tests: Add test for >4GB reads with g_file_load_contents()

The tests - one for sync, one for async - create a sparse file for
this purpose, so this should be cheap on the fileystem.

Of course, the test still allocates >4GB of memory for the data that it
returns from g_file_load_contents(), I hope the CI test runners can deal
with that.

gio/tests/file.c

@@ -2928,6 +2928,144 @@ test_load_bytes_async (void)
   g_main_loop_unref (data.main_loop);
 }
 
+static const gsize testfile_4gb_size = ((gsize) 1 << 32) + (1 << 16); /* 4GB + a bit */
+
+/* @filename will be modified as per g_mkstemp() */
+static gboolean
+create_testfile_4gb_or_skip (char *filename)
+{
+  GError *error = NULL;
+  int fd;
+  int ret;
+
+  fd = g_mkstemp (filename);
+  g_assert_cmpint (fd, !=, -1);
+  ret = ftruncate (fd, testfile_4gb_size);
+  g_clear_fd (&fd, &error);
+  g_assert_no_error (error);
+  if (ret == 1)
+    {
+      g_test_skip ("Could not create testfile >4GB");
+      g_assert_no_errno (g_unlink (filename));
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static void
+check_testfile_4gb_contents (const char *data,
+                             gsize       len)
+{
+  gsize i;
+
+  g_assert_nonnull (data);
+  g_assert_cmpuint (testfile_4gb_size, ==, len);
+
+  for (i = 0; i < testfile_4gb_size; i++)
+    {
+      if (data[i] != 0)
+        break;
+    }
+  g_assert_cmpint (i, ==, testfile_4gb_size);
+}
+
+static void
+test_load_contents_4gb (void)
+{
+  char filename[] = "g_file_load_contents_4gb_XXXXXX";
+  GError *error = NULL;
+  gboolean result;
+  char *data;
+  gsize len;
+  GFile *file;
+
+  if (!create_testfile_4gb_or_skip (filename))
+    return;
+
+  file = g_file_new_for_path (filename);
+  result = g_file_load_contents (file, NULL, &data, &len, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (result);
+
+  check_testfile_4gb_contents (data, len);
+
+  g_file_delete (file, NULL, NULL);
+
+  g_free (data);
+  g_object_unref (file);
+}
+
+static void
+load_contents_4gb_cb (GObject      *object,
+                      GAsyncResult *result,
+                      gpointer      user_data)
+{
+  GAsyncResult **result_out = user_data;
+
+  g_assert (*result_out == NULL);
+  *result_out = g_object_ref (result);
+
+  g_main_context_wakeup (NULL);
+}
+
+static void
+test_load_contents_4gb_async (void)
+{
+  char filename[] = "g_file_load_contents_4gb_async_XXXXXX";
+  GFile *file;
+  GAsyncResult *async_result = NULL;
+  GError *error = NULL;
+  char *data;
+  gsize len;
+  gboolean ret;
+
+  if (!create_testfile_4gb_or_skip (filename))
+    return;
+
+  file = g_file_new_for_path (filename);
+  g_file_load_contents_async (file, NULL, load_contents_4gb_cb, &async_result);
+
+  while (async_result == NULL)
+    g_main_context_iteration (NULL, TRUE);
+
+  ret = g_file_load_contents_finish (file, async_result, &data, &len, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (ret);
+
+  check_testfile_4gb_contents (data, len);
+
+  g_file_delete (file, NULL, NULL);
+
+  g_free (data);
+  g_object_unref (async_result);
+  g_object_unref (file);
+}
+
+static void
+test_load_bytes_4gb (void)
+{
+  char filename[] = "g_file_load_bytes_4gb_XXXXXX";
+  GError *error = NULL;
+  GBytes *bytes;
+  GFile *file;
+
+  if (!create_testfile_4gb_or_skip (filename))
+    return;
+
+  file = g_file_new_for_path (filename);
+  bytes = g_file_load_bytes (file, NULL, NULL, &error);
+  g_assert_no_error (error);
+  g_assert_true (bytes);
+
+  check_testfile_4gb_contents (g_bytes_get_data (bytes, NULL), g_bytes_get_size (bytes));
+
+  g_file_delete (file, NULL, NULL);
+
+  g_bytes_unref (bytes);
+  g_object_unref (file);
+}
+
 static void
 test_writev_helper (GOutputVector *vectors,
                     gsize          n_vectors,
@@ -4230,6 +4368,9 @@ main (int argc, char *argv[])
   g_test_add_func ("/file/measure-async", test_measure_async);
   g_test_add_func ("/file/load-bytes", test_load_bytes);
   g_test_add_func ("/file/load-bytes-async", test_load_bytes_async);
+  g_test_add_func ("/file/load-bytes-4gb", test_load_bytes_4gb);
+  g_test_add_func ("/file/load-contents-4gb", test_load_contents_4gb);
+  g_test_add_func ("/file/load-contents-4gb-async", test_load_contents_4gb_async);
   g_test_add_func ("/file/writev", test_writev);
   g_test_add_func ("/file/writev/no-bytes-written", test_writev_no_bytes_written);
   g_test_add_func ("/file/writev/no-vectors", test_writev_no_vectors);