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Observer pattern using gRPC - C#

Sorry, if this is a stupid question but I don't find any useful information in the internet.
Has anyone ever tried to implement the observer pattern in C# using gRPC as communication?
If yes, please show me the link.
Many thanks in advance and best regards.

I have implemented a client convenience class wrapper to turn server streaming calls into regular events for a project I am working. Not sure if this is what you are after. Here is a simple gRPC server that just publishes the time as a string once every second.
syntax = "proto3";
package SimpleTime;
service SimpleTimeService
{
rpc MonitorTime(EmptyRequest) returns (stream TimeResponse);
}
message EmptyRequest{}
message TimeResponse
{
string time = 1;
}
The server implementation, which just loops once a second returning the string representation of the current time until canceled, is as follows
public override async Task MonitorTime(EmptyRequest request, IServerStreamWriter<TimeResponse> responseStream, ServerCallContext context)
{
try
{
while (!context.CancellationToken.IsCancellationRequested)
{
var response = new TimeResponse
{
Time = DateTime.Now.ToString()
};
await responseStream.WriteAsync(response);
await Task.Delay(1000);
}
}
catch (Exception)
{
Console.WriteLine("Exception on Server");
}
}
For the client, I created a class that contains the gRPC client and exposes the results of the server streaming MonitorTime call as a plain ole .net event.
public class SimpleTimeEventClient
{
private SimpleTime.SimpleTimeService.SimpleTimeServiceClient mClient = null;
private CancellationTokenSource mCancellationTokenSource = null;
private Task mMonitorTask = null;
public event EventHandler<string> OnTimeReceived;
public SimpleTimeEventClient()
{
Channel channel = new Channel("127.0.0.1:50051", ChannelCredentials.Insecure);
mClient = new SimpleTime.SimpleTimeService.SimpleTimeServiceClient(channel);
}
public void Startup()
{
mCancellationTokenSource = new CancellationTokenSource();
mMonitorTask = Task.Run(() => MonitorTimeServer(mCancellationTokenSource.Token));
}
public void Shutdown()
{
mCancellationTokenSource.Cancel();
mMonitorTask.Wait(10000);
}
private async Task MonitorTimeServer(CancellationToken token)
{
try
{
using (var call = mClient.MonitorTime(new SimpleTime.EmptyRequest()))
{
while(await call.ResponseStream.MoveNext(token))
{
var timeResult = call.ResponseStream.Current;
OnTimeReceived?.Invoke(this, timeResult.Time);
}
}
}
catch(Exception e)
{
Console.WriteLine($"Exception encountered in MonitorTimeServer:{e.Message}");
}
}
}
Now create the client and subscribe to the event.
static void Main(string[] args)
{
SimpleTimeEventClient client = new SimpleTimeEventClient();
client.OnTimeReceived += OnTimeReceivedEventHandler;
client.Startup();
Console.WriteLine("Press any key to exit");
Console.ReadKey();
client.Shutdown();
}
private static void OnTimeReceivedEventHandler(object sender, string e)
{
Console.WriteLine($"Time: {e}");
}
Which when run produces
I have left out a lot of error checking and such to make the example smaller. One thing I have done is for gRPC interfaces with many server streaming calls that may or may not be of interest to call clients, is to implement the event accessor (add,remove) to only call the server side streaming method if there is a client that has subscribed to the wrapped event. Hope this is helpful

