How to pass some data through signalR header or query string in .net core 2.0 app

Question

Using signalR in .net 4.7 we were able to pass two variables from the client application to signalR server. Here is the code snippet:

public class MyHub : Hub
{
    protected (string myVar1, string myVar2) GetValues() =>
            (
            Context.QueryString["MyVariable1"] ?? string.Empty,
            Context.QueryString["MyVariable2"] ?? string.Empty,
            );
}

The javascript client would set these variables as follows:

$.connection.hub.qs = {'MyVariable1' : 'val1', 'MyVariable2' : 'val2'};

Now, we are trying to migrate to the alpha release of signalR for .net core 2.0 applications. The blocker is that we can no longer use this method to obtain myVar1 and myVar2 values. Not only QueryString is unavailable but also headers. What is the best way to overcome this situation to be able to pass variables from client app (Typescript) or even .net core app to signalR server side? Also - how do you set variables on client side?

Answer 1

Late joining in this thread. The only way I could get this mechanism to work in .net core 2.2 was by:

#1 Adding two Nuget packages

<ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Http.Connections" Version="1.1.0" />
    <PackageReference Include="Microsoft.AspNetCore.Http.Features" Version="2.2.0" />
</ItemGroup>

#2 Then in our methods pe OnConnectedAsync():

    public override Task OnConnectedAsync()
    {
        var httpContext = Context.GetHttpContext();
        if (httpContext == null)
            throw new Exception("...");

        var query = httpContext.Request.Query;
        var userId = query.GetQueryParameterValue<long>("Foo");
        var clientId = query.GetQueryParameterValue<string>("Bar");
        var connectionId = Context.ConnectionId;

        [...]

        return base.OnConnectedAsync();
    }

#3 Also introduced some handy SignalR extensions:

    static public class SignalrExtensions
    {
       static public HttpContext GetHttpContext(this HubCallerContext context) =>
          context
            ?.Features
            .Select(x => x.Value as IHttpContextFeature)
            .FirstOrDefault(x => x != null)
            ?.HttpContext;

       static public T GetQueryParameterValue<T>(this IQueryCollection httpQuery, string queryParameterName) =>
          httpQuery.TryGetValue(queryParameterName, out var value) && value.Any()
            ? (T) Convert.ChangeType(value.FirstOrDefault(), typeof(T))
            : default;
    }

Hope this helps.

Answer 2

You can access the HttpContext in your hub like this:

var httpContext = Context.Connection.GetHttpContext();

and then use httpContext.Request.Query["MyVariable"] to get the variable value

Edit for ASPNetCore 2.1 and later

GetHttpContext() extension method is directly accessible on Context object

using Microsoft.AspNetCore.Http.Connections;
....
var httpContext = Context.GetHttpContext();