ASP.NET SignalR Hubs API Guide - Server (SignalR 1.x)
by Patrick Fletcher, Tom Dykstra
Warning
This documentation isn't for the latest version of SignalR. Take a look at ASP.NET Core SignalR.
This document provides an introduction to programming the server side of the ASP.NET SignalR Hubs API for SignalR version 1.1, with code samples demonstrating common options.
The SignalR Hubs API enables you to make remote procedure calls (RPCs) from a server to connected clients and from clients to the server. In server code, you define methods that can be called by clients, and you call methods that run on the client. In client code, you define methods that can be called from the server, and you call methods that run on the server. SignalR takes care of all of the client-to-server plumbing for you.
SignalR also offers a lower-level API called Persistent Connections. For an introduction to SignalR, Hubs, and Persistent Connections, or for a tutorial that shows how to build a complete SignalR application, see SignalR - Getting Started.
Overview
This document contains the following sections:
How to register the SignalR route and configure SignalR options
How to define methods in the Hub class that clients can call
How to get information about the client from the Context property
How to call client methods and manage groups from outside the Hub class
For documentation on how to program clients, see the following resources:
Links to API Reference topics are to the .NET 4.5 version of the API. If you're using .NET 4, see the .NET 4 version of the API topics.
How to register the SignalR route and configure SignalR options
To define the route that clients will use to connect to your Hub, call the MapHubs method when the application starts. MapHubs
is an extension method for the System.Web.Routing.RouteCollection
class. The following example shows how to define the SignalR Hubs route in the Global.asax file.
using System.Web.Routing;
public class Global : System.Web.HttpApplication
{
protected void Application_Start(object sender, EventArgs e)
{
RouteTable.Routes.MapHubs();
}
}
If you are adding SignalR functionality to an ASP.NET MVC application, make sure that the SignalR route is added before the other routes. For more information, see Tutorial: Getting Started with SignalR and MVC 4.
The /signalr URL
By default, the route URL which clients will use to connect to your Hub is "/signalr". (Don't confuse this URL with the "/signalr/hubs" URL, which is for the automatically generated JavaScript file. For more information about the generated proxy, see SignalR Hubs API Guide - JavaScript Client - The generated proxy and what it does for you.)
There might be extraordinary circumstances that make this base URL not usable for SignalR; for example, you have a folder in your project named signalr and you don't want to change the name. In that case, you can change the base URL, as shown in the following examples (replace "/signalr" in the sample code with your desired URL).
Server code that specifies the URL
RouteTable.Routes.MapHubs("/signalr", new HubConfiguration());
JavaScript client code that specifies the URL (with the generated proxy)
$.connection.hub.url = "/signalr"
$.connection.hub.start().done(init);
JavaScript client code that specifies the URL (without the generated proxy)
var connection = $.hubConnection("/signalr", { useDefaultPath: false });
.NET client code that specifies the URL
var hubConnection = new HubConnection("http://contoso.com/signalr", useDefaultUrl: false);
Configuring SignalR Options
Overloads of the MapHubs
method enable you to specify a custom URL, a custom dependency resolver, and the following options:
Enable cross-domain calls from browser clients.
Typically if the browser loads a page from
http://contoso.com
, the SignalR connection is in the same domain, athttp://contoso.com/signalr
. If the page fromhttp://contoso.com
makes a connection tohttp://fabrikam.com/signalr
, that is a cross-domain connection. For security reasons, cross-domain connections are disabled by default. For more information, see ASP.NET SignalR Hubs API Guide - JavaScript Client - How to establish a cross-domain connection.Enable detailed error messages.
When errors occur, the default behavior of SignalR is to send to clients a notification message without details about what happened. Sending detailed error information to clients is not recommended in production, because malicious users might be able to use the information in attacks against your application. For troubleshooting, you can use this option to temporarily enable more informative error reporting.
Disable automatically generated JavaScript proxy files.
By default, a JavaScript file with proxies for your Hub classes is generated in response to the URL "/signalr/hubs". If you don't want to use the JavaScript proxies, or if you want to generate this file manually and refer to a physical file in your clients, you can use this option to disable proxy generation. For more information, see SignalR Hubs API Guide - JavaScript Client - How to create a physical file for the SignalR generated proxy.
