Connetion refused error with Rest api client in new plugin code

[kadivar]

Hi
I'm coding a plugin with colibri-software's plugin supported engine & inside it i'm using a restful api client for interacting with locomotivecms web service but right at starting , web server (puma) encounter to this error:

! Unable to load application: Errno::ECONNREFUSED: Connection refused - connect(2)
/home/kwair/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/1.9.1/net/http.rb:763:in `initialize': Connection refused - connect(2) (Errno::ECONNREFUSED)

I use httparty & rest-client and both of them have this problem. another thing that i have to mention is there is not any problem in shell and through curl , httparty , rest-client & also Advanced Rest client extention of chrome every thing works fine.
in my plugin at first i include this items:

require 'locomotive_plugins'
require "PLUGIN_NAME/version"
require 'uri'
require 'httparty'
require 'locomotive/mounter'

and then code my client same Didier's code sample at (https://gist.github.com/did/725202d5f4417cbbbc72/revisions) this way:

$api_base_url = "ADDRESS"
$api_key = "MY API CODE"
Locomotive::Mounter::EngineApi.set_token(uri: "http://#{$api_base_url}/locomotive/api", api_key: $api_key)
attributes = {
title: 'Hello world',
content: 'Lorem ipsum'
}
query = { query: { 'content_entry' => attributes } }
response = Locomotive::Mounter::EngineApi.post("/content_types/posts/entries.json", query)
if response.success?
puts "article created"
else
puts "failed to create an article"
end
Another official code sample with get & put also encountered to this error.
I test both localhost on my laptop(linux mint 17) and also domain name on my server(centos6) for $api_base_url.
please advice me to pass this big problem.

Thanks