fix(apple): Don't crash if tunnel manager session is unexpectedly nil (#7594)

In certain weird edge cases such as:

- The user removes the VPN profile while Firezone is signed in, causing
the `NETunnelProviderSession` to go invalid immediately
- The user approves the system extension to load before the VPN profile
access is granted

then the TunnelManager will not be able to obtain a valid reference to a
NETunnelProviderSession object.

In these cases, for now, it makes more sense to fail silently than to
crash, effectively making these operations a no-op until the user
remedies the VPN profile. Currently the user is prompted to re-grant VPN
profile whenever its status goes to `invalid`, so these cases don't
technically fail without prompting the user.

Draft because it's stacked on #7593 


Fixes #7579 
Fixes #7591

---------

Signed-off-by: Jamil <jamilbk@users.noreply.github.com>
Co-authored-by: Thomas Eizinger <thomas@eizinger.io>

swift/apple/FirezoneKit/Sources/FirezoneKit/Managers/TunnelManager.swift

@@ -248,7 +248,7 @@ public class TunnelManager {
     }
 
     do {
-      try session().startTunnel(options: options)
+      try session()?.startTunnel(options: options)
     } catch {
       Log.app.error("Error starting tunnel: \(error)")
     }
@@ -257,21 +257,21 @@ public class TunnelManager {
   func stop(clearToken: Bool = false) {
     if clearToken {
       do {
-        try session().sendProviderMessage(encoder.encode(TunnelMessage.signOut)) { _ in
-          self.session().stopTunnel()
+        try session()?.sendProviderMessage(encoder.encode(TunnelMessage.signOut)) { _ in
+          self.session()?.stopTunnel()
         }
       } catch {
         Log.app.error("\(#function): \(error)")
       }
     } else {
-      session().stopTunnel()
+      session()?.stopTunnel()
     }
   }
 
   func updateInternetResourceState() {
-    guard session().status == .connected else { return }
+    guard session()?.status == .connected else { return }
 
-    try? session().sendProviderMessage(encoder.encode(TunnelMessage.internetResourceEnabled(internetResourceEnabled))) { _ in }
+    try? session()?.sendProviderMessage(encoder.encode(TunnelMessage.internetResourceEnabled(internetResourceEnabled))) { _ in }
   }
 
   func toggleInternetResource(enabled: Bool) {
@@ -280,10 +280,10 @@ public class TunnelManager {
   }
 
   func fetchResources(callback: @escaping (ResourceList) -> Void) {
-    guard session().status == .connected else { return }
+    guard session()?.status == .connected else { return }
 
     do {
-      try session().sendProviderMessage(encoder.encode(TunnelMessage.getResourceList(resourceListHash))) { data in
+      try session()?.sendProviderMessage(encoder.encode(TunnelMessage.getResourceList(resourceListHash))) { data in
         if let data = data {
           self.resourceListHash = Data(SHA256.hash(data: data))
           let decoder = JSONDecoder()
@@ -301,7 +301,7 @@ public class TunnelManager {
   func clearLogs() async throws {
     return try await withCheckedThrowingContinuation { continuation in
       do {
-        try session().sendProviderMessage(
+        try session()?.sendProviderMessage(
           encoder.encode(TunnelMessage.clearLogs)
         ) { _ in continuation.resume() }
       } catch {
@@ -313,7 +313,7 @@ public class TunnelManager {
   func getLogFolderSize() async throws -> Int64 {
     return try await withCheckedThrowingContinuation { continuation in
       do {
-        try session().sendProviderMessage(
+        try session()?.sendProviderMessage(
           encoder.encode(TunnelMessage.getLogFolderSize)
         ) { data in
 
@@ -345,7 +345,7 @@ public class TunnelManager {
 
     func loop() {
       do {
-        try session().sendProviderMessage(
+        try session()?.sendProviderMessage(
           encoder.encode(TunnelMessage.exportLogs)
         ) { data in
           guard let data = data
@@ -385,7 +385,7 @@ public class TunnelManager {
   func consumeStopReason() async throws -> String {
     return try await withCheckedThrowingContinuation { continuation in
       do {
-        try session().sendProviderMessage(
+        try session()?.sendProviderMessage(
           encoder.encode(TunnelMessage.consumeStopReason)
         ) { data in
 
@@ -413,12 +413,8 @@ public class TunnelManager {
     }
   }
 
-  private func session() -> NETunnelProviderSession {
-    guard let manager = manager,
-          let session = manager.connection as? NETunnelProviderSession
-    else { fatalError("Could not cast tunnel connection to NETunnelProviderSession!") }
-
-    return session
+  private func session() -> NETunnelProviderSession? {
+    return manager?.connection as? NETunnelProviderSession
   }
 
   // Subscribe to system notifications about our VPN status changing

website/src/components/Changelog/Apple.tsx

@@ -12,6 +12,11 @@ export default function Apple() {
     >
       {/* When you cut a release, remove any solved issues from the "known issues" lists over in `client-apps`. This must not be done when the issue's PR merges. */}
       <Unreleased>
+        <ChangeItem pull="7594">
+          Fixes a race condition that could cause the app to crash in rare
+          circumstances if the VPN profile is removed from system settings while
+          the app is running.
+        </ChangeItem>
         <ChangeItem pull="7593">
           Fixes a bug where the VPN status would not properly update upon the
           first launch of the app.