pipewire: module-x11-bell: handle X11 errors

Unfortunately, libX11 has global error and I/O error handlers,
which make it inconvenient to use them from library code.

Since libX11 1.7.0, there is a per-display "exit_handler" which
is called from `_XIOError()`, however, the global I/O error
handler is still called before that, and that - by default -
calls `exit(1)` in `_XDefaultIOError()` after printing the error
to stderr.

To avoid exiting, custom handlers will be registered when
libpipewire-module-x11-bell.so is loaded given that at
that moment the default handlers are installed.

When the shared object is unloaded, the handlers will
be reset to the default ones given that the currently
registered handlers are the ones that were registered
when the module was loaded.

The logic only works correctly if there are no concurrent
calls to `XSet{IO}ErrorHandler()` while `{set,restore}_x11_handlers()`
is running. Since module-x11-bell is probably mostly going to
be loaded in `pipewire-pulse`, this seems like a reasonable
assumption to make.

meson.build

@@ -221,18 +221,6 @@ foreach h : check_headers
   cdata.set(h.get(1), cc.has_header(h.get(0)))
 endforeach
 
-check_functions = [
-  ['gettid', '#include <unistd.h>', ['-D_GNU_SOURCE']],
-  ['memfd_create', '#include <sys/mman.h>', ['-D_GNU_SOURCE']],
-  ['getrandom', '#include <stddef.h>\n#include <sys/random.h>', ['-D_GNU_SOURCE']],
-  ['sigabbrev_np', '#include <string.h>', ['-D_GNU_SOURCE']],
-]
-
-foreach f : check_functions
-  cdata.set('HAVE_' + f.get(0).to_upper(),
-            cc.has_function(f.get(0), prefix: f.get(1), args: f.get(2)))
-endforeach
-
 cdata.set('HAVE_PIDFD_OPEN',
           cc.get_define('SYS_pidfd_open', prefix: '#include <sys/syscall.h>') != '')
 
@@ -380,6 +368,22 @@ lilv_lib = dependency('lilv-0', required: get_option('lv2'))
 summary({'lilv (for lv2 plugins)': lilv_lib.found()}, bool_yn: true)
 cdata.set('HAVE_LILV', lilv_lib.found())
 
+check_functions = [
+  ['gettid', '#include <unistd.h>', ['-D_GNU_SOURCE'], []],
+  ['memfd_create', '#include <sys/mman.h>', ['-D_GNU_SOURCE'], []],
+  ['getrandom', '#include <stddef.h>\n#include <sys/random.h>', ['-D_GNU_SOURCE'], []],
+  ['sigabbrev_np', '#include <string.h>', ['-D_GNU_SOURCE'], []],
+  ['XSetIOErrorExitHandler', '#include <X11/Xlib.h>', [], [x11_dep]],
+]
+
+foreach f : check_functions
+  cdata.set('HAVE_' + f.get(0).to_upper(),
+            cc.has_function(f.get(0),
+                            prefix: f.get(1),
+                            args: f.get(2),
+                            dependencies: f.get(3)))
+endforeach
+
 installed_tests_metadir = pipewire_datadir / 'installed-tests' / pipewire_name
 installed_tests_execdir = pipewire_libexecdir / 'installed-tests' / pipewire_name
 installed_tests_enabled = get_option('installed_tests').allowed()

src/modules/module-x11-bell.c

@@ -40,8 +40,9 @@
 
 #include <canberra.h>
 
-#include "pipewire/pipewire.h"
-#include "pipewire/impl.h"
+#include <pipewire/pipewire.h>
+#include <pipewire/impl.h>
+#include <pipewire/private.h>
 
 /** \page page_module_x11_bell PipeWire Module: X11 Bell
  *
@@ -153,6 +154,22 @@ static void display_io(void *data, int fd, uint32_t mask)
 	}
 }
 
+#ifdef HAVE_XSETIOERROREXITHANDLER
+static void x11_io_error_exit_handler(Display *display, void *data)
+{
+	struct impl *impl = data;
+
+	spa_assert(display == impl->display);
+
+	pw_log_warn("X11 display (%s) has encountered a fatal I/O error", DisplayString(display));
+
+	pw_loop_destroy_source(impl->loop, impl->source);
+	impl->source = NULL;
+
+	pw_impl_module_schedule_destroy(impl->module);
+}
+#endif
+
 static int x11_connect(struct impl *impl, const char *name)
 {
 	int major, minor;
@@ -169,6 +186,10 @@ static int x11_connect(struct impl *impl, const char *name)
 	if (!impl->source)
 		return -errno;
 
+#ifdef HAVE_XSETIOERROREXITHANDLER
+	XSetIOErrorExitHandler(impl->display, x11_io_error_exit_handler, impl);
+#endif
+
 	major = XkbMajorVersion;
 	minor = XkbMinorVersion;
 
@@ -285,3 +306,52 @@ error:
 	return res;
 
 }
+
+static int x11_error_handler(Display *display, XErrorEvent *error)
+{
+	pw_log_warn("X11 error handler called on display %s with error %d",
+		    DisplayString(display), error->error_code);
+	return 0;
+}
+
+static int x11_io_error_handler(Display *display)
+{
+	pw_log_warn("X11 I/O error handler called on display %s", DisplayString(display));
+	return 0;
+}
+
+__attribute__((constructor))
+static void set_x11_handlers(void)
+{
+	{
+		XErrorHandler prev = XSetErrorHandler(NULL);
+		XErrorHandler def = XSetErrorHandler(x11_error_handler);
+
+		if (prev != def)
+			XSetErrorHandler(prev);
+	}
+
+	{
+		XIOErrorHandler prev = XSetIOErrorHandler(NULL);
+		XIOErrorHandler def = XSetIOErrorHandler(x11_io_error_handler);
+
+		if (prev != def)
+			XSetIOErrorHandler(prev);
+	}
+}
+
+__attribute__((destructor))
+static void restore_x11_handlers(void)
+{
+	{
+		XErrorHandler prev = XSetErrorHandler(NULL);
+		if (prev != x11_error_handler)
+			XSetErrorHandler(prev);
+	}
+
+	{
+		XIOErrorHandler prev = XSetIOErrorHandler(NULL);
+		if (prev != x11_io_error_handler)
+			XSetIOErrorHandler(prev);
+	}
+}