Amazon S3 request generator class

aws_S3.rb

class AwsS3
  AWS_ACCESS_KEY = ENV['AWS_ACCESS_KEY_ID']
  AWS_SECRET_KEY = ENV['AWS_SECRET_ACCESS_KEY']
  S3_BUCKET      = ENV['S3_BUCKET'] || "#{Rails.application.class.parent_name}_#{Rails.env}".downcase

  attr_accessor :file_name, :mime_type, :path, :acl, :expires_in
  attr_writer :as_attachment

  def initialize(file_name, mime_type, acl: 'private', path: '/')
    @file_name = esc file_name # escape for spaces and the like
    @mime_type = mime_type
    @acl       = acl
    @path      = path
  end


  # NOTE why we use non subdomain uris http://stackoverflow.com/questions/5208851/is-there-a-workaround-to-open-urls-containing-underscores-in-ruby
  def self.base_url
    "https://s3.amazonaws.com/#{S3_BUCKET}"
  end

  def base_url
    self.class.base_url
  end

  def file_path
    fp = File.join(path, file_name).gsub /^\//, '' # remove leading /

    return fp+"?response-content-disposition=attachment" if as_attachment?
    fp
  end

  def url
    File.join(base_url, file_path)
  end

  def expires_in
    @expires_in ||= 60.minutes.from_now.to_i
  end

  def as_attachment?
    @as_attachment == true
  end


  def method_missing(method, *args, &block)
    if method.to_s =~ /^(get|put|delete)_signature$/
      esc Base64.encode64(OpenSSL::HMAC
                          .digest(sha1, AWS_SECRET_KEY, __send__("#{$1}_request"))).gsub("\n","")

    elsif method.to_s =~ /^(get|put|delete)_signed_request(!)?$/
      _url = [
        url, 
        %{#{key_and_expires_params}&Signature=#{__send__("#{$1}_signature")}}
      ].join(as_attachment? ? '&' : '?')

      $2 == '!' ? esc(_url) : _url

    else
      super
    end
  end

  def respond_to?(meth, include_private: false)
    return true if meth =~ /^(get|put|delete)_signature$/
    return true if meth =~ /^(get|put|delete)_signed_request(!)?$/
    super
  end


  private

  def key_and_expires_params
    "AWSAccessKeyId=#{AWS_ACCESS_KEY}&Expires=#{expires_in}"
  end

  def amz_acl_header
    "x-amz-acl:#{acl}"
  end

  def amz_date_header
    "x-amz-date:#{expires_in}"
  end

  def bucket_file_path
    "/#{S3_BUCKET}/#{file_path}"
  end

  def put_request
    ['PUT', '', mime_type, expires_in, amz_acl_header, bucket_file_path].join("\n").encode('UTF-8')
  end

  def get_request
    ['GET', '', '', expires_in, bucket_file_path].join("\n").encode('UTF-8')
  end

  def delete_request
    ['DELETE', '', '', expires_in, bucket_file_path].join("\n").encode('UTF-8')
  end

  def sha1
    OpenSSL::Digest::Digest.new('sha1')
  end

  def esc(val)
    CGI.escape val
  end
end