ServerSentEventsClient.cs

using System;
using System.IO;
using System.Net;
using System.Text;
using System.Collections.Generic;


public class SSEvent {
    public string Name { get; set; }
    public string Data { get; set; }
}


public class Application {
    public static List<string> Queue = new List<string>(1024);


    public static void Main() {
        Console.Write("Hello World\n");
        Console.Write("Attempting to open stream\n");

        var response = Application.OpenSSEStream("https://api.spark.io/v1/events?access_token=<YOUR_ACCESS_TOKEN>");
        Console.Write("Success! \n");
    }


     public static Stream OpenSSEStream(string url) {
        /*
            Optionally ignore certificate errors
            ServicePointManager.ServerCertificateValidationCallback =
             new System.Net.Security.RemoteCertificateValidationCallback(AcceptAllCertifications);
        */


        var request = WebRequest.Create( new Uri(url));
        ((HttpWebRequest)request).AllowReadStreamBuffering = false;
        var response = request.GetResponse();
        var stream = response.GetResponseStream();

        Application.ReadStreamForever(stream);

        return stream;
    }

    public static void ReadStreamForever(Stream stream) {
        var encoder = new UTF8Encoding();
        var buffer = new byte[2048];
        while(true) {
            //TODO: Better evented handling of the response stream

            if (stream.CanRead) {
                int len = stream.Read(buffer, 0, 2048);
                if (len > 0) {
                    var text = encoder.GetString(buffer, 0, len);
                    Application.Push(text);
                }
            }
            //System.Threading.Thread.Sleep(250);
        }
    }

   public static void Push(string text) {
        if (String.IsNullOrWhiteSpace(text)) {
            return;
        }

        var lines = text.Trim().Split('\n');
        Application.Queue.AddRange(lines);

        if (text.Contains("data:")) {
            Application.ProcessLines();
        }
    }

    public static void ProcessLines() {
        var lines = Application.Queue;

        SSEvent lastEvent = null;
        int index = 0;
        int lastEventIdx = -1;

        for(int i=0;i<lines.Count;i++) {
            var line = lines[i];
            if (String.IsNullOrWhiteSpace(line)) {
                continue;
            }
            line = line.Trim();

            if (line.StartsWith("event:")) {
                    lastEvent = new SSEvent() {
                    Name = line.Replace("event:", String.Empty)
                };
            }
            else if (line.StartsWith("data:")) {
                if (lastEvent == null) {
                    continue;
                }


                lastEvent.Data = line.Replace("data:", String.Empty);

                Console.WriteLine("Found event: " + index);
                Console.WriteLine("Name was: " + lastEvent.Name);
                Console.WriteLine("Data was: " + lastEvent.Data);
                index++;
                lastEventIdx = i;
            }
        }
        //trim previously processed events
        if (lastEventIdx >= 0) {
            lines.RemoveRange(0, lastEventIdx); 
        }
        

    }

    /*
        Optionally ignore certificate errors

    */
    public bool AcceptALlCertifications(object sender,
        System.Security.Cryptography.X509Certificates.X509Certificate cert,
        System.Security.Cryptography.X509Certificates.X509Chain chain,
        System.Net.Security.SslPolicyErrors errors)
    {
        return true;
    }
}

Please can you also share the server side code.
thanks.

Thank you. I've been searching for 2 days for a sse c# client, and got sidetracked by signal r, and a lot of sse server examples.

Thanks! And I'd like to know how does it make any difference between using stream.Read and stream.ReadAsync

Probably worth using an async version if you can, this was just a very very basic example from quite a long time ago