nss/nss_readline.c

   1 /* Read a line from an nss_files database file.
   2    Copyright (C) 2020-2022 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <nss_files.h>
  20
  21 #include <ctype.h>
  22 #include <errno.h>
  23 #include <string.h>
  24
  25 int
  26 __nss_readline (FILE *fp, char *buf, size_t len, off64_t *poffset)
  27 {
  28   /* We need space for at least one character, the line terminator,
  29      and the NUL byte.  */
  30   if (len < 3)
  31     {
  32       *poffset = -1;
  33       __set_errno (ERANGE);
  34       return ERANGE;
  35     }
  36
  37   while (true)
  38     {
  39       /* Keep original offset for retries.  */
  40       *poffset = __ftello64 (fp);
  41
  42       buf[len - 1] = '\xff';        /* Marker to recognize truncation.  */
  43       if (__fgets_unlocked (buf, len, fp) == NULL)
  44         {
  45           if (__feof_unlocked (fp))
  46             {
  47               __set_errno (ENOENT);
  48               return ENOENT;
  49             }
  50           else
  51             {
  52               /* Any other error.  Do not return ERANGE in this case
  53                  because the caller would retry.  */
  54               if (errno == ERANGE)
  55                 __set_errno (EINVAL);
  56               return errno;
  57             }
  58         }
  59       else if (buf[len - 1] != '\xff')
  60         /* The buffer is too small.  Arrange for re-reading the same
  61            line on the next call.  */
  62         return __nss_readline_seek (fp, *poffset);
  63
  64       /* __fgets_unlocked succeeded.  */
  65
  66       /* Remove leading whitespace.  */
  67       char *p = buf;
  68       while (isspace (*p))
  69         ++p;
  70       if (*p == '\0' || *p == '#')
  71         /* Skip empty lines and comments.  */
  72         continue;
  73       if (p != buf)
  74         memmove (buf, p, strlen (p));
  75
  76       /* Return line to the caller.  */
  77       return 0;
  78     }
  79 }
  80 libc_hidden_def (__nss_readline)
  81
  82 int
  83 __nss_readline_seek (FILE *fp, off64_t offset)
  84 {
  85   if (offset < 0 /* __ftello64 failed.  */
  86       || __fseeko64 (fp, offset, SEEK_SET) < 0)
  87     {
  88       /* Without seeking support, it is not possible to
  89          re-read the same line, so this is a hard failure.  */
  90       fseterr_unlocked (fp);
  91       __set_errno (ESPIPE);
  92       return ESPIPE;
  93     }
  94   else
  95     {
  96       __set_errno (ERANGE);
  97       return ERANGE;
  98     }
  99 }