PCSC.InvalidContextException when running as a Windows service

I have been working on a small smart card scanner using pcsc-sharp library. The app works fine when run as a console app, the code looks like this:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Configuration;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Text;
using System.Drawing.Printing;
using System.Net;
using System.Net.Sockets;
using System.Data.SqlClient;
using System.Threading;
using System.IO.Ports;
using System.Text.RegularExpressions;
using System.Speech.Synthesis;
using System.Diagnostics;
using PCSC;
using System.Media;

namespace MeterTestingApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            // Retrieve the names of all installed readers.
            string[] readerNames;
            using (var context = new SCardContext())
            {
                context.Establish(SCardScope.System);
                readerNames = context.GetReaders();
                context.Release();
            }

            if (readerNames == null || readerNames.Length == 0)
            {
                Console.WriteLine("There are currently no readers installed.");
                return;
            }

            // Create a monitor object with its own PC/SC context. 
            // The context will be released after monitor.Dispose()
            using (var monitor = new SCardMonitor(new SCardContext(), SCardScope.System))
            {
                // Point the callback function(s) to the anonymous & static defined methods below.
                monitor.CardInserted += (sender, args0) => DisplayEvent("CardInserted", args0);
                //monitor.CardRemoved += (sender, args0) => DisplayEvent("CardRemoved", args0);
                //monitor.Initialized += (sender, args0) => DisplayEvent("Initialized", args0);
                //monitor.StatusChanged += StatusChanged;
                monitor.MonitorException += MonitorException;

                monitor.Start(readerNames);

                // Keep the window open
                Console.ReadLine();
            }
        }

        private static void DisplayEvent(string eventName, CardStatusEventArgs unknown)
        {
            Console.WriteLine(">> {0} Event for reader: {1}", eventName, unknown.ReaderName);
            Console.WriteLine("ATR: {0}", BitConverter.ToString(unknown.Atr ?? new byte[0]));
            Console.WriteLine("State: {0}\n", unknown.State);


            //Works fine here
        }

        private static void StatusChanged(object sender, StatusChangeEventArgs args)
        {
            //Console.WriteLine(">> StatusChanged Event for reader: {0}", args.ReaderName);
            //Console.WriteLine("ATR: {0}", BitConverter.ToString(args.Atr ?? new byte[0]));
            //Console.WriteLine("Last state: {0}\nNew state: {1}\n", args.LastState, args.NewState);
        }

        private static void MonitorException(object sender, PCSCException ex)
        {
            Console.WriteLine("Monitor exited due an error:");
            Console.WriteLine(SCardHelper.StringifyError(ex.SCardError));
        }
    }
}

      

However, when trying to start it as a Windows service - allow card scanning to update the database - the event never fires and it seems to fail when starting the service. The event log is showing error PCSC.InvalidContextException. The code for the service is almost identical, but here's a sample.

    using System;
using System.Diagnostics;
using System.ServiceProcess;
using System.Timers;
using System.Configuration;
using System.Linq;
using System.Data.SqlClient;
using System.Collections.Generic;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Text;
using System.Drawing.Printing;
using System.Threading;
using System.Speech.Synthesis;
using System.IO.Ports;
using System.Text.RegularExpressions;
using PCSC;
using System.Media;
using log4net;


namespace CardScannerService
{
    public partial class CardScanner : ServiceBase
    {
        private ILog logger;

        private SCardContext context;
        private string[] readerNames;
        private SCardMonitor monitor;

        private static System.Timers.Timer aTimer;

        public CardScanner()
        {
            InitializeComponent();
        }

        static void Main()
        {
            ServiceBase.Run(new CardScanner());
        }


        //
        // Start Service
        //

        protected override void OnStart(string[] args)
        {
            aTimer = new System.Timers.Timer();
            aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            aTimer.Interval = (1000 * 60 * 60 * 24); // Once a day; 1000ms * 60s * 60m * 24h
            aTimer.Enabled = true;

            //// Entry point
            using (context = new SCardContext())
            {
                context.Establish(SCardScope.System);
                readerNames = context.GetReaders();
                context.Release();
            }

            if (readerNames == null || readerNames.Length == 0)
            {
                EventLog.WriteEntry("CardReaderService", "There are currently no readers installed.");
                return;
            }

