How would one modify an incoming request

[CedricVanhaverbeke]

Use case

incoming request looks like this:

{
   "params": {
    "user": "@me"
     ...
   }
   "user" : {
     // user content here
   }
   ...
}

I would like to change the user parameter to the current user's id. This one is fetched from a JWT token that is passed along with the request. Let's say req.user contains the user object.

First solution

My first solution consists of creating a plugin (with fastify-plugin) to do this:

import fp from 'fastify-plugin'

// translates every "@me" query parameter to the current user's id
const plugin = fp(function (fastify: FastifyInstance) {
  fastify.addHook('preHandler', (req) => {
    const meEntries = Object.entries(req.params).filter(([_, value]) => value === '@me')
    if (meEntries.length > 0) {

      const myIdEntries = meEntries.map(([key]) => ([key, req.user.id]))

      req.params = {
        ...req.params as Record<string, any>,
        ...Object.fromEntries(myIdEntries),
      }
    }
  })
})

But this feels not right. I assume modifying the request-object is not the way to go

Alternative ideas

• Create a decorator to modify the request. It seems designed for this use case. However, there's no documentation about changing an existing entry in the request
• Modifying the request and redirecting to this modified request.

Question

How should this be approached?

[zekth]

Meanwhile technically this is correct, it's pretty confusing in a sense. Because params are supposed to be the client parameters sent within the request and not being mutated in the request lifecycle. If your server grows a lot it can lead to confusions.

I'd rather decorate the request with a proper name like parsedUser or something else; a bit like session handling.

[simoneb]

@CedricVanhaverbeke did you manage to solve your issue?

[Mazuh]

Let me take a look on this today.

[Mazuh]

afaik, we have two choices:

• document how to add custom properties more properly (and not recycling existing ones)
• or create an interface where users can set custom properties on FastifyInstance type, like maybe a property called .custom or another hook

considering the usage of typescript, I'm thinking on the second approach.

can a maintainer give some feedback on this? I'm available to work on it in any case.

[mcollina]

cc @fastify/typescript I think the latter would be amazing but I don't know if it's possible

[fox1t]

The latter should be feasible with the current type definitions! (Some genetics wizardry is required, though 😁).

[Mazuh]

I managed to make what I believe to be a more proper way to do what you're wanting with typescript.

First, I generated a new project with fastify-cli using typescript template:

fastify generate hello-fastify-ts --lang=typescript

and then I created another file on plugin folder (in this setup, anything there will be autoloaded):

import fp from 'fastify-plugin'

export default fp(async (fastify, opts) => {
  fastify.addHook('preHandler', async (req) => {
    req.authenticatedUser = {
      id: 42,
      name: 'Marcell',
      token: 'wadda.wadda.wadda',
      isAdmin: true,
    };
  })
})

interface AuthenticatedUser {
  id: number,
  name: string;
  token: string;
  isAdmin: boolean;
}

declare module 'fastify' {
  export interface FastifyRequest {
    authenticatedUser?: AuthenticatedUser;
  }
}

it works pretty well, my type validations were working just fine, I got warnings when trying to use the new custom property in a wrong way both in controller and hook, tests ok, etc etc.

so, after some thought, I don't think it'd be very useful to add a builtin API to support that, imho the current one seems very straightforward, maybe there's some place to put this example in a documentation?

@CedricVanhaverbeke, do you think this is enough for what you're looking for?

maintainers, any recommended course of action for this?

[simoneb]

I agree with your conclusions. If anything, all we need to do here is write some docs, or point at some resources, or both :)

[mcollina]

Would you like to send a PR improving the docs?

[simoneb]

Would you like to send a PR improving the docs?

@Mazuh ^

[Mazuh]

Sure! I'll be opening until EOD.

[CedricVanhaverbeke]

Thanks for the effort! Looks great! Wishing you all the best :D

[alzalabany]

I managed to make what I believe to be a more proper way to do what you're wanting with typescript.

First, I generated a new project with fastify-cli using typescript template:

fastify generate hello-fastify-ts --lang=typescript

and then I created another file on plugin folder (in this setup, anything there will be autoloaded):

import fp from 'fastify-plugin'

export default fp(async (fastify, opts) => {
  fastify.addHook('preHandler', async (req) => {
    req.authenticatedUser = {
      id: 42,
      name: 'Marcell',
      token: 'wadda.wadda.wadda',
      isAdmin: true,
    };
  })
})

interface AuthenticatedUser {
  id: number,
  name: string;
  token: string;
  isAdmin: boolean;
}

declare module 'fastify' {
  export interface FastifyRequest {
    authenticatedUser?: AuthenticatedUser;
  }
}

it works pretty well, my type validations were working just fine, I got warnings when trying to use the new custom property in a wrong way both in controller and hook, tests ok, etc etc.

so, after some thought, I don't think it'd be very useful to add a builtin API to support that, imho the current one seems very straightforward, maybe there's some place to put this example in a documentation?

@CedricVanhaverbeke, do you think this is enough for what you're looking for?

maintainers, any recommended course of action for this?

one problem with this approach is typescript now will expect authenticatedUser?: AuthenticatedUser; even tho it should really be authenticatedUser: AuthenticatedUser;

anyone have anysolution for that ?

i tried

fastify.addHook('preHandler', async (req) asserts FastifyRequest & {authenticatedUser: NonNullable<FastifyRequest["authenticatedUser"]>} => { }

but that broke down my type provider