Sample function in a post model to share to the post Facebook and Twitter

Gemfile

gem 'koala'
gem 'bitly', '~> 0.8.0'
gem 'twitter'

post.rb

# Post model of Rails
class Post
  field :text, type: String, default: ''
  # NOTE: field image is an image object of Dragonfly

  belongs_to :user

  def share_to user, targets={}
    logger.debug "[share_to] <<< user: #{user.inspect}, targets = #{targets.inspect}"

    return nil if !user || targets.delete_if do |key, value| !value end.empty?

    shared = false
    message = self.text
    tiny_url = self.tiny_url

    if targets[:facebook] && (facebook = user.facebook_client)
      logger.debug "[share_to]> Sharing to Facebook via #{facebook.inspect}"

      facebook.put_picture(File.open(self.image.path), "image/jpeg",
            { :message => message + " | " + tiny_url }) if self.image
      shared ||= true
    end

    if targets[:twitter] && (twitter = user.twitter_client)
      logger.debug "[share_to]> Sharing to Twitter via #{twitter.inspect}"
      twit = ''
      message.each_char do |c|
        break if twit.bytesize + c.bytesize > 139 - tiny_url.size
        twit << c
      end

      twitter.update_with_media(twit + ' ' + tiny_url,
          File.open(self.image.path))
      shared ||= true
    end

    shared
  rescue Exception
    logger.info "[share_to]> #{$!.class}: #{$!}\n\t#{$@.join("\n\t")}"
    false
  end

  protected

  def tiny_url
    Bitly.use_api_version_3 # required for short link
    bitly = Bitly.new(Settings.bitly_key, Settings.bitly_secret)
    short_url = bitly.shorten(File.join(Settings.app_url,
        'post',self.id.to_s)).short_url
    logger.debug "[tiny_url]>>> #{short_url.inspect}"
    short_url
  end
end

posts_controller.rb

# Posts Controller of Rails
class PostsController < ApplicationController
  # NOTE: before filtering the share we calls find_post method
  # NOTE: current_user is method of Devise (or may be predefined)

  def share
    shared = @post.share_to(current_user,
        :facebook => params[:share_facebook] == 'true',
        :twitter => params[:share_twitter] == 'true' )
    head( shared && :created || :bad_requests ) if action_name == 'share'
  end
end

user.rb

# User model of Rails
class User
  field :facebook_token, type: String
  field :twitter_token, type: String
  field :twitter_secret, type: String

  # NOTE: UserException::InvalidSocial is an invalid social exception for the User model

  def authenticated_in_social? social
    case social.to_s.to_sym
    when :twitter
      !self.twitter_token.blank? && !self.twitter_secret.blank?
    when :facebook
      !self.facebook_token.blank?
    else
      raise UserException::InvalidSocial
    end
  end

  def facebook_client
    return nil unless self.authenticated_in_social? :facebook

    Koala::Facebook::API.new(self.token)
  rescue
    nil
  end

  def twitter_client
    return nil unless self.authenticated_in_social? :twitter

    Twitter::Client.new(
        :oauth_token => self.twitter_token,
        :oauth_token_secret => self.twitter_secret
      )
  rescue
    nil
  end
end