Class: CGI::Session::CookieStore

Inherits:
Object
  • Object
show all
Defined in:
lib/action_controller/session/cookie_store.rb

Overview

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. 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!

Defined Under Namespace

Classes: CookieOverflow, TamperedWithCookie

Constant Summary collapse

MAX =

Cookies can typically store 4096 bytes.

4096
SECRET_MIN_LENGTH =

characters

30

Instance Method Summary collapse

Constructor Details

#initialize(session, options = {}) ⇒ CookieStore

Called from CGI::Session only.


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# File 'lib/action_controller/session/cookie_store.rb', line 52

def initialize(session, options = {})
  # The session_key option is required.
  if options['session_key'].blank?
    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'
  end

  # The secret option is required.
  ensure_secret_secure(options['secret'])

  # Keep the session and its secret on hand so we can read and write cookies.
  @session, @secret = session, options['secret']

  # Message digest defaults to SHA1.
  @digest = options['digest'] || 'SHA1'

  # Default cookie options derived from session settings.
  @cookie_options = {
    'name'    => options['session_key'],
    'path'    => options['session_path'],
    'domain'  => options['session_domain'],
    'expires' => options['session_expires'],
    'secure'  => options['session_secure'],
    'http_only' => options['session_http_only']
  }

  # Set no_hidden and no_cookies since the session id is unused and we
  # set our own data cookie.
  options['no_hidden'] = true
  options['no_cookies'] = true
end

Instance Method Details

#closeObject

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


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# File 'lib/action_controller/session/cookie_store.rb', line 109

def close
  if defined?(@data) && !@data.blank?
    updated = marshal(@data)
    raise CookieOverflow if updated.size > MAX
    write_cookie('value' => updated) unless updated == @original
  end
end

#deleteObject

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


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# File 'lib/action_controller/session/cookie_store.rb', line 118

def delete
  @data = nil
  clear_old_cookie_value
  write_cookie('value' => nil, 'expires' => 1.year.ago)
end

#ensure_secret_secure(secret) ⇒ Object

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.


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# File 'lib/action_controller/session/cookie_store.rb', line 85

def ensure_secret_secure(secret)
  # There's no way we can do this check if they've provided a proc for the
  # secret.
  return true if secret.is_a?(Proc)

  if secret.blank?
    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}
  end

  if secret.length < SECRET_MIN_LENGTH
    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}
  end
end

#generate_digest(data) ⇒ Object

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


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# File 'lib/action_controller/session/cookie_store.rb', line 125

def generate_digest(data)
  key = @secret.respond_to?(:call) ? @secret.call(@session) : @secret
  OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(@digest), key, data)
end

#restoreObject

Restore session data from the cookie.


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# File 'lib/action_controller/session/cookie_store.rb', line 100

def restore
  @original = read_cookie
  @data = unmarshal(@original) || {}
end

#updateObject

Wait until close to write the session data cookie.


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# File 'lib/action_controller/session/cookie_store.rb', line 106

def update; end