xssxss, an LD_PRELOAD to suspend XScreenSaver with XScreenSaverSuspend

10 files changed, 595 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ae5540b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+# Editor backup files
+*~
+\#*
+.\#*
+.*.swp
+
+*.o
+*.so
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..d0c4879
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,33 @@
+How to contribute
+=================
+
+We'd love to accept your patches and contributions to this project. There are
+just a few small guidelines you need to follow.
+
+
+Contributor License Agreement
+-----------------------------
+
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution;
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <https://cla.developers.google.com/> to see
+your current agreements on file or to sign a new one.
+
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+again.
+
+
+Submitting code
+---------------
+
+Submit patches either via a GitHub pull request or by sending mail to
+bbaren@google.com.
+
+
+Community Guidelines
+--------------------
+
+This project follows
+[Google's Open Source Community Guidelines](https://opensource.google.com/conduct/).
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
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diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..05b4a83
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,32 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations under
+# the License.
+
+CPPFLAGS = -D_GNU_SOURCE
+CFLAGS = -O2 -flto -Wall -Werror=format-security -fvisibility=hidden -fpic -pthread
+LDFLAGS = -Wl,-O2 -flto -Wl,-z,relro -Wl,-z,now -fpic -pthread -shared -s
+LDLIBS = -lX11 -ldl
+
+.PHONY: all
+all: libxssxss.so
+
+libxssxss.so: xssbase.o xsslog.o xssxss.o
+	$(LINK.o) $^ $(LDLIBS) -o $@
+
+xssbase.o: xssbase.c xssbase.h
+xsslog.o: xsslog.c xssbase.h xsslog.h
+xssxss.o: xssxss.c xssbase.h xsslog.h
+
+.PHONY: clean
+clean:
+	$(RM) xssbase.o xsslog.o xssxss.o libxssxss.so
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..cd83dcf
--- /dev/null
+++ b/README.md
@@ -0,0 +1,54 @@
+xssxss
+======
+
+Normally, [Chrome](https://www.google.com/chrome/) pauses your screensaver while
+you’re watching video. If you use [xmonad](https://xmonad.org/) and
+[XScreenSaver](https://www.jwz.org/xscreensaver/) together, though, it won’t.
+xssxss fixes this behavior; simply run
+
+    make
+    LD_PRELOAD=$PWD/libxssxss.so google-chrome
+
+and ta-da, Chrome will disable your screensaver like it’s supposed to.
+
+Motivation
+----------
+
+Chromium disables the screensaver through D-Bus. Neither XScreenSaver nor xmonad
+implements a D-Bus interface, so [Chromium falls back][XSSSuspendSet] to calling
+[`XScreenSaverSuspend`][Xss(3)]. Despite its name, this is an X library function
+and [completely unrelated to XScreenSaver][Ubuntu 718176 comment 3], so
+XScreenSaver never picks up on it and remains active.
+
+xssxss (“`XScreenSaver`/XScreenSaver”) translates between X’s `XScreenSaver`
+functions and XScreenSaver’s interface by executing `xdg-screensaver reset` when
+Chrome calls `XScreenSaverSuspend`.
+
+[Ubuntu 718176 comment 3]: https://bugs.launchpad.net/ubuntu/+source/xscreensaver/+bug/718176/comments/3
+[XSSSuspendSet]: https://cs.chromium.org/chromium/src/services/device/wake_lock/power_save_blocker/power_save_blocker_x11.cc?l=225&rcl=2edab67ba89b69c8b6117440faf1b8397a62ace6
+[Xss(3)]: https://www.x.org/releases/X11R7.7/doc/man/man3/Xss.3.xhtml
+
+Future work
+-----------
+
+Ideally, users would be able to control XScreenSaver using D-Bus. However, I
+think adding a D-Bus dependency to XScreenSaver is not the best approach;
+instead, someone should write an adapter daemon that implements [a reasonable
+D-Bus interface][idle-inhibition-spec] and executes `xscreensaver-command` to
+control XScreenSaver.
+
+Once that daemon’s written, Chromium will need to use it. There are multiple
+D-Bus interfaces for disabling various screensavers, and Chromium [currently
+picks based on the running desktop environment][SelectAPI]. Chromium will need
+modification to probe the available interfaces on the bus and select an
+appropriate one. There’s a [`TODO` to this effect][SelectAPI TODO], which
+suggests the project would be receptive to a patch.
