net/sockatmark.3

   1 .\" Copyright (c) 2002 William C. Fenner.  All rights reserved.
   2 .\"
   3 .\" Redistribution and use in source and binary forms, with or without
   4 .\" modification, are permitted provided that the following conditions
   5 .\" are met:
   6 .\" 1. Redistributions of source code must retain the above copyright
   7 .\"    notice, this list of conditions and the following disclaimer.
   8 .\" 2. Redistributions in binary form must reproduce the above copyright
   9 .\"    notice, this list of conditions and the following disclaimer in the
  10 .\"    documentation and/or other materials provided with the distribution.
  11 .\"
  12 .\" THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS ``AS IS'' AND
  13 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  14 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  15 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  16 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  17 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  18 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  19 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  20 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  21 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  22 .\" SUCH DAMAGE.
  23 .\"
  24 .\" $FreeBSD: src/lib/libc/net/sockatmark.3,v 1.4 2002/12/19 09:40:22 ru Exp $
  25 .\"
  26 .Dd October 13, 2002
  27 .Dt SOCKATMARK 3
  28 .Os
  29 .Sh NAME
  30 .Nm sockatmark
  31 .Nd determine whether the read pointer is at the OOB mark
  32 .Sh LIBRARY
  33 .Lb libc
  34 .Sh SYNOPSIS
  35 .In sys/socket.h
  36 .Ft int
  37 .Fn sockatmark "int s"
  38 .Sh DESCRIPTION
  39 To find out if the read pointer is currently pointing at
  40 the mark in the data stream, the
  41 .Fn sockatmark
  42 function is provided.
  43 If
  44 .Fn sockatmark
  45 returns 1, the next read will return data
  46 after the mark.
  47 Otherwise (assuming out of band data has arrived),
  48 the next read will provide data sent by the client prior
  49 to transmission of the out of band signal.
  50 The routine used
  51 in the remote login process to flush output on receipt of an
  52 interrupt or quit signal is shown below.
  53 It reads the normal data up to the mark (to discard it),
  54 then reads the out-of-band byte.
  55 .Bd -literal -offset indent
  56 #include <sys/socket.h>
  57 \&...
  58 oob()
  59 {
  60         int out = FWRITE, mark;
  61         char waste[BUFSIZ];
  62
  63         /* flush local terminal output */
  64         ioctl(1, TIOCFLUSH, (char *)&out);
  65         for (;;) {
  66                 if ((mark = sockatmark(rem)) < 0) {
  67                         perror("sockatmark");
  68                         break;
  69                 }
  70                 if (mark)
  71                         break;
  72                 (void) read(rem, waste, sizeof (waste));
  73         }
  74         if (recv(rem, &mark, 1, MSG_OOB) < 0) {
  75                 perror("recv");
  76                 ...
  77         }
  78         ...
  79 }
  80 .Ed
  81 .Sh RETURN VALUES
  82 Upon successful completion, the
  83 .Fn sockatmark
  84 function returns the value 1 if the read pointer is pointing at
  85 the OOB mark, 0 if it is not.
  86 Otherwise, the value \-1 is returned
  87 and the global variable
  88 .Va errno
  89 is set to
  90 indicate the error.
  91 .Sh ERRORS
  92 The
  93 .Fn sockatmark
  94 call fails if:
  95 .Bl -tag -width Er
  96 .It Bq Er EBADF
  97 The
  98 .Fa s
  99 argument
 100 is not a valid descriptor.
 101 .It Bq Er ENOTTY
 102 The
 103 .Fa s
 104 argument
 105 is a descriptor for a file, not a socket.
 106 .El
 107 .Sh SEE ALSO
 108 .Xr recv 2 ,
 109 .Xr send 2
 110 .Sh HISTORY
 111 The
 112 .Fn sockatmark
 113 function was introduced by
 114 .St -p1003.1-2001 ,
 115 to standardize the historical
 116 .Dv SIOCATMARK
 117 .Xr ioctl 2 .
 118 The
 119 .Er ENOTTY
 120 error instead of the usual
 121 .Er ENOTSOCK
 122 is to match the historical behavior of
 123 .Dv SIOCATMARK .