SignalR intercept every incoming message (client side)

user_7461937 0
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I have a question regarding SignalR on the clientside (JS). Is there a way to intercept incoming messages at the clientside? I am working on a chat application with a lot traffic on the socket. I want to be able to execute code (catch errors if any) on every incoming event.

Looking at the docs I can't find any existing solution for this. Is there one?

signalr typescript error-handling javascript
1 Answers
After a bit of research, this does not seem to be possible.

My first thought for a workaround was using a function to 'pipe' the callback functions through first.

E.G.

  private pipeSignal(cb: (arg: any) => void): (arg: any) => void {
    const errors = checkForErrors();
    if(errors){
      return () => {
        // Handle error here
      };
    }
    return cb;
  }

I then thought setting up the handlers could look as follows:

this.hubConnection.on(
  'MyMethod1',
  this.pipeSignal((method1Val) => {
    console.log(method1Val);
  })
);

this.hubConnection.on(
  'MyMethod2',
  this.pipeSignal((method2Val) => {
    console.log(method2Val);
  })
);

BUT, this results in the 'pipeSignal' function being called only once when setting up the event listener. Thereafter, it will not be called.

I think the only option here would be to have a function that checks for errors in every event listener callback.

   private hasErrors(arg: any): boolean {
     const errors = checkForErrors();
     if(errors){
         // Handle error here
         return true;
     }
     return false;
   }

Then in each signal event callback you can try checking for errors like this:

this.hubConnection.on(
  'MyMethod1',
  (method1Val) => {
     if(!this.hasErrors(method1Val)){ 
       // Can continue knowing there are no errors
       console.log(method1Val);
     }
  }
);

UPDATE

Turns out I was close with my 'pipeSignal' function. Rather than running the error logic in the pipeSignal function, I return a function that wraps the error logic and the callback:

  private pipeSignal(cb: (arg: any) => void): (arg: any) => void {
    return (arg) => {
      const errors = checkForErrors();
      if(errors){
          // handle errors
      } else {
         // proceed with callback as there are no errors
         cb(arg);
      }
    };
  }

Now this can be used as I imagined before:

this.hubConnection.on(
  'MyMethod1',
  this.pipeSignal((method1Val) => {
    console.log(method1Val);
  })
);
user_147179050
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