Automatically reload device list after configurable number of hours

Make reloading device list happen asynchronously
Reload file list during startup
Send error message if device list trying to be changed at the same time a scan request is happening
Don't overwrite existing device configuration when device is reloaded

src/sanescansrv/server.py

@@ -1,6 +1,6 @@
 """Scanner Web Server - Website to talk to SANE scanners.
 
-Copyright (C) 2022-2023  CoolCat467
+Copyright (C) 2022-2024  CoolCat467
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
@@ -442,7 +442,7 @@ async def scan_status_get() -> AsyncIterator[str] | WerkzeugResponse:
 
     progress: ScanProgress | None = None
     time_deltas_ns: list[int] | None = None
-    delay = 3
+    delay = 5
     estimated_wait: int = 9999
 
     if status == ScanStatus.IN_PROGRESS:
@@ -458,7 +458,7 @@ async def scan_status_get() -> AsyncIterator[str] | WerkzeugResponse:
         estimated_wait_ns = delta_total * average_wait_ns
         # nanoseconds -> seconds
         estimated_wait = math.ceil(estimated_wait_ns // 1e9)
-        delay = max(delay, min(5, estimated_wait))
+        delay = max(delay, min(10, estimated_wait))
 
     return await stream_template(
         "scan-status_get.html.jinja",
@@ -525,13 +525,44 @@ async def root_post() -> WerkzeugResponse | AsyncIterator[str]:
     return app.redirect("/scan-status")
 
 
+def update_scanners() -> None:
+    """Update scanners list."""
+    APP_STORAGE["scanners"] = get_devices()
+    for _model, device in APP_STORAGE["scanners"].items():
+        if device not in APP_STORAGE["device_settings"]:
+            APP_STORAGE["device_settings"][device] = get_device_settings(device)
+
+
+async def update_scanners_async() -> bool:
+    """Update scanners list asynchronously. Return if successful."""
+    if SCAN_LOCK.locked():
+        return False
+    async with SCAN_LOCK:
+        await trio.to_thread.run_sync(update_scanners)
+    return True
+
+
+async def refresh_devices(delay_sec: int = 60 * 60) -> None:
+    """Refresh devices list every delay_sec seconds."""
+    while True:
+        try:
+            await update_scanners_async()
+            await trio.sleep(delay_sec)
+        except trio.Cancelled:
+            return
+
+
 @app.get("/update_scanners")
 @pretty_exception
 async def update_scanners_get() -> WerkzeugResponse:
     """Update scanners get handling."""
-    APP_STORAGE["scanners"] = get_devices()
-    for _model, device in APP_STORAGE["scanners"].items():
-        APP_STORAGE["device_settings"][device] = get_device_settings(device)
+    success = await update_scanners_async()
+    if not success:
+        return await send_error(
+            "Scan Currently Running",
+            "There is a scan request currently running, updating the device list at this time might not be smart.",
+            return_link="/update_scanners",
+        )
     return app.redirect("scanners")
 
 
@@ -610,10 +641,11 @@ async def settings_post() -> WerkzeugResponse:
     return app.redirect(request.url)
 
 
-async def serve_async(app: QuartTrio, config_obj: Config) -> None:
+async def serve_async(app: QuartTrio, config_obj: Config, auto_refresh_time: int = 60 * 60) -> None:
     """Serve app within a nursery."""
     async with trio.open_nursery(strict_exception_groups=True) as nursery:
         APP_STORAGE["nursery"] = nursery
+        nursery.start_soon(refresh_devices, auto_refresh_time)
         await nursery.start(serve, app, config_obj)
 
 
@@ -624,6 +656,7 @@ def serve_scanner(
     insecure_bind_port: int | None = None,
     ip_addr: str | None = None,
     hypercorn: dict[str, object] | None = None,
+    auto_refresh_sec: int = 60 * 60,
 ) -> None:
     """Asynchronous Entry Point."""
     if secure_bind_port is None and insecure_bind_port is None:
@@ -702,7 +735,7 @@ def serve_scanner(
 
         print("(CTRL + C to quit)")
 
-        trio.run(serve_async, app, config_obj)
+        trio.run(serve_async, app, config_obj, auto_refresh_sec)
     except BaseExceptionGroup as exc:
         caught = False
         for ex in exc.exceptions:
@@ -734,6 +767,10 @@ def run() -> None:
 # You might want to consider changing this to 80
 port = 3004
 
+# Duration to wait before automatically refreshing scanner list
+# Supports fractional hours, ex 1.5 hours -> refresh every 90 minutes
+auto_refresh_hours = 1.0
+
 # Port for SSL secured server to run on
 #ssl_port = 443
 
@@ -761,6 +798,7 @@ def run() -> None:
     target = main_section.get("printer", None)
     insecure_bind_port = main_section.get("port", None)
     secure_bind_port = main_section.get("ssl_port", None)
+    auto_refresh_sec = float(main_section.get("auto_refresh_hours", 1)) * 60 * 60
 
     hypercorn: dict[str, object] = config.get("hypercorn", {})
 
@@ -774,6 +812,7 @@ def run() -> None:
         secure_bind_port=secure_bind_port,
         insecure_bind_port=insecure_bind_port,
         hypercorn=hypercorn,
+        auto_refresh_sec=auto_refresh_sec,
     )