Keep inhibits across daemon restarts

Save held inhibits to $XDG_RUNTIME_DIR/xautolock-inhibit.json and restore them on start if the previous instance stopped within --restore-window (default 30s) on the same bus and the senders are still connected. The file is touched every 10s while inhibits are held, so crashes are timed too.

PKGBUILD

@@ -3,7 +3,7 @@
 # Maintainer: Daniele Fucini <dfucini [at] gmail [dot] com>
 
 pkgname=xautolock-inhibit
-pkgver=0.1.2
+pkgver=0.2
 pkgrel=1
 pkgdesc='Honor org.freedesktop.ScreenSaver inhibit requests by disabling xautolock'
 arch=('any')

README.md

@@ -16,6 +16,7 @@ xautolock stays your locker; xautolock-inhibit only switches it off and on.
 - Runs `xautolock` only when the number of active requests goes from 0 to 1 or back to 0. Re-enabling waits a few seconds (`--release-delay`), because browsers send short bursts of requests when a video starts.
 - Pauses X blanking with `XScreenSaverSuspend`, the same mechanism mpv uses, instead of changing `xset` settings. The X server ends the pause by itself if the daemon exits or crashes.
 - Requests whose reason is on an ignore list (default: `Playing audio`) are accepted and logged, but don't block locking. Firefox-based browsers send one for audio playback, which would otherwise keep the screen unlocked while music plays with nobody at the computer.
+- Keeps the requests it holds in `$XDG_RUNTIME_DIR/xautolock-inhibit.json`, so a restarted or crashed daemon takes them over. They are taken over only if the previous daemon stopped at most 30 seconds ago (`--restore-window`) on the same session bus, and only for clients still connected. A request released while no daemon was running can't be seen, so an old file isn't trusted.
 - On exit (including SIGTERM), it re-enables xautolock. The systemd unit also runs `xautolock -enable` when it stops, as a fallback.
 - If another program (a desktop environment) already owns `org.freedesktop.ScreenSaver`, it exits with status 2 instead of taking over.
 
@@ -45,12 +46,13 @@ The unit has no `[Install]` section on purpose. Enabling it at login would also
 ## Usage
 
 ```
-xautolock-inhibit [-i REASON] [--count-all] [-d SECONDS]
+xautolock-inhibit [-i REASON] [--count-all] [-d SECONDS] [--restore-window SECONDS]
 ```
 
 - `-i`, `--ignore-reason REASON`: request reason that doesn't block locking. Can be repeated; replaces the default (`Playing audio`).
 - `--count-all`: every request blocks locking; no reasons are ignored.
 - `-d`, `--release-delay SECONDS`: wait this long after the last release before re-enabling xautolock (default 5).
+- `--restore-window SECONDS`: take over requests from a previous daemon that stopped at most this long ago (default 30; 0 disables).
 
 To change the options used by the service:
 
@@ -84,7 +86,7 @@ journalctl --user -u xautolock-inhibit
 
 ## Limitations
 
-- Restarting the daemon loses the requests it holds; apps don't send them again. Avoid restarting it while a video or game is running.
+- A release sent while the daemon is down is lost: if the daemon is back within `--restore-window`, that request stays active until its app exits. After a longer stop, all held requests are dropped and apps don't send them again.
 - `SimulateUserActivity` is accepted but does nothing. Calls are logged once when a client starts sending them and once, with a count, after 5 minutes without any.
 - `GetActive` always returns `false`.
 

xautolock-inhibit

@@ -6,13 +6,15 @@ While an inhibit is active, X screen blanking is also paused (like mpv does).
 
 import argparse
 import ctypes
-import itertools
+import json
+import os
 import signal
 import subprocess
 import sys
 import time
 from dataclasses import dataclass
 from datetime import timedelta
+from typing import Any
 
 from gi.repository import Gio, GLib
 
@@ -26,6 +28,8 @@ BUS_NAME = "org.freedesktop.ScreenSaver"
 OBJECT_PATHS = ("/org/freedesktop/ScreenSaver", "/ScreenSaver")  # Vivaldi uses the first, Zen the second
 EXIT_NAME_TAKEN = 2
 ACTIVITY_QUIET = 300  # seconds without SimulateUserActivity that end a logged burst
+STATE_FILE = "xautolock-inhibit.json"  # in $XDG_RUNTIME_DIR
+STATE_HEARTBEAT = 10  # seconds between state file touches while inhibits are held
 
