feat: add whyoolw/dropwall (#6)

Co-authored-by: whyoolw <whyoolw@gmail.com>

dropwall/dropwall_supervisor.py

@@ -0,0 +1,83 @@
+#!/usr/bin/env python3
+"""Keep one DropWall GTK target attached to a single Noctalia stream."""
+
+import argparse
+import ctypes
+import os
+import signal
+import subprocess
+import sys
+import time
+
+
+# Exit immediately when Noctalia closes runStream's stdout pipe.
+signal.signal(signal.SIGPIPE, signal.SIG_DFL)
+
+
+def arm_parent_death_signal():
+    """Ask Linux to terminate us if Noctalia disappears."""
+    parent = os.getppid()
+    try:
+        libc = ctypes.CDLL(None, use_errno=True)
+        if libc.prctl(1, signal.SIGTERM, 0, 0, 0) != 0:  # PR_SET_PDEATHSIG
+            return
+        if os.getppid() != parent:
+            os.kill(os.getpid(), signal.SIGTERM)
+    except (AttributeError, OSError):
+        return
+
+
+def emit(line):
+    print(line, flush=True)
+
+
+def worker_command(args):
+    helper = os.path.join(os.path.dirname(os.path.abspath(__file__)), "dropwall_helper.py")
+    return [sys.executable, "-B", helper, "--layer", args.layer]
+
+
+def run_worker(command):
+    process = subprocess.Popen(
+        command,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+        encoding="utf-8",
+        errors="replace",
+        bufsize=1,
+    )
+    assert process.stdout is not None
+    for line in process.stdout:
+        emit(line.rstrip("\n"))
+    return process.wait()
+
+
+def main():
+    parser = argparse.ArgumentParser(description="DropWall helper supervisor")
+    parser.add_argument("--layer", choices=("background", "bottom"), default="background")
+    args = parser.parse_args()
+
+    arm_parent_death_signal()
+    command = worker_command(args)
+    lock_retry_seconds = 2
+
+    while True:
+        try:
+            exit_code = run_worker(command)
+        except OSError as error:
+            emit("ERR\tcould not start the GTK helper: %s" % str(error).replace("\n", " "))
+            exit_code = 127
+
+        emit("RESTART\t%d" % exit_code)
+        if exit_code == 3:
+            # A collision normally means the previous runtime is still
+            # shutting down. Back off if it is a genuinely persistent owner.
+            time.sleep(lock_retry_seconds)
+            lock_retry_seconds = min(lock_retry_seconds * 2, 60)
+        else:
+            lock_retry_seconds = 2
+            time.sleep(30)
+
+
+if __name__ == "__main__":
+    sys.exit(main())