Support custom Request types

[wilkmaia]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

Support for the request object (instance of the Request (lib/request.js) class) to inherit from a custom class besides stream.Readable.

Motivation

Starting from v12.0.9, next.js validates the request object's type is an http.IncomingMessage instance. If it's not, no error is thrown but the request will fail due to an internal type conversion not being made.

This is an issue for using light-my-request to test API requests that use next.js. Specifically, this is currently blocking bumping next.js' version in fastify-nextjs (fastify/fastify-nextjs#514) because tests don't pass with the current structure of light-my-request.

Example

Supporting a new options flag, namely customRequestType and adding the following snippet in lib/request.js:124 (Request function definition) should do the trick:

  if (options.customRequestType) {
    util.inherits(this.constructor, options.customRequestType)
  }

[mcollina]

When did Next.js make this change? I think it would be better to approach them and see if it could be relaxed somehow.

Making it pluggable would be impossible as there is specific behavior that is needed - and it's not possible to bolt it on top of another prototype. This library does not use IncomingMessage because it'd be very hard to do so. It's not impossible, so you might give that a try.

[wilkmaia]

@mcollina in https://github.com/vercel/next.js/releases/tag/v12.0.9.

Specifically in this commit.

The issue is that before they simply set the TypeScript request type to http.IncomingRequest (e.g. packages/next/server/base-server.ts:367). In that commit they started using the BaseNextRequest type for the request object in the base-server file and moved the front-end implementation to packages/next/server/next-server.ts, adding a conversion from http.IncomingMessage to BaseNextRequest with the normalizeReq function.