Low level implementation of multipart post, using net/http

multipart.rb

# Low level implementation of multipart post, using net/http
class MultipartPost
  def initialize(uri:)
    @uri = uri
    @post_body = []
  end

  def send
    request = Net::HTTP::Post.new(@uri.request_uri)
    request.body = build_body
    request["Content-Type"] = "multipart/form-data; boundary=#{multipart_boundary}"
    request["Origin"] = "http://#{@uri.host}"

    http_connection.request(request)
  end

  def multipart_boundary
    @multipart_boundary ||= SecureRandom.hex
  end

  def http_connection
    @http_connection ||= Net::HTTP.new(@uri.host, @uri.port)
  end

  def build_body
    fail "No post fields added" if @post_body.empty?
    @post_body.join + "--#{multipart_boundary}--\r\n"
  end

  def add_field(name:, value:)
    @post_body << "--#{multipart_boundary}\r\n"
    @post_body << "Content-Disposition: form-data; name=\"#{name}\"\r\n"
    @post_body << "\r\n"
    @post_body << value
    @post_body << "\r\n"
  end

  def add_file(name:, contents:, filename:, content_type: "application/octet-stream")
    @post_body << "--#{multipart_boundary}\r\n"
    @post_body << "Content-Disposition: form-data; name=\"#{name}\"; filename=\"#{filename}\"\r\n"
    @post_body << "Content-Type: #{content_type}; charset=#{contents.encoding.to_s}\r\n"
    @post_body << "\r\n"
    @post_body << contents
    @post_body << "\r\n"
  end
end