Faraday multipart request with json & file data

Question

When trying to POST multipart data (file & json) with Faraday gem, remote server is not recognizing json data parameter and failing with validation error as it is required parameter.

connection = Faraday.new(url: "#{uri.scheme}://#{uri.host}:#{uri.port}") do |faraday|
              faraday.request :multipart
              faraday.request :url_encoded

              faraday.adapter :net_http
            end

request_data = { file: Faraday::UploadIO.new('somefile.png', 'image/png'), jsonBody: JSON.dump({ id: 'foo', name: 'bar' }) }

response = connection.post(uri.request_uri) do |request|
  request = Ff::Api::RequestHeaders.set(request, self.api_options)
  request.headers['content-type'] = 'multipart/form-data; boundary=-----------RubyMultipartPost'
  request.body = request_data
end

Working CURL request:

curl -v -H 'Authorization: bearer 7d70fb31-0eb9-4846-9ea8-933dfb69d8f1' \
-H 'Accept: application/xml,application/xhtml+xml,application/json,text/html,text/plain' \
-H 'Content-Type: multipart/form-data' \
-F 'jsonBody={"id":"foo","name":"bar"};type=application/json' \
'http://localhost:8080/localproject/rest-resource/items'

Curl Log:

*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8080 (#0)
> POST /localproject/rest-resource/items HTTP/1.1
> Host: localhost:8080
> Authorization: bearer 7d70fb31-0eb9-4846-9ea8-933dfb69d8f1
> USER_IP_ADDR: 127.0.0.1
> Accept: application/xml,application/xhtml+xml,application/json,text/html,text/plain
> Content-Length: 555
> Expect: 100-continue
> Content-Type: multipart/form-data; boundary=------------------------0c5f3acb5a4731ff
> 
< HTTP/1.1 100 Continue
< HTTP/1.1 200 OK
< Server: Apache-Coyote/1.1
< Cache-Control: no-cache, no-store, max-age=0, must-revalidate
< Pragma: no-cache
< Expires: 0
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: DENY
< X-Content-Type-Options: nosniff
< Content-Type: application/xml
< Transfer-Encoding: chunked
< Date: Thu, 08 Feb 2018 10:50:06 GMT
< 
* Connection #0 to host localhost left intact
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><updateResponse><id>5ce0b335-4638-474c-8c4a-9adb6c54b057</id><success>true</success></updateResponse>% 

Additional prefix "type=application/json" to request body seems to be making difference with CURL. Did not find any way to do the same with Faraday.

Faraday Version : 0.12.2 & 0.14.0

Ruby Version : 2.3.3

Rails : 5.2

Any help will be greatly appreciated.

Answer 1

Found that Faraday doesn't support mix multipart request (file upload with json/xml data). This is because mixing file and json data is not restful approach and should be avoided entirely. More discussion is happening here https://github.com/lostisland/faraday/issues/769

I have temporarily fixed the issue by patching Faraday::Mulitipart class to allow mixing JSON data,

class Faraday::Request::Multipart
  def create_multipart(env, params)
    boundary = env.request.boundary
    parts = process_params(params) do |key, value|
      if (JSON.parse(value) rescue false)
        Faraday::Parts::Part.new(boundary, key, value, 'Content-Type' => 'application/json')
      else
        Faraday::Parts::Part.new(boundary, key, value)
      end
    end
    parts << Faraday::Parts::EpiloguePart.new(boundary)

    body = Faraday::CompositeReadIO.new(parts)
    env.request_headers[Faraday::Env::ContentLength] = body.length.to_s
    return body
  end
end

But in long term one should change server implementation to avoid mix multipart requests.

Answer 2

Not sure if it's an option for others, but the server I was trying to POST to will accept the json as a file part (rather than the message body). In which case something like this will work:

require 'faraday'

conn = Faraday.new("http://server:port") do |f|
    f.request:multipart
    f.request:url_encoded
    f.adapter:net_http
end

payload = {
    filePart:Faraday::UploadIO.new("image.jpg", 'image/jpeg'),
    jsonPart:Faraday::UploadIO.new("stamp.json", 'application/json')
}

res = conn.post('/my/url/', payload)
puts res.body