ASP.NET Identity Phone Number Token lifespan and SMS limit

I'm building 2 factor registration API using ASP.NET Identity 2.0.
I'd like to give users ability to confirm their phone numer on demand, so even if they didn't confirm they're phone number when registering they always can request new token (making request to my API) that will be send via SMS and enter it on page (also making request to my API).
In method that is responsible for sending token I'm generating token and sending it as shown below:
var token = await UserManager.GeneratePhoneConfirmationTokenAsync(user.Id);
var message = new SmsMessage
{
Id = token,
Recipient = user.PhoneNumber,
Body = string.Format("Your token: {0}", token)
};
await UserManager.SmsService.SendAsync(message);
and inside UserManager:
public virtual async Task<string> GeneratePhoneConfirmationTokenAsync(TKey userId)
{
var number = await GetPhoneNumberAsync(userId);
return await GenerateChangePhoneNumberTokenAsync(userId, number);
}
Each time I call my method I get SMS message that contains token, problem is user can call that metod unlimited number of times and easily can generate costs - each SMS = cost.
I'd like to limit number of requests user can do to that method to one every X minutes.
Also I noticed that when I do multiple requests I get same token, I've tested my method and it looks that this token is valid for 3 minutes, so if I do request in that minutes time window I'll get same token.
Ideally I'd like to have single parameter that would allow me to specify time interval between requests and phone confirmation token lifespan.
I've tried setting token lifespan inside UserManager class using:
appUserManager.UserTokenProvider = new DataProtectorTokenProvider<User,int>(dataProtectionProvider.Create("ASP.NET Identity"))
{
TokenLifespan = new TimeSpan(0,2,0)//2 minutes
};
but this only affects tokens in email confirmation links.
Do I need to add extra field to my user table that will hold token validity date and check it every time I want to generate and send new token or is there easier way?
How can I specify time interval in which ASP.NET Identity will generate same phone number confirmation token?

I'm no expert but i had the same question and found these two threads with a little help from google.
https://forums.asp.net/t/2001843.aspx?Identity+2+0+Two+factor+authentication+using+both+email+and+sms+timeout
https://github.com/aspnet/Identity/issues/465
I'm going to assume you are correct that the default time limit is 3minutes based on the AspNet Identity github discussion.
Hopefully the linked discussions contain the answers you need to configure a new time limit.
Regarding the rate limiting i'm using the following code which is loosely based on this discussions How do I implement rate limiting in an ASP.NET MVC site?
class RateLimitCacheEntry
{
public int RequestsLeft;
public DateTime ExpirationDate;
}
/// <summary>
/// Partially based on
/// https://stackoverflow.com/questions/3082084/how-do-i-implement-rate-limiting-in-an-asp-net-mvc-site
/// </summary>
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public class RateLimitAttribute : ActionFilterAttribute
{
private static Logger Log = LogManager.GetCurrentClassLogger();
/// <summary>
/// Window to monitor <see cref="RequestCount"/>
/// </summary>
public int Seconds { get; set; }
/// <summary>
/// Maximum amount of requests to allow within the given window of <see cref="Seconds"/>
/// </summary>
public int RequestCount { get; set; }
/// <summary>
/// ctor
/// </summary>
public RateLimitAttribute(int s, int r)
{
Seconds = s;
RequestCount = r;
}
public override void OnActionExecuting(HttpActionContext actionContext)
{
try
{
var clientIP = RequestHelper.GetClientIp(actionContext.Request);
// Using the IP Address here as part of the key but you could modify
// and use the username if you are going to limit only authenticated users
// filterContext.HttpContext.User.Identity.Name
var key = string.Format("{0}-{1}-{2}",
actionContext.ActionDescriptor.ControllerDescriptor.ControllerName,
actionContext.ActionDescriptor.ActionName,
clientIP
);
var allowExecute = false;
var cacheEntry = (RateLimitCacheEntry)HttpRuntime.Cache[key];
if (cacheEntry == null)
{
var expirationDate = DateTime.Now.AddSeconds(Seconds);
HttpRuntime.Cache.Add(key,
new RateLimitCacheEntry
{
ExpirationDate = expirationDate,
RequestsLeft = RequestCount,
},
null,
expirationDate,
Cache.NoSlidingExpiration,
CacheItemPriority.Low,
null);
allowExecute = true;
}
else
{
// Allow and decrement
if (cacheEntry.RequestsLeft > 0)
{
HttpRuntime.Cache.Insert(key,
new RateLimitCacheEntry
{
ExpirationDate = cacheEntry.ExpirationDate,
RequestsLeft = cacheEntry.RequestsLeft - 1,
},
null,
cacheEntry.ExpirationDate,
Cache.NoSlidingExpiration,
CacheItemPriority.Low,
null);
allowExecute = true;
}
}
if (!allowExecute)
{
Log.Error("RateLimited request from " + clientIP + " to " + actionContext.Request.RequestUri);
actionContext.Response
= actionContext.Request.CreateResponse(
(HttpStatusCode)429,
string.Format("You can call this {0} time[s] every {1} seconds", RequestCount, Seconds)
);
}
}
catch(Exception ex)
{
Log.Error(ex, "Error in filter attribute");
throw;
}
}
}
public static class RequestHelper
{
/// <summary>
/// Retrieves the client ip address from request
/// </summary>
public static string GetClientIp(HttpRequestMessage request)
{
if (request.Properties.ContainsKey("MS_HttpContext"))
{
return ((HttpContextWrapper)request.Properties["MS_HttpContext"]).Request.UserHostAddress;
}
if (request.Properties.ContainsKey(RemoteEndpointMessageProperty.Name))
{
RemoteEndpointMessageProperty prop;
prop = (RemoteEndpointMessageProperty)request.Properties[RemoteEndpointMessageProperty.Name];
return prop.Address;
}
return null;
}
}
I've also seen this library recommended a few times:
https://github.com/stefanprodan/WebApiThrottle

