Ensure atomicity between (re)connection attempts

ios/PacketTunnelCore/Actor/Actor+ConnectionMonitoring.swift

@@ -47,28 +47,14 @@ extension PacketTunnelActor {
         }
     }
 
-    /// Increment connection attempt counter and reconnect the tunnel.
+    /// Tell the tunnel to reconnect providing the correct reason to ensure that the attempt counter is incremented before reconnect.
     private func onHandleConnectionRecovery() async {
         switch state {
-        case var .connecting(connState):
-            connState.incrementAttemptCount()
-            state = .connecting(connState)
-
-        case var .reconnecting(connState):
-            connState.incrementAttemptCount()
-            state = .reconnecting(connState)
-
-        case var .connected(connState):
-            connState.incrementAttemptCount()
-            state = .connected(connState)
+        case .connecting, .reconnecting, .connected:
+            commandChannel.send(.reconnect(.random, reason: .connectionLoss))
 
         case .initial, .disconnected, .disconnecting, .error:
-            // Explicit return to prevent reconnecting the tunnel.
-            return
+            break
         }
-
-        // Tunnel monitor should already be paused at this point so don't stop it to avoid a reset of its internal
-        // counters.
-        commandChannel.send(.reconnect(.random, stopTunnelMonitor: false))
     }
 }

ios/PacketTunnelCore/Actor/Actor.swift

@@ -87,8 +87,8 @@ public actor PacketTunnelActor {
                 case .stop:
                     await stop()
 
-                case let .reconnect(nextRelay, stopTunnelMonitor):
-                    await reconnect(to: nextRelay, shouldStopTunnelMonitor: stopTunnelMonitor)
+                case let .reconnect(nextRelay, reason):
+                    await reconnect(to: nextRelay, reason: reason)
 
                 case let .error(reason):
                     await setErrorStateInternal(with: reason)
@@ -173,16 +173,22 @@ extension PacketTunnelActor {
 
      - Parameters:
          - nextRelay: next relay to connect to
-         - shouldStopTunnelMonitor: whether tunnel monitor should be stopped
+         - reason: reason for reconnect
      */
-    private func reconnect(to nextRelay: NextRelay, shouldStopTunnelMonitor: Bool) async {
+    private func reconnect(to nextRelay: NextRelay, reason: ReconnectReason) async {
         do {
             switch state {
             case .connecting, .connected, .reconnecting, .error:
-                if shouldStopTunnelMonitor {
+                switch reason {
+                case .connectionLoss:
+                    // Tunnel monitor is already paused at this point. Avoid calling stop() to prevent the reset of
+                    // internal state
+                    break
+                case .userInitiated:
                     tunnelMonitor.stop()
                 }
-                try await tryStart(nextRelay: nextRelay)
+
+                try await tryStart(nextRelay: nextRelay, reason: reason)
 
             case .disconnected, .disconnecting, .initial:
                 break
@@ -205,12 +211,14 @@ extension PacketTunnelActor {
      - Start tunnel monitor.
      - Reactivate default path observation (disabled when configuring tunnel adapter)
 
-     - Parameter nextRelay: which relay should be selected next.
+     - Parameters:
+         - nextRelay: which relay should be selected next.
+         - reason: reason for reconnect
      */
-    private func tryStart(nextRelay: NextRelay = .random) async throws {
+    private func tryStart(nextRelay: NextRelay = .random, reason: ReconnectReason = .userInitiated) async throws {
         let settings: Settings = try settingsReader.read()
 
-        guard let connectionState = try makeConnectionState(nextRelay: nextRelay, settings: settings),
+        guard let connectionState = try makeConnectionState(nextRelay: nextRelay, settings: settings, reason: reason),
               let targetState = state.targetStateForReconnect else { return }
 
         let activeKey: PrivateKey
@@ -261,10 +269,15 @@ extension PacketTunnelActor {
      - Parameters:
          - nextRelay: relay preference that should be used when selecting next relay.
          - settings: current settings
+         - reason: reason for reconnect
 
      - Returns: New connection state or `nil` if current state is at or past `.disconnecting` phase.
      */
-    private func makeConnectionState(nextRelay: NextRelay, settings: Settings) throws -> ConnectionState? {
+    private func makeConnectionState(
+        nextRelay: NextRelay,
+        settings: Settings,
+        reason: ReconnectReason
+    ) throws -> ConnectionState? {
         let relayConstraints = settings.relayConstraints
         let privateKey = settings.privateKey
 
@@ -284,7 +297,18 @@ extension PacketTunnelActor {
                 connectionAttemptCount: 0
             )
 
-        case var .connecting(connState), var .connected(connState), var .reconnecting(connState):
+        case var .connecting(connState), var .reconnecting(connState):
+            switch reason {
+            case .connectionLoss:
+                // Increment attempt counter when reconnection is requested due to connectivity loss.
+                connState.incrementAttemptCount()
+            case .userInitiated:
+                break
+            }
+            // Explicit fallthrough
+            fallthrough
+
+        case var .connected(connState):
             connState.selectedRelay = try selectRelay(
                 nextRelay: nextRelay,
                 relayConstraints: relayConstraints,

ios/PacketTunnelCore/Actor/Command.swift

@@ -17,9 +17,7 @@ enum Command {
     case stop
 
     /// Reconnect tunnel.
-    /// `stopTunnelMonitor = false` is only used when tunnel monitor is paused in response to connectivity loss and shouldn't be stopped explicitly,
-    /// as this would reset its internal counters.
-    case reconnect(NextRelay, stopTunnelMonitor: Bool = true)
+    case reconnect(NextRelay, reason: ReconnectReason = .userInitiated)
 
