errorHandler not handling global resolver errors/exceptions?

[lucashfreitas]

Hi There,

Is global error supposed to catch unhandled errors/exception from resolvers? I don't want to handle errors in every resolver itself and trying to handle that and log in a global handler for the graphql operations, but for some reason the errorHandler function is not being called whenever I throw an error from the graphql resolvers.

The code below shows how I am registering the error Handler, therefore I can confirm that is not being called:

 app.register(mercurius, {
    path: options.path,
    routes: true,
    defineMutation: true,
    errorHandler: (
      error: MercuriusError,
      request: FastifyRequest,
      reply: FastifyReply
    ) => {
   // I can confirm this code is not being executed by debugging it and also adding a thumb code like throw new Error("test");
      reply.send({
        data: null,
        errors: [
          {
            message: error.message,
            code: error.code,
          },
        ],
      });
    },

Also another question is about what is the recommended way to access the context inside the error handler as I am planning to log custom errors using this function.

Thanks

[mcollina]

You have to handle all errors in your resolvers, it's how you prevent all sort of problems. Note that this concept is true for all Node.js code and not specific to Mercurius.

Could you upload an example to reproduce your problem? So we can help you.

[lucashfreitas]

Hey @mcollina ,

I hope you are well! Thank you very much for the quick response.

I actually handle expected errors on all resolvers, therefore for unexpected errors I would like to log it and return a custom generic response e.g, Sorry, something went wrong, please try again.... bla bla bla. So instead of doing that for every resolver I thought of delegating this to a global error handler.

The main goal is to avoid adding a generic error handler that produces the same output for every single resolver in the code

Here is the resolver code

try {
 //resolver stuff...
}

catch (error) {
 if(error.code === 'knownError') return handleError(err);
 //this error was unexpected.
 throw error;
}

Here is the errorHandler code:

app.register(mercurius, {
    path: options.path,
    routes: true,
    defineMutation: true,
    errorHandler: (
      error: MercuriusError,
      request: FastifyRequest,
      reply: FastifyReply
    ) => {
   //every unhandled/unexpected error would fall into this method.
//I would grab the graphql context/logger service and log the error and return a custom exception
      reply.send({
        data: null,
        errors: [
          {
            message: error.message,
            code: error.code,
          },
        ],
      });
    },

[lucashfreitas]

Yeap, I was wondering if would be possible to override the mercurius handler using errorHandler in order to do things such as logging instead of doing that manually on every resolver function?

I have pinojs logger instances in my graphql context, so my idea would be to override the way mercurius handle errors and add a logging step to automatically log unhandledErrors in resolvers.

[mcollina]

It is possible.

[lucashfreitas]

hmm, that's what I am trying to do as described in the code below, but despite I am trowing an error in my resolver the generic errorHandler is not being called:

app.register(mercurius, {
    path: options.path,
    routes: true,
    defineMutation: true,
    errorHandler: (
      error: MercuriusError,
      request: FastifyRequest,
      reply: FastifyReply
    ) => {
   // I can confirm this code is not being executed by debugging it/console logging, etc.
      reply.send({
        data: null,
        errors: [
          {
            message: error.message,
            code: error.code,
          },
        ],
      });
    },

[mcollina]

The only way we can help you is for you to produce an example of code that should be working but it's not. All the code you provided are snippet and not something we can run to check - there is either a bug in our code or something in yours. I have asked for such an example twice already. This is the third time and I won't be asking a fourth (first and second).

[lucashfreitas]

Thanks for your patience. The reason why I kept the discussion is to understand if that's something that is being handled by mercurius - I will provide a repository with a sample. Sorry for taking your time :). Closing it for now.