glibc/libio/tst-ftell-append.c
Siddhesh Poyarekar 2482ae433a Fix offset computation for append+ mode on switching from read (BZ #16724)
The offset computation in write mode uses the fact that _IO_read_end
is kept in sync with the external file offset.  This however is not
true when O_APPEND is in effect since switching to write mode ought to
send the external file offset to the end of file without making the
necessary adjustment to _IO_read_end.

Hence in append mode, offset computation when writing should only
consider the effect of unflushed writes, i.e. from _IO_write_base to
_IO_write_ptr.

The wiki has a detailed document that describes the rationale for
offsets returned by ftell in various conditions:

https://sourceware.org/glibc/wiki/File%20offsets%20in%20a%20stdio%20stream%20and%20ftell
2014-05-27 13:54:19 +05:30

170 lines
3.9 KiB
C

/* Verify that ftell returns the correct value after a read and a write on a
file opened in a+ mode.
Copyright (C) 2014 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library 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.
The GNU C Library 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 the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <locale.h>
#include <wchar.h>
/* data points to either char_data or wide_data, depending on whether we're
testing regular file mode or wide mode respectively. Similarly,
fputs_func points to either fputs or fputws. data_len keeps track of the
length of the current data and file_len maintains the current file
length. */
#define BUF_LEN 4
static void *buf;
static char char_buf[BUF_LEN];
static wchar_t wide_buf[BUF_LEN];
static const void *data;
static const char *char_data = "abcdefghijklmnopqrstuvwxyz";
static const wchar_t *wide_data = L"abcdefghijklmnopqrstuvwxyz";
static size_t data_len;
static size_t file_len;
typedef int (*fputs_func_t) (const void *data, FILE *fp);
fputs_func_t fputs_func;
typedef void *(*fgets_func_t) (void *s, int size, FILE *stream);
fgets_func_t fgets_func;
static int do_test (void);
#define TEST_FUNCTION do_test ()
#include "../test-skeleton.c"
static FILE *
init_file (const char *filename)
{
FILE *fp = fopen (filename, "w");
if (fp == NULL)
{
printf ("fopen: %m\n");
return NULL;
}
int written = fputs_func (data, fp);
if (written == EOF)
{
printf ("fputs failed to write data\n");
fclose (fp);
return NULL;
}
file_len = data_len;
fclose (fp);
fp = fopen (filename, "a+");
if (fp == NULL)
{
printf ("fopen(a+): %m\n");
return NULL;
}
return fp;
}
static int
do_one_test (const char *filename)
{
FILE *fp = init_file (filename);
if (fp == NULL)
return 1;
void *ret = fgets_func (buf, BUF_LEN, fp);
if (ret == NULL)
{
printf ("read failed: %m\n");
fclose (fp);
return 1;
}
int written = fputs_func (data, fp);
if (written == EOF)
{
printf ("fputs failed to write data\n");
fclose (fp);
return 1;
}
file_len += data_len;
long off = ftell (fp);
if (off != file_len)
{
printf ("Incorrect offset %ld, expected %zu\n", off, file_len);
fclose (fp);
return 1;
}
else
printf ("Correct offset %ld after write.\n", off);
return 0;
}
/* Run the tests for regular files and wide mode files. */
static int
do_test (void)
{
int ret = 0;
char *filename;
int fd = create_temp_file ("tst-ftell-append-tmp.", &filename);
if (fd == -1)
{
printf ("create_temp_file: %m\n");
return 1;
}
close (fd);
/* Tests for regular files. */
puts ("Regular mode:");
fputs_func = (fputs_func_t) fputs;
fgets_func = (fgets_func_t) fgets;
data = char_data;
buf = char_buf;
data_len = strlen (char_data);
ret |= do_one_test (filename);
/* Tests for wide files. */
puts ("Wide mode:");
if (setlocale (LC_ALL, "en_US.UTF-8") == NULL)
{
printf ("Cannot set en_US.UTF-8 locale.\n");
return 1;
}
fputs_func = (fputs_func_t) fputws;
fgets_func = (fgets_func_t) fgetws;
data = wide_data;
buf = wide_buf;
data_len = wcslen (wide_data);
ret |= do_one_test (filename);
return ret;
}