+
+[idle-inhibition-spec]: https://people.freedesktop.org/~hadess/idle-inhibition-spec/re01.html
+[SelectAPI]: https://cs.chromium.org/chromium/src/services/device/wake_lock/power_save_blocker/power_save_blocker_x11.cc?l=450&rcl=fdece9dd1e1f7840a643c85e2d89f356b153fe2c
+[SelectAPI TODO]: https://cs.chromium.org/chromium/src/services/device/wake_lock/power_save_blocker/power_save_blocker_x11.cc?l=447-448&rcl=999b2f18d8c62250dd19c85f6c2bb370e68fba8f
+
+Disclaimer
+----------
+
+This is not an official Google product.
diff --git a/xssbase.c b/xssbase.c
new file mode 100644
index 0000000..f8b8055
--- /dev/null
+++ b/xssbase.c
@@ -0,0 +1,17 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#include "xssbase.h"
+
+const char kProjectName[] = "xssxss";
diff --git a/xssbase.h b/xssbase.h
new file mode 100644
index 0000000..ec3ea87
--- /dev/null
+++ b/xssbase.h
@@ -0,0 +1,20 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#pragma once
+
+#define LOCAL __attribute__((visibility("hidden")))
+#define PUBLIC __attribute__((visibility("default")))
+
+LOCAL extern const char kProjectName[];
diff --git a/xsslog.c b/xsslog.c
new file mode 100644
index 0000000..e6d7a63
--- /dev/null
+++ b/xsslog.c
@@ -0,0 +1,61 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#include "xsslog.h"
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void StrAppend4(char target[], const char a[], const char b[],
+                       const char c[], const char d[]) {
+  stpcpy(stpcpy(stpcpy(stpcpy(target, a), b), c), d);
+}
+
+void CheckErrnoImpl(const bool condition, const char description[]) {
+  if (condition) {
+    return;
+  }
+  const int e = errno;
+  char buf[128];
+  fprintf(stderr, "%s: check %s failed: %s\n", kProjectName, description,
+          strerror_r(e, buf, 128));
+  _Exit(1);
+}
+
+void CheckRetImpl(const int e, const char description[]) {
+  if (e == 0) {
+    return;
+  }
+  char buf[128];
+  fprintf(stderr, "%s: %s failed: %s\n", kProjectName, description,
+          strerror_r(e, buf, 128));
+  _Exit(1);
+}
+
+void LogDebug(const char* const format, ...) {
+  const char colon_space[] = ": ";
+  char* const prefixed_format =
+      calloc(strlen(kProjectName) + strlen(colon_space) + strlen(format) + 2,
+             sizeof(char));
+  CHECK_ERRNO(prefixed_format != NULL);
+  StrAppend4(prefixed_format, kProjectName, ": ", format, "\n");
+  va_list args;
+  va_start(args, format);
+  vfprintf(stderr, prefixed_format, args);
+  va_end(args);
+  free(prefixed_format);
+}
diff --git a/xsslog.h b/xsslog.h
new file mode 100644
index 0000000..cc897c5
--- /dev/null
+++ b/xsslog.h
@@ -0,0 +1,27 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#pragma once
+
+#include <stdbool.h>
+
+#include "xssbase.h"
+
+LOCAL void CheckErrnoImpl(const bool condition, const char description[]);
+#define CHECK_ERRNO(condition) (CheckErrnoImpl((condition), #condition))
+
+LOCAL void CheckRetImpl(const int, const char description[]);
+#define CHECK_RET(call) (CheckRetImpl((call), #call))
+
+LOCAL void LogDebug(const char* const format, ...);
diff --git a/xssxss.c b/xssxss.c
new file mode 100644
index 0000000..17966de
--- /dev/null
+++ b/xssxss.c
@@ -0,0 +1,141 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+
+#include <X11/Xlib.h>
+#include <dlfcn.h>
+#include <pthread.h>
+#include <signal.h>
+#include <spawn.h>
+#include <unistd.h>
+
+#include "xssbase.h"
+#include "xsslog.h"
+
+static const int kWakeupSeconds = 10;
+
+// Runs `xdg-screensaver reset` every `kWakeupSeconds` seconds.
+static void* WakerThreadMain(void* const ignored) {
+  // We'd like the new process to start with all signals in the default state.
+  // Set up the appropriate attributes to pass to `posix_spawn`.
