mod_session: Introduce SessionExpiryUpdateInterval which allows to

configure the session/cookie expiry's update interval. PR 57300.

Submitted by: Paul Spangler <paul.spangler ni.com>
Reviewed/Committed by: ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1709121 13f79535-47bb-0310-9956-ffa450edef68

CHANGES

@@ -1,6 +1,10 @@
                                                          -*- coding: utf-8 -*-
 Changes with Apache 2.5.0
 
+  *) mod_session: Introduce SessionExpiryUpdateInterval which allows to
+     configure the session/cookie expiry's update interval. PR 57300.
+     [Paul Spangler <paul.spangler ni.com>]
+
   *) mod_ssl: Extend expression parser registration to support ssl variables
      in any expression using mod_rewrite syntax "%{SSL:VARNAME}" or function
      syntax "ssl(VARIABLE)". [Rainer Jung]

docs/manual/mod/mod_session.xml

@@ -487,4 +487,41 @@ AuthName "realm"
 </usage>
 </directivesynopsis>
 
+<directivesynopsis>
+<name>SessionExpiryUpdateInterval</name>
+<description>Define the number of seconds a session's expiry may change without
+the session being updated</description>
+<syntax>SessionExpiryUpdateInterval <var>interval</var></syntax>
+<default>SessionExpiryUpdateInterval 0 (always update)</default>
+<contextlist><context>server config</context>
+<context>virtual host</context>
+<context>directory</context>
+<context>.htaccess</context>
+</contextlist>
+
+<usage>
+    <p>The <directive>SessionExpiryUpdateInterval</directive> directive allows
+    sessions to avoid the cost associated with writing the session each request
+    when only the expiry time has changed. This can be used to make a website
+    more efficient or reduce load on a database when using
+    <module>mod_session_dbd</module>. The session is always written if the data
+    stored in the session has changed or the expiry has changed by more than the
+    configured interval.</p>
+
+    <p>Setting the interval to zero disables this directive, and the session
+    expiry is refreshed for each request.</p>
+
+    <p>This directive only has an effect when combined with
+    <directive module="mod_session">SessionMaxAge</directive> to enable session
+    expiry. Sessions without an expiry are only written when the data stored in
+    the session has changed.</p>
+
+    <note type="warning"><title>Warning</title>
+    <p>Because the session expiry may not be refreshed with each request, it's
+    possible for sessions to expire up to <var>interval</var> seconds early.
+    Using a small interval usually provides sufficient savings while having a
+    minimal effect on expiry resolution.</p></note>
+</usage>
+</directivesynopsis>
+
 </modulesynopsis>

modules/session/mod_session.c

@@ -177,6 +177,7 @@ static apr_status_t ap_session_save(request_rec * r, session_rec * z)
 {
     if (z) {
         apr_time_t now = apr_time_now();
+        apr_time_t initialExpiry = z->expiry;
         int rv = 0;
 
         session_dir_conf *dconf = ap_get_module_config(r->per_dir_config,
@@ -207,6 +208,17 @@ static apr_status_t ap_session_save(request_rec * r, session_rec * z)
             z->expiry = now + z->maxage * APR_USEC_PER_SEC;
         } 
 
+        /* don't save if the only change is the expiry by a small amount */
+        if (!z->dirty && dconf->expiry_update_time
+                && (z->expiry - initialExpiry < dconf->expiry_update_time)) {
+            return APR_SUCCESS;
+        }
+
+        /* also don't save sessions that didn't change at all */
+        if (!z->dirty && !z->maxage) {
+            return APR_SUCCESS;
+        }
+
         /* encode the session */
         rv = ap_run_session_encode(r, z);
         if (OK != rv) {
@@ -551,6 +563,10 @@ static void *merge_session_dir_config(apr_pool_t * p, void *basev, void *addv)
     new->env_set = add->env_set || base->env_set;
     new->includes = apr_array_append(p, base->includes, add->includes);
     new->excludes = apr_array_append(p, base->excludes, add->excludes);
+    new->expiry_update_time = (add->expiry_update_set == 0)
+                                ? base->expiry_update_time
+                                : add->expiry_update_time;
+    new->expiry_update_set = add->expiry_update_set || base->expiry_update_set;
 
     return new;
 }
@@ -620,6 +636,21 @@ static const char *add_session_exclude(cmd_parms * cmd, void *dconf, const char
     return NULL;
 }
 
