Mailing-List: contact cygwin-help AT sourceware DOT cygnus DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT sources DOT redhat DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT sources DOT redhat DOT com>
List-Help: <mailto:cygwin-help AT sources DOT redhat DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT sources DOT redhat DOT com
Delivered-To: mailing list cygwin AT sources DOT redhat DOT com
Date: Fri, 13 Jul 2001 20:21:46 -0400
From: Christopher Faylor <cgf AT redhat DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: data in socketpair() channel lost if writer closes or exits without shutting down
Message-ID: <20010713202146.B11377@redhat.com>
Reply-To: cygwin AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
References: <20010713181435 DOT 3695 DOT qmail AT lizard DOT curl DOT com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.3.11i
In-Reply-To: <20010713181435.3695.qmail@lizard.curl.com>; from jik@curl.com on Fri, Jul 13, 2001 at 02:14:35PM -0400

Thanks for the diagnosis.  Would you be willing to look at the
Cygwin socket code and suggest a fix?

cgf

On Fri, Jul 13, 2001 at 02:14:35PM -0400, Jonathan Kamens wrote:
>The test program below creates a socketpair and then forks.  The child
>writes some data to the socketpair and then exits, and the parent
>tries to read that data.
>
>Instead of printing "PARENT: foo (exiting)" as it should, the parent
>prints "PARENT: read: Connection reset by peer".  This is also true if
>you compile the program with "-DUSE_CLOSE" to tell the child to close
>the write end of the socketpair before exiting.  However, it works
>properly if you compile the program with "-DUSE_SHUTDOWN" to tell the
>child to shutdown its end of the socketpair before exiting.
>
>There are two different bugs here:
>
>1) close() on an end of a socketpair should behave the same as
>   shutdown(..., 2), in terms of flushing data to the other end of the
>   socketpair.
>
>2) Data sent by the writer should be flushed to the reader, not lost,
>   when the writer exits.
>
>This problem causes recent versions of rsync, when they are compiled
>to use socketpairs (which is the default), to report a bogus "read
>error: connection reset by peer" at the end of every rsync, even when
>it in fact copied everything successfully.  I'm going to submit a
>patch to the rsync maintainers suggesting that they work around this
>problem by calling shutdown() before exiting.
>
>  jik
>
>                      *************************
>
>#include <unistd.h>
>#include <stdio.h>
>#include <sys/types.h>
>#include <signal.h>
>#include <sys/socket.h>
>
>main()
>{
>  int pipefds[2];
>  int readfd, writefd;
>  char inbuf[4];
>  char outbuf[4] = "foo";
>  int pid;
>  fd_set readfds, exceptfds;
>
>  socketpair(AF_UNIX, SOCK_STREAM, 0, pipefds);
>  /* pipe(pipefds); */
>  
>  readfd = pipefds[0];
>  writefd = pipefds[1];
>
>  if (pid = fork()) {
>    fprintf(stderr, "PARENT: close(writefd)\n");
>    close(writefd);
>
>    FD_ZERO(&readfds);
>    FD_SET(readfd, &readfds);
>    exceptfds = readfds;
>
>    fprintf(stderr, "PARENT: selecting\n");
>    if (select(readfd + 1, &readfds, NULL, &exceptfds, NULL) <= 0) {
>      perror("PARENT: select");
>      exit(1);
>    }
>
>    if (FD_ISSET(readfd, &exceptfds)) {
>      fprintf(stderr, "PARENT: exception is set\n");
>    }
>
>    if (FD_ISSET(readfd, &readfds)) {
>      fprintf(stderr, "PARENT: read is set\n");
>    }
>
>    fprintf(stderr, "PARENT: reading\n");
>    if (read(readfd, inbuf, sizeof(inbuf)) != sizeof(inbuf)) {
>      perror("PARENT: read");
>      exit(1);
>    }
>
>    printf("PARENT: %s (exiting)\n", inbuf);
>    exit(0);
>  }
>  else {
>    fprintf(stderr, "CHILD: close(readfd)\n");
>    close(readfd);
>
>    fprintf(stderr, "CHILD: writing\n");
>    if (write(writefd, outbuf, sizeof(outbuf)) != sizeof(outbuf)) {
>      perror("CHILD: write");
>      exit(1);
>    }
>#ifdef USE_SHUTDOWN
>    shutdown(writefd, 2);
>#endif
>#ifdef USE_CLOSE
>    close(writefd);
>#endif
>
>    fprintf(stderr, "CHILD: exiting\n");
>    exit(0);
>  }
>}
>
>--
>Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
>Bug reporting:         http://cygwin.com/bugs.html
>Documentation:         http://cygwin.com/docs.html
>FAQ:                   http://cygwin.com/faq/

-- 
cgf AT cygnus DOT com                        Red Hat, Inc.
http://sources.redhat.com/            http://www.redhat.com/

--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Bug reporting:         http://cygwin.com/bugs.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/