Add support for FormData request body

[octet-stream]

This PR brings general support for multipart/form-data encoding and allows to use any spec-comliant FormData object as request body. This PR also introduces a new dependency form-data-encoder, so you might expect it to add about 37 KB of extra size into the install size of got.

Before it's done I would like to get a feedback on few more things:

• How should I deal with custom content-type header? The encoder will generate this header and use internally to produce body content and if user will override this header - body will not be send as of now. Should I create and use the encoder in request body anyway?
• Do I need some more tests? Perhaps for request body? The encoder.encode() method returns AsyncIterableIterator so it basically reuse the logic for async iterator body consuming.
• How would I document these changes? Should I add alternative packages (both formdata-node and formdata-polyfill) into the docs?

I will keep this PR as WIP until my questions is resolved.

Further suggestions: As I said before, the good old form-data package is not spec-compliant and I think it should be deprecated. At least node-fetch will do so in near future (see refs section of this PR for more information).

Refs:

• Support multipart/form-data encoding #1810
• Drop support for Form-Data? node-fetch/node-fetch#1167
• fix(Body): Discourage form-data and buffer() node-fetch/node-fetch#1212

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests.
• If it's a new feature, I have included documentation updates in both the README and the types.

[octet-stream]

Ah, I forgot to mention that while tests are passing, I have issues with XO. But they not seem to be related to this PR.

[szmarczak]

Thanks for the draft! Looking forward to this ^_^

How should I deal with custom content-type header? The encoder will generate this header and use internally to produce body content and if user will override this header - body will not be send as of now.

It should be sent no matter the content type.

Do I need some more tests? Perhaps for request body?

You read my mind :) Basically read the payload on the server and check if it's valid.

How would I document these changes? Should I add alternative packages (both formdata-node and formdata-polyfill) into the docs?

👍

the good old form-data package is not spec-compliant and I think it should be deprecated.

I agree.

/cc @sindresorhus

[sindresorhus]

👍

This will also need documentation updates.

[octet-stream]

It should be sent no matter the content type.

So I should keep header set by developer and not override it. Right?

You read my mind :) Basically read the payload on the server and check if it's valid.

👍

I agree.

Should I include form-data deprecation in this PR? If so, how should I mention this? With util.deprecate or/and documentation? I'm asking in case if got has some guidelines for this case :)

This will also need documentation updates.

Will do!

[szmarczak]

So I should keep header set by developer and not override it. Right?

Correct. Only set content-type if noContentType.

With util.deprecate or/and documentation?

👍 (and)

Should I include form-data deprecation in this PR?

To be honest, I'm not sure. I'm leaving this up to @sindresorhus

[octet-stream]

Hmm. Do you guys have a body parser to handle FomrData bodies in your test server?

[szmarczak]

Do you guys have a body parser to handle FomrData bodies in your test server?

We don't. Feel free to include one.

[octet-stream]

About then-busboy: To be honest, I am not familiar with express ecosystem and if there's any multipart/form-data parser that can produce a single object with files and fields. I just needed a parser that will help be to get files, read them and send back along with the fields. Maybe multer can handle this? It seems like they allow to upload only files with specific field names (only those you mention in .array(), .fields() and .single()), otherwise if you will use multer.any() you will get files as an array.

I was ended up trying to make a bare minimal parser, but realised that I basically re-implement my solution... Sooo I just added it for tests. It seem to work as expected.

[octet-stream]

I think I gonna mark this PR as ready for a review and wait for your feedback, because I do not have any more significant changes for this feature.

[octet-stream]

Looks like I have fixed XO errors related to this PR.

For some reason I also have these errors on my local machine.

But they don't seem to be a thing in previous run of CI workflow.

[octet-stream]

I think this tests failing is not related to the PR...

[szmarczak]

Big thank you @octet-stream ❤️

[octet-stream]

It was a pleasure :)

[tutods]

Is possible now use Got with multipart/formdata?