fgets: more tests

Add more tests for unusual situations fgets() might see:

* zero size file
* zero sized buffer
* NULL buffer
* NUL data
* writable stream
* closed stream

Reviewed-by: Florian Weimer <fweimer@redhat.com>

2 files changed, 254 insertions, 0 deletions

diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 89871d0..03d597f 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -209,6 +209,7 @@ tests := \
   tst-fdopen \
   tst-ferror \
   tst-fgets \
+  tst-fgets2 \
   tst-fileno \
   tst-fmemopen \
   tst-fmemopen2 \
diff --git a/stdio-common/tst-fgets2.c b/stdio-common/tst-fgets2.c
new file mode 100644
index 0000000..5b78447
--- /dev/null
+++ b/stdio-common/tst-fgets2.c
@@ -0,0 +1,253 @@
+/* Test for additional fgets error handling.
+   Copyright (C) 2024 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <libc-diag.h>
+#include <stdio.h>
+#include <error.h>
+#include <errno.h>
+#include <limits.h>
+#include <mcheck.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#include <support/support.h>
+#include <support/check.h>
+
+/* This avoids compiler warnings about passing NULL where a valid
+   pointer is expected.  */
+static void *volatile null = NULL;
+
+/* Implementation of our FILE stream backend.  */
+
+static int bytes_read;
+static int cookie_valid = 0;
+struct Cookie {
+  const char *buffer;
+  int bufptr;
+  int bufsz;
+};
+
+#define VALIDATE_COOKIE() if (! cookie_valid) { \
+  FAIL ("call to %s after file closed", __FUNCTION__); \
+  return -1;    \
+  }
+
+static ssize_t
+io_read (void *vcookie, char *buf, size_t size)
+{
+  struct Cookie *cookie = (struct Cookie *) vcookie;
+
+  VALIDATE_COOKIE ();
+
+  if (size > cookie->bufsz - cookie->bufptr)
+    size = cookie->bufsz - cookie->bufptr;
+
+  memcpy (buf, cookie->buffer + cookie->bufptr, size);
+  cookie->bufptr += size;
+  bytes_read += size;
+  return size;
+}
+
+static ssize_t
+io_write (void *vcookie, const char *buf, size_t size)
+{
+  VALIDATE_COOKIE ();
+  FAIL_EXIT1 ("io_write called");
+}
+
+static int
+io_seek (void *vcookie, off64_t *position, int whence)
+{
+  VALIDATE_COOKIE ();
+  FAIL_EXIT1 ("io_seek called");
+}
+
+static int
+io_clean (void *vcookie)
+{
+  struct Cookie *cookie = (struct Cookie *) vcookie;
+
+  VALIDATE_COOKIE ();
+
+  cookie->buffer = NULL;
+  cookie->bufsz = 0;
+  cookie->bufptr = 0;
+
+  cookie_valid = 0;
+  free (cookie);
+  return 0;
+}
+
+cookie_io_functions_t io_funcs = {
+  .read = io_read,
+  .write = io_write,
+  .seek = io_seek,
+  .close = io_clean
+};
+
+FILE *
+io_open (const char *buffer, int buflen, const char *mode, void **vcookie)
+{
+  FILE *f;
+  struct Cookie *cookie;
+
+  cookie = (struct Cookie *) xcalloc (1, sizeof (struct Cookie));
+  *vcookie = cookie;
+  cookie_valid = 1;
+
+  cookie->buffer = buffer;
+  cookie->bufsz = buflen;
+  bytes_read = 0;
+
+  f = fopencookie (cookie, mode, io_funcs);
+  if (f == NULL)
+    FAIL_EXIT1 ("fopencookie failed");
+
+  clearerr (f);
+  return f;
+}
+
+/* The test cases.  */
+
+#define my_open(s,l,m) io_open (s, l, m, (void *) &cookie)
+
+#define TEST_COMPARE_0x11(buf, len)			\
+  TEST_COMPARE_BLOB (buf + (len), sizeof (buf) - (len),	\
+		     buf2, sizeof (buf) - (len));
+
+#define check_flags(f, expected_eof, expected_err)	\
+  {							\
+    if (expected_eof)					\
+      TEST_VERIFY (feof (f) != 0);			\
+    else						\
+      TEST_VERIFY (feof (f) == 0);			\
+    if (expected_err)					\
+      TEST_VERIFY (ferror (f) != 0);			\
+    else						\
+      TEST_VERIFY (ferror (f) == 0);			\
+  }
+
+static int
+do_test (void)
+{
+  FILE *f;
+  struct Cookie *cookie;
+  char buf [10];
+  char buf2 [10];
+  char *returned_string;
+
+  memset (buf2, 0x11, sizeof (buf2));
+
+  printf ("testing base operation...\n");
+  f = my_open ("hello\n", 6, "r");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == buf);
+  TEST_COMPARE_BLOB (buf, bytes_read + 1, "hello\n\0", 7);
+  TEST_COMPARE_0x11 (buf, bytes_read + 1);
+  check_flags (f, 0, 0);
+
+  fclose (f);
+
+  printf ("testing zero size file...\n");
+  f = my_open ("hello\n", 0, "r");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+  check_flags (f, 1, 0);
+  fclose (f);
+
+  printf ("testing zero size buffer...\n");
+  f = my_open ("hello\n", 6, "r");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, 0, f);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+  check_flags (f, 0, 0);
+  fclose (f);
+
+  printf ("testing NULL buffer with empty stream...\n");
+  f = my_open ("hello\n", 0, "r");
+  memset (buf, 0x11, sizeof (buf));
+
+  returned_string = fgets (null, sizeof (buf), f);
+
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+  check_flags (f, 1, 0);
+  fclose (f);
+
+  printf ("testing embedded NUL...\n");
+  f = my_open ("hel\0lo\n", 7, "r");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == buf);
+  TEST_COMPARE_BLOB (buf, bytes_read + 1, "hel\0lo\n\0", 8);
+  TEST_COMPARE_0x11 (buf, bytes_read + 1);
+  check_flags (f, 0, 0);
+  fclose (f);
+
+  printf ("testing writable stream...\n");
+  f = my_open ("hel\0lo\n", 7, "w");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+  check_flags (f, 0, 1);
+  fclose (f);
+
+  printf ("testing closed fd stream...\n");
+  int fd = open ("/dev/null", O_RDONLY);
+  f = fdopen (fd, "r");
+  close (fd);
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+  check_flags (f, 0, 1);
+  fclose (f);
+
+#ifdef IO_DEBUG
+  /* These tests only pass if glibc is built with -DIO_DEBUG, but are
+     included for reference.  */
+
+  printf ("testing NULL descriptor...\n");
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, null);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+
+  printf ("testing closed descriptor...\n");
+  f = my_open ("hello\n", 7, "r");
+  fclose (f);
+  memset (buf, 0x11, sizeof (buf));
+  returned_string = fgets (buf, sizeof (buf) - 1, f);
+  TEST_VERIFY (returned_string == NULL);
+  TEST_VERIFY (bytes_read == 0);
+#endif
+
+  return 0;
+}
+
+#include <support/test-driver.c>