Wait I’m confused, is parseAs not required if 3 arguments are passed? If not, what will the body get parsed as? Also, if you do provide three arguments, doesn’t the callback require three arguments?

Here there's an explanation https://www.fastify.io/docs/latest/ContentTypeParser/#body-parser

I already read that but it is incomplete. For example, if I provide parseAs: 'string', but only 2 arguments in the callback, is it just swallowing the body? When does it even make sense to do this:

server.addContentTypeParser('foo/bar', { parseAs: 'string' }, (req, done) => {
  ...
})

Maybe the documentation is not so clear.
Anyway reading the code

The signature is:

• (req, done) / (req) => Promise if the option is not given or if the resultAs is not specified
• (req, body, done) / (req, body) => Promise if and only if the option.resultAs is string or buffer

Ok so based on that the following test would be invalid:

server.addContentTypeParser('foo/bar', { parseAs: 'string' }, (req, done) => {
    ...
})

since it should take 3 arguments in the callback.

I've updated the rest of the types and tests accordingly.

Fixed the "The array parameter is supported everywhere in addContentTypeParser". And, I added back "server.addContentTypeParser('foo/bar', {}, (req, done) => {" already.

I would say that it's clear to use from the docs. It was complicated here because the type system needs to account for every possible valid way to use the api. Most of the calls in the tests are redundant ways to do the same thing. It's important that typescript types account for them, but I don't really think it matters if the docs provide them.

The maintainers and the collaborators are not mainly typescript users. If you are interested, we'll be happy to review a PR about a rework of the typescript test suite!

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