The following example shows how to specify the SignalR connection URL and these options in a call to the MapHubs
method. To specify a custom URL, replace "/signalr" in the example with the URL that you want to use.
var hubConfiguration = new HubConfiguration();
hubConfiguration.EnableCrossDomain = true;
hubConfiguration.EnableDetailedErrors = true;
hubConfiguration.EnableJavaScriptProxies = false;
RouteTable.Routes.MapHubs("/signalr", hubConfiguration);
How to create and use Hub classes
To create a Hub, create a class that derives from Microsoft.Aspnet.Signalr.Hub. The following example shows a simple Hub class for a chat application.
public class ContosoChatHub : Hub
{
public void NewContosoChatMessage(string name, string message)
{
Clients.All.addNewMessageToPage(name, message);
}
}
In this example, a connected client can call the NewContosoChatMessage
method, and when it does, the data received is broadcasted to all connected clients.
Hub object lifetime
You don't instantiate the Hub class or call its methods from your own code on the server; all that is done for you by the SignalR Hubs pipeline. SignalR creates a new instance of your Hub class each time it needs to handle a Hub operation such as when a client connects, disconnects, or makes a method call to the server.
Because instances of the Hub class are transient, you can't use them to maintain state from one method call to the next. Each time the server receives a method call from a client, a new instance of your Hub class processes the message. To maintain state through multiple connections and method calls, use some other method such as a database, or a static variable on the Hub class, or a different class that does not derive from Hub
. If you persist data in memory, using a method such as a static variable on the Hub class, the data will be lost when the app domain recycles.
If you want to send messages to clients from your own code that runs outside the Hub class, you can't do it by instantiating a Hub class instance, but you can do it by getting a reference to the SignalR context object for your Hub class. For more information, see How to call client methods and manage groups from outside the Hub class later in this topic.
Camel-casing of Hub names in JavaScript clients
By default, JavaScript clients refer to Hubs by using a camel-cased version of the class name. SignalR automatically makes this change so that JavaScript code can conform to JavaScript conventions. The previous example would be referred to as contosoChatHub
in JavaScript code.
Server
public class ContosoChatHub : Hub
JavaScript client using generated proxy
var contosoChatHubProxy = $.connection.contosoChatHub;
If you want to specify a different name for clients to use, add the HubName
attribute. When you use a HubName
attribute, there is no name change to camel case on JavaScript clients.
Server
[HubName("PascalCaseContosoChatHub")]
public class ContosoChatHub : Hub
JavaScript client using generated proxy
var contosoChatHubProxy = $.connection.PascalCaseContosoChatHub;
Multiple Hubs
You can define multiple Hub classes in an application. When you do that, the connection is shared but groups are separate:
All clients will use the same URL to establish a SignalR connection with your service ("/signalr" or your custom URL if you specified one), and that connection is used for all Hubs defined by the service.
There is no performance difference for multiple Hubs compared to defining all Hub functionality in a single class.
All Hubs get the same HTTP request information.
Since all Hubs share the same connection, the only HTTP request information that the server gets is what comes in the original HTTP request that establishes the SignalR connection. If you use the connection request to pass information from the client to the server by specifying a query string, you can't provide different query strings to different Hubs. All Hubs will receive the same information.
The generated JavaScript proxies file will contain proxies for all Hubs in one file.
For information about JavaScript proxies, see SignalR Hubs API Guide - JavaScript Client - The generated proxy and what it does for you.
Groups are defined within Hubs.
In SignalR you can define named groups to broadcast to subsets of connected clients. Groups are maintained separately for each Hub. For example, a group named "Administrators" would include one set of clients for your
ContosoChatHub
class, and the same group name would refer to a different set of clients for yourStockTickerHub
class.
How to define methods in the Hub class that clients can call
To expose a method on the Hub that you want to be callable from the client, declare a public method, as shown in the following examples.
public class ContosoChatHub : Hub
{
public void NewContosoChatMessage(string name, string message)
{
Clients.All.addNewMessageToPage(name, message);
}
}
public class StockTickerHub : Hub
{
public IEnumerable<Stock> GetAllStocks()
{
return _stockTicker.GetAllStocks();
}
}
You can specify a return type and parameters, including complex types and arrays, as you would in any C# method. Any data that you receive in parameters or return to the caller is communicated between the client and the server by using JSON, and SignalR handles the binding of complex objects and arrays of objects automatically.
