Error in Twilio .net SDK making TaskRouterCapability for TaskQueue

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I am trying to pull some statistics for a TaskQueue using the TaskRouter.js SDK. For this I need to generate a capability router token, which allows access to the TaskQueue. According to the sample at twilio docs, I am supposed to pass null as the channel parameter(look in C# .Net sample), to generate the TaskRouterCapability token. But when I do this, I get an exception (object is null in get_Claims).

Looking at the source code, I should pass in the TaskQueue Sid as the channel id instead of null. When I did this a token was correctly generated.

To start off, am using the basic token generation example code at twilio docs :

class Program {
    static void Main(string[] args)
    {
        // Find your Account Sid and Auth Token at twilio.com/console
        const string accountSid = "ACbe0c12d747XXXXXXXXXXXXXXXXXb";
        const string authToken = "your_auth_token";
        const string workspaceSid = "WSXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
        const string taskQueueSid = "WQXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";

        var urls = new PolicyUrlUtils(workspaceSid, taskQueueSid);

        var allowFetchSubresources = new Policy($"{urls.TaskQueue}/**",
                                                HttpMethod.Get);

        var allowUpdates = new Policy(urls.TaskQueue, HttpMethod.Post);

        var policies = new List<Policy>
    {
        allowFetchSubresources,
        allowUpdates
    };

        // By default, tokens are good for one hour.
        // Override this default timeout by specifiying a new value (in seconds).
        // For example, to generate a token good for 8 hours:
        var capability = new TaskRouterCapability(
            accountSid,
            authToken,
            workspaceSid,
            null,
            policies: policies,
            expiration: DateTime.UtcNow.AddSeconds(28800) // 60 * 60 * 8
            );

        Console.WriteLine(capability.ToJwt());
    } }

class PolicyUrlUtils {
    const string taskRouterBaseUrl = "https://taskrouter.twilio.com";
    const string taskRouterVersion = "v1";

    readonly string _workspaceSid;
    readonly string _taskQueueSid;

    public PolicyUrlUtils(string workspaceSid, string taskQueueSid)
    {
        _workspaceSid = workspaceSid;
        _taskQueueSid = taskQueueSid;
    }

    public string TaskQueue => $"{Workspace}/TaskQueue/{_taskQueueSid}";

    string Workspace =>
        $"{taskRouterBaseUrl}/{taskRouterVersion}/Workspaces/{_workspaceSid}";

}

This gives me an exception on the last line(capability.ToJwt()). Exception is:

System.NullReferenceException occurred
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=<Cannot evaluate the exception source>
  StackTrace:
   at Twilio.Jwt.Taskrouter.TaskRouterCapability.get_Claims()
   at Twilio.Jwt.BaseJwt.ToJwt()
   at DeleteMe.Program.Main(String[] args) in D:\Projects\DeleteMe\DeleteMe\Program.cs:line 46

Now, I looked at the source code of TaskRouterCapability at twilio-csharp github, and seems to be the queue sid should be passed as the channel parameter. When I do this, the token is created. So I took the token generated here, and put it into this HTML file:

<html>
<head>
    <script type="text/javascript" src="https://media.twiliocdn.com/taskrouter/js/v1.11/taskrouter.min.js"></script>
    <script type="text/javascript">
        var taskQueue = new Twilio.TaskRouter.TaskQueue("token generated by console application");

        taskQueue.on("ready", function (taskQueue) {
            console.log(taskQueue.sid)                // 'WQxxx'
            console.log(taskQueue.friendlyName)       // 'Simple FIFO Queue'
            console.log(taskQueue.targetWorkers)      // '1==1'
            console.log(taskQueue.maxReservedWorkers) // 20
        });
    </script>
</head>
<body>

</body>

This then gives me some messages in the console:

taskrouter.min.js:1 Websocket opened: wss://event-bridge.twilio.com/v1/wschannels/ACxxxxxxxxxxxxxx/WQxxxxxxxx?token=eyJh.....&closeExistingSessions=false taskrouter.min.js:1 Received a message of type [connected] taskrouter.min.js:1 POST https://event-bridge.twilio.com/v1/wschannels/ACxxxxxxxxx/WQxxxxxxxxxxx 403 (Policies defined such that we cannot access the given resource)

So the connected event is called, but the ready event never happens.

twilio
asked on Stack Overflow Oct 17, 2017 by Shailesh • edited Oct 18, 2017 by Shailesh

1 Answer

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Turns out there are 2 errors in the sample:

  1. The channel parameter of TaskRouterCapability constructor should be passed the TaskQueue Sid rather than null. A value of null causes an Exception System.NullReferenceException occurred HResult=0x80004003 Message=Object reference not set to an instance of an object. Source= StackTrace: at Twilio.Jwt.Taskrouter.TaskRouterCapability.get_Claims() at Twilio.Jwt.BaseJwt.ToJwt()

  2. There is a typo in the TaskQueue property of PolicyUrlUtils. The URL should have TaskQueues instead of TaskQueue

Have submitted a pull request for the same https://github.com/TwilioDevEd/api-snippets/pull/539

answered on Stack Overflow Oct 18, 2017 by Shailesh

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