Option to attach to body as key-value pairs

[zone117x]

Adds an option attachFieldsToBody: 'valueOnly'. When this is option is enabled, the field values are attached to the body directly, similar to what is described in the readme:

  const body = Object.fromEntries(
    Object.keys(req.body).map((key) => [key, req.body[key].value])
  ) // Request body in key-value pairs, like req.body in Express

This would be a convenient feature to include so that json-schemas can be shared more easily between the content types application/json, application/x-www-form-urlencoded, and multipart/form-data.

Without this capability, this needs to be performed in awkward route handler transforms, e.g.:

fastify.post<{ Body: ServiceAuthRequest, Reply: ServiceAuthResponse }>('/request_key', {
  preValidation: (request, _reply, done) => {
    if (request.isMultipart()) {
      // 🤢
      const body = request.body as unknown as Record<string, { value: string } | { _buf: Buffer }>;
      for (let [k, v] of Object.entries(body)) {
        const value = 'value' in v ? v.value : v._buf.toString();
        (request.body as any)[k] = value;
      }
    }
    done();
  },
  schema: {
    body: ServiceAuthRequestSchema,
    headers: ServiceAuthRequestHeadersSchema,
    response: {
      200: ServiceAuthResponseSchema,
    }
  },
}, 
async (request, reply) => {
  ...
});

---

Please let me know if the the convention attachFieldsToBody: 'valueOnly' should be changed to something else.

Also, currently files are converted to a string via .toBuffer().toString(). It's possible to use the onFile handler to customize the file buffer decoding, which is performed in one of the new tests.

Let me know if this feature make sense, and I'm happy to add info to the docs/readme.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[kibertoad]

This makes sense to me.
@Uzlopak wdyt?

[Uzlopak]

It looks kind of confusing that valuesOnly still creates key value pairs. Also is the for loop fast? I would do classical with Object.keys.
And lastly does it not potentially needs protection against prototype pollution?

[zone117x]

It looks kind of confusing that valuesOnly still creates key value pairs.

I agree, the option name could be better. Any suggestions? Maybe something like attachFieldsToBody: 'keyValues'?

Also is the for loop fast? I would do classical with Object.keys.

Will do!

And lastly does it not potentially needs protection against prototype pollution?

Good catch. Is it adequate to use Object.fromEntries(...)? Or perhaps there's a more standard/typical way to handle this in Fastify projects?

[zone117x]

And lastly does it not potentially needs protection against prototype pollution?

On second look, I don't think additional changes are need for this. The request body is using the same set of keys, and only re-assigning the value. Prototype pollution should already be handled for these keys by the time this path is reached, right?

[Uzlopak]

I think it is now good.

[climba03003]

Documentation is required.

[zone117x]

Documentation added for the new attachFieldsToBody: 'valueOnly' option, and also how it improves JSON Schema validation.

[kibertoad]

Thank you!