SignalR Troubleshooting-白红宇

SignalR Troubleshooting

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发布时间：2019-06-14

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This document contains the following sections.

Calling methods between the client and server silently fails

This section describes possible causes for a method call between client and server to fail without a meaningful error message. In a SignalR application, the server has no information about the methods that the client implements; when the server invokes a client method, the method name and parameter data are sent to the client, and the method is executed only if it exists in the format that the server specified. If no matching method is found on the client, nothing happens, and no error message is raised on the server.

To further investigate client methods not getting called, you can turn on logging before the calling the start method on the hub to see what calls are coming from the server. To enable logging in a JavaScript application, see . To enable logging in a .NET client application, see .

Misspelled method, incorrect method signature, or incorrect hub name

If the name or signature of a called method does not exactly match an appropriate method on the client, the call will fail. Verify that the method name called by the server matches the name of the method on the client. Also, SignalR creates the hub proxy using camel-cased methods, as is appropriate in JavaScript, so a method called SendMessage on the server would be called sendMessage in the client proxy. If you use the HubName attribute in your server-side code, verify that the name used matches the name used to create the hub on the client. If you do not use the HubName attribute, verify that the name of the hub in a JavaScript client is camel-cased, such as chatHub instead of ChatHub.

Duplicate method name on client

Verify that you do not have a duplicate method on the client that differs only by case. If your client application has a method calledsendMessage, verify that there isn't also a method called SendMessage as well.

Missing JSON parser on the client

SignalR requires a JSON parser to be present to serialize calls between the server and the client. If your client doesn't have a built-in JSON parser (such as Internet Explorer 7), you'll need to include one in your application. You can download the JSON parser .

Mixing Hub and PersistentConnection syntax

SignalR uses two communication models: Hubs and PersistentConnections. The syntax for calling these two communication models is different in the client code. If you have added a hub in your server code, verify that all of your client code uses the proper hub syntax.

JavaScript client code that creates a PersistentConnection in a JavaScript client

var myConnection = $.connection('/echo');

JavaScript client code that creates a Hub Proxy in a Javascript client

var myHub = $.connection.MyHub;

C# server code that maps a route to a PersistentConnection

RouteTable.Routes.MapConnection
    
     ("my", "/echo");

C# server code that maps a route to a Hub, or to mulitple hubs if you have multiple applications

App.MapSignalR();

Connection started before subscriptions are added

If the Hub's connection is started before methods that can be called from the server are added to the proxy, messages will not be received. The following JavaScript code will not start the hub properly:

Incorrect JavaScript client code that will not allow Hubs messages to be received

var chat = $.connection.chatHub; $.connection.hub.start().done(function () { chat.client.broadcastMessage = function (name, message) {...}; });

Instead, add the method subscriptions before calling Start:

JavaScript client code that correctly adds subscriptions to a hub

var chat = $.connection.chatHub; chat.client.broadcastMessage = function (name, message) {...}; $.connection.hub.start().done(function () { ... });

Missing method name on the hub proxy

Verify that the method defined on the server is subscribed to on the client. Even though the server defines the method, it must still be added to the client proxy. Methods can be added to the client proxy in the following ways (Note that the method is added to the client member of the hub, not the hub directly):

JavaScript client code that adds methods to a hub proxy

// Method added to proxy in JavaScript:myHubProxy.server.method1 = function (param1, param2) {...}; //Multiple methods added to proxy in JavaScript using jQuery: $.extend(myHubProxy.server, { method1: function (param1, param2) {...}, method2: function (param3, param4) {...} });

Hub or hub methods not declared as Public

To be visible on the client, the hub implementation and methods must be declared as public.

Accessing hub from a different application

SignalR Hubs can only be accessed through applications that implement SignalR clients. SignalR cannot interoperate with other communication libraries (like SOAP or WCF web services.) If there is no SignalR client available for your target platform, you cannot access the server's endpoint directly.

Manually serializing data

SignalR will automatically use JSON to serialize your method parameters- there's no need to do it yourself.

