Content-Type: multipart/form-data; boundary=301405

RestClient.post '/data', :myfile => File.new("/path/to/image.jpg", 'rb')

RestClient.post '/data', :myfile => File.new("/path/to/image.jpg", 'rb'), :content_type => 'multipart/related'

files = { File.new("myfile1","rb"), File.new("myfile2","rb")}
mpost = Mutipart("main", "<my xml main part content which refers to file names>",files )
mpost.post("our_url","post")

require 'net/http'
require 'uri'
require 'pp'
require 'mime/types'

class Multipart

  def initialize( main_part_id, main_part_content, file_names )
    @file_names = file_names
    @main_part_id = main_part_id
    @main_part_content = main_part_content
  end

  def post( to_url, method = :post )
    boundary = "###-------#{Time.new}-----####"

    parts = []
    streams = []
    # write main part first
    parts << StringPart.new( "--" + boundary + "rn")
    parts << StringPart.new("Content-Disposition: name="#{@main_part_id}";"rn" +
      "Content-ID: #{@main_part_id}rnrn"+
      "Content-Type: application/xmlrnrn" +
    @main_part_content + "rnrn")
    parts << StringPart.new( "rn--" + boundary + "rn")

    @file_names.each do |param_name, filestream|
      raise 'mutlipartsend: empty file object' if filestream.blank?

      filename= filestream.respond_to?(:original_path) ? filestream.original_path : filestream.path
      ctype = filestream.respond_to?(:content_type) ? filestream.content_type: nil
      fsize = filestream.respond_to?(:lstat) ? filestream.lstat.size : filestream.size


      if !ctype
        begin
            pos = filename.rindex('/') # if filename is a path
            fname = filename[pos + 1, filename.length - pos]
            mm = MIME::Types.type_for(fname)
            ctype = mm.first.content_type if !mm.blank?
        rescue Exception => e
          p e.message
        end
      end
      if !ctype
        ctype= 'application/binary'
        p "mutlipartsend: failed to determine contenttype for #{filename}. using application/binary"
      end


      parts << StringPart.new("Content-Disposition: name="" + param_name.to_s + ""; filename="" + filename + ""rn" +
        "Content-Type: #{ctype}rnrn")
        #"Content-Type: application/binaryrnrn")
      begin
        stream = File.open(filestream.path,"rb")
        streams << stream
        parts << StreamPart.new(stream, fsize)
        parts << StringPart.new( "rn--" + boundary + "rn" )
      rescue Exception => e
        p 'failed to load filestream '+ filestream.path
        p e.message
        raise 'failed to load filestream ' + e.message
      end

    end

    post_stream = MultipartStream.new( parts )

    url = URI.parse( to_url )
    req = method == :post ? Net::HTTP::Post.new(url.path) : Net::HTTP::Put.new(url.path)
    req.content_length = post_stream.size
    req.content_type = 'multipart/mixed; boundary=' + boundary
    req["myheader1"] = 'header1'
    req["myheader2"] = 'header2'

    req.body_stream = post_stream
    res = Net::HTTP.new(url.host, url.port).start {|http| http.request(req) }

    streams.each do |stream|
      stream.close();
    end

    res
  end

end

class StreamPart
  def initialize( stream, size )
    @stream, @size = stream, size
  end

  def size
    @size
  end

  def read( offset, how_much )
    @stream.read( how_much )
  end
end

class StringPart
  def initialize ( str )
    @str = str
  end

  def size
    @str.length
  end

  def read ( offset, how_much )
    @str[offset, how_much]
  end
end

class MultipartStream
  def initialize( parts )
    @parts = parts
    @part_no = 0;
    @part_offset = 0;
  end



  def size
    total = 0
    @parts.each do |part|
      total += part.size
    end
    total
  end

  def read ( how_much )
    if @part_no >= @parts.size
      return nil;
    end

    how_much_current_part = @parts[@part_no].size - @part_offset

    how_much_current_part = if how_much_current_part > how_much
      how_much
    else
      how_much_current_part
    end

    how_much_next_part = how_much - how_much_current_part

    current_part = @parts[@part_no].read(@part_offset, how_much_current_part )

    if how_much_next_part > 0
      @part_no += 1
      @part_changed=true
      @part_offset = 0
      next_part = read( how_much_next_part  )
      current_part + if next_part
        next_part
      else
        ''
      end
    else
      @part_offset += how_much_current_part
      current_part
    end
  end

end