vmod_purge - Varnish Purge Module

          Copyright (c) 2017 Varnish Software AS
          All rights reserved.

          Author: Dridi Boukelmoune <dridi.boukelmoune@gmail.com>

          SPDX-License-Identifier: BSD-2-Clause

          Redistribution and use in source and binary forms, with or without
          modification, are permitted provided that the following conditions
          are met:
          1. Redistributions of source code must retain the above copyright
             notice, this list of conditions and the following disclaimer.
          2. Redistributions in binary form must reproduce the above copyright
             notice, this list of conditions and the following disclaimer in the
             documentation and/or other materials provided with the distribution.

          THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
          ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
          IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
          ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
          FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
          DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
          OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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                                                                                                   VMOD_PURGE(3)

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.

          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);
              }
          }

   INThard()
       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();

       Restricted to: vcl_hit, vcl_miss.

   INTsoft(DURATIONttl,DURATIONgrace,DURATIONkeep)
          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.

       Restricted to: vcl_hit, vcl_miss.

       vmod_purge - Varnish Purge Module

       • vcl(7)

          import purge [as name] [from "path"]

          INT hard()

          INT soft(DURATION ttl, DURATION grace, DURATION keep)