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 6070b008823d8acdf959f9f04288a6ae22fd8c3d..297d2adaa5b48cb4e03af2d5a60759fa39b78e76 100644 (file)
--- 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. */