class CGI::Session
Overview¶ ↑
This file provides the CGI::Session class, which provides session support for CGI scripts. A session is a sequence of HTTP requests and responses linked together and associated with a single client. Information associated with the session is stored on the server between requests. A session id is passed between client and server with every request and response, transparently to the user. This adds state information to the otherwise stateless HTTP request/response protocol.
Lifecycle¶ ↑
A CGI::Session instance is created from a CGI object. By default, this CGI::Session instance will start a new session if
none currently exists, or continue the current session for this client if
one does exist. The new_session
option can be used to either
always or never create a new session. See new() for more details.
delete() deletes a session from session storage. It does not however remove the session id from the client. If the client makes another request with the same id, the effect will be to start a new session with the old session's id.
Setting and retrieving session data.¶ ↑
The Session class associates data with a session as key-value pairs. This data can be set and retrieved by indexing the Session instance using '[]', much the same as hashes (although other hash methods are not supported).
When session processing has been completed for a request, the session should be closed using the close() method. This will store the session's state to persistent storage. If you want to store the session's state to persistent storage without finishing session processing for this request, call the update() method.
Storing session state¶ ↑
The caller can specify what form of storage to use for the session's
data with the database_manager
option to ::new. The following storage classes
are provided as part of the standard library:
- CGI::Session::FileStore
-
stores data as plain text in a flat file. Only works with String data. This is the default storage type.
- CGI::Session::MemoryStore
-
stores data in an in-memory hash. The data only persists for as long as the current Ruby interpreter instance does.
- CGI::Session::PStore
-
stores data in Marshalled format. Provided by cgi/session/pstore.rb. Supports data of any type, and provides file-locking and transaction support.
Custom storage types can also be created by defining a class with the following methods:
new(session, options) restore # returns hash of session data. update close delete
Changing storage type mid-session does not work. Note in particular that by default the FileStore and PStore session data files have the same name. If your application switches from one to the other without making sure that filenames will be different and clients still have old sessions lying around in cookies, then things will break nastily!
Maintaining the session id.¶ ↑
Most session state is maintained on the server. However, a session id must be passed backwards and forwards between client and server to maintain a reference to this session state.
The simplest way to do this is via cookies. The CGI::Session class provides transparent support for session id communication via cookies if the client has cookies enabled.
If the client has cookies disabled, the session id must be included as a parameter of all requests sent by the client to the server. The CGI::Session class in conjunction with the CGI class will transparently add the session id as a hidden input field to all forms generated using the CGI#form() HTML generation method. No built-in support is provided for other mechanisms, such as URL re-writing. The caller is responsible for extracting the session id from the #session_id attribute and manually encoding it in URLs and adding it as a hidden input to HTML forms created by other mechanisms. Also, session expiry is not automatically handled.
Examples of use¶ ↑
Setting the user's name¶ ↑
require 'cgi' require 'cgi/session' require 'cgi/session/pstore' # provides CGI::Session::PStore cgi = CGI.new("html4") session = CGI::Session.new(cgi, 'database_manager' => CGI::Session::PStore, # use PStore 'session_key' => '_rb_sess_id', # custom session key 'session_expires' => Time.now + 30 * 60, # 30 minute timeout 'prefix' => 'pstore_sid_') # PStore option if cgi.has_key?('user_name') and cgi['user_name'] != '' # coerce to String: cgi[] returns the # string-like CGI::QueryExtension::Value session['user_name'] = cgi['user_name'].to_s elsif !session['user_name'] session['user_name'] = "guest" end session.close
Creating a new session safely¶ ↑
require 'cgi' require 'cgi/session' cgi = CGI.new("html4") # We make sure to delete an old session if one exists, # not just to free resources, but to prevent the session # from being maliciously hijacked later on. begin session = CGI::Session.new(cgi, 'new_session' => false) session.delete rescue ArgumentError # if no old session end session = CGI::Session.new(cgi, 'new_session' => true) session.close
Attributes
The id of this session.
The id of this session.
Public Class Methods
Create a new CGI::Session object for
request
.
request
is an instance of the CGI
class (see
cgi.rb). option
is a hash of options for initialising this CGI::Session instance. The following options are
recognised:
- session_key
-
the parameter name used for the session id. Defaults to '_session_id'.
