Add warning about default routes

I hope this puts a lot of questions about SIM cards to rest. I found
that the warning also sometimes applies to "dead" SIM cards which have
expired a long time ago.

Run `busybox ip route` to determine whether the device has an active SIM
card. That command has been manually tested on Moxee, Orbic and TP-Link.
It's prefixed with `busybox` because that makes it more likely it would
work on UZ801, though it wasn't tested there. If the command invocation
fails, the alert is suppressed and a warning is logged.

The command is only run once on pageload. It could've been part of the
status endpoint, but then the UI would poll it way too often.

daemon/src/main.rs

@@ -25,7 +25,7 @@ use crate::server::{
     ServerState, debug_set_display_state, get_config, get_qmdl, get_zip, serve_static, set_config,
     test_notification,
 };
-use crate::stats::{get_qmdl_manifest, get_system_stats};
+use crate::stats::{get_qmdl_manifest, get_route_status, get_system_stats};
 
 use analysis::{
     AnalysisCtrlMessage, AnalysisStatus, get_analysis_status, run_analysis_thread, start_analysis,
@@ -58,6 +58,7 @@ fn get_router() -> AppRouter {
         .route("/api/qmdl/{name}", get(get_qmdl))
         .route("/api/zip/{name}", get(get_zip))
         .route("/api/system-stats", get(get_system_stats))
+        .route("/api/route-status", get(get_route_status))
         .route("/api/qmdl-manifest", get(get_qmdl_manifest))
         .route("/api/log", get(get_log))
         .route("/api/start-recording", post(start_recording))

daemon/src/stats.rs

@@ -174,3 +174,25 @@ pub async fn get_log() -> Result<String, (StatusCode, String)> {
         .await
         .map_err(|e| (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))
 }
+
+#[derive(Debug, Serialize)]
+pub struct RouteStatus {
+    pub has_default_route: bool,
+}
+
+pub async fn get_route_status() -> Json<RouteStatus> {
+    let mut cmd = Command::new("busybox");
+    cmd.args(["ip", "route"]);
+
+    let has_default_route = match get_cmd_output(cmd).await {
+        Ok(output) => output.lines().any(|line| line.starts_with("default ")),
+        Err(err) => {
+            log::warn!("Failed to check default route: {err}");
+            // More likely than not, this is a portability issue. The logic hasn't been fully
+            // tested on all devices. We shouldn't scare users unnecessarily.
+            true
+        }
+    };
+
+    Json(RouteStatus { has_default_route })
+}