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

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6184 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

3 files changed, 118 insertions, 3 deletions

diff --git a/actionpack/lib/action_controller/cgi_process.rb b/actionpack/lib/action_controller/cgi_process.rb
index aa4cba1066..5712abc701 100644
--- a/actionpack/lib/action_controller/cgi_process.rb
+++ b/actionpack/lib/action_controller/cgi_process.rb
@@ -2,6 +2,7 @@ require 'action_controller/cgi_ext/cgi_ext'
 require 'action_controller/cgi_ext/cookie_performance_fix'
 require 'action_controller/cgi_ext/raw_post_data_fix'
 require 'action_controller/cgi_ext/session_performance_fix'
+require 'action_controller/session/cookie_store'
 
 module ActionController #:nodoc:
   class Base
@@ -36,9 +37,9 @@ module ActionController #:nodoc:
     attr_accessor :cgi, :session_options
 
     DEFAULT_SESSION_OPTIONS = {
-      :database_manager => CGI::Session::PStore,
-      :prefix           => "ruby_sess.",
-      :session_path     => "/"
+      :database_manager => CGI::Session::CookieStore, # store data in cookie
+      :prefix           => "ruby_sess.",    # prefix session file names
+      :session_path     => "/"              # available to all paths in app
     } unless const_defined?(:DEFAULT_SESSION_OPTIONS)
 
     def initialize(cgi, session_options = {})
diff --git a/actionpack/lib/action_controller/session/cookie_store.rb b/actionpack/lib/action_controller/session/cookie_store.rb
new file mode 100644
index 0000000000..25717cc5e7
--- /dev/null
+++ b/actionpack/lib/action_controller/session/cookie_store.rb
@@ -0,0 +1,113 @@
+require 'cgi'
+require 'cgi/session'
+require 'base64'        # to make marshaled data HTTP header friendly
+require 'digest/sha2'   # to generate the data integrity hash
+
+# 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.
+#
+# A secure hash 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 session :secret option in
+# Application Controller. Set your own for old apps you're upgrading.
+# Note that changing the secret invalidates all existing sessions!
+#
+# 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.
+class CGI::Session::CookieStore
+  # Cookies can typically store 4096 bytes.
+  MAX = 4096
+
+  # Raised when storing more than 4K of session data.
+  class CookieOverflow < StandardError; end
+
+  # Raised when the cookie fails its integrity check.
+  class TamperedWithCookie < StandardError; end
+
+  # Called from CGI::Session only.
+  def initialize(session, options = {})
+    # The secret option is required.
+    if options['secret'].blank?
+      raise ArgumentError, 'A secret is required to generate an integrity hash for cookie session data. Use session :secret => "some secret phrase" in ApplicationController.'
+    end
+
+    # Keep the session and its secret on hand so we can read and write cookies.
+    @session, @secret = session, options['secret']
+
+    # 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']
+    }
+
+    # 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
+
+  # Restore session data from the cookie.
+  def restore
+    @original = read_cookie
+    @data = unmarshal(@original) || {}
+  end
+
+  # Wait until close to write the session data cookie.
+  def update; end
+
+  # Write the session data cookie if it was loaded and has changed.
+  def close
+    if defined? @data
+      updated = marshal(@data)
+      raise CookieOverflow if updated.size > MAX
+      write_cookie('value' => updated) unless updated == @original
+    end
+  end
+
+  # Delete the session data by setting an expired cookie with no data.
+  def delete
+    write_cookie('value' => '', 'expires' => 1.year.ago)
+  end
+
+  private
+    # Marshal a session hash into safe cookie data. Include an integrity hash.
+    def marshal(session)
+      data = Base64.encode64(Marshal.dump(session)).chop
+      "#{data}--#{generate_digest(data)}"
+    end
+
+    # Unmarshal cookie data to a hash and verify its integrity.
+    def unmarshal(cookie)
+      if cookie
+        data, digest = cookie.split('--')
+        raise TamperedWithCookie unless digest == generate_digest(data)
+        Marshal.load(Base64.decode64(data))
+      end
+    end
+
+    # Generate the inline SHA512 message digest. Larger (128 bytes) than SHA256
+    # (64 bytes) or RMD160 (40 bytes), but small relative to the 4096 byte
+    # max cookie size.
+    def generate_digest(data)
+      Digest::SHA512.hexdigest "#{data}#{@secret}"
+    end
+
+    # Read the session data cookie.
+    def read_cookie
+      @session.cgi.cookies[@cookie_options['name']].first
+    end
+
+    # CGI likes to make you hack.
+    def write_cookie(options)
+      cookie = CGI::Cookie.new(@cookie_options.merge(options))
+      @session.cgi.send :instance_variable_set, '@output_cookies', [cookie]
+    end
+end
diff --git a/actionpack/lib/action_controller/session_management.rb b/actionpack/lib/action_controller/session_management.rb
index 24f1651b00..bf402c93e1 100644
--- a/actionpack/lib/action_controller/session_management.rb
+++ b/actionpack/lib/action_controller/session_management.rb
@@ -1,3 +1,4 @@
+require 'action_controller/session/cookie_store'
 require 'action_controller/session/drb_store'
 require 'action_controller/session/mem_cache_store'
 if Object.const_defined?(:ActiveRecord)