MEDIUM: mux-quic: Add consumer-side fast-forwarding support

The QUIC multiplexer now implements callbacks to consume fast-forwarded
data. It relies on the H3 stack to acquire the buffer and format the frame.

include/haproxy/mux_quic-t.h

@@ -189,6 +189,8 @@ struct qcc_app_ops {
 	int (*attach)(struct qcs *qcs, void *conn_ctx);
 	ssize_t (*decode_qcs)(struct qcs *qcs, struct buffer *b, int fin);
 	size_t (*snd_buf)(struct qcs *qcs, struct htx *htx, size_t count);
+	size_t (*nego_ff)(struct qcs *qcs, size_t count);
+	size_t (*done_ff)(struct qcs *qcs);
 	int (*close)(struct qcs *qcs, enum qcc_app_ops_close_side side);
 	void (*detach)(struct qcs *qcs);
 	int (*finalize)(void *ctx);

src/h3.c

@@ -1836,6 +1836,69 @@ static size_t h3_snd_buf(struct qcs *qcs, struct htx *htx, size_t count)
 	return total;
 }
 
+static size_t h3_nego_ff(struct qcs *qcs, size_t count)
+{
+	struct buffer *res;
+	int hsize;
+	size_t sz, ret = 0;
+
+	h3_debug_printf(stderr, "%s\n", __func__);
+
+	/* FIXME: no check on ALLOC ? */
+	res = mux_get_buf(qcs);
+
+	/* h3 DATA headers : 1-byte frame type + varint frame length */
+	hsize = 1 + QUIC_VARINT_MAX_SIZE;
+	while (1) {
+		if (b_contig_space(res) >= hsize || !b_space_wraps(res))
+			break;
+		b_slow_realign(res, trash.area, b_data(res));
+	}
+
+	/* Not enough room for headers and at least one data byte, block the
+	 * stream. It is expected that the stream connector layer will subscribe
+	 * on SEND.
+	 */
+	if (b_contig_space(res) <= hsize) {
+		qcs->flags |= QC_SF_BLK_MROOM;
+		qcs->sd->iobuf.flags |= IOBUF_FL_FF_BLOCKED;
+		goto end;
+	}
+
+	/* Cannot forward more than available room in output buffer */
+	sz = b_contig_space(res) - hsize;
+	if (count > sz)
+		count = sz;
+
+	qcs->sd->iobuf.buf = res;
+	qcs->sd->iobuf.offset = hsize;
+	qcs->sd->iobuf.data = 0;
+
+	ret = count;
+  end:
+	return ret;
+}
+
+static size_t h3_done_ff(struct qcs *qcs)
+{
+	size_t total = qcs->sd->iobuf.data;
+
+	h3_debug_printf(stderr, "%s\n", __func__);
+
+	if (qcs->sd->iobuf.data) {
+		b_sub(qcs->sd->iobuf.buf, qcs->sd->iobuf.data);
+		b_putchr(qcs->sd->iobuf.buf, 0x00); /* h3 frame type = DATA */
+		b_quic_enc_int(qcs->sd->iobuf.buf, qcs->sd->iobuf.data, QUIC_VARINT_MAX_SIZE); /* h3 frame length */
+		b_add(qcs->sd->iobuf.buf, qcs->sd->iobuf.data);
+	}
+
+	qcs->sd->iobuf.buf = NULL;
+	qcs->sd->iobuf.offset = 0;
+	qcs->sd->iobuf.data = 0;
+
+	return total;
+}
+
 /* Notify about a closure on <qcs> stream requested by the remote peer.
  *
  * Stream channel <side> is explained relative to our endpoint : WR for
@@ -2132,6 +2195,8 @@ const struct qcc_app_ops h3_ops = {
 	.attach      = h3_attach,
 	.decode_qcs  = h3_decode_qcs,
 	.snd_buf     = h3_snd_buf,
+	.nego_ff     = h3_nego_ff,
+	.done_ff     = h3_done_ff,
 	.close       = h3_close,
 	.detach      = h3_detach,
 	.finalize    = h3_finalize,

src/mux_quic.c

@@ -21,6 +21,7 @@
 #include <haproxy/stconn.h>
 #include <haproxy/time.h>
 #include <haproxy/trace.h>
+#include <haproxy/xref.h>
 
