[PATCH] QUIC: optimized immediate close

[Roman Arutyunyan]

# HG changeset patch
# User Roman Arutyunyan <arut at nginx.com>
# Date 1683035693 -14400
#      Tue May 02 17:54:53 2023 +0400
# Branch quic
# Node ID 0ae438bff8e8788f6972b2f8268194b571d728c0
# Parent  558cdf07793de4108527ed6757fd3864e9694b93
QUIC: optimized immediate close.

Previously, before sending CONNECTION_CLOSE to client, all pending frames
were sent.  This is redundant and could prevent CONNECTION_CLOSE from being
sent due to congestion control.  Now pending frames are freed and
CONNECTION_CLOSE is sent without congestion control, as advised by RFC 9002:

  Packets containing frames besides ACK or CONNECTION_CLOSE frames
  count toward congestion control limits and are considered to be in flight.

diff --git a/src/event/quic/ngx_event_quic.c b/src/event/quic/ngx_event_quic.c
--- a/src/event/quic/ngx_event_quic.c
+++ b/src/event/quic/ngx_event_quic.c
@@ -482,6 +482,7 @@ ngx_quic_close_connection(ngx_connection
 
         /* drop packets from retransmit queues, no ack is expected */
         for (i = 0; i < NGX_QUIC_SEND_CTX_LAST; i++) {
+            ngx_quic_free_frames(c, &qc->send_ctx[i].frames);
             ngx_quic_free_frames(c, &qc->send_ctx[i].sent);
         }
 
diff --git a/src/event/quic/ngx_event_quic_output.c b/src/event/quic/ngx_event_quic_output.c
--- a/src/event/quic/ngx_event_quic_output.c
+++ b/src/event/quic/ngx_event_quic_output.c
@@ -882,7 +882,7 @@ ngx_quic_send_stateless_reset(ngx_connec
 ngx_int_t
 ngx_quic_send_cc(ngx_connection_t *c)
 {
-    ngx_quic_frame_t       *frame;
+    ngx_quic_frame_t        frame;
     ngx_quic_connection_t  *qc;
 
     qc = ngx_quic_get_connection(c);
@@ -898,27 +898,22 @@ ngx_quic_send_cc(ngx_connection_t *c)
         return NGX_OK;
     }
 
-    frame = ngx_quic_alloc_frame(c);
-    if (frame == NULL) {
-        return NGX_ERROR;
-    }
+    ngx_memzero(&frame, sizeof(ngx_quic_frame_t));
 
-    frame->level = qc->error_level;
-    frame->type = qc->error_app ? NGX_QUIC_FT_CONNECTION_CLOSE_APP
-                                : NGX_QUIC_FT_CONNECTION_CLOSE;
-    frame->u.close.error_code = qc->error;
-    frame->u.close.frame_type = qc->error_ftype;
+    frame.level = qc->error_level;
+    frame.type = qc->error_app ? NGX_QUIC_FT_CONNECTION_CLOSE_APP
+                               : NGX_QUIC_FT_CONNECTION_CLOSE;
+    frame.u.close.error_code = qc->error;
+    frame.u.close.frame_type = qc->error_ftype;
 
     if (qc->error_reason) {
-        frame->u.close.reason.len = ngx_strlen(qc->error_reason);
-        frame->u.close.reason.data = (u_char *) qc->error_reason;
+        frame.u.close.reason.len = ngx_strlen(qc->error_reason);
+        frame.u.close.reason.data = (u_char *) qc->error_reason;
     }
 
-    ngx_quic_queue_frame(qc, frame);
-
     qc->last_cc = ngx_current_msec;
 
-    return ngx_quic_output(c);
+    return ngx_quic_frame_sendto(c, &frame, 0, qc->path);
 }