandle};
+
+// Generate the client bindings for the vendored protocol XML inline (no build.rs), exactly like the
+// KWin virtual-output backend. Path is relative to CARGO_MANIFEST_DIR.
+#[allow(clippy::all, dead_code, non_camel_case_types, non_snake_case, unused)]
+pub mod fake {
+    use wayland_client;
+    use wayland_client::protocol::*;
+
+    pub mod __interfaces {
+        use wayland_client::protocol::__interfaces::*;
+        wayland_scanner::generate_interfaces!("protocols/fake-input.xml");
+    }
+    use self::__interfaces::*;
+
+    wayland_scanner::generate_client_code!("protocols/fake-input.xml");
+}
+
+use fake::org_kde_kwin_fake_input::OrgKdeKwinFakeInput as FakeInput;
+
+/// Highest interface version we drive. `keyboard_key` arrived at v4; KWin advertises ≥4.
+const MAX_VERSION: u32 = 4;
+
+/// `wl_pointer.axis` values used by `axis`.
+const AXIS_VERTICAL: u32 = 0;
+const AXIS_HORIZONTAL: u32 = 1;
+/// `code` value marking a horizontal scroll event (mirrors `gamestream::input` / the wlr backend).
+const SCROLL_HORIZONTAL: u32 = 1;
+
+/// Registry-bound globals (the Wayland dispatch state).
+#[derive(Default)]
+struct State {
+    fake: Option<FakeInput>,
+}
+
+impl Dispatch<WlRegistry, ()> for State {
+    fn event(
+        state: &mut Self,
+        registry: &WlRegistry,
+        event: wl_registry::Event,
+        _: &(),
+        _: &Connection,
+        qh: &QueueHandle<Self>,
+    ) {
+        if let wl_registry::Event::Global {
+            name,
+            interface,
+            version,
+        } = event
+        {
+            if interface == "org_kde_kwin_fake_input" {
+                state.fake = Some(registry.bind(name, version.min(MAX_VERSION), qh, ()));
+            }
+        }
+    }
+}
+
+// fake_input emits no events.
+impl Dispatch<FakeInput, ()> for State {
+    fn event(
+        _: &mut Self,
+        _: &FakeInput,
+        _: <FakeInput as Proxy>::Event,
+        _: &(),
+        _: &Connection,
+        _: &QueueHandle<Self>,
+    ) {
+    }
+}
+
+pub struct KwinFakeInjector {
+    conn: Connection,
+    queue: EventQueue<State>,
+    state: State,
+    fake: FakeInput,
+}
+
+impl KwinFakeInjector {
+    pub fn open() -> Result<Self> {
+        let conn = Connection::connect_to_env()
+            .context("connect to KWin Wayland (is WAYLAND_DISPLAY set to the KWin socket?)")?;
+        let mut queue = conn.new_event_queue();
+        let qh = queue.handle();
+        let _registry = conn.display().get_registry(&qh, ());
+        let mut state = State::default();
+        queue
+            .roundtrip(&mut state)
+            .context("Wayland registry roundtrip")?;
+
+        let fake = state.fake.clone().context(
+            "KWin does not expose org_kde_kwin_fake_input to this client — install the host's \
+             .desktop (io.unom.Punktfunk.Host.desktop, X-KDE-Wayland-Interfaces) and re-login so \
+             KWin authorizes it (the grant is cached per-exe on first connect), or this is not a \
+             KWin session",
+        )?;
+        // Authenticate (the legacy handshake; for an interface-authorized client KWin accepts it
+        // without a dialog — same as krdpserver/krfb headless).
+        fake.authenticate("punktfunk".into(), "remote streaming input".into());
+        queue
+            .roundtrip(&mut state)
+            .context("fake_input authenticate roundtrip")?;
+        conn.flush().ok();
+
+        tracing::info!("KWin fake_input ready (headless keyboard/mouse/touch — no portal)");
+        Ok(Self {
+            conn,
+            queue,
+            state,
+            fake,
+        })
+    }
+}
+
+impl InputInjector for KwinFakeInjector {
+    fn inject(&mut self, event: &InputEvent) -> Result<()> {
+        match event.kind {
+            InputKind::MouseMove => {
+                self.fake.pointer_motion(event.x as f64, event.y as f64);
+            }
+            InputKind::MouseMoveAbs => {
+                let w = (event.flags >> 16) & 0xffff;
+                let h = event.flags & 0xffff;
+                if w > 0 && h > 0 {
+                    let x = event.x.clamp(0, w as i32) as f64;
+                    let y = event.y.clamp(0, h as i32) as f64;
+                    self.fake.pointer_motion_absolute(x, y);
+                }
+            }
+            InputKind::MouseButtonDown | InputKind::MouseButtonUp => {
+                if let Some(btn) = gs_button_to_evdev(event.code) {
+                    let st = u32::from(event.kind == InputKind::MouseButtonDown);
+                    self.fake.button(btn, st);
+                }
+            }
+            InputKind::MouseScroll => {
+                // GameStream sends WHEEL_DELTA(120)-scaled units; a notch ≈ 15px. Vertical flips
+                // sign on the Wayland axis, horizontal passes through — same as the wlr backend.
+                let horizontal = event.code == SCROLL_HORIZONTAL;
+                let axis = if horizontal {
+                    AXIS_HORIZONTAL
+                } else {
+                    AXIS_VERTICAL
+                };
+                let notches = event.x as f64 / 120.0;
+                let sign = if horizontal { 1.0 } else { -1.0 };
+                self.fake.axis(axis, sign * notches * 15.0);
+            }
+            InputKind::KeyDown | InputKind::KeyUp => {
+                // Raw evdev keycode; KWin resolves it through the session's own keymap (and tracks
+                // modifier state itself, so no separate modifiers request is needed).
+                if let Some(evdev) = vk_to_evdev(event.code as u8) {
+                    let st = u32::from(event.kind == InputKind::KeyDown);
+                    self.fake.keyboard_key(evdev as u32, st);
+                } else {
+                    tracing::debug!(vk = event.code, "unmapped VK keycode — dropped");
+                }
+            }
+            // Touch: id = event.code, coords in the client surface w×h packed into flags (same
+            // absolute mapping as MouseMoveAbs). Each event is its own frame.
+            InputKind::TouchDown | InputKind::TouchMove => {
+                let w = (event.flags >> 16) & 0xffff;
+                let h = event.flags & 0xffff;
+                if w > 0 && h > 0 {
+                    let x = event.x.clamp(0, w as i32) as f64;
+                    let y = event.y.clamp(0, h as i32) as f64;
+                    if event.kind == InputKind::TouchDown {
+                        self.fake.touch_down(event.code, x, y);
+                    } else {
+                        self.fake.touch_motion(event.code, x, y);
+                    }
+                    self.fake.touch_frame();
+                }
+            }
+            InputKind::TouchUp => {
+                self.fake.touch_up(event.code);
+                self.fake.touch_frame();
+            }
+            // Gamepads are injected through uinput, not the compositor.
+            InputKind::GamepadButton | InputKind::GamepadAxis => {}
+        }
+        // Surface protocol errors / disconnects, then push the batch to the compositor.
+        self.queue
+            .dispatch_pending(&mut self.state)
+            .context("wayland dispatch")?;
+        self.conn.flush().context("wayland flush")?;
+        Ok(())
+    }
+}