Camel-casing of method names in JavaScript clients
By default, JavaScript clients refer to Hub methods by using a camel-cased version of the method name. SignalR automatically makes this change so that JavaScript code can conform to JavaScript conventions.
Server
public void NewContosoChatMessage(string userName, string message)
JavaScript client using generated proxy
contosoChatHubProxy.server.newContosoChatMessage($(userName, message);
If you want to specify a different name for clients to use, add the HubMethodName
attribute.
Server
[HubMethodName("PascalCaseNewContosoChatMessage")]
public void NewContosoChatMessage(string userName, string message)
JavaScript client using generated proxy
contosoChatHubProxy.server.PascalCaseNewContosoChatMessage(userName, message);
When to execute asynchronously
If the method will be long-running or has to do work that would involve waiting, such as a database lookup or a web service call, make the Hub method asynchronous by returning a Task (in place of void
return) or Task<T> object (in place of T
return type). When you return a Task
object from the method, SignalR waits for the Task
to complete, and then it sends the unwrapped result back to the client, so there is no difference in how you code the method call in the client.
Making a Hub method asynchronous avoids blocking the connection when it uses the WebSocket transport. When a Hub method executes synchronously and the transport is WebSocket, subsequent invocations of methods on the Hub from the same client are blocked until the Hub method completes.
The following example shows the same method coded to run synchronously or asynchronously, followed by JavaScript client code that works for calling either version.
Synchronous
public IEnumerable<Stock> GetAllStocks()
{
// Returns data from memory.
return _stockTicker.GetAllStocks();
}
Asynchronous - ASP.NET 4.5
public async Task<IEnumerable<Stock>> GetAllStocks()
{
// Returns data from a web service.
var uri = Util.getServiceUri("Stocks");
using (HttpClient httpClient = new HttpClient())
{
var response = await httpClient.GetAsync(uri);
return (await response.Content.ReadAsAsync<IEnumerable<Stock>>());
}
}
JavaScript client using generated proxy
stockTickerHubProxy.server.getAllStocks().done(function (stocks) {
$.each(stocks, function () {
alert(this.Symbol + ' ' + this.Price);
});
});
For more information about how to use asynchronous methods in ASP.NET 4.5, see Using Asynchronous Methods in ASP.NET MVC 4.
Defining Overloads
If you want to define overloads for a method, the number of parameters in each overload must be different. If you differentiate an overload just by specifying different parameter types, your Hub class will compile but the SignalR service will throw an exception at run time when clients try to call one of the overloads.
How to call client methods from the Hub class
To call client methods from the server, use the Clients
property in a method in your Hub class. The following example shows server code that calls addNewMessageToPage
on all connected clients, and client code that defines the method in a JavaScript client.
Server
public class ContosoChatHub : Hub
{
public void NewContosoChatMessage(string name, string message)
{
Clients.All.addNewMessageToPage(name, message);
}
}
JavaScript client using generated proxy
contosoChatHubProxy.client.addNewMessageToPage = function (name, message) {
// Add the message to the page.
$('#discussion').append('<li><strong>' + htmlEncode(name)
+ '</strong>: ' + htmlEncode(message) + '<li>');
};
You can't get a return value from a client method; syntax such as int x = Clients.All.add(1,1)
does not work.
You can specify complex types and arrays for the parameters. The following example passes a complex type to the client in a method parameter.
Server code that calls a client method using a complex object
public void SendMessage(string name, string message)
{
Clients.All.addContosoChatMessageToPage(new ContosoChatMessage() { UserName = name, Message = message });
}
Server code that defines the complex object
public class ContosoChatMessage
{
public string UserName { get; set; }
public string Message { get; set; }
}
JavaScript client using generated proxy
var contosoChatHubProxy = $.connection.contosoChatHub;
contosoChatHubProxy.client.addMessageToPage = function (message) {
console.log(message.UserName + ' ' + message.Message);
});
Selecting which clients will receive the RPC
The Clients property returns a HubConnectionContext object that provides several options for specifying which clients will receive the RPC:
All connected clients.
Clients.All.addContosoChatMessageToPage(name, message);
Only the calling client.
Clients.Caller.addContosoChatMessageToPage(name, message);
All clients except the calling client.
Clients.Others.addContosoChatMessageToPage(name, message);
A specific client identified by connection ID.
Clients.Client(Context.ConnectionId).addContosoChatMessageToPage(name, message);
This example calls
addContosoChatMessageToPage
on the calling client and has the same effect as usingClients.Caller
.All connected clients except the specified clients, identified by connection ID.
