lib/libc/stdio/fgets.c

   1 /*      $NetBSD: fgets.c,v 1.28 2012/03/15 18:22:30 christos Exp $      */
   2
   3 /*-
   4  * Copyright (c) 1990, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Chris Torek.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 #if 0
  38 static char sccsid[] = "@(#)fgets.c     8.2 (Berkeley) 12/22/93";
  39 #else
  40 __RCSID("$NetBSD: fgets.c,v 1.28 2012/03/15 18:22:30 christos Exp $");
  41 #endif
  42 #endif /* LIBC_SCCS and not lint */
  43
  44 #include <assert.h>
  45 #include <stdio.h>
  46 #include <errno.h>
  47 #include <string.h>
  48 #include "reentrant.h"
  49 #include "local.h"
  50 #ifdef _FORTIFY_SOURCE
  51 #undef fgets
  52 #endif
  53
  54 /*
  55  * Read at most n-1 characters from the given file.
  56  * Stop when a newline has been read, or the count runs out.
  57  * Return first argument, or NULL if no characters were read.
  58  */
  59 char *
  60 fgets(char *buf, int n, FILE *fp)
  61 {
  62         int len;
  63         char *s;
  64         unsigned char *p, *t;
  65
  66         _DIAGASSERT(buf != NULL);
  67         _DIAGASSERT(fp != NULL);
  68
  69         FLOCKFILE(fp);
  70         _SET_ORIENTATION(fp, -1);
  71         s = buf;
  72         n--;                    /* leave space for NUL */
  73         do {
  74                 /*
  75                  * If the buffer is empty, refill it.
  76                  */
  77                 if (fp->_r <= 0) {
  78                         if (__srefill(fp)) {
  79                                 /* EOF/error: stop with partial or no line */
  80                                 if (s == buf) {
  81                                         FUNLOCKFILE(fp);
  82                                         return (NULL);
  83                                 }
  84                                 break;
  85                         }
  86                 }
  87                 len = fp->_r;
  88                 p = fp->_p;
  89
  90                 /*
  91                  * Scan through at most n bytes of the current buffer,
  92                  * looking for '\n'.  If found, copy up to and including
  93                  * newline, and stop.  Otherwise, copy entire chunk
  94                  * and loop.
  95                  */
  96                 if (len > n) {
  97                         if (n < 0) {
  98                                 /*
  99                                  * Caller's length <= 0
 100                                  * We can't write into the buffer, so cannot
 101                                  * return a string, so must return NULL.
 102                                  * Set errno and __SERR so it is consistent.
 103                                  * TOG gives no indication of what to do here!
 104                                  */
 105                                 errno = EINVAL;
 106                                 fp->_flags |= __SERR;
 107                                 FUNLOCKFILE(fp);
 108                                 return NULL;
 109                         }
 110                         len = n;
 111                 }
 112                 t = memchr(p, '\n', (size_t)len);
 113                 if (t != NULL) {
 114                         len = (int)(++t - p);
 115                         fp->_r -= len;
 116                         fp->_p = t;
 117                         (void)memcpy(s, p, (size_t)len);
 118                         s[len] = 0;
 119                         FUNLOCKFILE(fp);
 120                         return buf;
 121                 }
 122                 fp->_r -= len;
 123                 fp->_p += len;
 124                 (void)memcpy(s, p, (size_t)len);
 125                 s += len;
 126                 n -= len;
 127         } while (n != 0);
 128         *s = 0;
 129         FUNLOCKFILE(fp);
 130         return buf;
 131 }