# CGI::Session (Class)

In: | cgi/session.rb cgi/session/pstore.rb
Parent: | Object

Class representing an HTTP session. See documentation for the file cgi/session.rb for an introduction to HTTP sessions.

## 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 CGI::Session::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

## Methods

[] []= []= close create_new_id delete new update

## Attributes

session_id | [R] | The id of this session.

## Classes and Modules

Class CGI::Session::FileStore
Class CGI::Session::MemoryStore
Class CGI::Session::PStore

## Public Class methods

create_new_id()

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.

[Source]

    # File cgi/session.rb, line 173
        def Session::create_new_id
          require 'digest/md5'
          md5 = Digest::MD5::new
          md5.update(String(Time::now))
          md5.update(String(rand(0)))
          md5.update(String($$))
          md5.update('foobar')
          md5.hexdigest[0,16]
        end

new(request, option={})

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`, and `PStore` (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 continue indefinitely.
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 initialiser; 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

[Source]

    # File cgi/session.rb, line 239
        def initialize(request, option={})
          session_key = option['session_key'] || '_session_id'
          id = option['session_id']
          unless id
            if option['new_session']
              id = Session::create_new_id
            end
          end
          unless id
            if request.key?(session_key)
              id = request[session_key]
              id = id.read if id.respond_to?(:read)
            end
            unless id
              id, = request.cookies[session_key]
            end
            unless id
              if option.key?('new_session') and not option['new_session']
                raise ArgumentError, "session_key `%s' should be supplied"%session_key
              end
              id = Session::create_new_id
            end
          end
          @session_id = id
          dbman = option['database_manager'] || FileStore
          @dbman = dbman::new(self, option)
          request.instance_eval do
            @output_hidden = {session_key => id}
            @output_cookies =  [
              Cookie::new("name" => session_key,
                          "value" => id,
                          "expires" => option['session_expires'],
                          "domain" => option['session_domain'],
                          "secure" => option['session_secure'],
                          "path" => if option['session_path'] then
                                      option['session_path']
                                    elsif ENV["SCRIPT_NAME"] then
                                      File::dirname(ENV["SCRIPT_NAME"])
                                    else
                                      ""
                                    end)
            ]
          end
          @dbprot = [@dbman]
          ObjectSpace::define_finalizer(self, Session::callback(@dbprot))
        end

## Public Instance methods

[](key)

Retrieve the session data for key `key`.

[Source]

    # File cgi/session.rb, line 287
        def [](key)
          unless @data
            @data = @dbman.restore
          end
          @data[key]
        end

[]=(key, val)

Set the session date for key `key`.

[Source]

    # File cgi/session.rb, line 295
        def []=(key, val)
          unless @write_lock
            @write_lock = true
          end
          unless @data
            @data = @dbman.restore
          end
          @data[key] = val
        end

update()

Store session data on the server. For some session storage types, this is a no-op.

[Source]

    # File cgi/session.rb, line 307
        def update
          @dbman.update
        end

close()

Store session data on the server and close the session storage. For some session storage types, this is a no-op.

[Source]

    # File cgi/session.rb, line 313
        def close
          @dbman.close
          @dbprot.clear
        end

delete()

Delete the session from storage. Also closes the storage.

Note that the session’s data is not automatically deleted upon the session expiring.

[Source]

    # File cgi/session.rb, line 322
        def delete
          @dbman.delete
          @dbprot.clear
        end

[]=(key, val)

[Source]

    # File cgi/session/pstore.rb, line 17
        def []=(key, val)
          unless @write_lock
            @write_lock = true
          end
          unless @data
            @data = @dbman.restore
          end
          #@data[key] = String(val)

          @data[key] = val
        end

[Validate]