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C# Grpc System.InvalidOperationException: 'Cannot write message after request is complete.'

At runtime I get the following error:
System.InvalidOperationException: 'Cannot write message after request
is complete.'
I'm using Grpc and reactive X to get data.
public class SensorService: Protos.Vehicule.VehiculeBase
{
private readonly ILogger<SensorService> _logger;
private DataProvider _dataProvider;
private CarSim.Vehicule _vehicule;
public SensorService(ILogger<SensorService> logger)
{
_dataProvider = new DataProvider(new CarSim.Vehicule());
_vehicule = _dataProvider.getVehicule();
_logger = logger;
_dataProvider.Start();
}
public System.IObserver<CarSim.Vehicule> GetData { get; private set; }
public override async Task Status(All request, IServerStreamWriter<StatusVehicule> responseStream, ServerCallContext context)
{
while (!context.CancellationToken.IsCancellationRequested)
{
_vehicule.VehiculeChangedState.Subscribe(onNext: new Action<CarSim.Vehicule>(async (t) =>
{
await responseStream.WriteAsync(new StatusVehicule()
{
Camera = t.Camera,
FuelLevel = t.FuelLevel,
GunStatus = true,
Light = t.Light,
OilLevel = t.OilLevel,
Peed = t.Speed,
Tempature = t.Tempature
}
);
; }));
}
}
}

This is likely not a bug. The exception means that you're trying to send a response after the RPC has actually finished. Usually this happens when the RPC deadline is exceeded (at which point the RPC is automatically cancelled) or when it was cancelled by the client. Both of these situations can happen at any time (from the server side handler's perspective) and they are basically an inherent race condition (the RPC could have been cancelled just before you decide to send the response).
The exception is just gRPC's way of informing you that the response could not be sent (and there is really no way to send a response AFTER the RPC has finished).

You must register SensorService in your gRpc Server code:
like this:
app.UseEndpoints(endpoints => { endpoints.MapGrpcService<SensorService >(); .....

I have found a solution that works. But i still have the same error.
public override async Task Status(All request, IServerStreamWriter<StatusVehicule> responseStream, ServerCallContext context){
try
{
var eventLoop = new EventLoopScheduler();
await _vehicule.VehiculeChangedState.ObserveOn(eventLoop).ForEachAsync<CarSim.Vehicule>(t =>
{
try
{
responseStream.WriteAsync(new StatusVehicule()
{
Camera = t.Camera,
FuelLevel = t.FuelLevel,
GunStatus = true,
Light = t.Light,
OilLevel = t.OilLevel,
Peed = t.Speed,
Status = t.GetState().ToString(),
StatusDoors = t.StatusDoors.ToString(),
Tempature = t.Tempature
}
).Wait();
}
catch (Exception)
{
// ignored
}
},
context.CancellationToken);
}
catch (Exception e)
{
_logger.LogError(e.Message);
}
}

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

SignalrR HubConnection disregards query parameter

I want to allow my users connect to a specific group in my SignalR hub, to do this i generate a unique id that the users in that group can share with others. Once a user connects to the hub, the id is generated. On the "connected" event their URL updates with the unique id. When I then use the URL to join the newly created room it seems like two negotiation requests are sent, both containing the the group id as well as the users connection id, yet sometimes(not always) I get a response from the Hub containing a newly generated Group.
Is the ?pod parameter I pass into the url not always assigned before the request is made?
To me it seems completely random, but it's most likely some error I've made in my connection code since I'm relatively new to Angular.
This request happened correctly and I joined the room I wanted.
Correct behavior
This one happened incorrectly and a new room was generated even though, seemingly(?), the request looks the same, save for the web socket connection containing the "pid".
Incorrect behavior
Any help is greatly appreciated!
The code for the Home component where the connection is initiated
export class HomeComponent implements OnInit, OnDestroy{
welcomeMessage:string;
podId:string;
users:User[];
constructor(private signalrService: SignalRService, private http: HttpClient, private activeRoute: ActivatedRoute,
private router: Router, private location: Location) {}
ngOnInit() {
this.activeRoute.queryParams.subscribe(params => {
this.podId = params['pod'];
this.connectToPod();
});
}
ngOnDestroy(): void {
}
connectToPod(){
this.signalrService.startConnection(this.podId);
this.signalrService.addPodConnectedLisener((data: Pod) => {
this.podId = data.id;
this.users = data.users;
this.location.replaceState('/?pod=' + this.podId)
this.welcomeMessage = window.location.origin + '/?pod=' + this.podId;
});
}
}
The code for the SignalR service
export class SignalRService {
private hubConnection: signalR.HubConnection;
private baseUrl = environment.apiUrl;
constructor() { }
public startConnection (podId?: string) {
let idToSend = podId == undefined ? '' : '?pid=' + podId;
this.hubConnection = new signalR.HubConnectionBuilder()
.withUrl(this.baseUrl + '/pod' + idToSend)
.build();
this.hubConnection
.start()
.then(() => console.log('Connection started'))
.catch(err => console.log('Error while starting connection: ' + err));
}
public addPodConnectedLisener (connectedCallback: Function) {
return this.hubConnection.on('connected', data => {
connectedCallback(data);
});
}
}
The code for the SignalR Hub
public class PodHub : Hub
{
private readonly IPodConnectionManger _podConnectionManager;
public PodHub(IPodConnectionManger podConnectionManager)
{
_podConnectionManager = podConnectionManager;
}
public override async Task OnConnectedAsync()
{
var podId = Context.GetHttpContext().Request.Query["pid"].ToString();
if (string.IsNullOrEmpty(podId))
{
await CreatePod();
}
else
{
await JoinPod(podId);
}
}
private async Task CreatePod()
{
var newPodId = await _podConnectionManager.AddPod();
var podToSend = await _podConnectionManager.GetPod(newPodId);
await podToSend.AddUser(Context.ConnectionId);
await Groups.AddToGroupAsync(Context.ConnectionId, podToSend.Id);
await Clients.Group(podToSend.Id).SendAsync("connected", podToSend);
}
private async Task JoinPod(string id)
{
var podToJoin = await _podConnectionManager.GetPod(id);
await podToJoin.AddUser(Context.ConnectionId);
await Groups.AddToGroupAsync(Context.ConnectionId, podToJoin.Id);
await Clients.Group(podToJoin.Id).SendAsync("connected", podToJoin);
}
}