Clients.AllExcept(connectionId1, connectionId2).addContosoChatMessageToPage(name, message);
All connected clients in a specified group.
Clients.Group(groupName).addContosoChatMessageToPage(name, message);
All connected clients in a specified group except the specified clients, identified by connection ID.
Clients.Group(groupName, connectionId1, connectionId2).addContosoChatMessageToPage(name, message);
All connected clients in a specified group except the calling client.
Clients.OthersInGroup(groupName).addContosoChatMessageToPage(name, message);
No compile-time validation for method names
The method name that you specify is interpreted as a dynamic object, which means there is no IntelliSense or compile-time validation for it. The expression is evaluated at run time. When the method call executes, SignalR sends the method name and the parameter values to the client, and if the client has a method that matches the name, that method is called and the parameter values are passed to it. If no matching method is found on the client, no error is raised. For information about the format of the data that SignalR transmits to the client behind the scenes when you call a client method, see Introduction to SignalR.
Case-insensitive method name matching
Method name matching is case-insensitive. For example, Clients.All.addContosoChatMessageToPage
on the server will execute AddContosoChatMessageToPage
, addcontosochatmessagetopage
, or addContosoChatMessageToPage
on the client.
Asynchronous execution
The method that you call executes asynchronously. Any code that comes after a method call to a client will execute immediately without waiting for SignalR to finish transmitting data to clients unless you specify that the subsequent lines of code should wait for method completion. The following code examples show how to execute two client methods sequentially, one using code that works in .NET 4.5, and one using code that works in .NET 4.
.NET 4.5 example
async public Task NewContosoChatMessage(string name, string message)
{
await Clients.Others.addContosoChatMessageToPage(data);
Clients.Caller.notifyMessageSent();
}
.NET 4 example
public void NewContosoChatMessage(string name, string message)
{
(Clients.Others.addContosoChatMessageToPage(data) as Task).ContinueWith(antecedent =>
Clients.Caller.notifyMessageSent());
}
If you use await
or ContinueWith
to wait until a client method finishes before the next line of code executes, that does not mean that clients will actually receive the message before the next line of code executes. "Completion" of a client method call only means that SignalR has done everything necessary to send the message. If you need verification that clients received the message, you have to program that mechanism yourself. For example, you could code a MessageReceived
method on the Hub, and in the addContosoChatMessageToPage
method on the client you could call MessageReceived
after you do whatever work you need to do on the client. In MessageReceived
in the Hub you can do whatever work depends on actual client reception and processing of the original method call.
How to use a string variable as the method name
If you want to invoke a client method by using a string variable as the method name, cast Clients.All
(or Clients.Others
, Clients.Caller
, etc.) to IClientProxy
and then call Invoke(methodName, args...).
public void NewContosoChatMessage(string name, string message)
{
string methodToCall = "addContosoChatMessageToPage";
IClientProxy proxy = Clients.All;
proxy.Invoke(methodToCall, name, message);
}
How to manage group membership from the Hub class
Groups in SignalR provide a method for broadcasting messages to specified subsets of connected clients. A group can have any number of clients, and a client can be a member of any number of groups.
To manage group membership, use the Add and Remove methods provided by the Groups
property of the Hub class. The following example shows the Groups.Add
and Groups.Remove
methods used in Hub methods that are called by client code, followed by JavaScript client code that calls them.
Server
public class ContosoChatHub : Hub
{
public Task JoinGroup(string groupName)
{
return Groups.Add(Context.ConnectionId, groupName);
}
public Task LeaveGroup(string groupName)
{
return Groups.Remove(Context.ConnectionId, groupName);
}
}
JavaScript client using generated proxy
contosoChatHubProxy.server.joinGroup(groupName);
contosoChatHubProxy.server.leaveGroup(groupName);
You don't have to explicitly create groups. In effect a group is automatically created the first time you specify its name in a call to Groups.Add
, and it is deleted when you remove the last connection from membership in it.
There is no API for getting a group membership list or a list of groups. SignalR sends messages to clients and groups based on a pub/sub model, and the server does not maintain lists of groups or group memberships. This helps maximize scalability, because whenever you add a node to a web farm, any state that SignalR maintains has to be propagated to the new node.
