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Blazor SignalR Create a List for all clients but only update it once

I just worked my way through this MS Learn Tutorial regarding SignalR in Blazor.
At the end of the tutorial, you get a program that can have multiple clients hooked up to a "ChatHub" to send and receive messages, like a "Townsquare-Chatroom"
While testing I realized, that if you send some messages and afterward create a new client, the new client does not display the previously send messages. This is because every client stores its received messages locally as shown here:
#code{
// ...
private List<string> messages = new();
// ...
}
I decided to implement such a feature.
To do so, I created ChatLog.cs which is supposed to log the messages for all clients instead of saving them inside of each individual client:
public class ChatLog
{
private List<string> _messages= new List<string>();
public List<string> Messages
{
get { return _messages; }
set
{
_messages = value;
}
}
}
Of course, I also had to make some changes inside of index.razor to make things work:
I added a new service in program.cs as singleton
==> Program.cs
// ...
builder.Services.AddSingleton<ChatLog>();
// ...
and injected ChatLog into my index.razor
==> Index.razor
// ...
#inject ChatLog ChatLogger
// ...
I changed the code in index.razor #code to add the messages to ChatLog.Messages instead of the "local" messages-List
protected override async Task OnInitializedAsync()
{
// Change
if(ChatLogger.Messages is null)
{
ChatLogger.Messages = new();
}
hubConnection = new HubConnectionBuilder()
.WithUrl(NavManager.ToAbsoluteUri("/chathub"))
.WithAutomaticReconnect()
.Build();
hubConnection.On<string, string>("ReceiveMessage", (user, message) =>
{
var formattedMessage = $"{user}: {message}";
// Change
ChatLogger.Messages.Add(formattedMessage);
InvokeAsync(StateHasChanged);
});
await hubConnection.StartAsync();
}
Now I run into a new problem.
Since the event
hubConnection.On<string, string>...
is called by every client, and all new messages get added into ChatLog.Messages X-times (x == amount of active clients).
I just can't think of a way to avoid this problem and only log every message exactly once.
Can someone help me?
Thanks in advance and sorry for the long explanation. Maybe someone can also help shorten it?
EDIT
To clarify the problem: Since the messages get added to the messages List inside of the event (as shown above), every instance (or every tab of the website) adds the message, resulting in multiple (and unwanted) adds.
E.g.
Two clients
Message "Hello" was sent once but added twice
Message "Ciao" was sent twice but added four times

From what I can gather this is more a learning exercise than something you're actually planning on using in a production environment, so we can ignore the fact that this isn't really a very robust implementation.
In any case, a simply solution would be to have the sender of the message store it in the messagelog, instead of storing it upon reception.
Taking from the tutorial you followed:
using Microsoft.AspNetCore.SignalR;
namespace BlazorServerSignalRApp.Server.Hubs
{
public class ChatHub : Hub
{
public async Task SendMessage(string user, string message)
{
// STORE YOUR MESSAGE IN YOUR MESSAGE LOG HERE
await Clients.All.SendAsync("ReceiveMessage", user, message);
}
}
}
You should be able to inject your MessageLog service into the ChatHub in order to access it from there. (If I'm understanding your project structure correctly)