Registering device on Azure Notification Hub from ASP.NET

I want to make use of Azure notification hub service. In all their examples. The clients directly register with azure to give the service their device token.
I want to change this model slightly in order to gain central control and also due to compatibility with existing clients.
I want all my clients to register with GCM or APNS and obtain their Token. I then want to send that token off to my own api. ASP.NET Web API. The api will then fire off a request to the Azure notification service and register on behalf of the device.
Can I achieve this? and how would I go about registering a device from the asp.net api.
In their Documentation examples it contains code to send the actual push notifications from an asp.net app. But not how to register a device (being of any type) from asp.net
Unless im being daft and missing something...

You can find this in the official documentation: Registering from your App Backend.
public class RegisterController : ApiController
{
private NotificationHubClient hub;
public RegisterController()
{
hub = NotificationHubClient.CreateClientFromConnectionString("Endpoint=sb://buildhub-ns.servicebus.windows.net/;SharedAccessKeyName=DefaultFullSharedAccessSignature;SharedAccessKey=DuWV4SQ08poV6HZly8O/KQNWv3YRTZlExJxu3pNCjGU=", "build2014_2");
}
public class DeviceRegistration
{
public string Platform { get; set; }
public string Handle { get; set; }
public string[] Tags { get; set; }
}
// POST api/register
// This creates a registration id
public async Task<string> Post()
{
return await hub.CreateRegistrationIdAsync();
}
// PUT api/register/5
// This creates or updates a registration (with provided PNS handle) at the specified id
public async void Put(string id, DeviceRegistration deviceUpdate)
{
// IMPORTANT: add logic to make sure that caller is allowed to register for the provided tags
RegistrationDescription registration = null;
switch (deviceUpdate.Platform)
{
case "mpns":
registration = new MpnsRegistrationDescription(deviceUpdate.Handle);
break;
case "wns":
registration = new WindowsRegistrationDescription(deviceUpdate.Handle);
break;
case "apns":
registration = new AppleRegistrationDescription(deviceUpdate.Handle);
break;
case "gcm":
registration = new GcmRegistrationDescription(deviceUpdate.Handle);
break;
default:
throw new HttpResponseException(HttpStatusCode.BadRequest);
}
registration.RegistrationId = id;
registration.Tags = new HashSet<string>(deviceUpdate.Tags);
try
{
await hub.CreateOrUpdateRegistrationAsync(registration);
} catch (MessagingException e) {
ReturnGoneIfHubResponseIsGone(e);
}
}
// DELETE api/register/5
public async void Delete(string id)
{
await hub.DeleteRegistrationAsync(id);
}
private static void ReturnGoneIfHubResponseIsGone(MessagingException e)
{
var webex = e.InnerException as WebException;
if (webex.Status == WebExceptionStatus.ProtocolError)
{
var response = (HttpWebResponse)webex.Response;
if (response.StatusCode == HttpStatusCode.Gone)
throw new HttpRequestException(HttpStatusCode.Gone.ToString());
}
}
}