 DECLARE_POOL(pool_head_qcc, "qcc", sizeof(struct qcc));
 DECLARE_POOL(pool_head_qcs, "qcs", sizeof(struct qcs));
@@ -2807,6 +2808,85 @@ static size_t qmux_strm_snd_buf(struct stconn *sc, struct buffer *buf,
 	return ret;
 }
 
+
+static size_t qmux_nego_ff(struct stconn *sc, struct buffer *input, size_t count, unsigned int may_splice)
+{
+	struct qcs *qcs = __sc_mux_strm(sc);
+	size_t ret = 0;
+
+	TRACE_ENTER(QMUX_EV_STRM_SEND, qcs->qcc->conn, qcs);
+
+	/* stream layer has been detached so no transfer must occur after. */
+	BUG_ON_HOT(qcs->flags & QC_SF_DETACH);
+
+	if (!qcs->qcc->app_ops->nego_ff || !qcs->qcc->app_ops->done_ff) {
+		/* Fast forwading is not supported by the QUIC application layer */
+		qcs->sd->iobuf.flags |= IOBUF_FL_NO_FF;
+		goto end;
+	}
+
+	/* Alawys disable splicing */
+	qcs->sd->iobuf.flags |= IOBUF_FL_NO_SPLICING;
+
+	ret = qcs->qcc->app_ops->nego_ff(qcs, count);
+	if (!ret)
+		goto end;
+
+	/* forward remaining input data */
+	if (b_data(input)) {
+		size_t xfer = ret;
+
+		if (xfer > b_data(input))
+			xfer = b_data(input);
+		b_add(qcs->sd->iobuf.buf, qcs->sd->iobuf.offset);
+		qcs->sd->iobuf.data = b_xfer(qcs->sd->iobuf.buf, input, xfer);
+		b_sub(qcs->sd->iobuf.buf, qcs->sd->iobuf.offset);
+
+		/* Cannot forward more data, wait for room */
+		if (b_data(input))
+			goto end;
+	}
+	ret -= qcs->sd->iobuf.data;
+
+ end:
+	TRACE_LEAVE(QMUX_EV_STRM_SEND, qcs->qcc->conn, qcs);
+	return ret;
+}
+
+static size_t qmux_done_ff(struct stconn *sc)
+{
+	struct qcs *qcs = __sc_mux_strm(sc);
+	struct qcc *qcc = qcs->qcc;
+	struct sedesc *sd = qcs->sd;
+	size_t total = 0;
+
+	TRACE_ENTER(QMUX_EV_STRM_SEND, qcs->qcc->conn, qcs);
+
+	if (sd->iobuf.flags & IOBUF_FL_EOI)
+		qcs->flags |= QC_SF_FIN_STREAM;
+
+	if (!(qcs->flags & QC_SF_FIN_STREAM) && !sd->iobuf.data)
+		goto end;
+
+	total = qcs->qcc->app_ops->done_ff(qcs);
+
+	qcc_send_stream(qcs, 0);
+	if (!(qcs->qcc->wait_event.events & SUB_RETRY_SEND))
+		tasklet_wakeup(qcc->wait_event.tasklet);
+
+  end:
+	if (!b_data(&qcs->tx.buf))
+		b_free(&qcs->tx.buf);
+
+	TRACE_LEAVE(QMUX_EV_STRM_SEND, qcs->qcc->conn, qcs);
+	return total;
+}
+
+static int qmux_resume_ff(struct stconn *sc, unsigned int flags)
+{
+	return 0;
+}
+
 /* Called from the upper layer, to subscribe <es> to events <event_type>. The
  * event subscriber <es> is not allowed to change from a previous call as long
  * as at least one event is still subscribed. The <event_type> must only be a
@@ -2927,6 +3007,9 @@ static const struct mux_ops qmux_ops = {
 	.detach      = qmux_strm_detach,
 	.rcv_buf     = qmux_strm_rcv_buf,
 	.snd_buf     = qmux_strm_snd_buf,
+	.nego_fastfwd = qmux_nego_ff,
+	.done_fastfwd = qmux_done_ff,
+	.resume_fastfwd = qmux_resume_ff,
 	.subscribe   = qmux_strm_subscribe,
 	.unsubscribe = qmux_strm_unsubscribe,
 	.wake        = qmux_wake,