Merge pull request #1017 from trainline-eu/add-part-params-class-to-a…

…llow-multipart-posts-with-json-content-and-file-upload

Create PartParams class to allow multipart posts with JSON content and file upload at the same time

lib/faraday.rb

@@ -160,7 +160,7 @@ def self.default_connection_options=(options)
 
   require_libs 'utils', 'options', 'connection', 'rack_builder', 'parameters',
                'middleware', 'adapter', 'request', 'response', 'upload_io',
-               'error'
+               'error', 'param_part'
 
   require_lib 'autoload' unless ENV['FARADAY_NO_AUTOLOAD']
 end

lib/faraday/param_part.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Faraday
+  # Allows multipart posts while specifying headers of a part
+  class ParamPart
+    def initialize(value, content_type, content_id = nil)
+      @value = value
+      @content_type = content_type
+      @content_id = content_id
+    end
+
+    def to_part(boundary, key)
+      Faraday::Parts::Part.new(boundary, key, value, headers)
+    end
+
+    def headers
+      {
+        'Content-Type' => content_type,
+        'Content-ID' => content_id
+      }
+    end
+
+    attr_reader :value, :content_type, :content_id
+  end
+end

lib/faraday/request/multipart.rb

@@ -52,7 +52,7 @@ def has_multipart?(obj) # rubocop:disable Naming/PredicateName
       def create_multipart(env, params)
         boundary = env.request.boundary
         parts = process_params(params) do |key, value|
-          Faraday::Parts::Part.new(boundary, key, value)
+          part(boundary, key, value)
         end
         parts << Faraday::Parts::EpiloguePart.new(boundary)
 
@@ -61,6 +61,14 @@ def create_multipart(env, params)
         body
       end
 
+      def part(boundary, key, value)
+        if value.respond_to?(:to_part)
+          value.to_part(boundary, key)
+        else
+          Faraday::Parts::Part.new(boundary, key, value)
+        end
+      end
+
       # @return [String]
       def unique_boundary
         "#{DEFAULT_BOUNDARY_PREFIX}-#{SecureRandom.hex}"

spec/faraday/request/multipart_spec.rb

@@ -68,6 +68,45 @@
     end
   end
 
+  context 'when providing json and IO content in the same payload' do
+    let(:io) { StringIO.new('io-content') }
+    let(:json) do
+      {
+        b: 1,
+        c: 2
+      }.to_json
+    end
+
+    let(:payload) do
+      {
+        json: Faraday::ParamPart.new(json, 'application/json'),
+        io: Faraday::UploadIO.new(io, 'application/pdf')
+      }
+    end
+
+    it_behaves_like 'a multipart request'
+
+    it 'forms a multipart request' do
+      response = conn.post('/echo', payload)
+
+      boundary = parse_multipart_boundary(response.headers['Content-Type'])
+      result = parse_multipart(boundary, response.body)
+      expect(result[:errors]).to be_empty
+
+      part_json, body_json = result.part('json')
+      expect(part_json).to_not be_nil
+      expect(part_json.mime).to eq('application/json')
+      expect(part_json.filename).to be_nil
+      expect(body_json).to eq(json)
+
+      part_io, body_io = result.part('io')
+      expect(part_io).to_not be_nil
+      expect(part_io.mime).to eq('application/pdf')
+      expect(part_io.filename).to eq('local.path')
+      expect(body_io).to eq(io.string)
+    end
+  end
+
   context 'when multipart objects in array param' do
     let(:payload) do
       {