ruby rest-client posting String as a file multipart/form-data

post_string_file.rb

# rest-client recognizes files in multipart/form-data by checking
#   the object type passed as the field content. We need to craft
#   our string to appear as a file IO. `#stringfile` does that.
# An alternative approach is to just write string to a file and
#   pass file IO to rest-client but this would be suboptimal
#   provided we already have the content as a String.

    def stringfile(string,
                   filename="file_#{rand 100000}",
                   type=MIME::Types.type_for("xml").first.content_type)
      file = StringIO.new(string)

      file.instance_variable_set(:@path, filename)
      def file.path
        @path
      end
      file.instance_variable_set(:@type, type)
      def file.content_type
        @type
      end

      return file
    end

RestClient.post(
  "my.url.example.com/api",
  {multipart: true, somefieldname: stringfile(xunit_str)},
  headers={content_type: "multipart/form-data", accept: :json}
)