Log the Windows service's connection failures at warn

The service now answers Pause and Continue only after rewriting the hosts
file, returning the write's error so the tray's ControlService call fails
and shows it. The tray's popup includes the error's source, which
windows-service's own message hides.

core/src/blocks.rs

@@ -0,0 +1,36 @@
+use crate::policies::Package;
+use serde::Serialize;
+use std::sync::Mutex;
+
+/// Bounded, so blocks pile up harmlessly while nothing collects them.
+const KEPT: usize = 50;
+
+static RECENT: Mutex<Vec<BlockedPackage>> = Mutex::new(Vec::new());
+
+#[derive(Serialize)]
+pub struct BlockedPackage {
+    pub eco: &'static str,
+    pub name: String,
+    pub version: Option<String>,
+    pub filter: &'static str,
+    pub reason: String,
+}
+
+pub fn record(eco: &'static str, pkg: &Package, filter: &'static str, reason: &str) {
+    let mut recent = RECENT.lock().unwrap_or_else(|e| e.into_inner());
+    if recent.len() == KEPT {
+        recent.remove(0);
+    }
+    recent.push(BlockedPackage {
+        eco,
+        name: pkg.name.clone(),
+        version: pkg.version.clone(),
+        filter,
+        reason: reason.to_owned(),
+    });
+}
+
+/// Hands each block over once.
+pub fn take() -> Vec<BlockedPackage> {
+    std::mem::take(&mut *RECENT.lock().unwrap_or_else(|e| e.into_inner()))
+}

core/src/config/mod.rs

@@ -48,7 +48,7 @@ impl Default for FirewallConfig {
         FirewallConfig {
             port: DEFAULT_PORT,
             fail_open: true,
-            min_age_hours: 0,
+            min_age_hours: 24,
             denylist: DenylistSource::default(),
             allow: HashMap::new(),
             telemetry: true,

core/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod aliasing;
+pub mod blocks;
 pub mod config;
 pub mod firewall;
 pub mod http;

core/src/os/macos/mod.rs

@@ -5,7 +5,7 @@ mod uninstall;
 pub use uninstall::uninstall;
 
 use crate::config::FirewallConfig;
-use crate::{mitm, telemetry};
+use crate::{blocks, mitm, telemetry};
 use crate::Firewall;
 use rama::bytes::Bytes;
 use rama::error::BoxError;
@@ -58,6 +58,7 @@ impl TransparentProxyHandler for Handler {
         let message = String::from_utf8_lossy(&message).into_owned();
         Some(Bytes::from(match message.as_str() {
             "ca" => self.ca.pem.clone(),
+            "blocks" => serde_json::to_string(&blocks::take()).expect("blocks serialize"),
             other => format!("error: unknown message {other}"),
         }))
     }

core/src/os/windows/service.rs

@@ -26,6 +26,7 @@ use std::net::{IpAddr, Ipv4Addr};
 use std::sync::Arc;
 use std::time::Duration;
 use tracing_appender::rolling::{RollingFileAppender, Rotation};
+use windows::Win32::Foundation::ERROR_GEN_FAILURE;
 use windows_service::service::*;
 use windows_service::service_control_handler::{
     self, ServiceControlHandlerResult, ServiceStatusHandle,
@@ -73,8 +74,12 @@ fn run_until_stopped() -> Result<(), BoxError> {
         | ServiceControl::Shutdown
         | ServiceControl::Pause
         | ServiceControl::Continue => {
-            let _ = control_sender.send(control);
-            ServiceControlHandlerResult::NoError
+            // Answered once handled, so a failed pause fails the caller's ControlService.
+            let (reply, handled) = tokio::sync::oneshot::channel();
+            let _ = control_sender.send((control, reply));
+            handled
+                .blocking_recv()
+                .unwrap_or(ServiceControlHandlerResult::NoError)
         }
         ServiceControl::Interrogate => ServiceControlHandlerResult::NoError,
         _ => ServiceControlHandlerResult::NotImplemented,
@@ -89,16 +94,26 @@ fn run_until_stopped() -> Result<(), BoxError> {
             }
         };
         // Only pausing removes our hosts entries; a stop or crash keeps them, failing closed.
-        while let Some(control) = control_receiver.recv().await {
+        while let Some((control, reply)) = control_receiver.recv().await {
             let (hosts, state) = match control {
                 ServiceControl::Pause => (&[][..], ServiceState::Paused),
                 ServiceControl::Continue => (&hosts[..], ServiceState::Running),
                 _ => break,
             };
-            match write_hosts_entries(hosts) {
-                Ok(()) => set_status(&status, state, false)?,
-                Err(error) => tracing::error!(%error, "could not rewrite the hosts file"),
-            }
+            let result = match write_hosts_entries(hosts) {
+                Ok(()) => {
+                    set_status(&status, state, false)?;
+                    ServiceControlHandlerResult::NoError
+                }
+                Err(error) => {
+                    tracing::error!(%error, "could not rewrite the hosts file");
+                    let code = error
+                        .raw_os_error()
+                        .map_or(ERROR_GEN_FAILURE.0, |code| code as u32);
+                    ServiceControlHandlerResult::Other(code)
+                }
+            };
+            let _ = reply.send(result);
         }
         Ok::<_, BoxError>(())
     });
@@ -147,7 +162,7 @@ async fn start_screening(status: &ServiceStatusHandle) -> Result<Vec<&'static st
                 resolver: resolver.clone(),
                 service: service.clone(),
             };
-            let upstream = ConsumeErrLayer::trace_as_debug().into_layer(upstream);
+            let upstream = ConsumeErrLayer::trace_as_warning().into_layer(upstream);
             tokio::spawn(listen_on(address, port, &exec)?.serve(upstream));
         }
     }

