[PATCH 1 of 8] QUIC: treat qc->error == -1 as a missing error

[Sergey Kandaurov]

On Thu, Jun 23, 2022 at 07:58:39PM +0400, Roman Arutyunyan wrote:
> # HG changeset patch
> # User Roman Arutyunyan <arut at nginx.com>
> # Date 1655889315 -14400
> #      Wed Jun 22 13:15:15 2022 +0400
> # Branch quic
> # Node ID 951d7116f37dc39d9eba20ceae49434592ce4677
> # Parent  5b1011b5702b5c5db2ba3d392a4da25596183cc2
> QUIC: treat qc->error == -1 as a missing error.
> 
> Previously, zero was used for this purpose.  However, NGX_QUIC_ERR_NO_ERROR is
> zero too.  As a result, NGX_QUIC_ERR_NO_ERROR was changed to
> NGX_QUIC_ERR_INTERNAL_ERROR when closing a QUIC connection.
> 
> diff --git a/src/event/quic/ngx_event_quic.c b/src/event/quic/ngx_event_quic.c
> --- a/src/event/quic/ngx_event_quic.c
> +++ b/src/event/quic/ngx_event_quic.c
> @@ -317,6 +317,8 @@ ngx_quic_new_connection(ngx_connection_t
>      qc->congestion.ssthresh = (size_t) -1;
>      qc->congestion.recovery_start = ngx_current_msec;
>  
> +    qc->error = (ngx_uint_t) -1;
> +
>      if (pkt->validated && pkt->retried) {
>          qc->tp.retry_scid.len = pkt->dcid.len;
>          qc->tp.retry_scid.data = ngx_pstrdup(c->pool, &pkt->dcid);
> @@ -523,7 +525,7 @@ ngx_quic_close_connection(ngx_connection
>                  qc->error = NGX_QUIC_ERR_NO_ERROR;
>  
>              } else {
> -                if (qc->error == 0 && !qc->error_app) {
> +                if (qc->error == (ngx_uint_t) -1 && !qc->error_app) {
>                      qc->error = NGX_QUIC_ERR_INTERNAL_ERROR;
>                  }
>  

A former initialization is in ngx_quic_handle_payload().
Leaving it there makes connection close on the error path, for example,
on ngx_quic_set_path() failure, with a wrong NO_ERROR code.

I'd just leave (a new value of) initialization in place:
ngx_quic_new_connection() gives an established quic connection or nothing,
it cannot fail with qc initialized. ngx_quic_handle_payload() is called
right after, and is a point of packet decryption, which implies qc->error
reset.  This makes it a suitable place.