Connecting Silverlight client to SignalR server

I've been driving myself nuts trying to resolve this issue so really hoping someone has some insight.
I have a console application which runs/hosts my signalR server.
I have already successfully connected to it using a web(javascript) client and a windows forms client with no trouble at all.
BUT for the life of me I cannot get a silverlight client to connect to it. Initially I was getting a
'System.Security.SecurityException' occurred in Microsoft.Threading.Tasks error
on
await Connection.Start();
I managed to fix that by force sending the clientaccesspolicy file using code i found on a random thread.
THREAD
However the connection still never establishes. The status goes thru connecting, disconnected, connection closed.
I am at my wits end as to why this won't work. Any input is appreciated. Code below.
MainPage.xaml.cs
public partial class MainPage : UserControl
{
private SignalRClient client;
public MainPage()
{
InitializeComponent();
dataGrid1.ItemsSource = new ItemsCollection();
client = new SignalRClient();
client.RunAsync();
Debug.WriteLine("Init Done");
}
}
-
SignalRClient.cs
public class SignalRClient
{
private HubConnection Connection { get; set; }
private IHubProxy HubProxy { get; set; }
const string url = "http://localhost:8080/";
public SignalRClient()
{
}
public async void RunAsync()
{
Connection = new HubConnection(url, useDefaultUrl: true);
Connection.Closed += Connection_Closed;
Connection.StateChanged += ConnectionDidSomething;
HubProxy = Connection.CreateHubProxy("TickerHub");
HubProxy.On<string>("receiveAllData", data => Debug.WriteLine("RECDATA={0}", data));
try
{
await Connection.Start();
}
catch (HttpClientException e)
{
Debug.WriteLine("Unable to connect to server.1 {0}", e.Message);
return;
}
catch (HttpRequestException e)
{
Debug.WriteLine("Unable to connect to server.2 {0}", e.Message);
return;
}
}
-
Server
class Program
{
static void Main(string[] args)
{
string url = "http://localhost:8080/";
using (WebApp.Start(url))
{
Console.WriteLine("SignalR server running on {0}", url);
Console.ReadLine();
}
Console.ReadLine();
}
}
class Startup
{
public void Configuration(IAppBuilder app)
{
Console.WriteLine("Configuration");
//Tried this approach too
/*app.Map("/signalr", map =>
{
map.UseCors(CorsOptions.AllowAll);
var hubConfiguration = new HubConfiguration
{
EnableJSONP = true
};
map.RunSignalR(hubConfiguration);
});*/
app.UseCors(CorsOptions.AllowAll);
app.MapSignalR<ClientAccessPolicyConnection>("/clientaccesspolicy.xml");
}
}
-
TickerHub.cs
public class TickerHub : Hub
{
public override Task OnConnected()
{
string connectionID = Context.ConnectionId;
Console.WriteLine("New Connection:" + connectionID);
InitNewClient(connectionID);
return base.OnConnected();
}
//send all data to newly connected client
public void InitNewClient(string connectionID)
{
}
//client requested all data
public void GetAllData()
{
Console.WriteLine("Get Data Triggered");
Clients.All.receiveAllData("TESTING123");
}
}

