signing an aws s3 url

gistfile1.rb

    # encoding : utf-8
    require 'openssl'
    require 'digest/sha1'
    require 'base64'
    
    module Aws
      extend self
      def signed_url(path, expire_date)
        digest = OpenSSL::Digest::Digest.new('sha1')
        can_string = "GET\n\n\n#{expire_date}\n/#{S3_BUCKET}/#{path}"
        hmac = OpenSSL::HMAC.digest(digest, S3_SECRET_ACCESS_KEY, can_string)
        signature = URI.escape(Base64.encode64(hmac).strip).encode_signs
        "https://s3.amazonaws.com/#{S3_BUCKET}/#{path}?AWSAccessKeyId=#{S3_ACCESS_KEY_ID}&Expires=#{expire_date}&Signature=#{signature}"
      end
    end

    class String
      def encode_signs
        signs = {'+' => "%2B", '=' => "%3D", '?' => '%3F', '@' => '%40',
          '$' => '%24', '&' => '%26', ',' => '%2C', '/' => '%2F', ':' => '%3A',
          ';' => '%3B', '?' => '%3F'}
        signs.keys.each do |key|
          self.gsub!(key, signs[key])
        end
        self
      end
    end