[PATCH]: unlink legacy unix socket when unit starts

[Scott van Kalken]

This will work well for cases where unit shuts down gracefully. If unit
does not shut down gracefully, then i think you will have the same startup
problem.

It’s a good point about the TCP socket.

On Tue, 26 Apr 2022 at 11:50 am, <shanlei at asiainfo.com> wrote:

> I have reconsided the situation:
> compare to TCP sockets, if a TCP bind fails, we know other programs are
> using the socket ,the ops team then fix the mis-configured port number,
> change unit or other programs.
> the unix socket should behave similarly.
> the diffrence is when a tcp server is done, the socket is recycled by
> system, while the unix socket file is left in disk, which block "unit"'s
> next boot.
> may the idea patch is to unlink the unix socket file on shutdown,
> instead of startup?
>
>
> On 2022-04-25 14:38，Scott van Kalken wrote：
> > What if it were a command line option to delete on start? This way you
> > preserve the existing behaviour while introducing the desired
> > behaviour. It’s up to the user / admin to decide if they want to
> > “force delete” as an example.
> >
> > On Mon, 25 Apr 2022 at 4:33 pm, <shanlei at asiainfo.com> wrote:
> >
> >> I know the concern, that if we misconfigure the socket file, other
> >> file
> >> may be deleted accidentally.
> >> But if the program wont delete the file, bind will fail , that means
> >> we
> >> have to delete the file manually before every start. that not a good
> >>
> >> option to maintain a system.
> >>
> >> 在 2022-04-24 18:05，Александр Поволоцкий
> >> wrote：
> >>> Unlink socket that can be in use? I think it's not a good idea.
> >>>
> >>> On 24.04.2022 12:25, shanlei at asiainfo.com wrote:
> >>>>
> >>>> hello,guys,
> >>>>
> >>>> We found if we add a unix socket listener, the file was left in
> >> disk
> >>>> when unit got shutdown.
> >>>> If the unit starts again and load configuration from its state
> >> folder,
> >>>> it would fail with error msg "file exists",
> >>>> so We think the proper process is to "delete the legacy unix
> >> socket
> >>>> before start", and we present following patch:
> >>>>
> >>>>
> >>>> # HG changeset patch
> >>>> # User stdanley <shanlei at asiainfo.com>
> >>>> # Date 1650792235 -28800
> >>>> #      Sun Apr 24 17:23:55 2022 +0800
> >>>> # Node ID 29738840c393f12c7d7aa8f3959ed1655b39cd4d
> >>>> # Parent  8e06a879600e83af11345d023c53c2ca445cf82c
> >>>> unlink legacy unix socket file before binding.
> >>>>
> >>>> diff -r 8e06a879600e -r 29738840c393 src/nxt_main_process.c
> >>>> --- a/src/nxt_main_process.c    Tue Apr 12 04:16:00 2022 +0100
> >>>> +++ b/src/nxt_main_process.c    Sun Apr 24 17:23:55 2022 +0800
> >>>> @@ -1142,6 +1142,15 @@
> >>>> }
> >>>>
> >>>> #endif
> >>>> +#if (NXT_HAVE_UNIX_DOMAIN)
> >>>> +
> >>>> +    if (sa->u.sockaddr.sa_family == AF_UNIX
> >>>> +        && sa->type == SOCK_STREAM
> >>>> +        && sa->u.sockaddr_un.sun_path[0] != '\0') {
> >>>> +
> >>>> +        (void) unlink(sa->u.sockaddr_un.sun_path);
> >>>> +}
> >>>> +#endif
> >>>>
> >>>> if (bind(s, &sa->u.sockaddr, sa->socklen) != 0) {
> >>>> err = nxt_errno;
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