class CGI::Session - cgi: Ruby Standard Library Documentation

# 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 `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

### Attributes

new_session[R]

The id of this session.

session_id[R]

The id of this session.

### Public Class Methods

new(request, option={}) click to toggle source

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 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.ruby-lang.org/ruby-list/37805)

    cgi = CGI.new("html4")
    class << cgi
        undef_method :fieldset
    end

    # File cgi/session.rb, line 289
    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

[](key) click to toggle source

Retrieve the session data for key `key`.

    # File cgi/session.rb, line 350
    def [](key)
      @data ||= @dbman.restore
      @data[key]
    end

[]=(key, val) click to toggle source

Set the session data for key `key`.

    # File cgi/session.rb, line 356
    def []=(key, val)
      @write_lock ||= true
      @data ||= @dbman.restore
      @data[key] = val
    end

close() click to toggle source

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

    # File cgi/session.rb, line 370
    def close
      @dbman.close
      @dbprot.clear
    end

delete() click to toggle source

Delete the session from storage. Also closes the storage.

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

    # File cgi/session.rb, line 379
    def delete
      @dbman.delete
      @dbprot.clear
    end

update() click to toggle source

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

    # File cgi/session.rb, line 364
    def update
      @dbman.update
    end

### Private Instance Methods

create_new_id() click to toggle source

Create a new session id.

The session id is a secure random number by SecureRandom if possible, otherwise an SHA512 hash based upon the time, a random number, and a constant string. This routine is used internally for automatically generated session ids.

    # File cgi/session.rb, line 171
    def create_new_id
      require 'securerandom'
      begin
        # by OpenSSL, or system provided entropy pool
        session_id = SecureRandom.hex(16)
      rescue NotImplementedError
        # never happens on modern systems
        require 'digest'
        d = Digest('SHA512').new
        now = Time::now
        d.update(now.to_s)
        d.update(String(now.usec))
        d.update(String(rand(0)))
        d.update(String($$))
        d.update('foobar')
        session_id = d.hexdigest[0, 32]
      end
      session_id
    end