core: follow up to r1891148: WC bucket defaulting to FLUSH bucket.

Define WC bucket semantics as:
/**
 * @brief Write Completion (WC) bucket
 *
 * A WC bucket is a FLUSH bucket with special ->data == &ap_bucket_wc_data,
 * still both AP_BUCKET_IS_WC() and APR_BUCKET_IS_FLUSH() hold for them so
 * they have the same semantics for most filters, namely:
 *   Everything produced before shall be passed to the next filter, including
 *   the WC/FLUSH bucket itself.
 * The distinction between WC and FLUSH buckets is only for filters that care
 * about write completion (calling ap_filter_reinstate_brigade() with non-NULL
 * flush_upto), those can setaside WC buckets and the preceding data provided
 * they have first determined that the next filter(s) have pending data
 * already, usually by calling ap_filter_should_yield(f->next).
 */

The only filters that care about write completion for now are
ap_core_output_filter() and ssl_io_filter_output(), which try to fill
in the pipe as much as possible, using ap_filter_reinstate_brigade(&flush_upto)
to determine whether they should flush (blocking) or setaside their remaining
data.

So ap_filter_reinstate_brigade() is made to not treat WC as FLUSH buckets and
keep the above filters working as before (and correctly w.r.t. above WC bucket
semantics).

* include/ap_mmn.h, include/util_filter.h:
  Axe specific ap_bucket_type_wc and define global &ap_bucket_wc_data address to
  mark WC buckets checked by AP_BUCKET_IS_WC().

* server/util_filter.c (ap_filter_reinstate_brigade):
  Don't treat WC buckets as FLUSH buckets.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1892468 13f79535-47bb-0310-9956-ffa450edef68

2 files changed, 20 insertions, 4 deletions

diff --git a/include/ap_mmn.h b/include/ap_mmn.h
index 0ddf227b90..4686cd3cb4 100644
--- a/include/ap_mmn.h
+++ b/include/ap_mmn.h
@@ -673,7 +673,7 @@
  *                         ap_proxy_tunnel_conn_get_transferred() change
  *                         ap_proxy_transfer_between_connections() sent to apr_off_t *.
  * 20210531.0 (2.5.1-dev)  add conn_rec->outgoing and ap_ssl_bind_outgoing()
- * 20210531.1 (2.5.1-dev)  Add ap_bucket_type_wc, ap_bucket_wc_make() and
+ * 20210531.1 (2.5.1-dev)  Add ap_bucket_wc_data, ap_bucket_wc_make() and
  *                         ap_bucket_wc_create() to util_filter.h
  * 20210531.2 (2.5.1-dev)  Add ap_proxy_get_worker_ex() and
  *                         ap_proxy_define_worker_ex() to mod_proxy.h
diff --git a/include/util_filter.h b/include/util_filter.h
index a0205a5f5c..a03e81c16c 100644
--- a/include/util_filter.h
+++ b/include/util_filter.h
@@ -763,15 +763,31 @@ AP_DECLARE(void) ap_filter_protocol(ap_filter_t* f, unsigned int proto_flags);
 /** Filter is incompatible with "Cache-Control: no-transform" */
 #define AP_FILTER_PROTO_TRANSFORM 0x20
 
-/** Write Completion (WC) bucket */
-AP_DECLARE_DATA extern const apr_bucket_type_t ap_bucket_type_wc;
+/**
+ * @brief Write Completion (WC) bucket
+ *
+ * A WC bucket is a FLUSH bucket with special ->data == &ap_bucket_wc_data,
+ * still both AP_BUCKET_IS_WC() and APR_BUCKET_IS_FLUSH() hold for them so
+ * they have the same semantics for most filters, namely:
+ *   Everything produced before shall be passed to the next filter, including
+ *   the WC/FLUSH bucket itself.
+ * The distinction between WC and FLUSH buckets is only for filters that care
+ * about write completion (calling ap_filter_reinstate_brigade() with non-NULL
+ * flush_upto), those can setaside WC buckets and the preceding data provided
+ * they have first determined that the next filter(s) have pending data
+ * already, usually by calling ap_filter_should_yield(f->next).
+ */
+
+/** Write Completion (WC) bucket data mark */
+AP_DECLARE_DATA extern const char ap_bucket_wc_data;
 
 /**
  * Determine if a bucket is a Write Completion (WC) bucket
  * @param e The bucket to inspect
  * @return true or false
  */
-#define AP_BUCKET_IS_WC(e) ((e)->type == &ap_bucket_type_wc)
+#define AP_BUCKET_IS_WC(e) (APR_BUCKET_IS_FLUSH(e) && \
+                            (e)->data == (void *)&ap_bucket_wc_data)
 
 /**
  * Make the bucket passed in a Write Completion (WC) bucket