http_session.pl -- HTTP Session management

This library defines session management based on HTTP cookies. Session management is enabled simply by loading this module. Details can be modified using http_set_session_options/1. By default, this module creates a session whenever a request is processes that is inside the hierarchy defined for session handling (see path option in http_set_session_options/1. Automatic creation of a session can be stopped using the option create(noauto). The predicate http_open_session/2 must be used to create a session if noauto is enabled. Sessions can be closed using http_close_session/1.

If a session is active, http_in_session/1 returns the current session and http_session_assert/1 and friends maintain data about the session. If the session is reclaimed, all associated data is reclaimed too.

Begin and end of sessions can be monitored using library(broadcast). The broadcasted messages are:

http_session(begin(SessionID, Peer)): Broadcasted if a session is started
http_session(end(SessionId, Peer)): Broadcasted if a session is ended. See http_close_session/1.

For example, the following calls end_session(SessionId) whenever a session terminates. Please note that sessions ends are not scheduled to happen at the actual timeout moment of the session. Instead, creating a new session scans the active list for timed-out sessions. This may change in future versions of this library.

:- listen(http_session(end(SessionId, Peer)),
          end_session(SessionId)).

http_set_session_options(+Options) is det

Set options for the session library. Provided options are:

timeout(+Seconds): Session timeout in seconds. Default is 600 (10 min). A timeout of 0 (zero) disables timeout.
cookie(+Cookiekname): Name to use for the cookie to identify the session. Default swipl_session.
path(+Path): Path to which the cookie is associated. Default is /. Cookies are only sent if the HTTP request path is a refinement of Path.
route(+Route): Set the route name. Default is the unqualified hostname. To cancel adding a route, use the empty atom. See route/1.
enabled(+Boolean): Enable/disable session management. Sesion management is enabled by default after loading this file.
create(+Atom): Defines when a session is created. This is one of auto (default), which creates a session if there is a request whose path matches the defined session path or noauto, in which cases sessions are only created by calling http_open_session/2 explicitely.
proxy_enabled(+Boolean): Enable/disable proxy session management. Proxy session management associates the originating IP address of the client to the session rather than the proxy IP address. Default is false.
gc(+When): When is one of active, which starts a thread that performs session cleanup at close to the moment of the timeout or passive, which runs session GC when a new session is created.

http_session_option(?Option) is nondet

True if Option is a current option of the session system.

session_setting(+SessionID, ?Setting) is semidet[private]

Find setting for SessionID. It is possible to overrule some session settings using http_session_set(Setting).

http_set_session(Setting) is det

http_set_session(SessionId, Setting) is det

Overrule a setting for the current or specified session. Currently, the only setting that can be overruled is timeout.

Errors: - permission_error(set, http_session, Setting) if setting a setting that is not supported on per-session basis.

http_session_id(-SessionId) is det

True if SessionId is an identifier for the current session.

Arguments:

SessionId

- is an atom.

Errors

- existence_error(http_session, _)

See also

- http_in_session/1 for a version that fails if there is no session.

http_in_session(-SessionId) is semidet

True if SessionId is an identifier for the current session. The current session is extracted from session(ID) from the current HTTP request (see http_current_request/1). The value is cached in a backtrackable global variable http_session_id. Using a backtrackable global variable is safe because continuous worker threads use a failure driven loop and spawned threads start without any global variables. This variable can be set from the commandline to fake running a goal from the commandline in the context of a session.

See also: - http_session_id/1

http_session(+RequestIn, -RequestOut, -SessionID) is semidet[private]

Maintain the notion of a session using a client-side cookie. This must be called first when handling a request that wishes to do session management, after which the possibly modified request must be used for further processing.

This predicate creates a session if the setting create is auto. If create is noauto, the application must call http_open_session/1 to create a session.

http_open_session(-SessionID, +Options) is det

Establish a new session. This is normally used if the create option is set to noauto. Options:

renew(+Boolean): If true (default false) and the current request is part of a session, generate a new session-id. By default, this predicate returns the current session as obtained with http_in_session/1.

Errors: - permission_error(open, http_session, CGI) if this call is used after closing the CGI header.
See also: - http_set_session_options/1 to control the create option.; - http_close_session/1 for closing the session.

peer(+Request, -Peer) is det[private]

Find peer for current request. If unknown we leave it unbound. Alternatively we should treat this as an error.

open_session(+SessionID, +Peer)[private]

Open a new session. Uses broadcast/1 with the term http_session(begin(SessionID, Peer)).

valid_session_id(+SessionID, +Peer) is semidet[private]

Check if this sessionID is known. If so, check the idle time and update the last_used for this session.

set_last_used(+SessionID, +Now, +TimeOut)[private]

Set the last-used notion for SessionID from the current time stamp. The time is rounded down to 10 second intervals to avoid many updates and simplify the scheduling of session GC.

http_session_asserta(+Data) is det

http_session_assert(+Data) is det

http_session_retract(?Data) is nondet

http_session_retractall(?Data) is det

Versions of assert/1, retract/1 and retractall/1 that associate data with the current HTTP session.

http_session_data(?Data) is nondet

True if Data is associated using http_session_assert/1 to the current HTTP session.