MassTransit custom Query/Command topology for Request/Response mechanism

I'm currently reworking a microservices-based solution into a modular monolith with four APIs (pro, cyclist, management, thirdparty). One of the changes that need to be done is adapting the topology of our broker (RabbitMQ) so it fits our requirements. These requirements are shown on the diagram below.
The idea is that we currently always use the Request/Response mechanism for all our commands and queries and Publish mechanism for events, meaning that we always expect a response, whenever issuing a query (obviously) or a command.
We want the topology to support scaling in a way that if API1 (any instance of this executable) has multiple instances
commands/queries issued by any instance of the API1 will be executed by the consumers running in any instance of the API1 - this means that if both API1 and API2 executables have the same consumer, API2 consumers cannot execute commands/queries issued by the API2
when scaling, queues for commands and queries should not be scaled, just new consumers will be added and round robin should fire up
events are always received by all registered consumers so when scaling new queues are created
Right now I'm trying to figure out how to create this topology in MassTransit but I can't seem to get rid of the default publish exchange of type fanout. Here's the code that I use for automatic registration of command/queries endpoints and queues
private static IRabbitMqBusFactoryConfigurator AddNonEventConsumer<TConsumer>(
IRabbitMqBusFactoryConfigurator config,
IRegistration context)
where TConsumer : class, IConsumer
{
var routingKey = Assembly.GetEntryAssembly().GetName().Name;
var messageType = typeof(TConsumer)
.GetInterfaces()
?.First(i => i.IsGenericType)
?.GetGenericArguments()
?.First();
if (messageType == null)
{
throw new InvalidOperationException(
$"Message type could not be extracted from the consumer type. ConsumerTypeName=[{typeof(TConsumer).Name}]");
}
config.ReceiveEndpoint(e =>
{
// var exchangeName = new StringBuilder(messageType.FullName)
// .Replace($".{messageType.Name}", string.Empty)
// .Append($":{messageType.Name}")
// .ToString();
var exchangeName = messageType.FullName;
e.ConfigureConsumeTopology = false;
e.ExchangeType = ExchangeType.Direct;
e.Consumer<TConsumer>(context);
e.Bind(exchangeName, b =>
{
e.ExchangeType = ExchangeType.Direct;
b.RoutingKey = routingKey;
});
});
config.Send<TestCommand>(c =>
{
c.UseRoutingKeyFormatter(x => routingKey);
});
config.Publish<TestCommand>(c =>
{
c.ExchangeType = ExchangeType.Direct;
});
return config;
}
Again, we do want to use Request/Response mechanism for queries/commands and Publish mechanism for events (events are not a part of this question, it's a topic on its own, just queries/commands).
The question is - how do I configure endpoints and queues in this method in order to achieve the desired topology?
Alternative question - how else can I achieve my goal?

Cyclist? Pro? What kind of modular monolith is this anyway??
You're almost there, but need to configure a couple of additional items. First, when publishing, you'll need to set the routing key, which can be done using a routing key formatter. Also, configure the message type to use a direct exchange.
configurator.Send<TestCommand>(x =>
{
x.UseRoutingKeyFormatter(context => /* something that gets your string, pro/cyclist */);
});
config.Publish<TestCommand>(c =>
{
c.ExchangeType = ExchangeType.Direct;
});
Also, if you're using custom exchange names, I'd add a custom entity name formatter. This will change the exchange names used for message types, so you can stick with message types in your application – keeping all the magic string stuff in one place.
class CustomEntityNameFormatter :
IEntityNameFormatter
{
public string FormatEntityName<T>()
where T : class
{
return new StringBuilder(typeof(T).FullName)
.Replace($".{typeof(T).Name}", string.Empty)
.Append($":{typeof(T).Name}")
.ToString();
}
}
config.MessageTopology
.SetEntityNameFormatter(new CustomEntityNameFormatter());
Then, when configuring your receive endpoint, do not change the endpoint's exchange type, only the bound exchange to match the publish topology. Using an endpoint name formatter, custom for you application, you can configure it manually as shown.
var routingKey = Assembly.GetEntryAssembly().GetName().Name;
var endpointNameFormatter = new CustomEndpointNameFormatter();
config.ReceiveEndpoint(endpointNameFormatter.Message<TMessage>(), e =>
{
e.ConfigureConsumeTopology = false;
e.Bind<TMessage>(b =>
{
e.ExchangeType = ExchangeType.Direct;
b.RoutingKey = routingKey;
});
e.Consumer<TConsumer>(context);
});
This is just a rough sample to get your started. There is a direct exchange sample on GitHub that you can look at as well to see how various things are done in there. You could likely clean up the message type detection as well to avoid having to do all the type based reflection stuff, but that's more complex.

ASP.NET Core - Identify if Request is Local [duplicate]

In the regular ASP.NET you could do this in a view to determine if the current request was from localhost:
HttpContext.Current.Request.IsLocal
But I can't find something similar in ASP.NET 6/Core/whatever it is meant to be called.

