Re: patch - fixing sample program in unix.7

[Alejandro Colomar <alx@kernel.org>]

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Hi Lili,

On Wed, Mar 06, 2024 at 09:02:47PM +0100, Lili Püspök wrote:
> Hi Alex, I tried to follow your instructions and applied your concept.
> I hope it is ok now.

It is.

> Cheers
> PuLi
> 
> 
> From fca55af92ec1993823e70a4460a08197fa8da01a Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?P=C3=BCsp=C3=B6k=20Lili?= <poordirtylili@gmail.com>
> Date: Wed, 6 Mar 2024 20:51:38 +0100
> Subject: [PATCH] [patch] sample program in man7/unix.7
> 
> Signed-off-by: PuLi <poordirtylili@gmail.com>
> Fixes: 15545eb6d7ae ("unix.7: Add example")
> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
> 
> Client wants to send END while server already closed the connection
> on DOWN, so connection is broken instead of the Result = 0 in the
> sample on sending a single DOWN.
> Now, the server disconnects only on first END. After DOWN, all further
> processing of number stops.
> Patch does not handle cases of double END sending, multiple clients
> etc.

Patch applied.  Thanks.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=4fe1c74b42f99b3682114e1dab1200f6ced6881f>

Have a lovely night!
Alex

> ---
>  man7/unix.7 | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/man7/unix.7 b/man7/unix.7
> index cb1dcae45..2dc4f489e 100644
> --- a/man7/unix.7
> +++ b/man7/unix.7
> @@ -1057,12 +1057,16 @@ main(int argc, char *argv[])
>  \&
>              if (!strncmp(buffer, "DOWN", sizeof(buffer))) {
>                  down_flag = 1;
> -                break;
> +                continue;
>              }
>  \&
>              if (!strncmp(buffer, "END", sizeof(buffer))) {
>                  break;
>              }
> +\&
> +            if (down_flag) {
> +                continue;
> +            }
>  \&
>              /* Add received summand. */
>  \&
> -- 
> 2.39.2
> 
> Alejandro Colomar <alx@kernel.org> ezt írta (időpont: 2024. márc. 6.,
> Sze, 13:19):
> >
> > [CC += Heinrich]
> >
> > Hi Lili,
> >
> > On Mon, Mar 04, 2024 at 05:41:17PM +0100, Lili Püspök wrote:
> > > Hi Alejandro,
> > > Thanks for replying.
> > >
> > > The client, after connecting, processes the argv items and sends all
> > > of them, then issues the sending of a final END which, on the server
> > > side, is not expected after DOWN which would halt the reading (In that
> > > case, too, the processing of argv + the END should happen).
> > > After the change,  DOWN does not break the reading, the closing END is
> > > processed and there is no broken connection when client tries to send
> > > END while the server closes after sending the result, which is not
> > > received by the client.
> >
> > Hmmm, now I understand.
> >
> > >
> > > --- without DOWN ----
> > > client         server
> > > argv1..N + END --->
> > > <----- result
> > > <---- connection closed
> > >
> > > -----------problem-----------
> > > argv1...N + DOWN ->
> > > <---- result
> > > END -> ?????
> > > <---- connection closed
> > >
> > > ------- solution:---------
> > > argv1...N + DOWN + END ->
> > > <---- result
> > > <---- connection closed
> >
> > Yep, I can reproduce this problem all the way back to the original
> > implementation of the example programs.  I extracted the original
> > programs with:
> >
> >         $ git show 15545eb6d7:man7/unix.7 | man /dev/stdin | cat
> >
> > And then cut and paste to the C files.
> >
> >         $ cc -Wall -o server server.c
> >         $ cc -Wall -o client client.c
> >         $ ./server &
> >         [1] 94644
> >         $ ./client 3 4
> >         Result = 7
> >         $ ./client 11 -5
> >         Result = 6
> >         $ ./client DOWN
> >         recv: Connection reset by peer
> >         [1]+  Done                    ./server
> >         $
> >
> > This behavior conflicts with the behavior shown in the manual page,
> > which shows (for the last command):
> >
> >         $ ./client DOWN
> >         Result = 0