I figured it out! Hopefully this helps someone in the future.
Its quite simple. This is what you need to have in your startup class configuration method.
Below that is the code required to send the clientaccesspolicy.xml.
class Startup
{
public void Configuration(IAppBuilder app)
{
// Branch the pipeline here for requests that start with "/signalr"
app.Map("/signalr", map =>
{
// Setup the CORS middleware to run before SignalR.
// By default this will allow all origins. You can
// configure the set of origins and/or http verbs by
// providing a cors options with a different policy.
map.UseCors(CorsOptions.AllowAll);
var hubConfiguration = new HubConfiguration
{
// You can enable JSONP by uncommenting line below.
// JSONP requests are insecure but some older browsers (and some
// versions of IE) require JSONP to work cross domain
EnableJSONP = true
};
// Run the SignalR pipeline. We're not using MapSignalR
// since this branch already runs under the "/signalr"
// path.
map.RunSignalR(hubConfiguration);
});
app.UseCors(CorsOptions.AllowAll);
app.MapSignalR<ClientAccessPolicyConnection>("/clientaccesspolicy.xml");
}
}
-
public class ClientAccessPolicyConnection : PersistentConnection
{
public override Task ProcessRequest(Microsoft.AspNet.SignalR.Hosting.HostContext context)
{
string[] urlArray = context.Request.Url.ToString().Split('/');
string path = urlArray[urlArray.Length - 1];
if (path.Equals("clientaccesspolicy.xml", StringComparison.InvariantCultureIgnoreCase))
{
//Convert policy to byteArray
var array = Encoding.UTF8.GetBytes(ClientAccessPolicy);
var segment = new ArraySegment<byte>(array);
//Write response
context.Response.ContentType = "text/xml";
context.Response.Write(segment);
//Return empty task to escape from SignalR's default Connection/Transport checks.
return EmptyTask;
}
return EmptyTask;
}
private static readonly Task EmptyTask = MakeTask<object>(null);
public static Task<T> MakeTask<T>(T value)
{
var tcs = new TaskCompletionSource<T>();
tcs.SetResult(value);
return tcs.Task;
}
public static readonly string ClientAccessPolicy =
"<?xml version=\"1.0\" encoding=\"utf-8\"?>"
+ "<access-policy>"
+ "<cross-domain-access>"
+ "<policy>"
+ "<allow-from http-request-headers=\"*\">"
+ "<domain uri=\"*\"/>"
+ "</allow-from>"
+ "<grant-to>"
+ "<resource path=\"/\" include-subpaths=\"true\"/>"
+ "</grant-to>"
+ "</policy>"
+ "</cross-domain-access>"
+ "</access-policy>";
}

How to obtain connection ID of signalR client on the server side?

I need to get the connection ID of a client. I know you can get it from the client side using $.connection.hub.id. What I need is to get in while in a web service I have which updates records in a database, in turn displaying the update on a web page. I am new to signalR and stackoverflow, so any advice would be appreciated. On my client web page I have this:
<script type="text/javascript">
$(function () {
// Declare a proxy to reference the hub.
var notify = $.connection.notificationHub;
// Create a function that the hub can call to broadcast messages.
notify.client.broadcastMessage = function (message) {
var encodedMsg = $('<div />').text(message).html();// Html encode display message.
$('#notificationMessageDisplay').append(encodedMsg);// Add the message to the page.
};//end broadcastMessage
// Start the connection.
$.connection.hub.start().done(function () {
$('#btnUpdate').click(function () {
//call showNotification method on hub
notify.server.showNotification($.connection.hub.id, "TEST status");
});
});
});//End Main function
</script>
everything works up until I want to update the page using signalR. The show notification function in my hub is this:
//hub function
public void showNotification(string connectionId, string newStatus){
IHubContext context = GlobalHost.ConnectionManager.GetHubContext<notificationHub>();
string connection = "Your connection ID is : " + connectionId;//display for testing
string statusUpdate = "The current status of your request is: " + newStatus;//to be displayed
//for testing, you can display the connectionId in the broadcast message
context.Clients.Client(connectionId).broadcastMessage(connection + " " + statusUpdate);
}//end show notification
how can I send the connectionid to my web service?
Hopefully I'm not trying to do something impossible.