UPDATE: ASP.NET Core 2.0 has a method called Url.IsLocalUrl (see this Microsoft Docs).
I think this code will work, but I haven't been able to test it completely
var callingUrl = Request.Headers["Referer"].ToString();
var isLocal = Url.IsLocalUrl(callingUrl);
But see Will Dean's comment below about this approach:
Anyone thinking about using the 'updated' version which checks the Referrer header should bear in mind that headers are extremely easy to spoof, to a degree that doesn't apply to loopback IP addresses.
Original solution
I came across this looking for a solution to knowing if a request is local. Unfortunately ASP.NET version 1.1.0 does not have a IsLocal method on a connection. I found one solution on a web site called Strathweb but that is out of date too.
I have created my own IsLocal extension, and it seems to work, but I can't say I have tested it in all circumstances, but you are welcome to try it.
public static class IsLocalExtension
{
private const string NullIpAddress = "::1";
public static bool IsLocal(this HttpRequest req)
{
var connection = req.HttpContext.Connection;
if (connection.RemoteIpAddress.IsSet())
{
//We have a remote address set up
return connection.LocalIpAddress.IsSet()
//Is local is same as remote, then we are local
? connection.RemoteIpAddress.Equals(connection.LocalIpAddress)
//else we are remote if the remote IP address is not a loopback address
: IPAddress.IsLoopback(connection.RemoteIpAddress);
}
return true;
}
private static bool IsSet(this IPAddress address)
{
return address != null && address.ToString() != NullIpAddress;
}
}
You call it in a controller action from using the Request property, i.e.
public IActionResult YourAction()
{
var isLocal = Request.IsLocal();
//... your code here
}
I hope that helps someone.

At the time of writing HttpContext.Connection.IsLocal is now missing from .NET Core.
Other working solution checks only for a first loopback address (::1 or 127.0.0.1) which might not be adequate.
I find the solution below useful:
using Microsoft.AspNetCore.Http;
using System.Net;
namespace ApiHelpers.Filters
{
public static class HttpContextFilters
{
public static bool IsLocalRequest(HttpContext context)
{
if (context.Connection.RemoteIpAddress.Equals(context.Connection.LocalIpAddress))
{
return true;
}
if (IPAddress.IsLoopback(context.Connection.RemoteIpAddress))
{
return true;
}
return false;
}
}
}
And the example use case:
app.UseWhen(HttpContextFilters.IsLocalRequest, configuration => configuration.UseElmPage());

None of the above worked for me.
Url.IsLocalUrl works very different and I find it a bit useless:
For example, the following URLs are considered local:
/Views/Default/Index.html
~/Index.html
The following URLs are non-local:
../Index.html
http://www.contoso.com/
http://localhost/Index.html
HttpContext.Connection.IsLocal doesn't exist in .Net Core 2.2
Comparing ControllerContext.HttpContext.Connection.RemoteIpAddress and ControllerContext.HttpContext.Connection.LocalIpAddress also doesn't work in my test because I get "::1" for remote ip and "127.0.0.1" for local ip.
Finally, I used this piece:
IPAddress addr = System.Net.IPAddress.Parse( HttpContext.Connection.RemoteIpAddress.ToString() );
if (System.Net.IPAddress.IsLoopback(addr) )
{
//do something
}

Late to the party, but if I want to check IsLocal in razor views in .Net core 2.2+, I just do this:
#if (Context.Request.Host.Value.StartsWith("localhost"))
{
//do local stuff
}

UPDATE for ASP.NET Core 3.1
You can use this:
if (Request.Host.Host == "localhost") {// do something }

I would also mention that it may be useful to add the below clause to the end of your custom IsLocal() check
if (connection.RemoteIpAddress == null && connection.LocalIpAddress == null)
{
return true;
}
This would account for the scenario where the site is being ran using the Microsoft.AspNetCore.TestHost and the site is being ran entirely locally in memory without an actual TCP/IP connection.

now its
HttpContext.Connection.IsLocal
and if you need to check that outside of a controller then you take a dependency on IHttpContextAccessor to get access to it.
Update based on comment:
HttpContext is intrinsically available in Views
#if (Context.Connection.IsLocal)
{
}