Errors: - existence_error(http_session,_)

http_current_session(?SessionID, ?Data) is nondet

Enumerate the current sessions and associated data. There are two Pseudo data elements:

idle(Seconds): Session has been idle for Seconds.
peer(Peer): Peer of the connection.

http_close_session(+SessionID) is det

Closes an HTTP session. This predicate can be called from any thread to terminate a session. It uses the broadcast/1 service with the message below.

http_session(end(SessionId, Peer))

The broadcast is done before the session data is destroyed and the listen-handlers are executed in context of the session that is being closed. Here is an example that destroys a Prolog thread that is associated to a thread:

:- listen(http_session(end(SessionId, _Peer)),
          kill_session_thread(SessionID)).

kill_session_thread(SessionID) :-
        http_session_data(thread(ThreadID)),
        thread_signal(ThreadID, throw(session_closed)).

Succeed without any effect if SessionID does not refer to an active session.

If http_close_session/1 is called from a handler operating in the current session and the CGI stream is still in state header, this predicate emits a Set-Cookie to expire the cookie.

Errors: - type_error(atom, SessionID)
See also: - listen/2 for acting upon closed sessions

expire_session_cookie(+SessionId) is det[private]

Emit a request to delete a session cookie. This is only done if http_close_session/1 is still in `header mode'.

http_gc_sessions is det[private]

http_gc_sessions(+TimeOut) is det[private]

Delete dead sessions. Currently runs session GC if a new session is opened and the last session GC was more than a TimeOut ago.

start_session_gc_thread is det[private]

stop_session_gc_thread is det[private]

Create/stop a thread that listens for timeout-at timing and wakes up to run http_gc_sessions/1 shortly after a session is scheduled to timeout.

http_session_cookie(-Cookie) is det

Generate a random cookie that can be used by a browser to identify the current session. The cookie has the format XXXX-XXXX-XXXX-XXXX[.<route>], where XXXX are random hexadecimal numbers and [.<route>] is the optionally added routing information.

route(-RouteID) is semidet[private]

Fetch the route identifier. This value is added as .<route> to the session cookie and used by -for example- the apache load balanching module. The default route is the local name of the host. Alternatives may be provided using http_set_session_options/1.

urandom(-Handle) is semidet[private]

Handle is a stream-handle for /dev/urandom. Originally, this simply tried to open /dev/urandom, failing if this device does not exist. It turns out that trying to open /dev/urandom can block indefinitely on some Windows installations, so we no longer try this on Windows.

random_4(-R1, -R2, -R3, -R4) is det[private]

Generate 4 2-byte random numbers. Uses /dev/urandom when available to make prediction of the session IDs hard.

http_set_session(Setting) is det

http_set_session(SessionId, Setting) is det

Overrule a setting for the current or specified session. Currently, the only setting that can be overruled is timeout.

Errors: - permission_error(set, http_session, Setting) if setting a setting that is not supported on per-session basis.

http_session_asserta(+Data) is det

http_session_assert(+Data) is det

http_session_retract(?Data) is nondet

http_session_retractall(?Data) is det

Versions of assert/1, retract/1 and retractall/1 that associate data with the current HTTP session.

http_session_asserta(+Data) is det

http_session_assert(+Data) is det

http_session_retract(?Data) is nondet

http_session_retractall(?Data) is det

Versions of assert/1, retract/1 and retractall/1 that associate data with the current HTTP session.

http_session_asserta(+Data) is det

http_session_assert(+Data) is det

http_session_retract(?Data) is nondet

http_session_retractall(?Data) is det

Versions of assert/1, retract/1 and retractall/1 that associate data with the current HTTP session.

http_gc_sessions is det[private]

http_gc_sessions(+TimeOut) is det[private]

Delete dead sessions. Currently runs session GC if a new session is opened and the last session GC was more than a TimeOut ago.

start_session_gc_thread is det[private]

stop_session_gc_thread is det[private]

Create/stop a thread that listens for timeout-at timing and wakes up to run http_gc_sessions/1 shortly after a session is scheduled to timeout.