encode_multipart_form_data

# File lib/net/http/generic_request.rb, line 235
  def encode_multipart_form_data(out, params, opt)
    charset = opt[:charset]
    boundary = opt[:boundary]
    require 'securerandom' unless defined?(SecureRandom)
    boundary ||= SecureRandom.urlsafe_base64(40)
    chunked_p = chunked?

    buf = ''
    params.each do |key, value, h={}|
      key = quote_string(key, charset)
      filename =
        h.key?(:filename) ? h[:filename] :
        value.respond_to?(:to_path) ? File.basename(value.to_path) :
        nil

      buf << "--#{boundary}\r\n"
      if filename
        filename = quote_string(filename, charset)
        type = h[:content_type] || 'application/octet-stream'
        buf << "Content-Disposition: form-data; "            "name=\"#{key}\"; filename=\"#{filename}\"\r\n"            "Content-Type: #{type}\r\n\r\n"
        if !out.respond_to?(:write) || !value.respond_to?(:read)
          # if +out+ is not an IO or +value+ is not an IO
          buf << (value.respond_to?(:read) ? value.read : value)
        elsif value.respond_to?(:size) && chunked_p
          # if +out+ is an IO and +value+ is a File, use IO.copy_stream
          flush_buffer(out, buf, chunked_p)
          out << "%x\r\n" % value.size if chunked_p
          IO.copy_stream(value, out)
          out << "\r\n" if chunked_p
        else
          # +out+ is an IO, and +value+ is not a File but an IO
          flush_buffer(out, buf, chunked_p)
          1 while flush_buffer(out, value.read(4096), chunked_p)
        end
      else
        # non-file field:
        #   HTML5 says, "The parts of the generated multipart/form-data
        #   resource that correspond to non-file fields must not have a
        #   Content-Type header specified."
        buf << "Content-Disposition: form-data; name=\"#{key}\"\r\n\r\n"
        buf << (value.respond_to?(:read) ? value.read : value)
      end
      buf << "\r\n"
    end
    buf << "--#{boundary}--\r\n"
    flush_buffer(out, buf, chunked_p)
    out << "0\r\n\r\n" if chunked_p
  end