Asynchronous execution of Add and Remove methods
The Groups.Add
and Groups.Remove
methods execute asynchronously. If you want to add a client to a group and immediately send a message to the client by using the group, you have to make sure that the Groups.Add
method finishes first. The following code examples show how to do that, one by using code that works in .NET 4.5, and one by using code that works in .NET 4
.NET 4.5 example
async public Task JoinGroup(string groupName)
{
await Groups.Add(Context.ConnectionId, groupName);
Clients.Group(groupname).addContosoChatMessageToPage(Context.ConnectionId + " added to group");
}
.NET 4 example
public void JoinGroup(string groupName)
{
(Groups.Add(Context.ConnectionId, groupName) as Task).ContinueWith(antecedent =>
Clients.Group(groupName).addContosoChatMessageToPage(Context.ConnectionId + " added to group"));
}
Group membership persistence
SignalR tracks connections, not users, so if you want a user to be in the same group every time the user establishes a connection, you have to call Groups.Add
every time the user establishes a new connection.
After a temporary loss of connectivity, sometimes SignalR can restore the connection automatically. In that case, SignalR is restoring the same connection, not establishing a new connection, and so the client's group membership is automatically restored. This is possible even when the temporary break is the result of a server reboot or failure, because connection state for each client, including group memberships, is round-tripped to the client. If a server goes down and is replaced by a new server before the connection times out, a client can reconnect automatically to the new server and re-enroll in groups it is a member of.
When a connection can't be restored automatically after a loss of connectivity, or when the connection times out, or when the client disconnects (for example, when a browser navigates to a new page), group memberships are lost. The next time the user connects will be a new connection. To maintain group memberships when the same user establishes a new connection, your application has to track the associations between users and groups, and restore group memberships each time a user establishes a new connection.
For more information about connections and reconnections, see How to handle connection lifetime events in the Hub class later in this topic.
Single-user groups
Applications that use SignalR typically have to keep track of the associations between users and connections in order to know which user has sent a message and which user(s) should be receiving a message. Groups are used in one of the two commonly used patterns for doing that.
Single-user groups.
You can specify the user name as the group name, and add the current connection ID to the group every time the user connects or reconnects. To send messages to the user you send to the group. A disadvantage of this method is that the group doesn't provide you with a way to find out if the user is online or offline.
Track associations between user names and connection IDs.
You can store an association between each user name and one or more connection IDs in a dictionary or database, and update the stored data each time the user connects or disconnects. To send messages to the user you specify the connection IDs. A disadvantage of this method is that it takes more memory.
How to handle connection lifetime events in the Hub class
Typical reasons for handling connection lifetime events are to keep track of whether a user is connected or not, and to keep track of the association between user names and connection IDs. To run your own code when clients connect or disconnect, override the OnConnected
, OnDisconnected
, and OnReconnected
virtual methods of the Hub class, as shown in the following example.
public class ContosoChatHub : Hub
{
public override Task OnConnected()
{
// Add your own code here.
// For example: in a chat application, record the association between
// the current connection ID and user name, and mark the user as online.
// After the code in this method completes, the client is informed that
// the connection is established; for example, in a JavaScript client,
// the start().done callback is executed.
return base.OnConnected();
}
public override Task OnDisconnected()
{
// Add your own code here.
// For example: in a chat application, mark the user as offline,
// delete the association between the current connection id and user name.
return base.OnDisconnected();
}
public override Task OnReconnected()
{
// Add your own code here.
// For example: in a chat application, you might have marked the
// user as offline after a period of inactivity; in that case
// mark the user as online again.
return base.OnReconnected();
}
}
When OnConnected, OnDisconnected, and OnReconnected are called
Each time a browser navigates to a new page, a new connection has to be established, which means SignalR will execute the OnDisconnected
method followed by the OnConnected
method. SignalR always creates a new connection ID when a new connection is established.
The OnReconnected
method is called when there has been a temporary break in connectivity that SignalR can automatically recover from, such as when a cable is temporarily disconnected and reconnected before the connection times out. The OnDisconnected
method is called when the client is disconnected and SignalR can't automatically reconnect, such as when a browser navigates to a new page. Therefore, a possible sequence of events for a given client is OnConnected
, OnReconnected
, OnDisconnected
; or OnConnected
, OnDisconnected
. You won't see the sequence OnConnected
, OnDisconnected
, OnReconnected
for a given connection.
