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 6070b00..297d2ad 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -1843,6 +1843,15 @@
/* 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 @@
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. */