MINOR: quic: use server cache for ALPN on BE side

On the backend side, the ALPN may not be available in transport layer if
the MUX was started before handshake completion. Thus, it is necessary
to retrieve it from the server cache.

Author: a-denoyelle

src/mux_quic.c

@@ -1695,13 +1695,25 @@ int qcc_install_app_ops(struct qcc *qcc)
 {
 	struct connection *conn = qcc->conn;
 	const struct qcc_app_ops *app_ops;
+	struct server *srv;
 	const char *alpn;
 	int alpn_len;
 
 	TRACE_ENTER(QMUX_EV_QCC_NEW, conn);
 
-	if (!conn_get_alpn(conn, &alpn, &alpn_len))
-		goto err;
+	if (!conn_get_alpn(conn, &alpn, &alpn_len)) {
+		if (!conn_is_back(conn))
+			goto err;
+
+		srv = __objt_server(conn->target);
+		HA_RWLOCK_RDLOCK(SERVER_LOCK, &srv->path_params.param_lock);
+		alpn = srv->path_params.nego_alpn;
+		HA_RWLOCK_RDUNLOCK(SERVER_LOCK, &srv->path_params.param_lock);
+
+		if (!alpn)
+			goto err;
+		alpn_len = strlen(srv->path_params.nego_alpn);
+	}
 
 	app_ops = quic_alpn_to_app_ops(alpn, alpn_len);
 	if (!app_ops)

src/xprt_quic.c

@@ -245,6 +245,7 @@ static int qc_get_alpn(const struct connection *conn, void *xprt_ctx, const char
 	int ret = 0;
 
 	TRACE_ENTER(QUIC_EV_CONN_NEW, qc);
+
 	if (qc->alpn) {
 		*str = qc->alpn;
 		*len = strlen(qc->alpn);