Adding data to multipart request not from file

[davidsoncasey]

I've been working using Rack to submit multipart requests to the Apple News API. This works fine when just submitting data from a JSON file, but there are cases in which an additional metadata part is required and is not expected to have the filename field in the Content-Disposition header. Here is the example from the Apple News Documentation:

--535e329ca936f79a19ac9a251f7d48f7
Content-Type: application/json
Content-Disposition: form-data; name=metadata

{
   "data": {
        "revision": "AAAAAAAAAAAAAAAAAAAAev=="
    }
}
--535e329ca936f79a19ac9a251f7d48f7

The issue that I was running into when using Multipart::build_multipart is that it if there is no original_filename attribute, then it uses Generator#content_for_other to create this part of the request, which does not specify Content-Type (lines 83-90 of multipart/generator.rb). If I were to use a file (or file like object) and build this with Multipart::UploadedFile, then the filename is included in the Content-Disposition, which I do not want.

What I was hoping to see (and I'd be willing to help contribute to) is a class similar to Multipart::UploadedFile that instead of receiving the path to a file upon initialization could simply receive a string of the content, and corresponding changes to Multipart::Generator that would allow for an instance of this class to be passed to the generator and build the part of the request correctly.

I'm not sure if this is an issue with other APIs that expect multipart requests, but for the Apple News API there are several different metadata fields that we will need to be submitting, so this functionality would be very useful. Thanks for all the hard work on Rack and let me know if I can provide any clarification or help make these changes.

[jeremyevans]

It does seem useful to make it possible to generate that format. I have an implementation that I will submit in a pull request. As it requires a new (though backwards-compatible) API for UploadedFile, I'll want review by another core team member before merging it.