SignalR server --> client call not working

I'm currently using SignalR to communicate between a server and multiple separate processes spawned by the server itself.
Both Server & Client are coded in C#. I'm using SignalR 2.2.0.0
On the server side, I use OWIN to run the server.
I am also using LightInject as an IoC container.
Here is my code:
public class AgentManagementStartup
{
public void ConfigurationOwin(IAppBuilder app, IAgentManagerDataStore dataStore)
{
var serializer = new JsonSerializer
{
PreserveReferencesHandling = PreserveReferencesHandling.Objects,
TypeNameHandling = TypeNameHandling.Auto,
TypeNameAssemblyFormat = FormatterAssemblyStyle.Simple
};
var container = new ServiceContainer();
container.RegisterInstance(dataStore);
container.RegisterInstance(serializer);
container.Register<EventHub>();
container.Register<ManagementHub>();
var config = container.EnableSignalR();
app.MapSignalR("", config);
}
}
On the client side, I register this way:
public async Task Connect()
{
try
{
m_hubConnection = new HubConnection(m_serverUrl, false);
m_hubConnection.Closed += OnConnectionClosed;
m_hubConnection.TraceLevel = TraceLevels.All;
m_hubConnection.TraceWriter = Console.Out;
var serializer = m_hubConnection.JsonSerializer;
serializer.TypeNameHandling = TypeNameHandling.Auto;
serializer.PreserveReferencesHandling = PreserveReferencesHandling.Objects;
m_managementHubProxy = m_hubConnection.CreateHubProxy(AgentConstants.ManagementHub.Name);
m_managementHubProxy.On("closeRequested", CloseRequestedCallback);
await m_hubConnection.Start();
}
catch (Exception e)
{
m_logger.Error("Exception encountered in Connect method", e);
}
}
On the server side I send a close request the following way:
var managementHub = GlobalHost.ConnectionManager.GetHubContext<ManagementHub>();
managementHub.Clients.All.closeRequested();
I never receive any callback in CloseRequestedCallback. Neither on the Client side nor on the server side I get any errors in the logs.
What did I do wrong here ?
EDIT 09/10/15
After some research and modifications, I found out it was linked with the replacement of the IoC container. When I removed everything linked to LightInject and used SignalR as is, everything worked. I was surprised about this since LightInject documented their integration with SignalR.
After I found this, I realised that the GlobalHost.DependencyResolver was not the same as the one I was supplying to the HubConfiguration. Once I added
GlobalHost.DependencyResolver = config.Resolver;
before
app.MapSignalR("", config);
I am now receiving callbacks within CloseRequestedCallback. Unfortunately, I get the following error as soon as I call a method from the Client to the Server:
Microsoft.AspNet.SignalR.Client.Infrastructure.SlowCallbackException
Possible deadlock detected. A callback registered with "HubProxy.On"
or "Connection.Received" has been executing for at least 10 seconds.
I am not sure about the fix I found and what impact it could have on the system. Is it OK to replace the GlobalHost.DependencyResolver with my own without registering all of its default content ?
EDIT 2 09/10/15
According to this, changing the GlobalHost.DependencyResolver is the right thing to do. Still left with no explanation for the SlowCallbackException since I do nothing in all my callbacks (yet).

Issue 1: IoC Container + Dependency Injection
If you want to change the IoC for you HubConfiguration, you also need to change the one from the GlobalHost so that returns the same hub when requesting it ouside of context.
Issue 2: Unexpected SlowCallbackException
This exception was caused by the fact that I was using SignalR within a Console Application. The entry point of the app cannot be an async method so to be able to call my initial configuration asynchronously I did as follow:
private static int Main()
{
var t = InitAsync();
t.Wait();
return t.Result;
}
Unfortunately for me, this causes a lot of issues as described here & more in details here.
By starting my InitAsync as follow:
private static int Main()
{
Task.Factory.StartNew(async ()=> await InitAsync());
m_waitInitCompletedRequest.WaitOne(TimeSpan.FromSeconds(30));
return (int)EndpointErrorCode.Ended;
}
Everything now runs fine and I don't get any deadlocks.
For more details on the issues & answers, you may also refer to the edits in my question.

C# WCF closing channels and using functions Func<T>

This is the point, I have a WCF service, it is working now. So I begin to work on the client side. And when the application was running, then an exception showed up: timeout. So I began to read, there are many examples about how to keep the connection alive, but, also I found that the best way, is create channel, use it, and dispose it. And honestly, I liked that. So, now reading about the best way to close the channel, there are two links that could be useful to anybody who needs them:
1. Clean up clients, the right way
2. Using Func
In the first link, this is the example:
IIdentityService _identitySvc;
...
if (_identitySvc != null)
{
((IClientChannel)_identitySvc).Close();
((IDisposable)_identitySvc).Dispose();
_identitySvc = null;
}
So, if the channel is not null, then is closed, disposed, and assign null. But I have a little question. In this example the channel has a .Close() method, but, in my case, intellisense is not showing a Close() method. It only exists in the factory object. So I believe I have to write it. But, in the interface that has the contracts or the class that implemets it??. And, what should be doing this method??.
Now, the next link, this has something I haven't try before. Func<T>. And after reading the goal, it's quite interesting. It creates a funcion that with lambdas creates the channel, uses it, closes it, and dipose it. This example implements that function like a Using() statement. It's really good, and a excellent improvement. But, I need a little help, to be honest, I can't understand the function, so, a little explanatino from an expert will be very useful. This is the function:
TReturn UseService<TChannel, TReturn>(Func<TChannel, TReturn> code)
{
var chanFactory = GetCachedFactory<TChannel>();
TChannel channel = chanFactory.CreateChannel();
bool error = true;
try {
TReturn result = code(channel);
((IClientChannel)channel).Close();
error = false;
return result;
}
finally {
if (error) {
((IClientChannel)channel).Abort();
}
}
}
And this is how is being used:
int a = 1;
int b = 2;
int sum = UseService((ICalculator calc) => calc.Add(a, b));
Console.WriteLine(sum);
Yep, I think is really, really good, I'd like to understand it to use it in the project I have.
And, like always, I hope this could be helpful to a lot of people.

