Merge pull request #441 from Yubico/bugfix/yesdk-831-device-listener-…

…runs-with-no-service

SmartCardDeviceListener should be dormant if no smart card service present

Yubico.Core/src/Yubico/Core/Devices/SmartCard/DesktopSmartCardDeviceListener.cs

@@ -46,10 +46,23 @@ internal class DesktopSmartCardDeviceListener : SmartCardDeviceListener, IDispos
         public DesktopSmartCardDeviceListener()
         {
             _log.LogInformation("Creating DesktopSmartCardDeviceListener.");
+            Status = DeviceListenerStatus.Stopped;
 
             uint result = SCardEstablishContext(SCARD_SCOPE.USER, out SCardContext context);
             _log.SCardApiCall(nameof(SCardEstablishContext), result);
 
+            // If we failed to establish context to the smart card subsystem, something substantially wrong
+            // has occured. We should not continue, and the device listener should remain dormant.
+            if (result != ErrorCode.SCARD_S_SUCCESS)
+            {
+                context.Dispose(); // Needed to satisfy analyzer (even though it should be null already)
+                _context = new SCardContext(IntPtr.Zero);
+                _readerStates = Array.Empty<SCARD_READER_STATE>();
+                Status = DeviceListenerStatus.Error;
+                _log.LogWarning("SmartCardDeviceListener dormant as SDK was unable to establish a context to the PCSC service.");
+                return;
+            }
+
             _context = context;
             _readerStates = GetReaderStateList();
 
@@ -68,6 +81,7 @@ private void StartListening()
                     IsBackground = true
                 };
                 _isListening = true;
+                Status = DeviceListenerStatus.Started;
                 _listenerThread.Start();
             }
         }
@@ -142,6 +156,7 @@ private void StopListening()
 
             ClearEventHandlers();
             _isListening = false;
+            Status = DeviceListenerStatus.Stopped;
             _listenerThread.Join();
         }
 

Yubico.Core/src/Yubico/Core/Devices/SmartCard/DeviceListenerStatus.cs

@@ -0,0 +1,37 @@
+// Copyright 2022 Yubico AB
+//
+// Licensed under the Apache License, Version 2.0 (the "License").
+// You may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace Yubico.Core.Devices.SmartCard
+{
+    /// <summary>
+    /// An enumeration that represents the status of a device listener.
+    /// </summary>
+    public enum DeviceListenerStatus
+    {
+        /// <summary>
+        /// The listener has not been started, and is not currently listening for devices. No events will be raised.
+        /// </summary>
+        Stopped,
+
+        /// <summary>
+        /// The listener has been successfully started.
+        /// </summary>
+        Started,
+
+        /// <summary>
+        /// The listener encountered an error and could not start. No events will be raised.
+        /// </summary>
+        Error
+    }
+}

Yubico.Core/src/Yubico/Core/Devices/SmartCard/SmartCardDeviceListener.cs

@@ -47,6 +47,11 @@ public abstract class SmartCardDeviceListener
         /// </summary>
         public event EventHandler<SmartCardDeviceEventArgs>? Removed;
 
+        /// <summary>
+        /// A status that indicates the state of the device listener.
+        /// </summary>
+        public DeviceListenerStatus Status { get; set; }
+
         /// <summary>
         /// Creates an instance of a <see cref="SmartCardDeviceListener"/>.
         /// </summary>