IncomingMessage and ServerMessage typings are too specific

[erunion]

We're gradually migrating our Express and Fastify hybrid codebase over to Typescript and have begun running into issues with various data we have in our Request objects:

pino({
  customProps: (req) => {
    return {
      '@type': 'http-request',
      '@service': 'readme',
      '@environment': process.env.NODE_ENV,
      '@timestamp': new Date().toISOString(),
      project: req.project?.subdomain ?? undefined,
    };
  },
})

The above code works normally in JS but in TS req.project is undefined because it does not exist on the customProps req parameter of IncomingMessage. We're already overloading the Express Request object to allow for req.proejct exist, but adding that, and everything else we're adding to that is a non-starter for us:

declare global {
  namespace Express {
    interface Request {
      project: ProjectDocument;
    }
  }
}

I have tried to type req as req: Request but even though Express' Request extends IncomingMessage the IncomingMessage typing on that is too specific:

error TS2769: No overload matches this call.
  Overload 1 of 2, '(opts?: Options | undefined, stream?: DestinationStream | undefined): HttpLogger', gave the following error.
    Type '(req: Request) => { '@type': string; '@service': string; '@environment': "backup" | "development" | "next" | "pr" | "preview" | "production" | "stage" | "test"; '@timestamp': string; project: string; }' is not assignable to type '(req: IncomingMessage, res: ServerResponse<IncomingMessage>) => object'.
      Types of parameters 'req' and 'req' are incompatible.
        Type 'IncomingMessage' is missing the following properties from type 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>': get, header, accepts, acceptsCharsets, and 56 more.
  Overload 2 of 2, '(stream?: DestinationStream | undefined): HttpLogger', gave the following error.
    Argument of type '{ customProps: (req: Request) => { '@type': string; '@service': string; '@environment': "backup" | "development" | "next" | "pr" | "preview" | "production" | "stage" | "test"; '@timestamp': string; project: string; }; }' is not assignable to parameter of type 'DestinationStream'.
      Object literal may only specify known properties, and 'customProps' does not exist in type 'DestinationStream'.

 28   return pino({
             ~~~~~~
 29     customProps: (req: Request) => {
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
... 
 37     },
    ~~~~~~
 38   });

I have also attempted to monkeypatch the Options interface to allow us to type req and res as Request and Response but TS doesn't like that either:

declare module 'pino-http' {
  export interface Options {
    customProps?: ((req: Request, res: Response) => object) | undefined;
  }
}

Subsequent property declarations must have the same type. Property 'customProps' must be of type '((req: IncomingMessage, res: ServerResponse) => object) | undefined', but here has type '((req: Request, res: Response) => object) | undefined'. ts(2717)

It would be really nice if when calling pino() we could supply it with a generic of our Express and Fastify Request and Response interfaces and let that populate down into wherever IncomingMessage and ServerResponse are being used. Something like this:

pino<Request, Response>({
  customProps: (req) => { // <-- This is a `Request` object now.
    return {
      '@type': 'http-request',
      '@service': 'readme',
      '@environment': process.env.NODE_ENV,
      '@timestamp': new Date().toISOString(),
      project: req.project?.subdomain ?? undefined, // <-- `req.project` now works because `project` exists on `Request`.
    };
  },
});

[mcollina]

+1, would you like to send a PR?

[erunion]

sure!