the UseService method accepts a delegate, which uses the channel to send request. The delegate has a parameter and a return value. You can put the call to WCF service in the delegate.
And in the UseService, it creates the channel and pass the channel to the delegate, which should be provided by you. After finishing the call, it closes the channel.

The proxy object implements more than just your contract - it also implements IClientChannel which allows control of the proxy lifetime
The code in the first example is not reliable - it will leak if the channel is already busted (e.g. the service has gone down in a session based interaction). As you can see in the second version, in the case of an error it calls Abort on the proxy which still cleans up the client side
You can also do this with an extension method as follows:
enum OnError
{
Throw,
DontThrow
}
static class ProxyExtensions
{
public static void CleanUp(this IClientChannel proxy, OnError errorBehavior)
{
try
{
proxy.Close();
}
catch
{
proxy.Abort();
if (errorBehavior == OnError.Throw)
{
throw;
}
}
}
}
However, the usage of this is a little cumbersome
((IClientChannel)proxy).CleanUp(OnError.DontThrow);
But you can make this more elegant if you make your own proxy interface that extends both your contract and IClientChannel
interface IPingProxy : IPing, IClientChannel
{
}

To answer the question left in the comment in Jason's answer, a simple example of GetCachedFactory may look like the below. The example looks up the endpoint to create by finding the endpoint in the config file with the "Contract" attribute equal to the ConfigurationName of the service the factory is to create.
ChannelFactory<T> GetCachedFactory<T>()
{
var endPointName = EndPointNameLookUp<T>();
return new ChannelFactory<T>(endPointName);
}
// Determines the name of the endpoint the factory will create by finding the endpoint in the config file which is the same as the type of the service the factory is to create
string EndPointNameLookUp<T>()
{
var contractName = LookUpContractName<T>();
foreach (ChannelEndpointElement serviceElement in ConfigFileEndPoints)
{
if (serviceElement.Contract == contractName) return serviceElement.Name;
}
return string.Empty;
}
// Retrieves the list of endpoints in the config file
ChannelEndpointElementCollection ConfigFileEndPoints
{
get
{
return ServiceModelSectionGroup.GetSectionGroup(
ConfigurationManager.OpenExeConfiguration(
ConfigurationUserLevel.None)).Client.Endpoints;
}
}
// Retrieves the ConfigurationName of the service being created by the factory
string LookUpContractName<T>()
{
var attributeNamedArguments = typeof (T).GetCustomAttributesData()
.Select(x => x.NamedArguments.SingleOrDefault(ConfigurationNameQuery));
var contractName = attributeNamedArguments.Single(ConfigurationNameQuery).TypedValue.Value.ToString();
return contractName;
}
Func<CustomAttributeNamedArgument, bool> ConfigurationNameQuery
{
get { return x => x.MemberInfo != null && x.MemberInfo.Name == "ConfigurationName"; }
}
A better solution though is to let an IoC container manage the creation of the client for you. For example, using autofac it would like the following. First you need to register the service like so:
var builder = new ContainerBuilder();
builder.Register(c => new ChannelFactory<ICalculator>("WSHttpBinding_ICalculator"))
.SingleInstance();
builder.Register(c => c.Resolve<ChannelFactory<ICalculator>>().CreateChannel())
.UseWcfSafeRelease();
container = builder.Build();
Where "WSHttpBinding_ICalculator" is the name of the endpoint in the config file. Then later you can use the service like so:
using (var lifetime = container.BeginLifetimeScope())
{
var calc = lifetime.Resolve<IContentService>();
var sum = calc.Add(a, b);
Console.WriteLine(sum);
}