C# class that reads RFID cards and inserts each new read into a local MongoDB store. Reads are then pushed to a RESTful web service in a background task.

EventLog.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading.Tasks;
using System.Windows.Forms;

using RFIDeas_pcProxAPI;
using System.Net;
using System.Threading;
using System.IO;
using Newtonsoft.Json;

namespace Node {

    public partial class EventLog : Form {

        // Local cache task list
        private List<Task> activeTasks = new List<Task>();

        // Database polling task
        private Task dbPollingTask;

        // Cancellation Token
        private CancellationTokenSource databasePollCancel = new CancellationTokenSource();

        // Event grid and last card tracking by reader ID
        private BindingList<EventData> eventDataGrid = new BindingList<EventData>();
        private static Dictionary<short, String> lastCardIDbyDeviceID = new Dictionary<short, String>();

        // Tap metrics
        private int tapsRecorded = 0;
        private int tapsSentToWeb = 0;
        private int tapsDuplicate = 0;

        // Set of devices that was present during last polling cycle.
        HashSet<short> lastPolledDevices = new HashSet<short>();

        public EventLog() {
            InitializeComponent();

            loadConfig();

            // Only search for USB prox readers
            pcProxDLLAPI.SetConnectProduct( pcProxDLLAPI.PRODUCT_PCPROX );
            pcProxDLLAPI.SetDevTypeSrch( pcProxDLLAPI.PRXDEVTYP_USB );

            // See what's out there
            RefreshDevices();

            // Start the read timer. Hardware limits polling to no less than 250ms between reads.
            readProxTimer.Start();

            dataGridView1.DataSource = eventDataGrid;

            // If enabled, start polling our local database for items that need to be pushed to web services.
            if ( chkWebEnabled.Checked ) {
                startDatabasePolling();
            }
        }

        private void RefreshDevices() {

            // Disconnect, reconnect, and update our visible device count.
            pcProxDLLAPI.USBDisconnect();

            if ( pcProxDLLAPI.usbConnect() == 1 ) {
                txtDeviceCount.Text = pcProxDLLAPI.GetDevCnt().ToString();
            }
            else {
                txtDeviceCount.Text = 0.ToString();
            }
        }

        private void EventLog_FormClosing( object sender, FormClosingEventArgs e ) {
            // Shut down all active tasks gracefully.
            readProxTimer.Stop();
            stopDatabasePolling();
            saveConfig();
            Task.WaitAll( activeTasks.ToArray() );
        }

        private void loadConfig() {
            txtUrl.Text = Properties.Settings.Default.WebServicesURL;
            txtEventID.Text = Properties.Settings.Default.WebServicesEventID;
            chkWebEnabled.Checked = Properties.Settings.Default.WebServicesEnabled;
        }

        private void saveConfig() {
            Properties.Settings.Default.WebServicesURL = txtUrl.Text;
            Properties.Settings.Default.WebServicesEventID = txtEventID.Text;
            Properties.Settings.Default.WebServicesEnabled = chkWebEnabled.Checked;
            Properties.Settings.Default.Save();
        }

        private void startDatabasePolling() {
            // Start a task that polls the database and posts to the web service
            dbPollingTask = Task.Factory.StartNew( async () =>  // <- marked async
            {
                while ( true ) {

                    foreach ( EventData data in Mongo.GetLocalEvents() ) {

                        try {
                            // Update event ID
                            data.EventID = txtEventID.Text;

                            // Serialize to JSON
                            string json = JsonConvert.SerializeObject( data );

                            // HTTP POST to the web service
                            HttpWebRequest http = WebRequest.CreateHttp( txtUrl.Text );

                            http.Accept = "application/json";
                            http.ContentType = "application/json";
                            http.Method = "POST";
                            http.ContentLength = json.Length;
                            http.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";

                            using ( var writer = new StreamWriter( http.GetRequestStream() ) ) {
                                writer.Write( json );
                                writer.Close();
                            }

                            HttpWebResponse response = null;

                            try {
                                response = (HttpWebResponse) http.GetResponse();

                                // If we get this far, the web post went fine.  Update the local database
                                data.SentToWeb = true;

                            }
                            catch ( WebException ex ) {
                                if ( ( (HttpWebResponse) ex.Response ).StatusCode == HttpStatusCode.Conflict ) {
                                    // Succeeded, but the server has identified this record as a duplicate.
                                    data.SentToWeb = true;
                                    Interlocked.Increment( ref this.tapsDuplicate );
                                }
                            }
                            finally {
                                if ( response != null ) {
                                    response.Close();
                                }
                            }

