MINOR: mux-quic/h3: emit SETTINGS via MUX tasklet handler

Previously, QUIC MUX application layer was installed and initialized via
MUX init. However, the latter stage involve I/O operations, for example
when using HTTP/3 with the emission of a SETTINGS frame.

Change this to prevent any I/O operations during MUX init. As such,
finalize app_ops callback is now called during the first invokation of
qcc_io_send(), in the context of MUX tasklet. To implement this, a new
application state value is added, to detect the transition from NULL to
INIT stage.

include/haproxy/mux_quic-t.h

@@ -33,6 +33,7 @@ enum qcs_type {
 };
 
 enum qcc_app_st {
+	QCC_APP_ST_NULL,
 	QCC_APP_ST_INIT,
 	QCC_APP_ST_SHUT,
 } __attribute__((packed));

src/h3.c

@@ -1488,7 +1488,7 @@ static ssize_t h3_rcv_buf(struct qcs *qcs, struct buffer *b, int fin)
 	return -1;
 }
 
-/* Function used to emit stream data from <qcs> control uni-stream.
+/* Emit SETTINGS frame on <qcs> control uni-stream.
  *
  * On success return the number of sent bytes. A negative code is used on
  * error.
@@ -2406,7 +2406,8 @@ static int h3_init(struct qcc *qcc)
 	return 0;
 }
 
-/* Initialize H3 control stream and prepare SETTINGS emission.
+/* Open control stream for <ctx> HTTP/3 connection and schedule a SETTINGS
+ * frame emission on it.
  *
  * Returns 0 on success else non-zero.
  */
@@ -2429,6 +2430,13 @@ static int h3_finalize(void *ctx)
 	qcs_send_metadata(qcs);
 	h3c->ctrl_strm = qcs;
 
+	/* RFC 9114 7.2.4.2. Initialization
+	 *
+	 * Endpoints MUST NOT require any data to be
+	 * received from the peer prior to sending the SETTINGS frame;
+	 * settings MUST be sent as soon as the transport is ready to
+	 * send data.
+	 */
 	if (h3_control_send(qcs, h3c) < 0) {
 		qcc_set_error(qcc, H3_ERR_INTERNAL_ERROR, 1);
 		goto err;

src/mux_quic.c

@@ -1474,28 +1474,13 @@ int qcc_install_app_ops(struct qcc *qcc, const struct qcc_app_ops *app_ops)
 	TRACE_ENTER(QMUX_EV_QCC_NEW, qcc->conn);
 
 	if (app_ops->init && !app_ops->init(qcc)) {
-		TRACE_ERROR("app ops init error", QMUX_EV_QCC_NEW, qcc->conn);
+		TRACE_ERROR("application layer install error", QMUX_EV_QCC_NEW, qcc->conn);
 		goto err;
 	}
 
-	TRACE_PROTO("application layer initialized", QMUX_EV_QCC_NEW, qcc->conn);
+	TRACE_PROTO("application layer installed", QMUX_EV_QCC_NEW, qcc->conn);
 	qcc->app_ops = app_ops;
 
-	/* RFC 9114 7.2.4.2. Initialization
-	 *
-	 * Endpoints MUST NOT require any data to be
-	 * received from the peer prior to sending the SETTINGS frame;
-	 * settings MUST be sent as soon as the transport is ready to
-	 * send data.
-	 */
-	if (qcc->app_ops->finalize) {
-		if (qcc->app_ops->finalize(qcc->ctx)) {
-			TRACE_ERROR("app ops finalize error", QMUX_EV_QCC_NEW, qcc->conn);
-			goto err;
-		}
-		tasklet_wakeup(qcc->wait_event.tasklet);
-	}
-
 	TRACE_LEAVE(QMUX_EV_QCC_NEW, qcc->conn);
 	return 0;
 
@@ -2480,6 +2465,29 @@ static void qcc_wakeup_pacing(struct qcc *qcc)
 	++qcc->tx.paced_sent_ctr;
 }
 
+/* Finalize <qcc> app layer initialization with I/O operations.
+ *
+ * Returns 0 on success else non-zero.
+ */
+static int qcc_app_init(struct qcc *qcc)
+{
+	TRACE_ENTER(QMUX_EV_QCC_SEND, qcc->conn);
+
+	if (qcc->app_ops->finalize && qcc->app_ops->finalize(qcc->ctx)) {
+		TRACE_ERROR("app ops finalize error", QMUX_EV_QCC_NEW, qcc->conn);
+		goto err;
+	}
+
+	qcc->app_st = QCC_APP_ST_INIT;
+
+	TRACE_LEAVE(QMUX_EV_QCC_SEND, qcc->conn);
+	return 0;
+
+ err:
+	TRACE_DEVEL("leaving on error", QMUX_EV_QCC_SEND, qcc->conn);
+	return 1;
+}
+
 /* Proceed to sending. Loop through all available streams for the <qcc>
  * instance and try to send as much as possible.
  *
@@ -2530,6 +2538,11 @@ static int qcc_io_send(struct qcc *qcc)
 		goto out;
 	}
 
+	if (qcc->app_st < QCC_APP_ST_INIT) {
+		if (qcc_app_init(qcc))
+			goto out;
+	}
+
 	if (!LIST_ISEMPTY(&qcc->lfctl.frms)) {
 		if (qcc_send_frames(qcc, &qcc->lfctl.frms, 0)) {
 			TRACE_DEVEL("flow-control frames rejected by transport, aborting send", QMUX_EV_QCC_SEND, qcc->conn);
@@ -3042,7 +3055,7 @@ static int qmux_init(struct connection *conn, struct proxy *prx,
 	conn->ctx = qcc;
 	qcc->nb_hreq = qcc->nb_sc = 0;
 	qcc->flags = 0;
-	qcc->app_st = QCC_APP_ST_INIT;
+	qcc->app_st = QCC_APP_ST_NULL;
 	qcc->glitches = 0;
 	qcc->err = quic_err_transport(QC_ERR_NO_ERROR);
 

src/qmux_trace.c

@@ -133,6 +133,7 @@ INITCALL1(STG_REGISTER, trace_register_source, TRACE_SOURCE);
 static char *qcc_app_st_to_str(const enum qcc_app_st st)
 {
 	switch (st) {
+	case QCC_APP_ST_NULL: return "NULL";
 	case QCC_APP_ST_INIT: return "INIT";
 	case QCC_APP_ST_SHUT: return "SHUT";
 	default:              return "";