Re: [PATCH] receive-pack: interrupt pre-receive when client disconnects

[Jiang Xin <worldhello.net@gmail.com>]

On Wed, Jan 26, 2022 at 12:09 AM Robin Jarry <robin.jarry@6wind.com> wrote:
>
> When hitting ctrl-c on the client while a remote pre-receive hook is
> running, receive-pack is not killed by SIGPIPE because the signal is
> ignored. This is a side effect of commit ec7dbd145bd8 ("receive-pack:
> allow hooks to ignore its standard input stream").
>
> The pre-receive hook itself is not interrupted and does not receive any
> error since its stdout is a pipe which is read in an async thread and
> output back to the client socket in a side band channel.
>
> After the pre-receive has exited the SIGPIPE default handler is restored
> and if the hook did not report any error, objects are migrated from
> temporary to permanent storage.

We used to ignore the SIGPIPE signal when calling "pre-receive" hook,
so we could tolerant a buggy "pre-receive" implementation which didn't
consume all the input from "receive-pack". On the other side, "ctrl-c"
from the client side will terminate "receive-pack", only if we do not
ignore the SIGPIPE signal when running "pre-receive".

Wouldn't this be much simpler: add a new configuration variable
"receive.loosePreReceiveImplementation", and only ignore SIGPIPE when
"receive-pack" turns off the config variable?

> diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> index 9f4a0b816cf9..0f41fe8c6a85 100644
> @@ -522,10 +540,24 @@ static int copy_to_sideband(int in, int out, void *arg)
>                  * Either we're not looking for a NUL signal, or we didn't see
>                  * it yet; just pass along the data.
>                  */
> -               send_sideband(1, 2, data, sz, use_sideband);
> +               if (proc && proc->pid > 0) {
> +                       if (send_sideband2(1, 2, data, sz, use_sideband) < 0)
> +                               goto error;
> +               } else
> +                       send_sideband(1, 2, data, sz, use_sideband);
>         }
>         close(in);
>         return 0;
> +error:
> +       close(in);
> +       if (proc && proc->pid > 0) {
> +               /*
> +                * SIGPIPE would be more relevant but we want to make sure that
> +                * the hook does not ignore the signal.
> +                */
> +               kill(proc->pid, SIGKILL);
> +       }
> +       return -1;
>  }

Kill the "pre-receive" process, so the calling of
"finish_command(&proc)" at the end of "run_and_feed_hook()" will
terminate "receive-pack".

> diff --git a/sideband.c b/sideband.c
> index 85bddfdcd4f5..27f8d653eb24 100644
> --- a/sideband.c
> +++ b/sideband.c
> +static int send_sideband_priv(int fd, int band, const char *data, ssize_t sz,
> +                             int packet_max, int ignore_errors)
>  {
>         const char *p = data;
>
> @@ -265,13 +279,24 @@ void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_ma
>                 if (0 <= band) {
>                         xsnprintf(hdr, sizeof(hdr), "%04x", n + 5);
>                         hdr[4] = band;
> -                       write_or_die(fd, hdr, 5);
> +                       if (ignore_errors)

"ignore_errors" or "die_on_errors"?

> +                               write_or_die(fd, hdr, 5);
> +                       else if (write_in_full(fd, hdr, 5) < 0)
> +                               return -1;

--
Jiang Xin