+static const char *
+     set_session_expiry_update(cmd_parms * parms, void *dconf, const char *arg)
+{
+    session_dir_conf *conf = dconf;
+
+    conf->expiry_update_time = atoi(arg);
+    if (conf->expiry_update_time < 0) {
+        return "SessionExpiryUpdateInterval must be positive or nul";
+    }
+    conf->expiry_update_time = apr_time_from_sec(conf->expiry_update_time);
+    conf->expiry_update_set = 1;
+
+    return NULL;
+}
+
 
 static const command_rec session_cmds[] =
 {
@@ -635,6 +666,9 @@ static const command_rec session_cmds[] =
                   "URL prefixes to include in the session. Defaults to all URLs"),
     AP_INIT_TAKE1("SessionExclude", add_session_exclude, NULL, RSRC_CONF|OR_AUTHCFG,
                   "URL prefixes to exclude from the session. Defaults to no URLs"),
+    AP_INIT_TAKE1("SessionExpiryUpdateInterval", set_session_expiry_update, NULL, RSRC_CONF|OR_AUTHCFG,
+                  "time interval for which a session's expiry time may change "
+                  "without having to be rewritten. Zero to disable"),
     {NULL}
 };
 

modules/session/mod_session.h

@@ -115,6 +115,9 @@ typedef struct {
                                    * URLs included if empty */
     apr_array_header_t *excludes; /* URL prefixes to be excluded. No
                                    * URLs excluded if empty */
+    apr_time_t expiry_update_time; /* seconds the session expiry may change and
+                                    * not have to be rewritten */
+    int expiry_update_set;
 } session_dir_conf;
 
 /**

modules/session/mod_session_cookie.c

@@ -60,9 +60,6 @@ static apr_status_t session_cookie_save(request_rec * r, session_rec * z)
     session_cookie_dir_conf *conf = ap_get_module_config(r->per_dir_config,
                                                     &session_cookie_module);
 
-    /* don't cache auth protected pages */
-    apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
-
     /* create RFC2109 compliant cookie */
     if (conf->name_set) {
         if (z->encoded && z->encoded[0]) {
@@ -162,6 +159,9 @@ static apr_status_t session_cookie_load(request_rec * r, session_rec ** z)
     /* put the session in the notes so we don't have to parse it again */
     apr_table_setn(m->notes, note, (char *)zz);
 
+    /* don't cache auth protected pages */
+    apr_table_addn(r->headers_out, "Cache-Control", "no-cache, private");
+
     return OK;
 
 }

modules/session/mod_session_dbd.c

@@ -245,6 +245,9 @@ static apr_status_t session_dbd_load(request_rec * r, session_rec ** z)
     /* put the session in the notes so we don't have to parse it again */
     apr_table_setn(m->notes, note, (char *)zz);
 
+    /* don't cache pages with a session */
+    apr_table_addn(r->headers_out, "Cache-Control", "no-cache, private");
+
     return OK;
 
 }
@@ -409,9 +412,6 @@ static apr_status_t session_dbd_save(request_rec * r, session_rec * z)
     if (conf->name_set || conf->name2_set) {
         char *oldkey = NULL, *newkey = NULL;
 
-        /* don't cache pages with a session */
-        apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
-
         /* if the session is new or changed, make a new session ID */
         if (z->uuid) {
             oldkey = apr_pcalloc(r->pool, APR_UUID_FORMATTED_LENGTH + 1);
@@ -458,7 +458,7 @@ static apr_status_t session_dbd_save(request_rec * r, session_rec * z)
     else if (conf->peruser) {
 
         /* don't cache pages with a session */
-        apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
+        apr_table_addn(r->headers_out, "Cache-Control", "no-cache, private");
 
         if (r->user) {
             ret = dbd_save(r, r->user, r->user, z->encoded, z->expiry);