From: Amaury Denoyelle <adenoyelle@haproxy.com>
Date: Wed, 3 May 2023 07:50:39 +0000 (+0200)
Subject: MINOR: mux-quic: do not send STREAM frames if already subscribe
X-Git-Tag: v2.8-dev12~70
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=04b2208aa0768bb7f69dc4a286e7e059409bdf09;p=thirdparty%2Fhaproxy.git

MINOR: mux-quic: do not send STREAM frames if already subscribe

Do not built STREAM frames if MUX is already subscribed for sending on
lower layer. Indeed, this means that either socket currently encountered
a transient error or congestion window is full.

This change is an optimization which prevents to allocate and release a
series of STREAM frames for nothing under congestion.

Note that nothing is done for other frames (flow-control, RESET_STREAM
and STOP_SENDING). Indeed, these frames are not restricted by flow
control. However, this means that they will be allocated for nothing if
send is blocked on a transient error.

This should be backported up to 2.7.
---

diff --git a/src/mux_quic.c b/src/mux_quic.c
index 6070b00882..297d2adaa5 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -1843,6 +1843,15 @@ static int _qc_send_qcs(struct qcs *qcs, struct list *frms)
 
 	/* Build a new STREAM frame with <out> buffer. */
 	if (qcs->tx.sent_offset != qcs->tx.offset || fin) {
+		/* Skip STREAM frame allocation if already subscribed for send.
+		 * Happens on sendto transient error or network congestion.
+		 */
+		if (qcc->wait_event.events & SUB_RETRY_SEND) {
+			TRACE_DEVEL("already subscribed for sending",
+			            QMUX_EV_QCS_SEND, qcc->conn, qcs);
+			goto err;
+		}
+
 		if (qcs_build_stream_frm(qcs, out, fin, frms) < 0)
 			goto err;
 	}
@@ -1871,6 +1880,12 @@ static int qc_send(struct qcc *qcc)
 
 	TRACE_ENTER(QMUX_EV_QCC_SEND, qcc->conn);
 
+	/* TODO if socket in transient error, sending should be temporarily
+	 * disabled for all frames. However, checking for send subscription is
+	 * not valid as this may be caused by a congestion error which only
+	 * apply for STREAM frames.
+	 */
+
 	/* Check for locally detected connection error. */
 	if (qcc->flags & QC_CF_ERRL) {
 		/* Prepare a CONNECTION_CLOSE if not already done. */