Data transmission is only possible when the connection is in the 'Connected' state

Question

Data transmission is only possible when the connection is in the 'Connected' state

Trying to set up a simple connection using SignalR in Angular 6, I wrote the following code:

signalR.helper.ts

  public static setupHub<T>(hubUrl: string, eventName: string, callback: (data: T) => void, ...params: SignalRParam[]): HubConnection {
    const token = localStorage.getItem(appConstant.token);
    const url = this.buidlUrl(hubUrl, ...params);
    const connection = new HubConnectionBuilder()
        .withUrl(url,
            { transport: HttpTransportType.WebSockets, accessTokenFactory: () => token })
        .build();
    environment.production && connection.start();
    !environment.production && connection.start().catch(err => console.error(err.toString()));
    connection.on(eventName, callback);
    return connection;
}

However, when trying to log in on my page, I keep encountering this error message in the console:

signalR.helper.ts:19 Error: Cannot send data if the connection is not in the 'Connected' State.

I'm relatively new to SignalR and Angular. Can someone explain why I am getting this error?

angular typescript signalr angular6 signalr-hub

Answer 1

Answer №1

Before proceeding, it is crucial to ensure that your connection has been initiated successfully

const connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub")
    .configureLogging(signalR.LogLevel.Information)
    .build();

async function start() {
    try {
        await connection.start();
        console.log("SignalR Connected.");
    } catch (err) {
        console.log(err);
        setTimeout(start, 5000);
    }
};

connection.onclose(async () => {
    await start();
});

// Begin the connection process.
start();

Answer 2

Before proceeding, it is crucial to ensure that your connection has been initiated successfully

const connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub")
    .configureLogging(signalR.LogLevel.Information)
    .build();

async function start() {
    try {
        await connection.start();
        console.log("SignalR Connected.");
    } catch (err) {
        console.log(err);
        setTimeout(start, 5000);
    }
};

connection.onclose(async () => {
    await start();
});

// Begin the connection process.
start();

Answer 3

Answer №2

It is essential to ensure that the promise returned by ".start()" has been resolved before executing any other methods. Consider modifying your method to return the promise for better chaining capabilities, or opt for utilizing the async/await pattern within the method.

Additionally, be cautious of inadvertently invoking ".stop()". I encountered a situation where an observable monitored user authentication status and triggered ".stop()" upon logout. The issue arose when the observable briefly indicated user non-authentication during page loading, leading to a potential race condition resulting in intermittent success and failure.

Answer 4

It is essential to ensure that the promise returned by ".start()" has been resolved before executing any other methods. Consider modifying your method to return the promise for better chaining capabilities, or opt for utilizing the async/await pattern within the method.

Additionally, be cautious of inadvertently invoking ".stop()". I encountered a situation where an observable monitored user authentication status and triggered ".stop()" upon logout. The issue arose when the observable briefly indicated user non-authentication during page loading, leading to a potential race condition resulting in intermittent success and failure.

Answer 5

Answer №3

To ensure SignalR functions correctly, make sure to include the necessary scripts in your code. This includes adding the following lines to your *.cshtml file:

<script src="~/lib/signalr/dist/browser/signalr.js"></script>
<script src="~/js/chat.js"></script>

If you do not navigate to a page with these script tags, SignalR will not be able to create the Hub. To have it available throughout the web app, consider placing the scripts in _Layout.cshtml.

Failure to include these scripts may result in errors like the following:

POST http://myserver.com/chatHub/negotiate 404 (Not Found)
(anonymous) @ XhrHttpClient.ts:84
XhrHttpClient.send @ XhrHttpClient.ts:30
Utils.ts:179 [2019-06-14T19:21:39.774Z] Error: Failed to complete negotiation with the server: Error: Not Found
ConsoleLogger.log @ Utils.ts:179
Utils.ts:179 [2019-06-14T19:21:39.774Z] Error: Failed to start the connection: Error: Not Found
Error: Cannot send data if the connection is not in the 'Connected' State.

For more information and resources on SignalR, please refer to the following links:

Overview: https://learn.microsoft.com/en-us/aspnet/core/signalr/introduction?view=aspnetcore-2.2

Hubs: https://learn.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-2.2

Clients: https://learn.microsoft.com/en-us/aspnet/core/signalr/javascript-client?view=aspnetcore-2.1#call-hub-methods-from-client

Answer 6

To ensure SignalR functions correctly, make sure to include the necessary scripts in your code. This includes adding the following lines to your *.cshtml file:

<script src="~/lib/signalr/dist/browser/signalr.js"></script>
<script src="~/js/chat.js"></script>

If you do not navigate to a page with these script tags, SignalR will not be able to create the Hub. To have it available throughout the web app, consider placing the scripts in _Layout.cshtml.

Failure to include these scripts may result in errors like the following:

POST http://myserver.com/chatHub/negotiate 404 (Not Found)
(anonymous) @ XhrHttpClient.ts:84
XhrHttpClient.send @ XhrHttpClient.ts:30
Utils.ts:179 [2019-06-14T19:21:39.774Z] Error: Failed to complete negotiation with the server: Error: Not Found
ConsoleLogger.log @ Utils.ts:179
Utils.ts:179 [2019-06-14T19:21:39.774Z] Error: Failed to start the connection: Error: Not Found
Error: Cannot send data if the connection is not in the 'Connected' State.

For more information and resources on SignalR, please refer to the following links:

Overview: https://learn.microsoft.com/en-us/aspnet/core/signalr/introduction?view=aspnetcore-2.2

Hubs: https://learn.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-2.2

Clients: https://learn.microsoft.com/en-us/aspnet/core/signalr/javascript-client?view=aspnetcore-2.1#call-hub-methods-from-client

Data transmission is only possible when the connection is in the 'Connected' state

Answer №1

Answer №2

Answer №3

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