#-
# Copyright (c) 2017 Varnish Software AS
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# Author: Dridi Boukelmoune <dridi.boukelmoune@gmail.com>
#
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$ABI strict
$Module purge 3 "Vinyl Cache Purge Module"

DESCRIPTION
===========

*vmod_purge* contains functions that offer a finer-grained control
than ``return(purge)`` from ``vcl_recv{}``. The functions can only be
called from ``vcl_hit{}`` or ``vcl_miss{}`` and they should in general
be used in both to ensure that all variants of a same object are taken
care of.

EXAMPLE
=======

::

    sub vcl_recv {
	if (req.method == "PURGE") {
	    if (client.ip !~ purge_acl) {
		return (synth(405));
	    }
	    return (hash);
	}
    }

    sub my_purge {
	set req.http.purged = purge.hard();
	if (req.http.purged == "0") {
	    return (synth(404));
	}
	else {
	    return (synth(200));
	}
    }

    sub vcl_hit {
	if (req.method == "PURGE") {
	    call my_purge;
	}
    }

    sub vcl_miss {
	if (req.method == "PURGE") {
	    call my_purge;
	}
    }

    sub vcl_synth {
	if (req.method == "PURGE") {
	    if (req.http.purged) {
		set resp.http.purged = req.http.purged;
	    }
	    return (deliver);
	}
    }

$Function INT hard()

This is equivalent to ``return(purge)`` but explicitly called from
``vcl_hit{}`` and ``vcl_miss{}``. It returns the number of purged
objects.

Example::

	set req.http.purged = purge.hard();

$Restrict vcl_hit vcl_miss

$Function INT soft(DURATION ttl = 0, DURATION grace = -1, DURATION keep = -1)

Sets the *ttl*, *grace* and *keep*. By default, *ttl* is set to ``0`` with
*grace* and *keep* periods left untouched. Setting *grace* or *keep* to a
negative value or to something higher than the objects current value leaves them
untouched. Setting all three parameters to ``0`` is equivalent to a hard purge.
Returns the number of soft-purged objects.

A soft-purge can only decrease the lifetime of an object. Let's consider an
object in cache created with *ttl*, *grace*, and *keep* of 60 seconds each:

``purge.soft(ttl = 0s, grace = -1s, keep = -1s);``

* If the object is **fresh**, the *ttl* is reduced to 0 seconds and the object
  expires after 120 seconds.
* If the object is **stale**, the expiry time is not changed.

``purge.soft(ttl = 0s, grace = 10s, keep = 10s);``

* If the object is **fresh**, the *ttl* is reduced to 0 seconds, *grace* and
  *keep* are reduced to 10 seconds. The object expires after 20 seconds.
* If the object has been **stale** for 5 seconds, *grace* is reduced to 5
  seconds and *keep* is reduced to 10 seconds. The object expires after 15
  seconds.
* If the object has been **stale** for 15 seconds, *grace* is reduced to 0
  seconds and *keep* is reduced to 5 seconds. The object expires after 5
  seconds.
* If the object has been **stale** for 20 seconds or more, the object
  immediately expires.

``purge.soft(ttl = 10s, grace = -1s, keep = -1s);``

* If the object has been **fresh** for 5 seconds, the *ttl* is reduced to 10
  seconds. The object expires after 130 seconds.
* If the object has been **fresh** for 55 seconds, the *ttl* is not changed. The
  object expires after 125 seconds.
* If the object is **stale**, the expiry time is not changed.

When the expiry time of an object is reduced due to a softpurge, an
``EXP_Reduce`` entry is logged under the ``ExpKill`` VSL tag. If a softpurge
does not reduce the expiry time of an object, an ``EXP_Unchanged`` entry is
logged instead.

$Restrict vcl_hit vcl_miss
SEE ALSO
========

* :ref:`vcl(7)`