 Cookie = tuple[str, str, str, bool]  # sender, application_name, reason, counts
 
@@ -120,12 +124,19 @@ class ActivityBurst:
 
 
 class Inhibitor:
-    def __init__(self, ignored_reasons: set[str], release_delay: int, blanking: XBlanking) -> None:
+    def __init__(
+        self, ignored_reasons: set[str], release_delay: int, blanking: XBlanking,
+        state_path: str | None, restore_window: int,
+    ) -> None:
         self.ignored_reasons = ignored_reasons
         self.blanking = blanking
         self.release_delay = release_delay
+        self.state_path = state_path
+        self.restore_window = restore_window
+        self.state_ready = False  # set once this instance owns the name and may write the state file
+        self.heartbeat_timer = 0
         self.cookies: dict[int, Cookie] = {}
-        self.next_cookie = itertools.count(1)
+        self.last_cookie = 0
         self.proc_names: dict[str, str] = {}  # sender -> "comm[pid]", for logging only
         self.activity: dict[str, ActivityBurst] = {}  # sender -> SimulateUserActivity burst
         self.disabled = False
@@ -171,20 +182,121 @@ class Inhibitor:
         if self.release_timer:
             GLib.source_remove(self.release_timer)
             self.release_timer = 0
+        self.save(stopped=True)
         if self.disabled:
             self.unblock()
 
+    # --- state file -------------------------------------------------------
+
+    def start(self) -> None:
+        """Take over inhibits saved by a previous instance, then set xautolock to match."""
+        self.restore()
+        self.state_ready = True
+        self.save()
+        if self.active_count():
+            self.block()
+        else:
+            # Start from a known state, in case a previous instance died while disabled.
+            xautolock("-enable")
+
+    def restore(self) -> None:
+        if not self.state_path:
+            log("XDG_RUNTIME_DIR is not set; inhibits will not survive a restart")
+            return
+        assert self.conn is not None
+        try:
+            with open(self.state_path) as f:
+                state = json.load(f)
+            age = time.time() - (state["stopped_at"] or os.stat(self.state_path).st_mtime)
+            bus_id = state["bus_id"]
+            last_cookie = int(state["last_cookie"])
+            saved = [(int(c), s, a, r) for c, s, a, r in state["cookies"]]
+        except FileNotFoundError:
+            return
+        except (OSError, ValueError, KeyError, TypeError) as e:
+            log(f"Ignoring unreadable state file {self.state_path}: {e}")
+            return
+        if bus_id != self.conn.get_guid():
+            # Unique names like :1.42 are reused by a new bus, so they would mean other clients.
+            if saved:
+                log(f"Not restoring {len(saved)} inhibit(s): saved on another session bus")
+            return
+        # Keep numbering after old cookies, so a late UnInhibit can't hit a new one.
+        self.last_cookie = last_cookie
+        if not saved:
+            return
+        if age > self.restore_window:
+            # An UnInhibit sent while no instance ran is lost; don't trust an old file.
+            log(f"Not restoring {len(saved)} inhibit(s): saved {age:.0f}s ago, "
+                f"over the {self.restore_window}s window")
+            return
+        for cookie, sender, app, reason in saved:
+            if not self.has_owner(sender):
+                log(f"Not restoring {cookie}: '{app}' '{reason}' ({sender} left the bus)")
+                continue
+            counts = reason not in self.ignored_reasons
+            self.cookies[cookie] = (sender, app, reason, counts)
+            note = "" if counts else " (reason ignored, does not block locking)"
+            log(f"Restored {cookie}: '{app}' '{reason}' from {self.proc_name(sender)}{note}")
+
+    def save(self, stopped: bool = False) -> None:
+        """Write the held inhibits atomically; while any are held, touch the file regularly.
+
+        The touches keep the mtime recent, so after a crash the next instance can tell how
+        long ago it happened. A clean stop records the time in `stopped_at` instead.
+        """
+        if not self.state_ready or not self.state_path:
+            return
+        assert self.conn is not None
+        state = {
+            "bus_id": self.conn.get_guid(),
+            "last_cookie": self.last_cookie,
+            "stopped_at": time.time() if stopped else None,
+            "cookies": [[c, s, a, r] for c, (s, a, r, _) in self.cookies.items()],
+        }
+        tmp = f"{self.state_path}.tmp"
+        try:
+            with open(tmp, "w") as f:
+                json.dump(state, f)
+            os.replace(tmp, self.state_path)
+        except OSError as e:
+            log(f"Cannot write state file {self.state_path}: {e}")
+        if self.cookies and not stopped:
+            if not self.heartbeat_timer:
+                self.heartbeat_timer = GLib.timeout_add_seconds(STATE_HEARTBEAT, self.on_heartbeat)
+        elif self.heartbeat_timer:
+            GLib.source_remove(self.heartbeat_timer)
+            self.heartbeat_timer = 0
+
+    def on_heartbeat(self) -> bool:
+        assert self.state_path is not None
+        try:
+            os.utime(self.state_path)
+        except OSError as e:
+            log(f"Cannot touch state file {self.state_path}: {e}")
+        return GLib.SOURCE_CONTINUE
+
     # --- D-Bus ------------------------------------------------------------
 