> >         [1]+  Done                    ./server
> >
> > So it seems like a bug.  Maybe the server program was slow enough when
> > it was implemented in 2016, that the server hadn't closed the socket
> > when the client sent "END", so the client didn't fail to read the
> > result??
> >
> > Anyway, we need to fix it.  Agree.
> >
> > Please add
> >
> >         Fixes: 15545eb6d7ae ("unix.7: Add example")
> >         Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
> >
> > to the commit message, as well as a small description of the problem.
> >
> > > I hope I did not overlook something.
> >
> > However, I'm not convinced by your patch.  It seems to allow
> >
> >         $ ./client DOWN 4 3
> >
> > which I don't think we want to support.  I think we have two options:
> >
> > -  The client avoids sending "END" after "DOWN" (so DOWN implies END).
> > -  The server only accepts "END" after "DOWN".
> >
> > Does it make sense to you?
> >
> > Have a lovely day!
> > Alex
> >
> > > OK, maybe with a unique message containing only the DOWN from client,
> > > the issue is not visible, because there is no result to return to
> > > client and we don't care it the connection is just broken....
> > >
> > > Cheers
> > > PuLi
> > >
> > > Alejandro Colomar <alx@kernel.org> ezt írta (időpont: 2024. márc. 4., H, 17:22):
> > > >
> > > > Hi Lili,
> > > >
> > > > > Subject: Re: patch - fixing sample program in unix.7
> > > >
> > > > On Sun, Mar 03, 2024 at 08:27:17PM +0100, Lili Püspök wrote:
> > > > > diff --git a/man7/unix.7 b/man7/unix.7
> > > >
> > > > Please add some commit message.  I don't understand what this patch
> > > > does.  How is it broken, and how does it fix it?
> > > >
> > > > > index cb1dcae45..7fb41af99 100644
> > > > > --- a/man7/unix.7
> > > > > +++ b/man7/unix.7
> > > > > @@ -1057,7 +1057,7 @@ main(int argc, char *argv[])
> > > > > \&
> > > > >             if (!strncmp(buffer, "DOWN", sizeof(buffer))) {
> > > > >                 down_flag = 1;
> > > > > -                break;
> > > > > +                continue;
> > > >
> > > > DOWN is used to stop the server.  How would 'continue' help?
> > > >
> > > >
> > > >         $ MANWIDTH=66 man unix | grep -C2 DOWN
> > > >              tegers.  The client prints the sum and exits.   The  server
> > > >              waits  for the next client to connect.  To stop the server,
> > > >              the client is called with the command‐line argument "DOWN".
> > > >
> > > >              The following output was recorded while running the  server
> > > >              in the background and repeatedly executing the client.  Ex‐
> > > >              ecution  of  the  server  program ends when it receives the
> > > >              "DOWN" command.
> > > >
> > > >            Example output
> > > >         --
> > > >                  $ ./client 11 -5
> > > >                  Result = 6
> > > >                  $ ./client DOWN
> > > >                  Result = 0
> > > >                  [1]+  Done                    ./server
> > > >         --
> > > >                          /* Handle commands. */
> > > >
> > > >                          if (!strncmp(buffer, "DOWN", sizeof(buffer))) {
> > > >                              down_flag = 1;
> > > >                              break;
> > > >         --
> > > >                      close(data_socket);
> > > >
> > > >                      /* Quit on DOWN command. */
> > > >
> > > >                      if (down_flag) {
> > > >
> > > > Have a lovely day,
> > > > Alex
> > > >
> > > >
> > > > >             }
> > > > > \&
> > > > >             if (!strncmp(buffer, "END", sizeof(buffer))) {
> > > > >
> > > >
> > > > --
> > > > <https://www.alejandro-colomar.es/>
> > > > Looking for a remote C programming job at the moment.
> >
> > --
> > <https://www.alejandro-colomar.es/>
> > Looking for a remote C programming job at the moment.

-- 
<https://www.alejandro-colomar.es/>

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