/* 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;

}