Proxy multipart/form-data requests through Rails controller to foreign API using Faraday and Dropzone

dropZone.js

// Somewhere in your client code after dropzone.js has been included

//...

var myZone = new Dropzone('.selector', {
  url: '/my/upload/path?parameters=true',
  sending: function(file, xhr, formData) {
    // Do some custom data transformation before file submission... blah blah blah
  },
  success: function(file, response) {
    // Do something with the file or response here!
  },
  error: function(file, error) {
    // Handle the error accordingly
  }
});

//...

Gemfile

# Make sure to add this to your Gemfile

gem 'faraday'

my_upload_controller.rb

class MyUploadController < ApplicationController
  def file_upload
    
    # Parse file data into an  UploadIO object...
    payload = {}
    payload[:file] = Faraday::UploadIO.new params[:file].path, params[:file].content_type

    connection = Faraday.new 'http://some.foreign.api' do |faraday|
      faraday.request :multipart
      faraday.headers['Content-Type'] = 'multipart/form-data'
      faraday.adapter Faraday.default_adapter
      
      # Any other faraday logic here...
    end
    
    # Optionally use a put request if you so desire
    response = connection.post '/path/to/resource', payload
    
    render json: response.body, status: response.status
  end
end