When a client invokes a function on the server side you can retrieve their connection ID via Context.ConnectionId. Now, if you'd like to access that connection Id via a mechanism outside of a hub, you could:
Just have the Hub invoke your external method passing in the connection id.
Manage a list of connected clients aka like public static ConcurrentDictionary<string, MyUserType>... by adding to the dictionary in OnConnected and removing from it in OnDisconnected. Once you have your list of users you can then query it via your external mechanism.
Ex 1:
public class MyHub : Hub
{
public void AHubMethod(string message)
{
MyExternalSingleton.InvokeAMethod(Context.ConnectionId); // Send the current clients connection id to your external service
}
}
Ex 2:
public class MyHub : Hub
{
public static ConcurrentDictionary<string, MyUserType> MyUsers = new ConcurrentDictionary<string, MyUserType>();
public override Task OnConnected()
{
MyUsers.TryAdd(Context.ConnectionId, new MyUserType() { ConnectionId = Context.ConnectionId });
return base.OnConnected();
}
public override Task OnDisconnected(bool stopCalled)
{
MyUserType garbage;
MyUsers.TryRemove(Context.ConnectionId, out garbage);
return base.OnDisconnected(stopCalled);
}
public void PushData(){
//Values is copy-on-read but Clients.Clients expects IList, hence ToList()
Clients.Clients(MyUsers.Keys.ToList()).ClientBoundEvent(data);
}
}
public class MyUserType
{
public string ConnectionId { get; set; }
// Can have whatever you want here
}
// Your external procedure then has access to all users via MyHub.MyUsers
Hope this helps!

Taylor's answer works, however, it doesn't take into consideration a situation where a user has multiple web browser tabs opened and therefore has multiple different connection IDs.
To fix that, I created a Concurrent Dictionary where the dictionary key is a user name and the value for each key is a List of current connections for that given user.
public static ConcurrentDictionary<string, List<string>> ConnectedUsers = new ConcurrentDictionary<string, List<string>>();
On Connected - Adding a connection to the global cache dictionary:
public override Task OnConnected()
{
Trace.TraceInformation("MapHub started. ID: {0}", Context.ConnectionId);
var userName = "testUserName1"; // or get it from Context.User.Identity.Name;
// Try to get a List of existing user connections from the cache
List<string> existingUserConnectionIds;
ConnectedUsers.TryGetValue(userName, out existingUserConnectionIds);
// happens on the very first connection from the user
if(existingUserConnectionIds == null)
{
existingUserConnectionIds = new List<string>();
}
// First add to a List of existing user connections (i.e. multiple web browser tabs)
existingUserConnectionIds.Add(Context.ConnectionId);
// Add to the global dictionary of connected users
ConnectedUsers.TryAdd(userName, existingUserConnectionIds);
return base.OnConnected();
}
On disconnecting (closing the tab) - Removing a connection from the global cache dictionary:
public override Task OnDisconnected(bool stopCalled)
{
var userName = Context.User.Identity.Name;
List<string> existingUserConnectionIds;
ConnectedUsers.TryGetValue(userName, out existingUserConnectionIds);
// remove the connection id from the List
existingUserConnectionIds.Remove(Context.ConnectionId);
// If there are no connection ids in the List, delete the user from the global cache (ConnectedUsers).
if(existingUserConnectionIds.Count == 0)
{
// if there are no connections for the user,
// just delete the userName key from the ConnectedUsers concurent dictionary
List<string> garbage; // to be collected by the Garbage Collector
ConnectedUsers.TryRemove(userName, out garbage);
}
return base.OnDisconnected(stopCalled);
}

I beg to differ on the reconnect. The client remains in the list but the connectid will change. I do an update to the static list on reconnects to resolve this.

As Matthew C is not completely thread safe in situation of one user request multiple connection at same time, I used this code:
public static Dictionary<string, List<string>> ConnectedUsers = new ();
public override Task OnConnected()
{
var connectionId = Context.ConnectionId;
var userId = Context.User.Identity.Name; // any desired user id
lock(ConnectedUsers)
{
if (!ConnectedUsers.ContainsKey(userId))
ConnectedUsers[userId] = new();
ConnectedUsers[userId].Add(connectionId);
}
}
public override Task OnDisconnected(bool stopCalled)
{
var connectionId = Context.ConnectionId;
var userId = Context.User.Identity.Name; // any desired user id
lock (ConnectedUsers)
{
if (ConnectedUsers.ContainsKey(userId))
{
ConnectedUsers[userId].Remove(connectionId);
if (ConnectedUsers[userId].Count == 0)
ConnectedUsers.Remove(userId);
}
}
}