From owner-freebsd-chat  Thu Nov 22 21:58:16 2001
Delivered-To: freebsd-chat@freebsd.org
Received: from mail.thpoon.com (CPE0080c8f2c614.cpe.net.cable.rogers.com [24.42.106.79])
	by hub.freebsd.org (Postfix) with SMTP id A81F637B405
	for <freebsd-chat@freebsd.org>; Thu, 22 Nov 2001 21:58:10 -0800 (PST)
Received: (qmail 43039 invoked from network); 23 Nov 2001 05:58:09 -0000
Received: from unknown (HELO tea.thpoon.com) (qmailr@192.168.1.2)
  by 192.168.1.1 with SMTP; 23 Nov 2001 05:58:09 -0000
Received: (qmail 10075 invoked by uid 1000); 23 Nov 2001 05:58:08 -0000
To: freebsd-chat@freebsd.org
Subject: Reentrant readn() and writen() for socket communication
From: Arcady Genkin <antipode@thpoon.com>
X-Face:  0=A/O5-+sE[Tf%X>rYr?Y5LD4,:^'jaJ!4jC&UR*ZrrK2>^`g22Qeb]!:d;}2YJ|Hq"LHdF
 OX`jWX|AT-WVFQ(TPhFVak)0nt$aEdlOq=1~D,:\z5QlVOrZ2(H,mKg=Xr|'VlHA="r
Mail-Copies-To: never
Date: 23 Nov 2001 00:58:08 -0500
Message-ID: <873d363u6n.fsf@tea.thpoon.com>
Lines: 42
User-Agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Academic Rigor)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: owner-freebsd-chat@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-chat.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-chat>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-chat>
X-Loop: FreeBSD.org

Stevens' UNIX Network Programming show sample readn()[1] and writen()
functions to read/write from/to a socket.

The functions handle interrupted read()/write() system calls by
examining errno value.  This approach is not thread-safe (because of
usage of errno global).

Is there a reentrant way to detect under-reads/writes, or had I better
off with just using recv() with MSG_WAITALL flag?

Footnotes:
[1]  Here's the code of readn() for easy reference:

ssize_t
readn( int fd, void *vptr, size_t n )
{
  size_t nleft;
  ssize_t nread;
  char *ptr;

  ptr = vptr;
  nleft = n;
  while ( nleft > 0 ) {
    if ( (nread = read(fd, ptr, nleft)) < 0 ) {
      if (errno == EINTR)
        nread = 0; /* and call read() again */
      else
        return (-1);
    }
    else if ( nread == 0 )
      break;  /* EOF */

    nleft -= nread;
    ptr += nread;
  }
  return (n - nleft);  /* >= 0 */
}

Many thanks,
-- 
Arcady Genkin
i=1; while 1, hilb(i); i=i+1; end

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-chat" in the body of the message