From f1ed1de31752892d58719d7afbe10acc7ce19b97 Mon Sep 17 00:00:00 2001
From: Amaury Denoyelle <adenoyelle@haproxy.com>
Date: Wed, 25 Mar 2026 14:14:20 +0100
Subject: [PATCH] MINOR: xprt_qstrm: implement sending of transport parameters

This patch implements QMux emission of transport parameters via
xprt_qstrm. Similarly to receive, this is performed in conn_send_qstrm()
which uses lower xprt snd_buf operation. The connection must first be
flagged with CO_FL_QSTRM_SEND to trigger this step.
---
 include/haproxy/connection-t.h |  2 +-
 src/xprt_qstrm.c               | 47 +++++++++++++++++++++++++++++++++-
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/include/haproxy/connection-t.h b/include/haproxy/connection-t.h
index f803aaf41..915818ebd 100644
--- a/include/haproxy/connection-t.h
+++ b/include/haproxy/connection-t.h
@@ -130,7 +130,7 @@ enum {
 
 	CO_FL_OPT_TOS       = 0x00000020,  /* connection has a special sockopt tos */
 
-	/* unused : 0x00000040 */
+	CO_FL_QSTRM_SEND    = 0x00000040,  /* connection uses QMux protocol, needs to exchange transport parameters before starting mux layer */
 	CO_FL_QSTRM_RECV    = 0x00000080,  /* connection uses QMux protocol, needs to exchange transport parameters before starting mux layer */
 
 	/* These flags indicate whether the Control and Transport layers are initialized */
diff --git a/src/xprt_qstrm.c b/src/xprt_qstrm.c
index 104197dab..ba14a3825 100644
--- a/src/xprt_qstrm.c
+++ b/src/xprt_qstrm.c
@@ -3,6 +3,7 @@
 #include <haproxy/connection.h>
 #include <haproxy/fd.h>
 #include <haproxy/global.h>
+#include <haproxy/mux_quic.h>
 #include <haproxy/pool.h>
 #include <haproxy/quic_frame.h>
 #include <haproxy/quic_tp-t.h>
@@ -69,12 +70,56 @@ int conn_recv_qstrm(struct connection *conn, struct xprt_qstrm_ctx *ctx, int fla
 	return 0;
 }
 
+int conn_send_qstrm(struct connection *conn, struct xprt_qstrm_ctx *ctx, int flag)
+{
+	struct quic_frame frm;
+	unsigned char *pos, *old, *end;
+	int ret;
+
+	if (!conn_ctrl_ready(conn))
+		goto fail;
+
+	frm.type = QUIC_FT_QX_TRANSPORT_PARAMETERS;
+	frm.qmux_transport_params.params.initial_max_streams_bidi = 100;
+	frm.qmux_transport_params.params.initial_max_streams_uni  = 3;
+	frm.qmux_transport_params.params.initial_max_stream_data_bidi_local = qmux_stream_rx_bufsz();
+	frm.qmux_transport_params.params.initial_max_stream_data_bidi_remote = qmux_stream_rx_bufsz();
+	frm.qmux_transport_params.params.initial_max_stream_data_uni = qmux_stream_rx_bufsz();
+
+	b_reset(&trash);
+	old = pos = (unsigned char *)b_head(&trash);
+	end = (unsigned char *)b_wrap(&trash);
+	ret = qc_build_frm(&frm, &pos, end, NULL);
+	BUG_ON(!ret);
+	b_add(&trash, pos - old);
+
+	ret = ctx->ops_lower->snd_buf(conn, ctx->ctx_lower, &trash, b_data(&trash),
+	                              NULL, 0, 0);
+	BUG_ON(!ret || ret != b_data(&trash));
+
+	conn->flags &= ~flag;
+
+	return 1;
+
+ fail:
+	conn->flags |= CO_FL_ERROR;
+	return 0;
+}
+
 struct task *xprt_qstrm_io_cb(struct task *t, void *context, unsigned int state)
 {
 	struct xprt_qstrm_ctx *ctx = context;
 	struct connection *conn = ctx->conn;
 	int ret;
 
+	if (conn->flags & CO_FL_QSTRM_SEND) {
+		if (!conn_send_qstrm(conn, ctx, CO_FL_QSTRM_SEND)) {
+			ctx->ops_lower->subscribe(conn, ctx->ctx_lower,
+			                          SUB_RETRY_SEND, &ctx->wait_event);
+			goto out;
+		}
+	}
+
 	if (conn->flags & CO_FL_QSTRM_RECV) {
 		if (!conn_recv_qstrm(conn, ctx, CO_FL_QSTRM_RECV)) {
 			ctx->ops_lower->subscribe(conn, ctx->ctx_lower,
@@ -85,7 +130,7 @@ struct task *xprt_qstrm_io_cb(struct task *t, void *context, unsigned int state)
 
  out:
 	if ((conn->flags & CO_FL_ERROR) ||
-	    !(conn->flags & CO_FL_QSTRM_RECV)) {
+	    !(conn->flags & (CO_FL_QSTRM_RECV|CO_FL_QSTRM_SEND))) {
 		/* MUX will access members from xprt_ctx on init, so create
 		 * operation should be called before any members are resetted.
 		 */