This cookie-based session store is the Rails default. Sessions typically contain at most a user_id and flash message; both fit within the 4K cookie size limit. Cookie-based sessions are dramatically faster than the alternatives.

If you have more than 4K of session data or don‘t want your data to be visible to the user, pick another session store.

CookieOverflow is raised if you attempt to store more than 4K of data.

A message digest is included with the cookie to ensure data integrity: a user cannot alter his user_id without knowing the secret key included in the hash. New apps are generated with a pregenerated secret in config/environment.rb. Set your own for old apps you‘re upgrading.

Session options:

  • :secret: An application-wide key string or block returning a string called per generated digest. The block is called with the CGI::Session instance as an argument. It‘s important that the secret is not vulnerable to a dictionary attack. Therefore, you should choose a secret consisting of random numbers and letters and more than 30 characters. Examples:
      :secret => '449fe2e7daee471bffae2fd8dc02313d'
      :secret => Proc.new { User.current_user.secret_key }
    
  • :digest: The message digest algorithm used to verify session integrity defaults to ‘SHA1’ but may be any digest provided by OpenSSL, such as ‘MD5’, ‘RIPEMD160’, ‘SHA256’, etc.

To generate a secret key for an existing application, run "rake secret" and set the key in config/environment.rb.

Note that changing digest or secret invalidates all existing sessions!

Methods
Included Modules
Classes and Modules
Class ActionController::Session::CookieStore::CookieOverflow
Constants
MAX = 4096
  Cookies can typically store 4096 bytes.
SECRET_MIN_LENGTH = 30
DEFAULT_OPTIONS = { :key => '_session_id', :domain => nil, :path => "/", :expire_after => nil, :httponly => true
ENV_SESSION_KEY = "rack.session".freeze
ENV_SESSION_OPTIONS_KEY = "rack.session.options".freeze
HTTP_SET_COOKIE = "Set-Cookie".freeze
Public Class methods
new(app, options = {})
    # File actionpack/lib/action_controller/session/cookie_store.rb, line 60
60:       def initialize(app, options = {})
61:         # Process legacy CGI options
62:         options = options.symbolize_keys
63:         if options.has_key?(:session_path)
64:           ActiveSupport::Deprecation.warn "Giving :session_path to SessionStore is deprecated, " <<
65:             "please use :path instead", caller
66:           options[:path] = options.delete(:session_path)
67:         end
68:         if options.has_key?(:session_key)
69:           ActiveSupport::Deprecation.warn "Giving :session_key to SessionStore is deprecated, " <<
70:             "please use :key instead", caller
71:           options[:key] = options.delete(:session_key)
72:         end
73:         if options.has_key?(:session_http_only)
74:           ActiveSupport::Deprecation.warn "Giving :session_http_only to SessionStore is deprecated, " <<
75:             "please use :httponly instead", caller
76:           options[:httponly] = options.delete(:session_http_only)
77:         end
78: 
79:         @app = app
80: 
81:         # The session_key option is required.
82:         ensure_session_key(options[:key])
83:         @key = options.delete(:key).freeze
84: 
85:         # The secret option is required.
86:         ensure_secret_secure(options[:secret])
87:         @secret = options.delete(:secret).freeze
88: 
89:         @digest = options.delete(:digest) || 'SHA1'
90:         @verifier = verifier_for(@secret, @digest)
91: 
92:         @default_options = DEFAULT_OPTIONS.merge(options).freeze
93: 
94:         freeze
95:       end
Public Instance methods
call(env)
     # File actionpack/lib/action_controller/session/cookie_store.rb, line 97
 97:       def call(env)
 98:         prepare!(env)
 99:         
100:         status, headers, body = @app.call(env)
101: 
102:         session_data = env[ENV_SESSION_KEY]
103:         options = env[ENV_SESSION_OPTIONS_KEY]
104:         request = ActionController::Request.new(env)
105:         
106:         if !(options[:secure] && !request.ssl?) && (!session_data.is_a?(AbstractStore::SessionHash) || session_data.loaded? || options[:expire_after])
107:           session_data.send(:load!) if session_data.is_a?(AbstractStore::SessionHash) && !session_data.loaded?
108: 
109:           persistent_session_id!(session_data)
110:           session_data = marshal(session_data.to_hash)
111: 
112:           raise CookieOverflow if session_data.size > MAX
113:           cookie = Hash.new
114:           cookie[:value] = session_data
115:           unless options[:expire_after].nil?
116:             cookie[:expires] = Time.now + options[:expire_after]
117:           end
118: 
119:           cookie = build_cookie(@key, cookie.merge(options))
120:           headers[HTTP_SET_COOKIE] = [] if headers[HTTP_SET_COOKIE].blank?
121:           headers[HTTP_SET_COOKIE] << cookie
122:         end
123: 
124:         [status, headers, body]
125:       end