The OnDisconnected
method doesn't get called in some scenarios, such as when a server goes down or the App Domain gets recycled. When another server comes on line or the App Domain completes its recycle, some clients may be able to reconnect and fire the OnReconnected
event.
For more information, see Understanding and Handling Connection Lifetime Events in SignalR.
Caller state not populated
The connection lifetime event handler methods are called from the server, which means that any state that you put in the state
object on the client will not be populated in the Caller
property on the server. For information about the state
object and the Caller
property, see How to pass state between clients and the Hub class later in this topic.
How to get information about the client from the Context property
To get information about the client, use the Context
property of the Hub class. The Context
property returns a HubCallerContext object which provides access to the following information:
The connection ID of the calling client.
string connectionID = Context.ConnectionId;
The connection ID is a GUID that is assigned by SignalR (you can't specify the value in your own code). There is one connection ID for each connection, and the same connection ID is used by all Hubs if you have multiple Hubs in your application.
HTTP header data.
System.Collections.Specialized.NameValueCollection headers = Context.Request.Headers;
You can also get HTTP headers from
Context.Headers
. The reason for multiple references to the same thing is thatContext.Headers
was created first, theContext.Request
property was added later, andContext.Headers
was retained for backward compatibility.Query string data.
System.Collections.Specialized.NameValueCollection queryString = Context.Request.QueryString; string parameterValue = queryString["parametername"]
You can also get query string data from
Context.QueryString
.The query string that you get in this property is the one that was used with the HTTP request that established the SignalR connection. You can add query string parameters in the client by configuring the connection, which is a convenient way to pass data about the client from the client to the server. The following example shows one way to add a query string in a JavaScript client when you use the generated proxy.
$.connection.hub.qs = { "version" : "1.0" };
For more information about setting query string parameters, see the API guides for the JavaScript and .NET clients.
You can find the transport method used for the connection in the query string data, along with some other values used internally by SignalR:
string transportMethod = queryString["transport"];
The value of
transportMethod
will be "webSockets", "serverSentEvents", "foreverFrame" or "longPolling". Note that if you check this value in theOnConnected
event handler method, in some scenarios you might initially get a transport value that is not the final negotiated transport method for the connection. In that case the method will throw an exception and will be called again later when the final transport method is established.Cookies.
System.Collections.Generic.IDictionary<string, Cookie> cookies = Context.Request.Cookies;
You can also get cookies from
Context.RequestCookies
.User information.
System.Security.Principal.IPrincipal user = Context.User;
The HttpContext object for the request :
System.Web.HttpContextBase httpContext = Context.Request.GetHttpContext();
Use this method instead of getting
HttpContext.Current
to get theHttpContext
object for the SignalR connection.
How to pass state between clients and the Hub class
The client proxy provides a state
object in which you can store data that you want to be transmitted to the server with each method call. On the server you can access this data in the Clients.Caller
property in Hub methods that are called by clients. The Clients.Caller
property is not populated for the connection lifetime event handler methods OnConnected
, OnDisconnected
, and OnReconnected
.
Creating or updating data in the state
object and the Clients.Caller
property works in both directions. You can update values in the server and they are passed back to the client.
The following example shows JavaScript client code that stores state for transmission to the server with every method call.
contosoChatHubProxy.state.userName = "Fadi Fakhouri";
contosoChatHubProxy.state.computerName = "fadivm1";
The following example shows the equivalent code in a .NET client.
contosoChatHubProxy["userName"] = "Fadi Fakhouri";
chatHubProxy["computerName"] = "fadivm1";
In your Hub class, you can access this data in the Clients.Caller
property. The following example shows code that retrieves the state referred to in the previous example.
public void NewContosoChatMessage(string data)
{
string userName = Clients.Caller.userName;
string computerName = Clients.Caller.computerName;
Clients.Others.addContosoChatMessageToPage(message, userName, computerName);
}
Note
This mechanism for persisting state is not intended for large amounts of data, since everything you put in the state
or Clients.Caller
property is round-tripped with every method invocation. It's useful for smaller items such as user names or counters.
How to handle errors in the Hub class
To handle errors that occur in your Hub class methods, use one or both of the following methods:
Wrap your method code in try-catch blocks and log the exception object. For debugging purposes you can send the exception to the client, but for security reasons sending detailed information to clients in production is not recommended.