Sockets, Nullreference Exception

I am trying to use web socket with my bot to communicate with the server. But on run time it throws the System.NullReferenceException. I am running socket in background on a different thread so that it does not interfear with the bot.
I am using WebsocketSharp library.
First message comes in just fine but on second message it throws exception at following line in HumanCollaboratorDialog class.
await context.PostAsync(e.Data);
My Socket Stream Class is as following:
public static class SocketStream
{
public static WebSocket ws;
private static List<string> serverMsg = new List<string>();
public static void initializeSocket()
{
ws = new WebSocket("ws://Some IP:8080/human-collaborator/data");
Debug.WriteLine("****** INITIALIZED SOCKET (should happen only once) *****");
Task.Run(() => startSocketStream());
}
private static void startSocketStream()
{
int attempts = 0;
while (!ws.IsAlive)
{
try
{
attempts++;
ws.Connect();
}
catch (WebSocketException)
{
Debug.WriteLine("Connection attempts: " + attempts.ToString());
}
}
ws.OnOpen += (sender, args) =>
{
Debug.WriteLine("# SOCKET OPENED");
};
ws.OnError += (sender, args) =>
{
Debug.WriteLine("# SOME ERROR OCCURED");
};
ws.OnClose += (sender, args) =>
{
Debug.WriteLine("# SOCKET CLOSED");
};
}
}
I am calling the initializeSocket() method in Global.asx to run it on application level
public class WebApiApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
GlobalConfiguration.Configure(WebApiConfig.Register);
SocketStream.initializeSocket();
}
}
My HumanCollaboratorDialog class is as following:
[Serializable]
public class HumanCollaboratorDialog : IDialog<object>
{
public async Task StartAsync(IDialogContext context)
{
context.Wait(this.MessageReceivedAsync);
}
private async Task MessageReceivedAsync(IDialogContext context, IAwaitable<IMessageActivity> result)
{
var message = await result;
SocketStream.ws.OnMessage += async (sender, e) =>
{
try
{
await context.PostAsync(e.Data);
}
catch (HttpRequestException ex)
{
throw ex;
}
};
Thread.Sleep(500);
string output = message.Text;
SocketStream.ws.Send(output);
Thread.Sleep(500);
context.Wait(MessageReceivedAsync);
}
}
My MessagesController has following POST method:
public virtual async Task<HttpResponseMessage> Post([FromBody]Activity activity)
{
if (activity.Type == ActivityTypes.Message)
{
await Conversation.SendAsync(activity, () => new HumanCollaboratorDialog());
}
else
{
HandleSystemMessage(activity);
}
var response = Request.CreateResponse(HttpStatusCode.OK);
return response;
}
Neithet e.Data nor context is empty. I think problem is with socket connection or may be i am doing something wrong in SocketStream class. following is the image

Your bot is a web service. Messages are sent to the service by the client (a web page, an application, another service, etc.) and received in the MessagesController's Post method. There's no need to have the socket code on the server for what you're trying to do. Web Sockets are useful for receiving messages on a client from the bot via a Direct Line connection.
Here is an example of using the Bot Framework's Direct Line Client and creating a web socket connection. Notice how the web socket is created from a conversation's StreamUrl:
DirectLineClientCredentials creds = new DirectLineClientCredentials(directLineSecret);
DirectLineClient directLineClient = new DirectLineClient(creds);
Conversation conversation = await directLineClient.Conversations.StartConversationAsync();
using (var webSocketClient = new WebSocket(conversation.StreamUrl))
{
webSocketClient.OnMessage += WebSocketClient_OnMessage;
webSocketClient.Connect();
while (true)
{
string input = Console.ReadLine().Trim();
if (input.ToLower() == "exit")
{
break;
}
else
{
if (input.Length > 0)
{
Activity userMessage = new Activity
{
From = new ChannelAccount(fromUser),
Text = input,
Type = ActivityTypes.Message
};
await directLineClient.Conversations.PostActivityAsync(conversation.ConversationId, userMessage);
}
}
}
}
private static void WebSocketClient_OnMessage(object sender, MessageEventArgs e)
{
// avoid null reference exception when no data received
if (string.IsNullOrWhiteSpace(e.Data))
{
return;
}
var activitySet = JsonConvert.DeserializeObject<ActivitySet>(e.Data);
var activities = from x in activitySet.Activities
where x.From.Id == botId
select x;
foreach (Activity activity in activities)
{
Console.WriteLine(activity.Text);
}
}
This is from a console application that is using the Direct Line to communicate with the Bot and is listening for messages using web sockets here:
https://github.com/Microsoft/BotBuilder-Samples/tree/master/CSharp/core-DirectLineWebSockets

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>";
}