+  sigset_t sigset;
+  posix_spawnattr_t attr;
+  CHECK_RET(posix_spawnattr_init(&attr));
+  CHECK_ERRNO(sigfillset(&sigset) == 0);
+  CHECK_RET(posix_spawnattr_setsigdefault(&attr, &sigset));
+  CHECK_ERRNO(sigemptyset(&sigset) == 0);
+  CHECK_RET(posix_spawnattr_setsigmask(&attr, &sigset));
+  CHECK_RET(posix_spawnattr_setflags(
+      &attr, POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK));
+
+  while (true) {
+    LogDebug("resetting screensaver");
+
+    // Start the process to wake up xscreensaver. When it exits, we'll get
+    // SIGCHLD, but we don't care; see notes in `SpawnWakerThread`.
+    pid_t waker_pid;
+    char* const waker[] = {"xdg-screensaver", "reset", NULL};
+    const int e = posix_spawnp(&waker_pid, waker[0], /*file_action=*/NULL,
+                               &attr, waker, environ);
+    if (e != 0) {
+      char buf[128];
+      LogDebug("failed to spawn waker: %d", strerror_r(e, buf, 128));
+    }
+    sleep(kWakeupSeconds);
+  }
+
+  CHECK_RET(posix_spawnattr_destroy(&attr));
+  return NULL;
+}
+
+// Starts a new thread at `WakerThreadMain`.
+static pthread_t SpawnWakerThread(void) {
+  // We'd like the new thread to start with all signals masked. The new thread
+  // inherits the state of our signal mask, so we need to temporarily mask off
+  // all signals before we call pthread_create.
+  //
+  // The new thread is going to be launching new processes, so you might think
+  // we should attract `SIGCHLD` to it. If this process has left the `SIGCHLD`
+  // handler at its default (i.e., to ignore it), this isn't necessary. If, on
+  // the other hand, this process has some thread with an actual `SIGCHLD`
+  // handler, we're screwed: that handler's going to get called spuriously when
+  // the new thread's child exits, and attracting `SIGCHLD` to the new thread
+  // won't solve that problem (the kernel will deliver the signal to an
+  // arbitrary thread that accepts it, so the original `SIGCHLD` handler might
+  // get called anyway). Hope that this process has no `SIGCHLD` handler active,
+  // and just ignore it.
+  sigset_t parent, child;
+  CHECK_ERRNO(sigfillset(&child) == 0);
+  CHECK_ERRNO(pthread_sigmask(SIG_SETMASK, &child, &parent) == 0);
+
+  pthread_t thread;
+  CHECK_ERRNO(pthread_create(&thread, /*attr=*/NULL, WakerThreadMain,
+                             /*arg=*/NULL) == 0);
+
+  CHECK_ERRNO(pthread_sigmask(SIG_SETMASK, &parent, /*oldset=*/NULL) == 0);
+  return thread;
+}
+
+static void CancelThread(const pthread_t thread) {
+  CHECK_ERRNO(pthread_cancel(thread) == 0);
+  CHECK_ERRNO(pthread_join(thread, /*retval=*/NULL) == 0);
+}
+
+// This function must be thread-safe (it overrides a function that is also
+// thread-safe.)
+PUBLIC void XScreenSaverSuspend(Display* const display, const Bool suspend) {
+  // These variables are guarded by the Xlib display lock. The real
+  // XScreenSaverSuspend also locks the Xlib display, but the lock is a
+  // recursive mutex, so the double-locking is safe.
+  static void (*real_XScreenSaverSuspend)(Display*, Bool) = NULL;
+  static int suspends_active = 0;
+  static pthread_t waker_thread;
+
+  LogDebug("%s requested", suspend ? "suspend" : "resume");
+
+  XLockDisplay(display);
+
+  if (real_XScreenSaverSuspend == NULL &&
+      (real_XScreenSaverSuspend = dlsym(RTLD_NEXT, "XScreenSaverSuspend")) ==
+          NULL) {
+    // We couldn't get the real function. This isn't a huge deal, because we can
+    // still shut off xscreensaver, but the user probably wants to know about
+    // it.
+    LogDebug("can't forward to real XScreenSaverSuspend: %s", dlerror());
+  }
+
+  if (real_XScreenSaverSuspend != NULL) {
+    real_XScreenSaverSuspend(display, suspend);
+  }
+
+  if (suspends_active == 0) {
+    if (suspend) {
+      LogDebug("starting waker thread");
+      waker_thread = SpawnWakerThread();
+    } else {
+      LogDebug("resume requested, but no suspends are active; ignoring");
+    }
+  } else if (suspends_active == 1 && !suspend) {
+    LogDebug("canceling waker thread");
+    CancelThread(waker_thread);
+  }
+  suspends_active += suspend ? 1 : -1;
+  LogDebug("%d suspend%s now active", suspends_active,
+           suspends_active == 1 ? " is" : "s are");
+
+  XUnlockDisplay(display);
+}