lib/read-file.c

   1 /* read-file.c -- read file contents into a string
   2    Copyright (C) 2006, 2009-2019 Free Software Foundation, Inc.
   3    Written by Simon Josefsson and Bruno Haible.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 #include "read-file.h"
  21
  22 /* Get fstat.  */
  23 #include <sys/stat.h>
  24
  25 /* Get ftello.  */
  26 #include <stdio.h>
  27
  28 /* Get SIZE_MAX.  */
  29 #include <stdint.h>
  30
  31 /* Get malloc, realloc, free. */
  32 #include <stdlib.h>
  33
  34 /* Get errno. */
  35 #include <errno.h>
  36
  37 /* Read a STREAM and return a newly allocated string with the content,
  38    and set *LENGTH to the length of the string.  The string is
  39    zero-terminated, but the terminating zero byte is not counted in
  40    *LENGTH.  On errors, *LENGTH is undefined, errno preserves the
  41    values set by system functions (if any), and NULL is returned.  */
  42 char *
  43 fread_file (FILE *stream, size_t *length)
  44 {
  45   char *buf = NULL;
  46   size_t alloc = BUFSIZ;
  47
  48   /* For a regular file, allocate a buffer that has exactly the right
  49      size.  This avoids the need to do dynamic reallocations later.  */
  50   {
  51     struct stat st;
  52
  53     if (fstat (fileno (stream), &st) >= 0 && S_ISREG (st.st_mode))
  54       {
  55         off_t pos = ftello (stream);
  56
  57         if (pos >= 0 && pos < st.st_size)
  58           {
  59             off_t alloc_off = st.st_size - pos;
  60
  61             /* '1' below, accounts for the trailing NUL.  */
  62             if (SIZE_MAX - 1 < alloc_off)
  63               {
  64                 errno = ENOMEM;
  65                 return NULL;
  66               }
  67
  68             alloc = alloc_off + 1;
  69           }
  70       }
  71   }
  72
  73   if (!(buf = malloc (alloc)))
  74     return NULL; /* errno is ENOMEM.  */
  75
  76   {
  77     size_t size = 0; /* number of bytes read so far */
  78     int save_errno;
  79
  80     for (;;)
  81       {
  82         /* This reads 1 more than the size of a regular file
  83            so that we get eof immediately.  */
  84         size_t requested = alloc - size;
  85         size_t count = fread (buf + size, 1, requested, stream);
  86         size += count;
  87
  88         if (count != requested)
  89           {
  90             save_errno = errno;
  91             if (ferror (stream))
  92               break;
  93
  94             /* Shrink the allocated memory if possible.  */
  95             if (size < alloc - 1)
  96               {
  97                 char *smaller_buf = realloc (buf, size + 1);
  98                 if (smaller_buf != NULL)
  99                   buf = smaller_buf;
 100               }
 101
 102             buf[size] = '\0';
 103             *length = size;
 104             return buf;
 105           }
 106
 107         {
 108           char *new_buf;
 109
 110           if (alloc == SIZE_MAX)
 111             {
 112               save_errno = ENOMEM;
 113               break;
 114             }
 115
 116           if (alloc < SIZE_MAX - alloc / 2)
 117             alloc = alloc + alloc / 2;
 118           else
 119             alloc = SIZE_MAX;
 120
 121           if (!(new_buf = realloc (buf, alloc)))
 122             {
 123               save_errno = errno;
 124               break;
 125             }
 126
 127           buf = new_buf;
 128         }
 129       }
 130
 131     free (buf);
 132     errno = save_errno;
 133     return NULL;
 134   }
 135 }
 136
 137 static char *
 138 internal_read_file (const char *filename, size_t *length, const char *mode)
 139 {
 140   FILE *stream = fopen (filename, mode);
 141   char *out;
 142   int save_errno;
 143
 144   if (!stream)
 145     return NULL;
 146
 147   out = fread_file (stream, length);
 148
 149   save_errno = errno;
 150
 151   if (fclose (stream) != 0)
 152     {
 153       if (out)
 154         {
 155           save_errno = errno;
 156           free (out);
 157         }
 158       errno = save_errno;
 159       return NULL;
 160     }
 161
 162   return out;
 163 }
 164
 165 /* Open and read the contents of FILENAME, and return a newly
 166    allocated string with the content, and set *LENGTH to the length of
 167    the string.  The string is zero-terminated, but the terminating
 168    zero byte is not counted in *LENGTH.  On errors, *LENGTH is
 169    undefined, errno preserves the values set by system functions (if
 170    any), and NULL is returned.  */
 171 char *
 172 read_file (const char *filename, size_t *length)
 173 {
 174   return internal_read_file (filename, length, "r");
 175 }
 176
 177 /* Open (on non-POSIX systems, in binary mode) and read the contents
 178    of FILENAME, and return a newly allocated string with the content,
 179    and set LENGTH to the length of the string.  The string is
 180    zero-terminated, but the terminating zero byte is not counted in
 181    the LENGTH variable.  On errors, *LENGTH is undefined, errno
 182    preserves the values set by system functions (if any), and NULL is
 183    returned.  */
 184 char *
 185 read_binary_file (const char *filename, size_t *length)
 186 {
 187   return internal_read_file (filename, length, "rb");
 188 }