Add a new fwrite test for memory streams

Ensure that fwrite() behaves correctly when using memory streams.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

stdio-common/Makefile

@@ -223,6 +223,7 @@ tests := \
   tst-freopen64-3 \
   tst-fseek \
   tst-fwrite \
+  tst-fwrite-memstrm \
   tst-fwrite-ro \
   tst-getline \
   tst-getline-enomem \

stdio-common/tst-fwrite-memstrm.c

@@ -0,0 +1,177 @@
+/* Test fwrite on a memory stream.
+   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 <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+void
+test_ro (void)
+{
+  FILE *f;
+  char *out;
+
+  /* Try to allocate a small buffer for this test. */
+  out = malloc (2);
+  TEST_VERIFY_EXIT (out != NULL);
+
+  /* Try to open the allocated buffer as a read-only stream.  */
+  f = fmemopen (out, 2, "r");
+  TEST_VERIFY_EXIT (f != NULL);
+
+  /* Try to write to the temporary file with nmemb = 0, then check that
+     fwrite returns 0.  No errors are expected from this.  */
+  TEST_COMPARE (fwrite ("a", 1, 0, f), 0);
+  TEST_COMPARE (ferror (f), 0);
+
+  /* Try to write to the temporary file with size = 0, then check that
+     fwrite returns 0.  No errors are expected from this.  */
+  TEST_COMPARE (fwrite ("a", 0, 1, f), 0);
+  TEST_COMPARE (ferror (f), 0);
+
+  /* Try to write a single byte to the temporary file, then check that
+     fwrite returns 0.  Check if an error was reported.  */
+  TEST_COMPARE (fwrite ("a", 1, 1, f), 0);
+  TEST_COMPARE (ferror (f), 1);
+
+  clearerr (f);
+  xfclose (f);
+  free (out);
+}
+
+/* Length of the output buffer in bytes. */
+#define RWBUF_SIZE 16 * 1024
+/* Maximum number of bytes to be written in output buffer. The rest will be
+   used to check against overflow.  */
+#define RWBUF_SIZE_WRITABLE RWBUF_SIZE-2048
+
+/* Use the following byte to identify areas that should have not been
+   modified.  */
+#define KNOWN_BYTE 0xaa
+
+void
+test_one_rw (const char *in, size_t size, size_t nmemb,
+             size_t expected_ret)
+{
+  FILE *f;
+  char *out, *expected_out;
+  /* Total number of bytes expected to be written.  */
+  size_t expected_bytes = size * nmemb;
+
+  printf ("Testing with size = %zd, nmemb = %zd\n", size, nmemb);
+
+  TEST_VERIFY_EXIT (expected_ret <= RWBUF_SIZE_WRITABLE);
+  TEST_VERIFY_EXIT (expected_bytes <= RWBUF_SIZE_WRITABLE);
+
+  /* Try to allocate a buffer for this test and initialize it with
+     known contents.  */
+  out = malloc (RWBUF_SIZE);
+  TEST_VERIFY_EXIT (out != NULL);
+  memset (out, KNOWN_BYTE, RWBUF_SIZE);
+
+  /* Try to allocate a buffer and fill it with the contents that are expected
+     to be in memory after flushing/closing the memory stream.  */
+  expected_out = malloc (RWBUF_SIZE);
+  TEST_VERIFY_EXIT (expected_out != NULL);
+  if (expected_bytes > 0)
+    {
+      memcpy (expected_out, in, expected_bytes);
+      expected_out[expected_bytes] = 0;
+      memset (expected_out + expected_bytes + 1, KNOWN_BYTE,
+              RWBUF_SIZE - expected_bytes - 1);
+    }
+  else
+    {
+      /* No changes to the output are expected.  */
+      memset (expected_out, KNOWN_BYTE, RWBUF_SIZE);
+    }
+
+  /* Try to open the allocated buffer as a read-write stream.  */
+  f = fmemopen (out, RWBUF_SIZE, "w");
+  TEST_VERIFY_EXIT (f != NULL);
+
+  /* Try to write to the memory stream.  Check if fwrite() returns the
+     expected value. No errors are expected.  */
+  TEST_COMPARE (fwrite (in, size, nmemb, f), expected_ret);
+  TEST_COMPARE (ferror (f), 0);
+
+  xfclose (f);
+
+  /* Ensure the output has the expected contents. */
+  TEST_COMPARE (memcmp (out, expected_out, expected_bytes), 0);
+
+  free (expected_out);
+  free (out);
+}
+
+void
+test_rw (void)
+{
+  char * in;
+  int i, j;
+  size_t size[] = {1, 8, 11, 16, 17, 0};
+  size_t nmemb[] = {32, 83, 278, 709, 4097, RWBUF_SIZE / 2,
+                    RWBUF_SIZE_WRITABLE, 0};
+  size_t n;
+
+  /* Try to write to the temporary file with nmemb = 0, then check that
+     fwrite returns 0;  */
+  test_one_rw ("a", 1, 0, 0);
+
+  /* Try to write to the temporary file with size = 0, then check that
+     fwrite returns 0;  */
+  test_one_rw ("a", 0, 1, 0);
+
+  /* Try to write a single byte to the temporary file, then check that
+     fwrite returns 1;  */
+  test_one_rw ("a", 1, 2, 2);
+
+  in = malloc (RWBUF_SIZE);
+  TEST_VERIFY_EXIT (in != NULL);
+  for (i = 0; i < RWBUF_SIZE / 2; i++)
+    in[i] = i % 0xff;
+
+  /* Test with all posibilities of size[] x nmemb[].  */
+  for (i = 0; nmemb[i] != 0; i++)
+    {
+      for (j = 0; size[j] != 0; j++)
+        {
+          n = nmemb[i] / size[j];
+          test_one_rw (in, size[j], n, n);
+        }
+      /* Run the test with a single item of maximum size.  */
+      test_one_rw (in, nmemb[i], 1, 1);
+    }
+
+  free (in);
+}
+
+static int
+do_test (void)
+{
+  test_ro ();
+  test_rw ();
+
+  return 0;
+}
+
+#include <support/test-driver.c>