Create a Hubs pipeline module that handles the OnIncomingError method. The following example shows a pipeline module that logs errors, followed by code in Global.asax that injects the module into the Hubs pipeline.
public class ErrorHandlingPipelineModule : HubPipelineModule { protected override void OnIncomingError(Exception ex, IHubIncomingInvokerContext context) { Debug.WriteLine("=> Exception " + ex.Message); if (ex.InnerException != null) { Debug.WriteLine("=> Inner Exception " + ex.InnerException.Message); } base.OnIncomingError(ex, context); } }
protected void Application_Start(object sender, EventArgs e) { GlobalHost.HubPipeline.AddModule(new ErrorHandlingPipelineModule()); RouteTable.Routes.MapHubs(); }
For more information about Hub pipeline modules, see How to customize the Hubs pipeline later in this topic.
How to enable tracing
To enable server-side tracing, add a system.diagnostics element to your Web.config file, as shown in this example:
<configuration>
<configSections>
<!-- For more information on Entity Framework configuration, visit https://go.microsoft.com/fwlink/?LinkID=237468 -->
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
<connectionStrings>
<add name="SignalRSamples" connectionString="Data Source=(local);Initial Catalog=SignalRSamples;Integrated Security=SSPI;Asynchronous Processing=True;" />
<add name="SignalRSamplesWithMARS" connectionString="Data Source=(local);Initial Catalog=SignalRSamples;Integrated Security=SSPI;Asynchronous Processing=True;MultipleActiveResultSets=true;" />
</connectionStrings>
<system.web>
<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" />
</system.web>
<system.webServer>
<modules runAllManagedModulesForAllRequests="true" />
</system.webServer>
<system.diagnostics>
<sources>
<source name="SignalR.SqlMessageBus">
<listeners>
<add name="SignalR-Bus" />
</listeners>
</source>
<source name="SignalR.ServiceBusMessageBus">
<listeners>
<add name="SignalR-Bus" />
</listeners>
</source>
<source name="SignalR.ScaleoutMessageBus">
<listeners>
<add name="SignalR-Bus" />
</listeners>
</source>
<source name="SignalR.Transports.WebSocketTransport">
<listeners>
<add name="SignalR-Transports" />
</listeners>
</source>
<source name="SignalR.Transports.ServerSentEventsTransport">
<listeners>
<add name="SignalR-Transports" />
</listeners>
</source>
<source name="SignalR.Transports.ForeverFrameTransport">
<listeners>
<add name="SignalR-Transports" />
</listeners>
</source>
<source name="SignalR.Transports.LongPollingTransport">
<listeners>
<add name="SignalR-Transports" />
</listeners>
</source>
<source name="SignalR.Transports.TransportHeartBeat">
<listeners>
<add name="SignalR-Transports" />
</listeners>
</source>
</sources>
<switches>
<add name="SignalRSwitch" value="Verbose" />
</switches>
<sharedListeners>
<add name="SignalR-Transports"
type="System.Diagnostics.TextWriterTraceListener"
initializeData="transports.log.txt" />
<add name="SignalR-Bus"
type="System.Diagnostics.TextWriterTraceListener"
initializeData="bus.log.txt" />
</sharedListeners>
<trace autoflush="true" />
</system.diagnostics>
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
<parameters>
<parameter value="v11.0" />
</parameters>
</defaultConnectionFactory>
</entityFramework>
</configuration>
When you run the application in Visual Studio, you can view the logs in the Output window.
How to call client methods and manage groups from outside the Hub class
To call client methods from a different class than your Hub class, get a reference to the SignalR context object for the Hub and use that to call methods on the client or manage groups.
The following sample StockTicker
class gets the context object, stores it in an instance of the class, stores the class instance in a static property, and uses the context from the singleton class instance to call the updateStockPrice
method on clients that are connected to a Hub named StockTickerHub
.