            // Create a monitor object with its own PC/SC context. 
            // The context will be released after monitor.Dispose()
            using (monitor = new SCardMonitor(new SCardContext(), SCardScope.System))
            {
                // Point the callback function(s) to the anonymous & static defined methods below.
                monitor.CardInserted += (sender, args0) => DisplayEvent("CardInserted", args0);
                //monitor.CardRemoved += (sender, args0) => DisplayEvent("CardRemoved", args0);
                //monitor.Initialized += (sender, args0) => DisplayEvent("Initialized", args0);
                //monitor.StatusChanged += StatusChanged;
                monitor.MonitorException += MonitorException;

                monitor.Start(readerNames);

                // Keep the window open
                //Console.ReadLine();
            }

            logger.InfoFormat("CardScannerService Started at {0}", DateTime.Now.ToLongTimeString());
        }


        //
        // Stop Service
        //

        protected override void OnStop()
        {
            logger.InfoFormat("CardScannerService Stopped at {0}", DateTime.Now.ToLongTimeString());
        }


        //
        // Execute timed event every hour and half hour
        //

        void OnTimedEvent(object source, ElapsedEventArgs e)
        {
            // Card scanner service entry point for timed event - any cleanup code can go here

        }

        private static void DisplayEvent(string eventName, CardStatusEventArgs unknown)
        {
            EventLog.WriteEntry("CardReaderService", ">> " + eventName + "v Event for Reader: " + unknown.ReaderName);
            EventLog.WriteEntry("CardReaderService", "ATR: " + BitConverter.ToString(unknown.Atr ?? new byte[0]));
            EventLog.WriteEntry("CardReaderService", "State: " + unknown.State);


            //Not firing
        }

        private static void StatusChanged(object sender, StatusChangeEventArgs args)
        {
            //Console.WriteLine(">> StatusChanged Event for reader: {0}", args.ReaderName);
            //Console.WriteLine("ATR: {0}", BitConverter.ToString(args.Atr ?? new byte[0]));
            //Console.WriteLine("Last state: {0}\nNew state: {1}\n", args.LastState, args.NewState);
        }

        private static void MonitorException(object sender, PCSCException ex)
        {
            EventLog.WriteEntry("CardReaderService", "Monitor exited due an error:");
            EventLog.WriteEntry("CardReaderService", SCardHelper.StringifyError(ex.SCardError));
        }
    }
}

      

I removed the actual database logic as it works fine, I believe it crashes when trying to either free the context variable or connect the monitor to smart cards.

It also needs to be pointed out that I tried to change the service from using the local system account to use the local service if it was some kind of access permission error.

If anyone can shed some light on where I am going, I would really appreciate some help. I'm relatively new to working with PC / SC and seem to hit a brick wall with this project at the moment.

UPDATE

Now I have solved the problem; it turns out that Windows services don't like using operators. Variables are placed at the end of a block, and therefore the context is invalidated.

Usage blocks were commented out and variable declarations were made in their place. The new code for the OnStart method is as follows:

protected override void OnStart(string[] args)
        {
            logger = LogManager.GetLogger(this.GetType().Name);
            aTimer = new System.Timers.Timer();
            aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            aTimer.Interval = (1000 * 60 * 60 * 24); // Once a day; 1000ms * 60s * 60m * 24h
            aTimer.Enabled = true;

            // Entry point

            //using (context = new SCardContext())
            //{
                context = new SCardContext();
                context.Establish(SCardScope.System);
                readerNames = context.GetReaders();
                context.Release();
            //}

            if (readerNames == null || readerNames.Length == 0)
            {
                EventLog.WriteEntry("CardReaderService", "There are currently no readers installed.");
                return;
            }

            // Create a monitor object with its own PC/SC context. 
            // The context will be released after monitor.Dispose()
            //using (monitor = new SCardMonitor(new SCardContext(), SCardScope.System))
            //{
                monitor = new SCardMonitor(new SCardContext(), SCardScope.System);
                // Point the callback function(s) to the anonymous & static defined methods below.
                monitor.CardInserted += (sender, args0) => DisplayEvent("CardInserted", args0);
                //monitor.CardRemoved += (sender, args0) => DisplayEvent("CardRemoved", args0);
                //monitor.Initialized += (sender, args0) => DisplayEvent("Initialized", args0);
                //monitor.StatusChanged += StatusChanged;
                monitor.MonitorException += MonitorException;

                monitor.Start(readerNames);

                // Keep the window open
                //Console.ReadLine();
            //}

            logger.InfoFormat("CardScannerService Started at {0}", DateTime.Now.ToLongTimeString());
        }

      

Hope this information helps someone else.

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1 answer


I was able to resolve the issue - the question has been updated to reflect the changes.



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