                            // Check if we need to update/save the local record.
                            if ( data.SentToWeb == true ) {
                                Mongo.UpdateEvent( data );
                                Interlocked.Increment( ref this.tapsSentToWeb );
                            }
                        }
                        catch {
                            // No matter what happens, keep trying to send.
                        }
                    }

                    await Task.Delay( 250, databasePollCancel.Token ); // <- await with cancellation
                }
            }, databasePollCancel.Token );
        }

        private void stopDatabasePolling() {

            if ( dbPollingTask != null ) {

                // Cancel the Polling
                databasePollCancel.Cancel();

                // Wait for the task to complete
                try {
                    dbPollingTask.Wait();
                }
                catch ( AggregateException ) {
                    // Task cancelled successfully
                }
            }
        }

        private void ReportPlugStatusChanges( ref HashSet<short> polledDevices ) {

            // current devices - previous devices = new devices
            HashSet<short> newDevices = new HashSet<short>( polledDevices );
            newDevices.ExceptWith( lastPolledDevices );

            foreach ( short newLUID in newDevices ) {
                HipChat.SendInfo( String.Format( "Reader #{0} attached.", newLUID ) );
            }

            // previous devices - current devices = removed devices
            HashSet<short> removedDevices = new HashSet<short>( lastPolledDevices );
            removedDevices.ExceptWith( polledDevices );

            foreach ( short newLUID in removedDevices ) {
                HipChat.SendError( String.Format( "Reader #{0} unplugged.", newLUID ) );
            }

            // Done reporting, current data becomes previous data.
            lastPolledDevices = polledDevices;
        }

        private void readProxTimer_Tick( object sender, EventArgs e ) {

            readProxTimer.Stop();

            HashSet<short> polledDevices = new HashSet<short>();

            for ( short devIdx = 0; devIdx < pcProxDLLAPI.GetDevCnt(); devIdx++ ) {

                if ( pcProxDLLAPI.SetActDev( devIdx ) != 0 ) {
                    // Device is valid, try to read a card
                    String newCardID = pcProxDLLAPI.getCardID();
                    short readerID = pcProxDLLAPI.GetLUID();

                    // Add this reader's LUID to our hash of polled devices.
                    polledDevices.Add( readerID );

                    // Initialize the last card ID if it's not already present
                    if ( !lastCardIDbyDeviceID.ContainsKey( readerID ) ) {
                        lastCardIDbyDeviceID[readerID] = "";
                    }

                    if ( newCardID != lastCardIDbyDeviceID[readerID] ) {
                        if ( newCardID != "" ) {

                            // Create the EventData object and add it to our log
                            EventData data = new EventData( newCardID, readerID );
                            eventDataGrid.Add( data );

                            // Only maintain the last 50 events
                            if ( eventDataGrid.Count > 50 ) {
                                eventDataGrid.RemoveAt( 0 );
                            }

                            // Create a new task for the actual database write. i.e. do it in another thread.
                            activeTasks.Add( Task.Factory.StartNew( () => {
                                // Add to the local database
                                Mongo.AddEvent( data );
                                Interlocked.Increment( ref tapsRecorded );
                            } ) );
                        }

                        // Update our saved card ID
                        lastCardIDbyDeviceID[readerID] = newCardID;
                    }
                }
            }

            statusLabel.Text = String.Format( "Recorded {0} / {1} Sent / {2} Duplicates", this.tapsRecorded, this.tapsSentToWeb, this.tapsDuplicate );

            ReportPlugStatusChanges( ref polledDevices );

            RefreshDevices();

            readProxTimer.Start();
        }

        private void chkWebEnabled_CheckedChanged( object sender, EventArgs e ) {
            txtEventID.Enabled = txtUrl.Enabled = !chkWebEnabled.Checked;

            if ( chkWebEnabled.Checked ) {
                startDatabasePolling();
            }
            else {
                stopDatabasePolling();
            }
        }

        private void status_DoubleClick( object sender, EventArgs e ) {
            // Clear metrics
            Interlocked.Exchange( ref tapsSentToWeb, 0 );
            Interlocked.Exchange( ref tapsRecorded, 0 );
            Interlocked.Exchange( ref tapsDuplicate, 0 );
        }
    }
}

Hi Scott,
May I ask how did you add the pcProxAPI dll to C#? I'm having trouble with that, it says:
A reference to 'pcProxAPI.dll' could not be added. Please make sure that the file is accessible, and that it is a valid assembly or COM component.
Thanks!

Hi Infiniium,

Did you managed to get this? Thanks!

Joie

Same here, how do you add the dll?

Ok, you don't add the dll "as reference" as usual in visual studio, and you need a wrapper for the api dll. Check this out https://github.com/imbenjamin/RadioTrackLineside/blob/master/RadioTrack_ReaderClient/RFIDeas_pcProxAPI.cs

String newCardID = pcProxDLLAPI.getCardID();
The wrapper did not define this, is there a different wrapper for this?

Mr. Vitale, can you post the RFIDeas_pcProxAPI.cs.
TIA

never mind, you must be having tight pockets