XInput keyboard: dispatch via XTestFakeDeviceKeyEvent (#642)

GDK3 (used by Firefox/Camoufox) selects XI2 for the seat keyboard at
startup and ignores core-protocol KeyPress events. XTestFakeKeyEvent
produces core events, so typed characters from the Neko viewer silently
never reach Firefox.

Fix: discover the "Virtual core XTEST keyboard" XInput1 device at
startup, cache it, and dispatch key events via XTestFakeDeviceKeyEvent
which goes through the XI path. Falls back to the old core XTest path
if the device isn't found.

Requires -lXi (libxi-dev at build, libxi6 at runtime).

server/pkg/xorg/xorg.c

@@ -1,17 +1,61 @@
 #include "xorg.h"
 
 static Display *DISPLAY = NULL;
+// XTEST virtual keyboard XInput1 device handle — cached so XKey() can dispatch
+// via XTestFakeDeviceKeyEvent (XI-aware) instead of XTestFakeKeyEvent (core-only).
+// GDK3 selects XI2 for the seat keyboard at startup and ignores core-protocol
+// KeyPress events, so core XTest silently drops every key into Firefox.
+static XDevice *XTEST_KEYBOARD = NULL;
 
 Display *getXDisplay(void) {
   return DISPLAY;
 }
 
+// Discover and open the "Virtual core XTEST keyboard" XInput1 device.
+// Must be called after XOpenDisplay. Returns NULL on failure; callers fall back
+// to XTestFakeKeyEvent (which doesn't work against modern GDK3, but at least
+// doesn't crash).
+static XDevice *openXTestKeyboardDevice(Display *display) {
+  int ndev = 0;
+  XDeviceInfo *devs = XListInputDevices(display, &ndev);
+  if (devs == NULL)
+    return NULL;
+
+  XDevice *dev = NULL;
+  for (int i = 0; i < ndev; i++) {
+    if (devs[i].name == NULL)
+      continue;
+    // Exact match against the XTEST extension's virtual keyboard. X.Org spawns
+    // this device at server startup. Use strstr to tolerate naming variations
+    // across X servers — e.g. "Virtual core XTEST keyboard" vs "XTEST keyboard".
+    if (strstr(devs[i].name, "XTEST") != NULL && strstr(devs[i].name, "keyboard") != NULL) {
+      dev = XOpenDevice(display, devs[i].id);
+      if (dev != NULL)
+        break;
+    }
+  }
+
+  XFreeDeviceList(devs);
+  return dev;
+}
+
 int XDisplayOpen(char *name) {
   DISPLAY = XOpenDisplay(name);
-  return DISPLAY == NULL;
+  if (DISPLAY == NULL)
+    return 1;
+
+  // Best-effort: cache the XTEST keyboard device. If this fails we still return
+  // success — XKey falls back to core XTest, which at least preserves the old
+  // behaviour (broken, but not a crash).
+  XTEST_KEYBOARD = openXTestKeyboardDevice(DISPLAY);
+  return 0;
 }
 
 void XDisplayClose(void) {
+  if (XTEST_KEYBOARD != NULL) {
+    XCloseDevice(DISPLAY, XTEST_KEYBOARD);
+    XTEST_KEYBOARD = NULL;
+  }
   XCloseDisplay(DISPLAY);
 }
 
@@ -225,7 +269,15 @@ void XKey(KeySym keysym, int down) {
   if (down)
     XKeyEntryAdd(keysym, keycode);
 
-  XTestFakeKeyEvent(display, keycode, down, CurrentTime);
+  // Prefer XTestFakeDeviceKeyEvent: it dispatches via the XTEST XInput device,
+  // so XI2 listeners (GDK3 inside Firefox) actually receive the event. The core
+  // XTestFakeKeyEvent path produces core-protocol events that GDK3's XI2 keyboard
+  // path silently drops.
+  if (XTEST_KEYBOARD != NULL) {
+    XTestFakeDeviceKeyEvent(display, XTEST_KEYBOARD, keycode, down, NULL, 0, CurrentTime);
+  } else {
+    XTestFakeKeyEvent(display, keycode, down, CurrentTime);
+  }
   XSync(display, 0);
 }
 

server/pkg/xorg/xorg.go

@@ -1,7 +1,7 @@
 package xorg
 
 /*
-#cgo LDFLAGS: -lX11 -lXrandr -lXtst -lXfixes -lxcvt
+#cgo LDFLAGS: -lX11 -lXrandr -lXtst -lXfixes -lXi -lxcvt
 
 #include "xorg.h"
 */

server/pkg/xorg/xorg.h

@@ -6,6 +6,7 @@
 #include <X11/extensions/Xrandr.h>
 #include <X11/extensions/XTest.h>
 #include <X11/extensions/Xfixes.h>
+#include <X11/extensions/XInput.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>