This is a record of my trial to use Google Drive API on Ruby (and on Rails).

For installed applications
Differences from web applications
-> Include some parameters in authorization code request at a first authorization (access_type=offline& approval_prompt=force)
-> Require refresh_token ( and access_token ,too).

My sample code is following.

qiita.rb

require 'google/api_client'
  ##
  # Retrieve a list of File resources.
  #
  CLIENT_ID = ' your client ID '
  CLIENT_SECRET = ' your client secret '
  REDIRECT_URI = ' your redirect url '
  OAUTH_SCOPE = 'https://www.googleapis.com/auth/drive'
  
 # Initialize the client & Google+ API
  client = Google::APIClient.new
  # Initialize OAuth 2.0 client
  # client.authorizaton returns Signet::OAuth2::Client objext

  client.authorization.client_id = CLIENT_ID
  client.authorization.client_secret = CLIENT_SECRET
  client.authorization.redirect_uri = REDIRECT_URI
  client.authorization.scope = OAUTH_SCOPE

  # Request authorization
  redirect_uri = client.authorization.authorization_uri
  # You will get a redirect URL, and input it to an address var of a browser.
  puts redirect_uri
  # When prompted ,copy an authorization code and paste it to your terminal.
  client.authorization.code = gets.strip

  # Get tokens
  # ex. {"access_token"=>"ya296ZSGyxLfflpv1ADxHjCKvZLoKyVylgjiLhW1sX_fKw",
  #      "token_type"=>"Bearer", "expires_in"=>3600,
  #      "refresh_token"=>"1/4jaoSQ_edOCVegeaORYEdlwMiwyLJB3E1uNz3hfKQto"}
  tokens = client.authorization.fetch_access_token
 
  #Update tokens and retrieve a list of File Resources.
 begin
    client.authorization.update_token!(
        :refresh_token => tokens["refresh_token"],
        :access_token => tokens["access_token"],
        :expires_in => tokens["expires_in"]
    )
    drive = client.discovered_api('drive', 'v2')  
rescue
    puts "Here is in resucue"
 ensure
    result = Array.new
    page_token = nil
    begin
      parameters = {}
      if page_token.to_s != ''
        parameters['pageToken'] = page_token
      end
      api_result = client.execute(
          :api_method => drive.files.list,
          :parameters => parameters)
      if api_result.status == 200
        files = api_result.data
        result.concat(files.items)
      else
        puts "An error occurred: #{result.data['error']['message']}"
        page_token = nil
      end
   end while page_token.to_s != ''
   # Printing file names
   result.each { |item|
      puts item.title
   }
end

参考にしたURL
http://www.eisbahn.jp/yoichiro/2012/10/google-drive-api-ruby-on-rails.html
http://www.eisbahn.jp/yoichiro/2012/05/google_oauth2_web_server_profile_refreshtoken.html
http://code.google.com/p/oauth-signet/wiki/SignetOAuth2Client
http://rubydoc.info/github/google/google-api-ruby-client/
https://developers.google.com/drive/v2/reference/files#resource
いじょ