Run filter "init" functions exactly once per request.  No longer run
init functions for connection filters (doing an "init" once per
handler invocation makes no sense for a connection filter).  No longer 

b) multiple times per filter per request if a subrequest is used.

* include/util_filter.h (ap_filter_rec_t): Clarify use of the init
  function pointer.

* server/config.c (invoke_filter_init): Drop ap_ prefix for private
  function; take a request_rec pointer and only invoke filters with
  matching request.
  (ap_invoke_handler): Adjust accordingly.

PR: 49328

Index: include/util_filter.h
===================================================================
--- include/util_filter.h	(revision 952827)
+++ include/util_filter.h	(working copy)
@@ -217,10 +217,13 @@
     /** The function to call when this filter is invoked. */
     ap_filter_func filter_func;
 
-    /** The function to call before the handlers are invoked. Notice
-     * that this function is called only for filters participating in
-     * the http protocol. Filters for other protocols are to be
-     * initialized by the protocols themselves.
+    /** The function to call directly before the handlers are invoked
+     * for a request.  The init function is called once directly
+     * before running the handlers for a request or subrequest.  The
+     * init function is never called for a connection filter (with
+     * ftype >= AP_FTYPE_CONNECTION).  Any use of this function for
+     * filters for protocols other than HTTP is specified by the
+     * module supported that protocol.
      */
     ap_init_filter_func filter_init_func;
 
Index: server/config.c
===================================================================
--- server/config.c	(revision 952827)
+++ server/config.c	(working copy)
@@ -312,10 +312,14 @@
     return create_empty_config(p);
 }
 
-static int ap_invoke_filter_init(ap_filter_t *filters)
+/* Invoke the filter_init_func for all filters with FILTERS where f->r
+ * matches R.  Restricting to a matching R avoids re-running init
+ * functions for filters configured for r->main where r is a
+ * subrequest.  */
+static int invoke_filter_init(request_rec *r, ap_filter_t *filters)
 {
     while (filters) {
-        if (filters->frec->filter_init_func) {
+        if (filters->frec->filter_init_func && filters->r == r) {
             int result = filters->frec->filter_init_func(filters);
             if (result != OK) {
                 return result;
@@ -354,11 +358,11 @@
      * run their init function to let them do any magic before we could
      * start generating data.
      */
-    result = ap_invoke_filter_init(r->input_filters);
+    result = invoke_filter_init(r, r->input_filters);
     if (result != OK) {
         return result;
     }
-    result = ap_invoke_filter_init(r->output_filters);
+    result = invoke_filter_init(r, r->output_filters);
     if (result != OK) {
         return result;
     }