Session Package

## Session Package

### Introduction

This is session management code. It provides an interface to allow you to generate and track a browser's visit as a "session", giving you a unique session ID and an interface for storing and retrieving data for that session on the server.

This is an alpha/beta release -- documentation is not in final form, but everything you need should be in this file.

Using sessions and their included ability to store and retrieve session-related data on the server, programmers can generate more secure and higher-performance websites. For example, hidden fields do not have to be included in forms (and the risk of them being manipulated by the user mitigated) since data that would be stored in hidden fields can now be stored in the session cache on the server. Forms are then faster since no hidden data is transmitted -- hidden fields must be sent twice, once in the form to the broswer and once in the response from it.

Robust login systems, etc, can be built on top of this code.

### Requirements

Currently has only been tested with Postgresql, MySql and Oracle. All DB interfacing is done through DIO, though, so it should be relatively easy to add support for other databases.

### Preparing To Use It

Create the tables in your SQL server. With Postgres, do a psql www or whatever DB you connect as, then a backslash-i on `session-create.sql`

(If you need to delete the tables, use `session-drop.sql`)

The session code by default requires a DIO handle called `DIO` (the name of which can be overridden). We get it by doing a

    	      RivetServerConf ChildInitScript "package require DIO"
    	      RivetServerConf ChildInitScript "::DIO::handle Postgresql DIO -user www"

### Example Usage

In your httpd.conf, add:

    RivetServerConf ChildInitScript "package require Session; Session SESSION"

This tells Rivet you want to create a session object named SESSION in every child process Apache creates.

You can configure the session at this point using numerous key-value pairs (which are defined later in this doc). Here's a quick example:

    RivetServerConf ChildInitScript "package require Session; Session SESSION \
      -cookieLifetime 120 -debugMode 1"

Turn debugging on -debugMode 1 to figure out what's going on -- it's really useful, if verbose.

In your .rvt file, when you're generating the <HEAD> section:

    SESSION activate

Activate handles everything for you with respect to creating new sessions, and for locating, validating, and updating existing sessions. Activate will either locate an existing session, or create a new one. Sessions will automatically be refreshed (their lifetimes extended) as additional requests are received during the session, all under the control of the key-value pairs controlling the session object.

### Using Sessions From Your Code

The main methods your code will use are:

  SESSION id
  After doing a SESSION activate, this will return a 32-byte ASCII-encoded random hexadecimal string. Every time this browser comes to us with a request within the timeout period, this same string will be returned (assuming they have cookies enabled).
  SESSION is_new_session
  returns 1 if it's a new session or 0 if it has previously existed (i.e. it's a zero if this request represents a "return" or subsequent visit to a current session.)
  SESSION new_session_reason
  This will return why this request is the first request of a new session, either "no_cookie" saying the browser didn't give us a session cookie, "no_session" indicating we got a cookie but couldn't find it in our session table, or "timeout" where they had a cookie and we found the matching session but the session has timed out.
  SESSION store ?`packageName`? ?`key`? ?`data`?
  Given the name of a package, a key, and some data. Stores the data in the rivet session cache table.
  SESSION fetch ?`packageName`? ?`key`?
  Given a package name and a key, return the data stored by the store method, or an empty string if none was set. (Status is set to the DIO error that occurred, it can be fetched using the status method.)

### Session Configuration Options

The following key-value pairs can be specified when a session object (like SESSION above) is created:

sessionLifetime
  how many seconds the session will live for. 7200 == 2 hours
sessionRefreshInterval
  If a request is processed for a browser that currently has a session and this long has elapsed since the session update time was last updated, update it. 900 == 15 minutes. so if at least 15 minutes has elapsed and we've gotten a new request for a page, update the session update time, extending the session lifetime (sessions that are in use keep getting extended).
cookieName
  name of the cookie stored on the user's web browser default rivetSession
dioObject
  The name of the DIO object we'll use to access the database (default DIO)
gcProbability
  The probability that garbage collection will occur in percent. (default 1%, i.e. 1)
gcMaxLifetime
  the number of seconds after which data will be seen as "garbage" and cleaned up -- defaults to 1 day (86400)
refererCheck
  The substring you want to check each HTTP referer for. If the referer was sent by the browser and the substring is not found, the session will be deleted. (not coded yet)
entropyFile
  The name of a file that random binary data can be read from. (`/dev/urandom`) Data will be used from this file to help generate a super-hard-to-guess session ID.
entropyLength
  The number of bytes which will be read from the entropy file. If 0, the entropy file will not be read (default 0)
scrambleCode
  Set the scramble code to something unique for the site or your app or whatever, to slightly increase the unguessability of session ids (default "some random string")
cookieLifetime
  The lifetime of the cookie in minutes. 0 means until the browser is closed (I think). (default 0)
cookiePath
  The webserver subpath that the session cookie applies to (defaults to `/`)
cookieSecure
  Specifies whether the cookie should only be sent over secure connections, 0 = any, 1 = secure connections only (default 0)
sessionTable
  The name of the table that session info will be stored in (default `rivet_session`)
sessionCacheTable
  The name of the table that contains cached session data (default `rivet_session_cache`)
debugMode
  Set debug mode to 1 to trace through and see the session object do its thing (default 0)
debugFile
  The file handle that debugging messages will be written to (default `stdout`)

### Session Methods

The following methods can be invoked to find out information about the current session, store and fetch server data identified with this session, etc:

  SESSION status
  Return the status of the last operation
  SESSION id
  Get the session ID of the current browser. Returns an empty string if there's no session (will not happen is SESSION activate has been issued.)
  SESSION new_session_reason
  Returns the reason why there wasn't a previous session, either "no_cookie" saying the browser didn't give us a session cookie, "no_session" indicating we got a cookie but couldn't find it in the session table, or "timeout" when we had a cookie and a session but the session had timed out.
  SESSION store ?`packageName`? ?`key`? ?`data`?
  Given a package name, a key string, and a data string, store the data in the rivet session cache.
  SESSION fetch ?`packageName`? ?`key`?
  Given a package name and a key, return the data stored by the store method, or an empty string if none was set. Status is set to the DIO error that occurred, it can be fetched using the status method.
  SESSION delete
  Given a user ID and looking at their IP address we inherited from the environment (thanks, Apache), remove them from the session table. (the session table is how the server remembers stuff about sessions). If the session ID was not specified the current session is deleted.
  SESSION activate
  Find and validate the session ID if they have one. If they don't have one or it isn't valid (timed out, etc), create a session and drop a cookie on them.

### Getting Additional Randomness From The Entropy File

    RivetServerConf ChildInitScript "Session SESSION -entropyFile /dev/urandom \
      -entropyLength 10 -debugMode 1"

This options say we want to get randomness from an entropy file (random data pseudo-device) of /dev/urandom, to get ten bytes of random data from that entropy device, and to turn on debug mode, which will cause the SESSION object to output all manner of debugging information as it does stuff. This has been tested on FreeBSD and appears to work.

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