Remote Hub method not executed on client in OnDisconnected function

This behavior is by design. When OnDisconnected is called, the hub has already entered the Disconnected state, which does not allow further hub methods to be called.

C# server code that correctly executes code in the OnDisconnected event

public class MyHub : Hub { public override Task OnDisconnected() { // Do what you want here return base.OnDisconnected(); } }

OnDisconnect not firing at consistent times

This behavior is by design. When a user attempts to navigate away from a page with an active SignalR connection, the SignalR client will then make a best-effort attempt to notify the server that the client connection will be stopped. If the SignalR client's best-effort attempt fails to reach the server, the server will dispose of the connection after a configurable DisconnectTimeout later, at which time the OnDisconnectedevent will fire. If the SignalR client's best-effort attempt is successful, the OnDisconnected event will fire immediately.

For information on setting the DisconnectTimeout setting, see .

Connection limit reached

When using the full version of IIS on a client operating system like Windows 7, a 10-connection limit is imposed. When using a client OS, use IIS Express instead to avoid this limit.

Cross-domain connection not set up properly

If a cross-domain connection (a connection for which the SignalR URL is not in the same domain as the hosting page) is not set up correctly, the connection may fail without an error message. For information on how to enable cross-domain communication, see .

Connection using NTLM (Active Directory) not working in .NET client

A connection in a .NET client application that uses Domain security may fail if the connection is not configured properly. To use SignalR in a domain environment, set the requisite connection property as follows:

C# client code that implements connection credentials

connection.Credentials = CredentialCache.DefaultCredentials;

Configuring IIS websockets to ping/pong to detect a dead client

SignalR servers don't know if the client is dead or not and they rely on notification from the underlying websocket for connection failures, that is, the OnClose callback. One solution to this problem is to configure IIS websockets to do the ping/pong for you. This ensures that your connection will close if it breaks unexpectedly. For more information see .

Other connection issues

This section describes the causes and solutions for specific symptoms or error messages that occur during a connection.

"Start must be called before data can be sent" error

This error is commonly seen if code references SignalR objects before the connection is started. The wireup for handlers and the like that will call methods defined on the server must be added after the connection completes. Note that the call to Start is asynchronous, so code after the call may be executed before it completes. The best way to add handlers after a connection starts completely is to put them into a callback function that is passed as a parameter to the start method:

JavaScript client code that correctly adds event handlers that reference SignalR objects

$.connection.hub.start().done(function () { // Wire up Send button to call NewContosoChatMessage on the server. $('#newContosoChatMessage').click(function () { contosoChatHubProxy.server.newContosoChatMessage( $('#displayname').val(), $('#message').val()); $('#message').val('').focus(); });

This error will also be seen if a connection stops while SignalR objects are still being referenced.

"301 Moved Permanently" or "302 Moved Temporarily" error

This error may be seen if the project contains a folder called SignalR, which will interfere with the automatically-created proxy. To avoid this error, do not use a folder called SignalR in your application, or turn automatic proxy generation off. See for more details.

"403 Forbidden" error in .NET or Silverlight client

This error may occur in cross-domain environments where cross-domain communication is not properly enabled. For information on how to enable cross-domain communication, see . To establish a cross-domain connection in a Silverlight client, see .

"404 Not Found" error

There are several causes for this issue. Verify all of the following:

Hub proxy address reference not formatted correctly: This error is commonly seen if the reference to the generated hub proxy address is not formatted correctly. Verify that the reference to the hub address is made properly. See for details.

Adding routes to application before adding the hub route: If your application uses other routes, verify that the first route added is the call to MapSignalR.

Using IIS 7 or 7.5 without the update for extensionless URLs: Using IIS 7 or 7.5 requires an update for extensionless URLs so that the server can provide access to the hub definitions at /signalr/hubs. The update can be found .