+    def bus_call(self, method: str, name: str, reply_type: str) -> Any:
+        """Call an org.freedesktop.DBus method that takes a bus name; return its single result."""
+        assert self.conn is not None  # set in on_bus_acquired, before any method call
+        return self.conn.call_sync(
+            "org.freedesktop.DBus", "/org/freedesktop/DBus", "org.freedesktop.DBus",
+            method, GLib.Variant("(s)", (name,)),
+            GLib.VariantType(reply_type), Gio.DBusCallFlags.NONE, 1000, None,
+        ).unpack()[0]
+
+    def has_owner(self, name: str) -> bool:
+        try:
+            return bool(self.bus_call("NameHasOwner", name, "(b)"))
+        except GLib.Error:
+            return False
+
     def proc_name(self, sender: str) -> str:
         if sender not in self.proc_names:
-            assert self.conn is not None  # set in on_bus_acquired, before any method call
             try:
-                pid = self.conn.call_sync(
-                    "org.freedesktop.DBus", "/org/freedesktop/DBus", "org.freedesktop.DBus",
-                    "GetConnectionUnixProcessID", GLib.Variant("(s)", (sender,)),
-                    GLib.VariantType("(u)"), Gio.DBusCallFlags.NONE, 1000, None,
-                ).unpack()[0]
+                pid = self.bus_call("GetConnectionUnixProcessID", sender, "(u)")
                 with open(f"/proc/{pid}/comm") as f:
                     self.proc_names[sender] = f"{f.read().strip()}[{pid}]"
             except (GLib.Error, OSError):
@@ -192,11 +304,13 @@ class Inhibitor:
         return f"{sender} {self.proc_names[sender]}"
 
     def inhibit(self, sender: str, app: str, reason: str) -> int:
-        cookie = next(self.next_cookie)
+        self.last_cookie += 1
+        cookie = self.last_cookie
         counts = reason not in self.ignored_reasons
         self.cookies[cookie] = (sender, app, reason, counts)
         note = "" if counts else " (reason ignored, does not block locking)"
         log(f"Inhibit {cookie}: '{app}' '{reason}' from {self.proc_name(sender)}{note}")
+        self.save()
         self.update()
         return cookie
 
@@ -208,6 +322,7 @@ class Inhibitor:
         del self.cookies[cookie]
         _, app, reason, _ = entry
         log(f"UnInhibit {cookie}: '{app}' '{reason}'")
+        self.save()
         self.update()
 
     def simulate_activity(self, sender: str) -> None:
@@ -247,6 +362,7 @@ class Inhibitor:
         self.end_activity(sender)
         self.proc_names.pop(sender, None)
         if gone:
+            self.save()
             self.update()
 
     def on_method_call(
@@ -304,6 +420,11 @@ def main() -> None:
         "-d", "--release-delay", type=int, default=5, metavar="SECONDS",
         help="wait this long after the last release before re-enabling xautolock (default: 5)",
     )
+    parser.add_argument(
+        "--restore-window", type=int, default=30, metavar="SECONDS",
+        help="take over inhibits from a previous instance that stopped at most this long ago "
+             "(default: 30; 0 disables)",
+    )
     args = parser.parse_args()
 
     ignored: set[str]
@@ -311,7 +432,11 @@ def main() -> None:
         ignored = set()
     else:
         ignored = set(args.ignore_reason or ["Playing audio"])
-    inhibitor = Inhibitor(ignored, max(args.release_delay, 0), XBlanking())
+    runtime_dir = os.environ.get("XDG_RUNTIME_DIR")
+    state_path = os.path.join(runtime_dir, STATE_FILE) if runtime_dir else None
+    inhibitor = Inhibitor(
+        ignored, max(args.release_delay, 0), XBlanking(), state_path, max(args.restore_window, 0),
+    )
     loop = GLib.MainLoop()
     exit_code = 0
     acquired = False
@@ -320,9 +445,9 @@ def main() -> None:
         nonlocal acquired
         acquired = True
         log(f"Owning {name}; ignored reasons: {sorted(ignored) or 'none'}")
-        # Start from a known state, in case a previous instance died while disabled.
-        # Only after owning the name, so a second instance can't undo an active inhibit.
-        xautolock("-enable")
+        # Only after owning the name, so a second instance can't undo an active inhibit
+        # or overwrite the state file.
+        inhibitor.start()
 
     def on_name_lost(conn: Gio.DBusConnection | None, name: str) -> None:
         nonlocal exit_code