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/* read-file.c -- read file contents into a string
Copyright (C) 2006, 2009-2025 Free Software Foundation, Inc.
Written by Simon Josefsson and Bruno Haible.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
This file 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include "read-file.h"
/* Get fstat. */
#include <sys/stat.h>
/* Get ftello. */
#include <stdio.h>
/* Get PTRDIFF_MAX. */
#include <stdint.h>
/* Get malloc, realloc, free. */
#include <stdlib.h>
/* Get memcpy, memset_explicit. */
#include <string.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.
If the RF_SENSITIVE flag is set in FLAGS:
- You should control the buffering of STREAM using 'setvbuf'. Either
clear the buffer of STREAM after closing it, or disable buffering of
STREAM before calling this function.
- The memory buffer internally allocated will be cleared upon failure. */
char *
fread_file (FILE *stream, int flags, 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 (PTRDIFF_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 saved_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)
{
saved_errno = errno;
if (ferror (stream))
break;
/* Shrink the allocated memory if possible. */
if (size < alloc - 1)
{
if (flags & RF_SENSITIVE)
{
char *smaller_buf = malloc (size + 1);
if (smaller_buf == NULL)
memset_explicit (buf + size, 0, alloc - size);
else
{
memcpy (smaller_buf, buf, size);
memset_explicit (buf, 0, alloc);
free (buf);
buf = smaller_buf;
}
}
else
{
char *smaller_buf = realloc (buf, size + 1);
if (smaller_buf != NULL)
buf = smaller_buf;
}
}
buf[size] = '\0';
*length = size;
return buf;
}
{
char *new_buf;
size_t saved_alloc = alloc;
if (alloc == PTRDIFF_MAX)
{
saved_errno = ENOMEM;
break;
}
if (alloc < PTRDIFF_MAX - alloc / 2)
alloc = alloc + alloc / 2;
else
alloc = PTRDIFF_MAX;
if (flags & RF_SENSITIVE)
{
new_buf = malloc (alloc);
if (!new_buf)
{
/* BUF should be cleared below after the loop. */
saved_errno = errno;
break;
}
memcpy (new_buf, buf, saved_alloc);
memset_explicit (buf, 0, saved_alloc);
free (buf);
}
else if (!(new_buf = realloc (buf, alloc)))
{
saved_errno = errno;
break;
}
buf = new_buf;
}
}
if (flags & RF_SENSITIVE)
memset_explicit (buf, 0, alloc);
free (buf);
errno = saved_errno;
return NULL;
}
}
/* 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.
If the RF_BINARY flag is set in FLAGS, the file is opened in binary
mode. If the RF_SENSITIVE flag is set in FLAGS, the memory buffer
internally allocated will be cleared upon failure. */
char *
read_file (const char *filename, int flags, size_t *length)
{
const char *mode = (flags & RF_BINARY) ? "rbe" : "re";
FILE *stream = fopen (filename, mode);
char *out;
if (!stream)
return NULL;
if (flags & RF_SENSITIVE)
setvbuf (stream, NULL, _IONBF, 0);
out = fread_file (stream, flags, length);
if (fclose (stream) != 0)
{
if (out)
{
if (flags & RF_SENSITIVE)
memset_explicit (out, 0, *length);
free (out);
}
return NULL;
}
return out;
}
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