IIS cache out of date or corrupt: To verify that the cache contents are not out of date, enter the following command in a PowerShell window to clear the cache:
```
net stop w3svcRemove-Item -Path "C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\*" -Force -Recurse net start w3svc
```

"500 Internal Server Error"

This is a very generic error that could have a wide variety of causes. The details of the error should appear in the server's event log, or can be found through debugging the server. More detailed error information may be obtained by turning on detailed errors on the server. For more information, see .

This error is also commonly seen if a firewall or proxy is not configured properly, causing the request headers to be rewritten. The solution is to make sure that port 80 is enabled on the firewall or proxy.

"Unexpected response code: 500"

This error may occur if the version of .NET framework used in the application does not match the version specified in Web.Config. The solution is to verify that .NET 4.5 is used in both the application settings and the Web.Config file.

"TypeError: <hubType> is undefined" error

This error will result if the call to MapSignalR is not made properly. See for more information.

JsonSerializationException was unhandled by user code

Verify that the parameters you send to your methods do not include non-serializable types (like file handles or database connections). If you need to use members on a server-side object that you don't want to be sent to the client (either for security or for reasons of serialization), use the JSONIgnore attribute.

"Protocol error: Unknown transport" error

This error may occur if the client does not support the transports that SignalR uses. See for information on which browsers can be used with SignalR.

"JavaScript Hub proxy generation has been disabled."

This error will occur if DisableJavaScriptProxies is set while also including a reference to the dynamically generated proxy atsignalr/hubs. For more information on creating the proxy manually, see .

"The connection ID is in the incorrect format" or "The user identity cannot change during an active SignalR connection" error

This error may be seen if authentication is being used, and the client is logged out before the connection is stopped. The solution is to stop the SignalR connection before logging the client out.

"Uncaught Error: SignalR: jQuery not found. Please ensure jQuery is referenced before the SignalR.js file" error

The SignalR JavaScript client requires jQuery to run. Verify that your reference to jQuery is correct, that the path used is valid, and that the reference to jQuery is before the reference to SignalR.

"Uncaught TypeError: Cannot read property '<property>' of undefined" error

This error results from not having jQuery or the hubs proxy referenced properly. Verify that your reference to jQuery and the hubs proxy is correct, that the path used is valid, and that the reference to jQuery is before the reference to the hubs proxy. The default reference to the hubs proxy should look like the following:

HTML client-side code that correctly references the Hubs proxy

"RuntimeBinderException was unhandled by user code" error

This error may occur when the incorrect overload of Hub.On is used. If the method has a return value, the return type must be specified as a generic type parameter:

Method defined on the client (without generated proxy)

MyHub.On
    
     ("MethodName", LocalMethod);

Connection ID is inconsistent or connection breaks between page loads

This behavior is by design. Since the hub object is hosted in the page object, the hub is destroyed when the page refreshes. A multi-page application needs to maintain the association between users and connection IDs so that they will be consistent between page loads. The connection IDs can be stored on the server in either a ConcurrentDictionary object or a database.

"Value cannot be null" error

Server-side methods with optional parameters are not currently supported; if the optional parameter is omitted, the method will fail. For more information, see .

"Firefox can't establish a connection to the server at <address>" error in Firebug

This error message can be seen in Firebug if negotiation of the WebSocket transport fails and another transport is used instead. This behavior is by design.

"The remote certificate is invalid according to the validation procedure" error in .NET client application

If your server requires custom client certificates, then you can add an x509certificate to the connection before the request is made. Add the certificate to the connection using Connection.AddClientCertificate.

Connection drops after authentication times out

This behavior is by design. Authentication credentials cannot be modified while a connection is active; to refresh credentials, the connection must be stopped and restarted.

OnConnected gets called twice when using jQuery Mobile

jQuery Mobile's initializePage function forces the scripts in each page to be re-executed, thus creating a second connection. Solutions for this issue include:

Include the reference to jQuery Mobile before your JavaScript file.

Disable the initializePage function by setting $.mobile.autoInitializePage = false.

Wait for the page to finish initializing before starting the connection.