     /// Enter blocked state.
     case error(BlockedStateReason)

ios/PacketTunnelCore/Actor/State.swift

@@ -212,3 +212,13 @@ public enum NextRelay: Equatable, Codable {
     /// Use pre-selected relay.
     case preSelected(SelectedRelay)
 }
+
+/// Describes the reason for reconnection request.
+public enum ReconnectReason {
+    /// Initiated by user.
+    case userInitiated
+
+    /// Initiated by tunnel monitor due to loss of connectivity.
+    /// Actor will increment the connection attempt counter before picking next relay.
+    case connectionLoss
+}

ios/PacketTunnelCoreTests/ActorTests.swift

@@ -99,4 +99,98 @@ final class ActorTests: XCTestCase {
 
         await fulfillment(of: allExpectations, timeout: 1, enforceOrder: true)
     }
+
+    /**
+     Each subsequent connection attempt should produce a single change to `state` containing the incremented attempt counter and new relay.
+
+     .connecting (attempt: 0) → .connecting (attempt: 1) → .connecting (attempt: 2) → ...
+     */
+    func testConnectionAttemptTransition() async throws {
+        let tunnelMonitor = TunnelMonitorStub { _, _ in }
+        let actor = PacketTunnelActor.mock(tunnelMonitor: tunnelMonitor)
+        let connectingStateExpectation = expectation(description: "Expect connecting state")
+        connectingStateExpectation.expectedFulfillmentCount = 5
+
+        var nextAttemptCount: UInt = 0
+        stateSink = await actor.$state
+            .receive(on: DispatchQueue.main)
+            .sink { newState in
+                switch newState {
+                case .initial:
+                    break
+
+                case let .connecting(connState):
+                    XCTAssertEqual(connState.connectionAttemptCount, nextAttemptCount)
+                    nextAttemptCount += 1
+                    connectingStateExpectation.fulfill()
+
+                    if nextAttemptCount < connectingStateExpectation.expectedFulfillmentCount {
+                        tunnelMonitor.dispatch(.connectionLost, after: .milliseconds(10))
+                    }
+
+                default:
+                    XCTFail("Received invalid state: \(newState.name).")
+                }
+            }
+
+        self.actor = actor
+
+        actor.start(options: StartOptions(launchSource: .app))
+
+        await fulfillment(of: [connectingStateExpectation], timeout: 1)
+    }
+
+    /**
+     Each subsequent re-connection attempt should produce a single change to `state` containing the incremented attempt counter and new relay.
+
+     .reconnecting (attempt: 0) → .reconnecting (attempt: 1) → .reconnecting (attempt: 2) → ...
+     */
+    func testReconnectionAttemptTransition() async throws {
+        let tunnelMonitor = TunnelMonitorStub { _, _ in }
+        let actor = PacketTunnelActor.mock(tunnelMonitor: tunnelMonitor)
+        let connectingStateExpectation = expectation(description: "Expect connecting state")
+        let connectedStateExpectation = expectation(description: "Expect connected state")
+        let reconnectingStateExpectation = expectation(description: "Expect reconnecting state")
+        reconnectingStateExpectation.expectedFulfillmentCount = 5
+
+        var nextAttemptCount: UInt = 0
+        stateSink = await actor.$state
+            .receive(on: DispatchQueue.main)
+            .sink { newState in
+                switch newState {
+                case .initial:
+                    break
+
+                case .connecting:
+                    connectingStateExpectation.fulfill()
+                    tunnelMonitor.dispatch(.connectionEstablished, after: .milliseconds(10))
+
+                case .connected:
+                    connectedStateExpectation.fulfill()
+                    tunnelMonitor.dispatch(.connectionLost, after: .milliseconds(10))
+
+                case let .reconnecting(connState):
+                    XCTAssertEqual(connState.connectionAttemptCount, nextAttemptCount)
+                    nextAttemptCount += 1
+                    reconnectingStateExpectation.fulfill()
+
+                    if nextAttemptCount < reconnectingStateExpectation.expectedFulfillmentCount {
+                        tunnelMonitor.dispatch(.connectionLost, after: .milliseconds(10))
+                    }
+
+                default:
+                    XCTFail("Received invalid state: \(newState.name).")
+                }
+            }
+
+        self.actor = actor
+
+        actor.start(options: StartOptions(launchSource: .app))
+
+        await fulfillment(
+            of: [connectingStateExpectation, connectedStateExpectation, reconnectingStateExpectation],
+            timeout: 1,
+            enforceOrder: true
+        )
+    }
 }

ios/PacketTunnelCoreTests/Mocks/TunnelMonitorStub.swift

@@ -64,7 +64,7 @@ class TunnelMonitorStub: TunnelMonitorProtocol {
 
     func onSleep() {}
 
-    private func dispatch(_ event: TunnelMonitorEvent, after delay: DispatchTimeInterval = .never) {
+    func dispatch(_ event: TunnelMonitorEvent, after delay: DispatchTimeInterval = .never) {
         if case .never = delay {
             onEvent?(event)
         } else {