summaryrefslogtreecommitdiff
path: root/gl/read-file.c
blob: 2418053642320eae46eff0fdaa4726ab07f73397 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
/* read-file.c -- read file contents into a string
   Copyright (C) 2006, 2009-2017 Free Software Foundation, Inc.
   Written by Simon Josefsson and Bruno Haible.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

#include "read-file.h"

/* Get fstat.  */
#include <sys/stat.h>

/* Get ftello.  */
#include <stdio.h>

/* Get SIZE_MAX.  */
#include <stdint.h>

/* Get malloc, realloc, free. */
#include <stdlib.h>

/* Get errno. */
#include <errno.h>

/* Read a STREAM and return a newly allocated string with the content,
   and set *LENGTH to the length of the string.  The string is
   zero-terminated, but the terminating zero byte is not counted in
   *LENGTH.  On errors, *LENGTH is undefined, errno preserves the
   values set by system functions (if any), and NULL is returned.  */
char *
fread_file (FILE *stream, size_t *length)
{
  char *buf = NULL;
  size_t alloc = BUFSIZ;

  /* For a regular file, allocate a buffer that has exactly the right
     size.  This avoids the need to do dynamic reallocations later.  */
  {
    struct stat st;

    if (fstat (fileno (stream), &st) >= 0 && S_ISREG (st.st_mode))
      {
        off_t pos = ftello (stream);

        if (pos >= 0 && pos < st.st_size)
          {
            off_t alloc_off = st.st_size - pos;

            /* '1' below, accounts for the trailing NUL.  */
            if (SIZE_MAX - 1 < alloc_off)
              {
                errno = ENOMEM;
                return NULL;
              }

            alloc = alloc_off + 1;
          }
      }
  }

  if (!(buf = malloc (alloc)))
    return NULL; /* errno is ENOMEM.  */

  {
    size_t size = 0; /* number of bytes read so far */
    int save_errno;

    for (;;)
      {
        /* This reads 1 more than the size of a regular file
           so that we get eof immediately.  */
        size_t requested = alloc - size;
        size_t count = fread (buf + size, 1, requested, stream);
        size += count;

        if (count != requested)
          {
            save_errno = errno;
            if (ferror (stream))
              break;

            /* Shrink the allocated memory if possible.  */
            if (size < alloc - 1)
              {
                char *smaller_buf = realloc (buf, size + 1);
                if (smaller_buf != NULL)
                  buf = smaller_buf;
              }

            buf[size] = '\0';
            *length = size;
            return buf;
          }

        {
          char *new_buf;

          if (alloc == SIZE_MAX)
            {
              save_errno = ENOMEM;
              break;
            }

          if (alloc < SIZE_MAX - alloc / 2)
            alloc = alloc + alloc / 2;
          else
            alloc = SIZE_MAX;

          if (!(new_buf = realloc (buf, alloc)))
            {
              save_errno = errno;
              break;
            }

          buf = new_buf;
        }
      }

    free (buf);
    errno = save_errno;
    return NULL;
  }
}

static char *
internal_read_file (const char *filename, size_t *length, const char *mode)
{
  FILE *stream = fopen (filename, mode);
  char *out;
  int save_errno;

  if (!stream)
    return NULL;

  out = fread_file (stream, length);

  save_errno = errno;

  if (fclose (stream) != 0)
    {
      if (out)
        {
          save_errno = errno;
          free (out);
        }
      errno = save_errno;
      return NULL;
    }

  return out;
}

/* Open and read the contents of FILENAME, and return a newly
   allocated string with the content, and set *LENGTH to the length of
   the string.  The string is zero-terminated, but the terminating
   zero byte is not counted in *LENGTH.  On errors, *LENGTH is
   undefined, errno preserves the values set by system functions (if
   any), and NULL is returned.  */
char *
read_file (const char *filename, size_t *length)
{
  return internal_read_file (filename, length, "r");
}

/* Open (on non-POSIX systems, in binary mode) and read the contents
   of FILENAME, and return a newly allocated string with the content,
   and set LENGTH to the length of the string.  The string is
   zero-terminated, but the terminating zero byte is not counted in
   the LENGTH variable.  On errors, *LENGTH is undefined, errno
   preserves the values set by system functions (if any), and NULL is
   returned.  */
char *
read_binary_file (const char *filename, size_t *length)
{
  return internal_read_file (filename, length, "rb");
}