Messages are delayed in Silverlight applications using Server Sent Events

Messages are delayed when using server sent events on Silverlight. To force long polling to be used instead, use the following when starting the connection:

connection.Start(new LongPollingTransport());

"Permission Denied" using Forever Frame protocol

This is a known issue, described . This symptom may be seen using the latest JQuery library; the workaround is to downgrade your application to JQuery 1.8.2.

"InvalidOperationException: Not a valid web socket request.

This error may occur if the WebSocket protocol is used, but the network proxy is modifying the request headers. The solution is to configure the proxy to allow WebSocket on port 80.

“Exception: <method name> method could not be resolved” when client calls method on server

This error can result from using data types that cannot be discovered in a JSON payload, such as Array. The workaround is to use a data type that is discoverable by JSON, such as IList. For more information, see .

Compilation and server-side errors

The following section contains possible solutions to compiler and server-side runtime errors.

Reference to Hub instance is null

Since a hub instance is created for each connection, you can't create an instance of a hub in your code yourself. To call methods on a hub from outside the hub itself, see for how to obtain a reference to the hub context.

HTTPContext.Current.Session is null

This behavior is by design. SignalR does not support the ASP.NET session state, since enabling the session state would break duplex messaging.

No suitable method to override

You may see this error if you are using code from older documentation or blogs. Verify that you are not referencing names of methods that have been changed or deprecated (like OnConnectedAsync).

HostContextExtensions.WebSocketServerUrl is null

This behavior is by design. This member is deprecated and should not be used.

"A route named 'signalr.hubs' is already in the route collection" error

This error will be seen if MapSignalR is called twice by your application. Some example applications call MapSignalR directly in the Startup class; others make the call in a wrapper class. Ensure that your application does not do both.

WebSocket is not used

If you have verified that your server and clients meet the requirements for WebSocket (listed in the document), you will need to enable WebSocket on your server. Instructions for doing this can be found .

$.connection is undefined

This error indicates that either the scripts on a page are not being loaded properly, or the hub proxy is not reachable or is being accessed incorrectly. Verify that the script references on your page correspond to the scripts loaded in your project, and that /signalr/hubs can be accessed in a browser when the server is running.

One or more types required to compile a dynamic expression cannot be found

This error indicates that the Microsoft.CSharp library is missing. Add it in the Assemblies->Framework tab.

Caller state cannot be accessed from Clients.Caller in Visual Basic or in a strongly typed hub; "Conversion from type 'Task(Of Object)' to type 'String' is not valid" error

To access caller state in Visual Basic or in a strongly typed hub, use the Clients.CallerState property (introduced in SignalR 2.1) instead ofClients.Caller.

Visual Studio issues

This section describes issues encountered in Visual Studio.

Script Documents node does not appear in Solution Explorer

Some of our tutorials direct you to the "Script Documents" node in Solution Explorer while debugging. This node is produced by the JavaScript debugger, and will only appear while debugging browser clients in Internet Explorer; the node will not appear if Chrome or Firefox are used. The JavaScript debugger will also not run if another client debugger is running, such as the Silverlight debugger.

SignalR does not work on Visual Studio 2008 or earlier

This behavior is by design. SignalR requires .NET Framework 4 or later; this requires that SignalR applications be developed in Visual Studio 2010 or later. The server component of SignalR requires .NET Framework 4.5.

IIS issues

This section contains issues with Internet Information Services.

SignalR works on Visual Studio development server, but not in IIS

SignalR is supported on IIS 7.0 and 7.5, but support for extensionless URLs must be added. To add support for extensionless URLs, see

SignalR requires ASP.NET to be installed on the server (ASP.NET is not installed on IIS by default). To install ASP.NET, see .

Microsoft Azure issues

This section contains issues with Microsoft Azure.

FileLoadException when hosting SignalR in an Azure Worker Role

Hosting SignalR in an Azure Worker Role might result in the exception "Could not load file or assembly 'Microsoft.Owin, Version=2.0.0.0". This is a known issue with NuGet; Binding redirects are not added automatically in Azure Worker Role projects. To fix this, you can add the binding redirects manually. Add the following lines to the app.config file for your Worker Role project.