What are the best practices for establishing a secure SignalR client connection?

Question

What are the best practices for establishing a secure SignalR client connection?

While tackling this issue may not be solely related to SignalR, it's more about approaching it in the most efficient way. In C#, creating a singleton of a shared object is achievable by making it static and utilizing a lock to prevent multiple threads from creating the same object. Similarly, when using the JavaScript SignalR client, the goal is to have a single connection instance that can be accessed by different components without conflicts. The current solution I have attempted still leads to a race condition where multiple web components end up with their own connection instances:

export class MessagingService {
    private static service: MessagingService;

    static async GetService(): Promise<MessagingService> {
        if (!this.service) {
            let service = new MessagingService();
            await service.start();
            this.service = service;
        }
        return this.service;
    }

    connection;

    async start() {
        this.connection = new signalR.HubConnectionBuilder().withUrl("/MyHub").withAutomaticReconnect().build();

        await this.connection.start();
    }
}

Surprisingly, two web components calling

await MessagingService.GetService()

from their async connectedCallback() methods end up having their individual instances of MessagingService along with separate connections. Numerous resources online suggest that locking might not be the appropriate solution here, indicating that there might be flaws in my approach. How can I ensure only one connection is ever created?

javascript typescript signalr singleton race-condition

Answer 1

Answer №1

My mind was not thinking in promises when working with C#. I had been implementing a lock on the static instance member, but it was not assigned until the SignalR connection was created and started. This resulted in different components accessing it simultaneously and not finding a ready instance. Although I could rearrange the code to assign it right away, those coming later in the call chain discovered the connection was present but not fully open yet, causing invoke calls to fail.

The solution was to check for the promise first and then wait for its completion. The revised code looked like this:

export class MessagingService {
    private static service: MessagingService;
    private static promise: Promise<void>;

    static async GetService(): Promise<MessagingService> {
        if (!this.promise) {
            const service = new MessagingService();
            this.promise = service.start();
            this.service = service;
        }
        await Promise.all([this.promise]);
        return this.service;
    }

    connection: any;

    private async start() {
        this.connection = new signalR.HubConnectionBuilder().withUrl("/MyHub").withAutomaticReconnect().build();
        await this.connection.start();
    }
}

The static promise now gets assigned to the start() method, responsible for initiating the connection. Before returning the service instance, I ensure it's completed by

await Promise.all([this.promise])

. This seems to resolve the race condition, although it still raises the question of whether two callers could reach the opening line of GetService() and find no existing promise.

Answer 2

My mind was not thinking in promises when working with C#. I had been implementing a lock on the static instance member, but it was not assigned until the SignalR connection was created and started. This resulted in different components accessing it simultaneously and not finding a ready instance. Although I could rearrange the code to assign it right away, those coming later in the call chain discovered the connection was present but not fully open yet, causing invoke calls to fail.

The solution was to check for the promise first and then wait for its completion. The revised code looked like this:

export class MessagingService {
    private static service: MessagingService;
    private static promise: Promise<void>;

    static async GetService(): Promise<MessagingService> {
        if (!this.promise) {
            const service = new MessagingService();
            this.promise = service.start();
            this.service = service;
        }
        await Promise.all([this.promise]);
        return this.service;
    }

    connection: any;

    private async start() {
        this.connection = new signalR.HubConnectionBuilder().withUrl("/MyHub").withAutomaticReconnect().build();
        await this.connection.start();
    }
}

The static promise now gets assigned to the start() method, responsible for initiating the connection. Before returning the service instance, I ensure it's completed by

await Promise.all([this.promise])

. This seems to resolve the race condition, although it still raises the question of whether two callers could reach the opening line of GetService() and find no existing promise.

What are the best practices for establishing a secure SignalR client connection?

Answer №1

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