common/xreadline.c

   1 /* xreadline.c - fgets replacement function
   2  * Copyright (C) 1999, 2004 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  19  * USA.
  20  */
  21
  22 #include <config.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <errno.h>
  26
  27 #include "util.h"
  28
  29
  30 /* Same as fgets() but if the provided buffer is too short a larger
  31    one will be allocated.  This is similar to getline. A line is
  32    considered a byte stream ending in a LF.
  33
  34    If MAX_LENGTH is not NULL, it shall point to a value with the
  35    maximum allowed allocation.
  36
  37    Returns the length of the line. EOF is indicated by a line of
  38    length zero. A truncated line is indicated my setting the value at
  39    MAX_LENGTH to 0.  If the returned value is less then 0 not enough
  40    memory was enable and ERRNO is set accordingly.
  41
  42    If a line has been truncated, the file pointer is moved forward to
  43    the end of the line so that the next read starts with the next
  44    line.  Note that MAX_LENGTH must be re-initialzied in this case.
  45
  46    Note: The returned buffer is allocated with enough extra space to
  47    append a CR,LF,Nul
  48  */
  49 ssize_t
  50 read_line (FILE *fp,
  51            char **addr_of_buffer, size_t *length_of_buffer,
  52            size_t *max_length)
  53 {
  54   int c;
  55   char  *buffer = *addr_of_buffer;
  56   size_t length = *length_of_buffer;
  57   size_t nbytes = 0;
  58   size_t maxlen = max_length? *max_length : 0;
  59   char *p;
  60
  61   if (!buffer)
  62     { /* No buffer given - allocate a new one. */
  63       length = 256;
  64       buffer = xtrymalloc (length);
  65       *addr_of_buffer = buffer;
  66       if (!buffer)
  67         {
  68           *length_of_buffer = 0;
  69           if (max_length)
  70             *max_length = 0;
  71           return -1;
  72         }
  73       *length_of_buffer = length;
  74     }
  75
  76   length -= 3; /* Reserve 3 bytes for CR,LF,EOL. */
  77   p = buffer;
  78   while  ((c = getc (fp)) != EOF)
  79     {
  80       if (nbytes == length)
  81         { /* Enlarge the buffer. */
  82           if (maxlen && length > maxlen) /* But not beyond our limit. */
  83             {
  84               /* Skip the rest of the line. */
  85               while (c != '\n' && (c=getc (fp)) != EOF)
  86                 ;
  87               *p++ = '\n'; /* Always append a LF (we reserved some space). */
  88               nbytes++;
  89               if (max_length)
  90                 *max_length = 0; /* Indicate truncation. */
  91               break; /* the while loop. */
  92             }
  93           length += 3; /* Adjust for the reserved bytes. */
  94           length += length < 1024? 256 : 1024;
  95           *addr_of_buffer = xtryrealloc (buffer, length);
  96           if (!*addr_of_buffer)
  97             {
  98               int save_errno = errno;
  99               xfree (buffer);
 100               *length_of_buffer = *max_length = 0;
 101               errno = save_errno;
 102               return -1;
 103             }
 104           buffer = *addr_of_buffer;
 105           *length_of_buffer = length;
 106           length -= 3;
 107           p = buffer + nbytes;
 108         }
 109       *p++ = c;
 110       nbytes++;
 111       if (c == '\n')
 112         break;
 113     }
 114   *p = 0; /* Make sure the line is a string. */
 115
 116   return nbytes;
 117 }