[QUIC] padding of Initial packets

[Sergey Kandaurov]

> On 2 Feb 2022, at 13:55, Vladimir Homutov <vl at nginx.com> wrote:
> 
> # HG changeset patch
> # User Vladimir Homutov <vl at nginx.com>
> # Date 1643796973 -10800
> #      Wed Feb 02 13:16:13 2022 +0300
> # Branch quic
> # Node ID fbfbcf66990e8964bcf308f3869f37d1a1acceeb
> # Parent  8c6645ecaeb6cbf27976fd9035440bfcab943117
> QUIC: fixed padding of initial packets in case of limited path.
> 
> Previously, non-padded initial packet could be sent as a result of the
> following situation:
> 
> - initial queue is not empty (so padding to 1200 is required)
> - handhsake queue is not empty (so padding is to be added after h/s packet)

handshake

> - path is limited
> 
> If serializing handshake packet would violate path limit, such packet was
> omitted, and the non-padded initial packet was sent.
> 
> The fix is to avoid sending the packet at all in such case.  This follows the
> original intention introduced in c5155a0cb12f.
> 
> diff --git a/src/event/quic/ngx_event_quic_output.c b/src/event/quic/ngx_event_quic_output.c
> --- a/src/event/quic/ngx_event_quic_output.c
> +++ b/src/event/quic/ngx_event_quic_output.c
> @@ -158,7 +158,14 @@ ngx_quic_create_datagrams(ngx_connection
>                   ? NGX_QUIC_MIN_INITIAL_SIZE - (p - dst) : 0;
> 
>             if (min > len) {
> -                continue;
> +                /* padding can't be applied - avoid sending the packet */
> +
> +                for (i = 0; i < NGX_QUIC_SEND_CTX_LAST; i++) {
> +                    ctx = &qc->send_ctx[i];
> +                    ngx_quic_revert_send(c, ctx, preserved_pnum[i]);

this could be simplified to reduce ctx variable:
    ngx_quic_revert_send(c, &qc->send_ctx[i], preserved_pnum[i]);

but it won't fit into 80 line, so that's good just as well

> +                }
> +
> +                return NGX_OK;
>             }
> 
>             n = ngx_quic_output_packet(c, ctx, p, len, min);
> 

-- 
Sergey Kandaurov