Class CGI::Session::CookieStore
In: vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb
Parent: Object

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. TamperedWithCookie is raised if the data integrity check fails.

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.

            Example:  :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

Classes and Modules

Class CGI::Session::CookieStore::CookieOverflow
Class CGI::Session::CookieStore::TamperedWithCookie

Constants

MAX = 4096   Cookies can typically store 4096 bytes.
SECRET_MIN_LENGTH = 30

Public Class methods

Called from CGI::Session only.

[Source]

    # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 53
53:   def initialize(session, options = {})
54:     # The session_key option is required.
55:     if options['session_key'].blank?
56:       raise ArgumentError, 'A session_key is required to write a cookie containing the session data. Use config.action_controller.session = { :session_key => "_myapp_session", :secret => "some secret phrase" } in config/environment.rb'
57:     end
58: 
59:     # The secret option is required.
60:     ensure_secret_secure(options['secret'])
61: 
62:     # Keep the session and its secret on hand so we can read and write cookies.
63:     @session, @secret = session, options['secret']
64: 
65:     # Message digest defaults to SHA1.
66:     @digest = options['digest'] || 'SHA1'
67: 
68:     # Default cookie options derived from session settings.
69:     @cookie_options = {
70:       'name'    => options['session_key'],
71:       'path'    => options['session_path'],
72:       'domain'  => options['session_domain'],
73:       'expires' => options['session_expires'],
74:       'secure'  => options['session_secure']
75:     }
76: 
77:     # Set no_hidden and no_cookies since the session id is unused and we
78:     # set our own data cookie.
79:     options['no_hidden'] = true
80:     options['no_cookies'] = true
81:   end

Public Instance methods

Write the session data cookie if it was loaded and has changed.

[Source]

     # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 109
109:   def close
110:     if defined?(@data) && !@data.blank?
111:       updated = marshal(@data)
112:       raise CookieOverflow if updated.size > MAX
113:       write_cookie('value' => updated) unless updated == @original
114:     end
115:   end

Delete the session data by setting an expired cookie with no data.

[Source]

     # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 118
118:   def delete
119:     @data = nil
120:     clear_old_cookie_value
121:     write_cookie('value' => '', 'expires' => 1.year.ago)
122:   end

To prevent users from using something insecure like "Password" we make sure that the secret they‘ve provided is at least 30 characters in length.

[Source]

    # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 85
85:   def ensure_secret_secure(secret)
86:     # There's no way we can do this check if they've provided a proc for the
87:     # secret.
88:     return true if secret.is_a?(Proc)
89: 
90:     if secret.blank?
91:       raise ArgumentError, %Q{A secret is required to generate an integrity hash for cookie session data. Use config.action_controller.session = { :session_key => "_myapp_session", :secret => "some secret phrase of at least #{SECRET_MIN_LENGTH} characters" } in config/environment.rb}
92:     end
93: 
94:     if secret.length < SECRET_MIN_LENGTH
95:       raise ArgumentError, %Q{Secret should be something secure, like "#{CGI::Session.generate_unique_id}".  The value you provided, "#{secret}", is shorter than the minimum length of #{SECRET_MIN_LENGTH} characters}
96:     end
97:   end

Generate the HMAC keyed message digest. Uses SHA1 by default.

[Source]

     # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 125
125:   def generate_digest(data)
126:     key = @secret.respond_to?(:call) ? @secret.call(@session) : @secret
127:     OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(@digest), key, data)
128:   end

Restore session data from the cookie.

[Source]

     # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 100
100:   def restore
101:     @original = read_cookie
102:     @data = unmarshal(@original) || {}
103:   end

Wait until close to write the session data cookie.

[Source]

     # File vendor/rails/actionpack/lib/action_controller/session/cookie_store.rb, line 106
106:   def update; end

[Validate]