[sysprof] cursor: handle NULL readers gracefully

[Christian Hergert <chergert src gnome org>]

commit 843585e00de143f2176cf1ad299f0554bd5fea1c
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 23 15:30:12 2021 -0800

    cursor: handle NULL readers gracefully
    
    Fixes #55

 src/libsysprof-capture/sysprof-capture-cursor.c | 22 +++++++++++++---------
 src/tests/test-capture-cursor.c                 | 11 +++++++++++
 2 files changed, 24 insertions(+), 9 deletions(-)
---
diff --git a/src/libsysprof-capture/sysprof-capture-cursor.c b/src/libsysprof-capture/sysprof-capture-cursor.c
index cf11bcd..6d4c83a 100644
--- a/src/libsysprof-capture/sysprof-capture-cursor.c
+++ b/src/libsysprof-capture/sysprof-capture-cursor.c
@@ -151,9 +151,11 @@ sysprof_capture_cursor_foreach (SysprofCaptureCursor         *self,
                                 void                         *user_data)
 {
   assert (self != NULL);
-  assert (self->reader != NULL);
   assert (callback != NULL);
 
+  if (self->reader == NULL)
+    return;
+
   for (;;)
     {
       const SysprofCaptureFrame *frame;
@@ -260,9 +262,9 @@ void
 sysprof_capture_cursor_reset (SysprofCaptureCursor *self)
 {
   assert (self != NULL);
-  assert (self->reader != NULL);
 
-  sysprof_capture_reader_reset (self->reader);
+  if (self->reader != NULL)
+    sysprof_capture_reader_reset (self->reader);
 }
 
 void
@@ -305,18 +307,20 @@ sysprof_capture_cursor_add_condition (SysprofCaptureCursor    *self,
  * sysprof_capture_cursor_new:
  * @self: a #SysprofCaptureCursor
  *
- * Returns: (transfer full): a new cursor for @reader
+ * Returns: (transfer full) (nullable): a new cursor for @reader
  */
 SysprofCaptureCursor *
 sysprof_capture_cursor_new (SysprofCaptureReader *reader)
 {
   SysprofCaptureCursor *self;
 
-  assert (reader != NULL);
-
   self = sysprof_capture_cursor_init ();
-  self->reader = sysprof_capture_reader_copy (reader);
-  sysprof_capture_reader_reset (self->reader);
+
+  if (reader != NULL)
+    {
+      self->reader = sysprof_capture_reader_copy (reader);
+      sysprof_capture_reader_reset (self->reader);
+    }
 
   return self;
 }
@@ -326,7 +330,7 @@ sysprof_capture_cursor_new (SysprofCaptureReader *reader)
  *
  * Gets the underlying reader that is used by the cursor.
  *
- * Returns: (transfer none): An #SysprofCaptureReader
+ * Returns: (transfer none) (nullable): An #SysprofCaptureReader
  */
 SysprofCaptureReader *
 sysprof_capture_cursor_get_reader (SysprofCaptureCursor *self)
diff --git a/src/tests/test-capture-cursor.c b/src/tests/test-capture-cursor.c
index 9dc2e6c..1549d71 100644
--- a/src/tests/test-capture-cursor.c
+++ b/src/tests/test-capture-cursor.c
@@ -69,6 +69,16 @@ test_cursor_basic (void)
   g_unlink ("capture-cursor-file");
 }
 
+static void
+test_cursor_null (void)
+{
+  SysprofCaptureCursor *cursor = sysprof_capture_cursor_new (NULL);
+  gint count = 0;
+  sysprof_capture_cursor_foreach (cursor, increment, &count);
+  g_assert_cmpint (count, ==, 0);
+  g_clear_pointer (&cursor, sysprof_capture_cursor_unref);
+}
+
 int
 main (int argc,
       char *argv[])
@@ -76,5 +86,6 @@ main (int argc,
   sysprof_clock_init ();
   g_test_init (&argc, &argv, NULL);
   g_test_add_func ("/SysprofCaptureCursor/basic", test_cursor_basic);
+  g_test_add_func ("/SysprofCaptureCursor/null", test_cursor_null);
   return g_test_run ();
 }