- #session_id
-
the session id to use. If not provided, then it is retrieved from the
session_key
parameter of the request, or automatically generated for a new session. - #new_session
-
if true, force creation of a new session. If not set, a new session is only created if none currently exists. If false, a new session is never created, and if none currently exists and the
session_id
option is not set, an ArgumentError is raised. - database_manager
-
the name of the class providing storage facilities for session state persistence. Built-in support is provided for
FileStore
(the default),MemoryStore
, andPStore
(from cgi/session/pstore.rb). See the documentation for these classes for more details.
The following options are also recognised, but only apply if the session id is stored in a cookie.
- session_expires
-
the time the current session expires, as a
Time
object. If not set, the session will terminate when the user's browser is closed. - session_domain
-
the hostname domain for which this session is valid. If not set, defaults to the hostname of the server.
- session_secure
-
if
true
, this session will only work over HTTPS. - session_path
-
the path for which this session applies. Defaults to the directory of the CGI script.
option
is also passed on to the session storage class
initializer; see the documentation for each session storage class for the
options they support.
The retrieved or created session is automatically added to
request
as a cookie, and also to its
output_hidden
table, which is used to add hidden input
elements to forms.
WARNING the output_hidden
fields are
surrounded by a <fieldset> tag in HTML 4 generation, which is
not invisible on many browsers; you may wish to disable the use of
fieldsets with code similar to the following (see blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-list/37805)
cgi = CGI.new("html4") class << cgi undef_method :fieldset end
# File lib/cgi/session.rb, line 245 def initialize(request, option={}) @new_session = false session_key = option['session_key'] || '_session_id' session_id = option['session_id'] unless session_id if option['new_session'] session_id = create_new_id @new_session = true end end unless session_id if request.key?(session_key) session_id = request[session_key] session_id = session_id.read if session_id.respond_to?(:read) end unless session_id session_id, = request.cookies[session_key] end unless session_id unless option.fetch('new_session', true) raise ArgumentError, "session_key `%s' should be supplied"%session_key end session_id = create_new_id @new_session = true end end @session_id = session_id dbman = option['database_manager'] || FileStore begin @dbman = dbman::new(self, option) rescue NoSession unless option.fetch('new_session', true) raise ArgumentError, "invalid session_id `%s'"%session_id end session_id = @session_id = create_new_id unless session_id @new_session=true retry end request.instance_eval do @output_hidden = {session_key => session_id} unless option['no_hidden'] @output_cookies = [ Cookie::new("name" => session_key, "value" => session_id, "expires" => option['session_expires'], "domain" => option['session_domain'], "secure" => option['session_secure'], "path" => if option['session_path'] option['session_path'] elsif ENV["SCRIPT_NAME"] File::dirname(ENV["SCRIPT_NAME"]) else "" end) ] unless option['no_cookies'] end @dbprot = [@dbman] ObjectSpace::define_finalizer(self, Session::callback(@dbprot)) end
Public Instance Methods
Retrieve the session data for key key
.
# File lib/cgi/session.rb, line 306 def [](key) @data ||= @dbman.restore @data[key] end
Set the session data for key key
.
# File lib/cgi/session.rb, line 312 def []=(key, val) @write_lock ||= true @data ||= @dbman.restore @data[key] = val end
Store session data on the server and close the session storage. For some session storage types, this is a no-op.
# File lib/cgi/session.rb, line 326 def close @dbman.close @dbprot.clear end
Delete the session from storage. Also closes the storage.
Note that the session's data is not automatically deleted upon the session expiring.
# File lib/cgi/session.rb, line 335 def delete @dbman.delete @dbprot.clear end
Store session data on the server. For some session storage types, this is a no-op.
# File lib/cgi/session.rb, line 320 def update @dbman.update end
Private Instance Methods
Create a new session id.
The session id is an MD5 hash based upon the time, a random number, and a constant string. This routine is used internally for automatically generated session ids.
# File lib/cgi/session.rb, line 170 def create_new_id require 'securerandom' begin session_id = SecureRandom.hex(16) rescue NotImplementedError require 'digest/md5' md5 = Digest::MD5::new now = Time::now md5.update(now.to_s) md5.update(String(now.usec)) md5.update(String(rand(0))) md5.update(String($$)) md5.update('foobar') session_id = md5.hexdigest end session_id end