tree c67709fc31b56eb92cd3f93779d5090d4c825561
parent e2ec9421ea769cc5673b664300720ddbb2c0c9ac
author Amaury Denoyelle <adenoyelle@haproxy.com> 1646926943 +0100
committer Amaury Denoyelle <adenoyelle@haproxy.com> 1646995051 +0100

MINOR: mux-quic: improve opportunistic retry sending for STREAM frames

For the moment, the transport layer function qc_send_app_pkts lacks
features. Most notably, it only send up to a single Tx buffer and won't
retry even if there is frames left and its Tx buffer is now empty.

To overcome this limitation, the MUX implements an opportunistic retry
sending mechanism. qc_send_app_pkts is repeatedly called until the
transport layer is blocked on an external condition (such as congestion
control or a sendto syscall error).

The blocking was detected by inspecting the frame list before and after
qc_send_app_pkts. If no frame has been poped by the function, we
considered the transport layer to be blocked and we stop to send. The
MUX is subscribed on the lower layer to send the frames left.

However, in case of STREAM frames, qc_send_app_pkts might use only a
portion of the data and update the frame offset. So, for STREAM frames,
a new mechanism is implemented : if the offset field of the first frame
has not been incremented, it means the transport layer is blocked.

This should improve transfers execution. Before this change, there is a
possibility of interrupted transfer if the mux has not sent everything
possible and is waiting on a transport signaling which will never
happen.

In the future, qc_send_app_pkts should be extended to retry sending by
itself. All this code burden will be removed from the MUX.