core/src/os/windows/tray.rs

@@ -144,7 +144,11 @@ impl Tray {
 }
 
 fn show_error(error: BoxError) {
-    let text = HSTRING::from(error.to_string());
+    let text = match error.source() {
+        Some(source) => format!("{error}: {source}"),
+        None => error.to_string(),
+    };
+    let text = HSTRING::from(text);
     unsafe { MessageBoxW(None, &text, w!("Strix Firewall"), MB_ICONERROR) };
 }
 

core/src/policies/mod.rs

@@ -69,7 +69,8 @@ pub async fn screen(url: &str, firewall: &Firewall) -> Option<String> {
     };
     info!(eco = registry.eco, pkg = %pkg.label(), %url, "screening");
     match consult(firewall, registry, &pkg).await {
-        Some((_, Verdict::Deny(reason))) => {
+        Some((filter, Verdict::Deny(reason))) => {
+            crate::blocks::record(registry.eco, &pkg, filter, &reason);
             Some(format!("{} {reason}", pkg.label()))
         }
         Some((filter, Verdict::Unknown(e))) if !firewall.config.fail_open => {

macos/App/BlockAlerts.swift

@@ -0,0 +1,32 @@
+import AppKit
+
+struct BlockedPackage: Codable, Hashable, Identifiable {
+    let eco: String
+    let name: String
+    let version: String?
+    let filter: String
+    let reason: String
+
+    var id: String { "\(eco)/\(name)@\(version ?? "")" }
+    var label: String { version.map { "\(name) \($0)" } ?? name }
+    /// The denylist and OSV only flag packages known to be malicious; the age check only holds back new ones.
+    var malicious: Bool { filter != "age" }
+}
+
+@MainActor
+enum BlockAlert {
+    static func show(_ package: BlockedPackage) {
+        let alert = NSAlert()
+        alert.addButton(withTitle: "OK")
+        if package.malicious {
+            alert.alertStyle = .critical
+            alert.messageText = "Blocked a malicious package"
+            alert.informativeText = "\(package.label) (\(package.eco)) \(package.reason). Do not install it."
+        } else {
+            alert.messageText = "Held back a new package"
+            alert.informativeText = "\(package.label) (\(package.eco)) \(package.reason)."
+        }
+        NSApp.activate(ignoringOtherApps: true)
+        alert.runModal()
+    }
+}

macos/App/FirewallModel.swift

@@ -51,6 +51,7 @@ final class FirewallModel: NSObject, ObservableObject {
     @Published private(set) var completed = false
     @Published private(set) var removed = false
     @Published private(set) var screening = false
+    @Published private(set) var blocked: [BlockedPackage] = []
 
     private let logger = Logger(subsystem: FirewallIDs.appBundleID, category: "installer")
     private var pendingRequest: (request: OSSystemExtensionRequest, continuation: CheckedContinuation<Void, Error>)?
@@ -72,6 +73,7 @@ final class FirewallModel: NSObject, ObservableObject {
             await refresh()
             if CommandLine.arguments.contains("--install") { await install() }
         }
+        Task { await watchBlocks() }
     }
 
     // MARK: - Flows
@@ -199,6 +201,21 @@ final class FirewallModel: NSObject, ObservableObject {
         if let url = URL(string: pane) { NSWorkspace.shared.open(url) }
     }
 
+    /// The extension cannot message the app, so the app asks it for blocks.
+    private func watchBlocks() async {
+        while true {
+            if screening, let reply = try? await providerMessage("blocks"),
+               let packages = try? JSONDecoder().decode([BlockedPackage].self, from: Data(reply.utf8)) {
+                for package in packages where !blocked.contains(package) {
+                    blocked.append(package)
+                    BlockAlert.show(package)
+                }
+                blocked = Array(blocked.suffix(10))
+            }
+            try? await Task.sleep(nanoseconds: 2_000_000_000)
+        }
+    }
+
     private func stage(_ step: ReferenceWritableKeyPath<FirewallModel, StepStatus>,
                        running: String,
                        work: @MainActor () async throws -> String) async -> Bool {

macos/App/MenuBarView.swift

@@ -22,5 +22,20 @@ struct MenuBarView: View {
             Task { await model.restart() }
         }
         .disabled(model.busy)
+
+        if !model.blocked.isEmpty {
+            Divider()
+            ForEach(model.blocked) { package in
+                if !package.malicious {
+                    Menu("Held back \(package.label) (\(package.eco))") {
+                        Text(package.reason)
+                    }
+                } else {
+                    Menu("Blocked \(package.label) (\(package.eco))") {
+                        Text("Malicious: \(package.reason)")
+                    }
+                }
+            }
+        }
     }
 }