// For the complete example, go to
// http://www.asp.net/signalr/overview/signalr-1x/getting-started/tutorial-server-broadcast-with-aspnet-signalr
// This sample only shows code related to getting and using the SignalR context.
public class StockTicker
{
// Singleton instance
private readonly static Lazy<StockTicker> _instance = new Lazy<StockTicker>(
() => new StockTicker(GlobalHost.ConnectionManager.GetHubContext<StockTickerHub>()));
private IHubContext _context;
private StockTicker(IHubContext context)
{
_context = context;
}
// This method is invoked by a Timer object.
private void UpdateStockPrices(object state)
{
foreach (var stock in _stocks.Values)
{
if (TryUpdateStockPrice(stock))
{
_context.Clients.All.updateStockPrice(stock);
}
}
}
If you need to use the context multiple-times in a long-lived object, get the reference once and save it rather than getting it again each time. Getting the context once ensures that SignalR sends messages to clients in the same sequence in which your Hub methods make client method invocations. For a tutorial that shows how to use the SignalR context for a Hub, see Server Broadcast with ASP.NET SignalR.
Calling client methods
You can specify which clients will receive the RPC, but you have fewer options than when you call from a Hub class. The reason for this is that the context is not associated with a particular call from a client, so any methods that require knowledge of the current connection ID, such as Clients.Others
, or Clients.Caller
, or Clients.OthersInGroup
, are not available. The following options are available:
All connected clients.
context.Clients.All.addContosoChatMessageToPage(name, message);
A specific client identified by connection ID.
context.Clients.Client(connectionID).addContosoChatMessageToPage(name, message);
All connected clients except the specified clients, identified by connection ID.
context.Clients.AllExcept(connectionId1, connectionId2).addContosoChatMessageToPage(name, message);
All connected clients in a specified group.
context.Clients.Group(groupName).addContosoChatMessageToPage(name, message);
All connected clients in a specified group except specified clients, identified by connection ID.
Clients.Group(groupName, connectionId1, connectionId2).addContosoChatMessageToPage(name, message);
If you are calling into your non-Hub class from methods in your Hub class, you can pass in the current connection ID and use that with Clients.Client
, Clients.AllExcept
, or Clients.Group
to simulate Clients.Caller
, Clients.Others
, or Clients.OthersInGroup
. In the following example, the MoveShapeHub
class passes the connection ID to the Broadcaster
class so that the Broadcaster
class can simulate Clients.Others
.
// For the complete example, see
// http://www.asp.net/signalr/overview/getting-started/tutorial-high-frequency-realtime-with-signalr
// This sample only shows code that passes connection ID to the non-Hub class,
// in order to simulate Clients.Others.
public class MoveShapeHub : Hub
{
// Code not shown puts a singleton instance of Broadcaster in this variable.
private Broadcaster _broadcaster;
public void UpdateModel(ShapeModel clientModel)
{
clientModel.LastUpdatedBy = Context.ConnectionId;
// Update the shape model within our broadcaster
_broadcaster.UpdateShape(clientModel);
}
}
public class Broadcaster
{
public Broadcaster()
{
_hubContext = GlobalHost.ConnectionManager.GetHubContext<MoveShapeHub>();
}
public void UpdateShape(ShapeModel clientModel)
{
_model = clientModel;
_modelUpdated = true;
}
// Called by a Timer object.
public void BroadcastShape(object state)
{
if (_modelUpdated)
{
_hubContext.Clients.AllExcept(_model.LastUpdatedBy).updateShape(_model);
_modelUpdated = false;
}
}
}
Managing group membership
For managing groups you have the same options as you do in a Hub class.
Add a client to a group
context.Groups.Add(connectionID, groupName);
Remove a client from a group
context.Groups.Remove(connectionID, groupName);
How to customize the Hubs pipeline
SignalR enables you to inject your own code into the Hub pipeline. The following example shows a custom Hub pipeline module that logs each incoming method call received from the client and outgoing method call invoked on the client:
public class LoggingPipelineModule : HubPipelineModule
{
protected override bool OnBeforeIncoming(IHubIncomingInvokerContext context)
{
Debug.WriteLine("=> Invoking " + context.MethodDescriptor.Name + " on hub " + context.MethodDescriptor.Hub.Name);
return base.OnBeforeIncoming(context);
}
protected override bool OnBeforeOutgoing(IHubOutgoingInvokerContext context)
{
Debug.WriteLine("<= Invoking " + context.Invocation.Method + " on client hub " + context.Invocation.Hub);
return base.OnBeforeOutgoing(context);
}
}
The following code in the Global.asax file registers the module to run in the Hub pipeline:
protected void Application_Start(object sender, EventArgs e)
{
GlobalHost.HubPipeline.AddModule(new LoggingPipelineModule());
RouteTable.Routes.MapHubs();
}
There are many different methods that you can override. For a complete list, see HubPipelineModule Methods.