libsysprof-capture: add writer buffer size helper

This could be useful to know what you can actually shove into the capture
file based on size.

src/libsysprof-capture/sysprof-capture-writer.c

@@ -1296,3 +1296,11 @@ sysprof_capture_writer_new_from_env (gsize buffer_size)
 
   return sysprof_capture_writer_new_from_fd (dup (fd), buffer_size);
 }
+
+gsize
+sysprof_capture_writer_get_buffer_size (SysprofCaptureWriter *self)
+{
+  g_return_val_if_fail (self != NULL, 0);
+
+  return self->len;
+}

src/libsysprof-capture/sysprof-capture-writer.h

@@ -36,6 +36,8 @@ SYSPROF_AVAILABLE_IN_ALL
 SysprofCaptureWriter *sysprof_capture_writer_new_from_fd     (int                                fd,
                                                               gsize                              buffer_size);
 SYSPROF_AVAILABLE_IN_ALL
+gsize                 sysprof_capture_writer_get_buffer_size (SysprofCaptureWriter              *self);
+SYSPROF_AVAILABLE_IN_ALL
 SysprofCaptureWriter *sysprof_capture_writer_ref             (SysprofCaptureWriter              *self);
 SYSPROF_AVAILABLE_IN_ALL
 void                  sysprof_capture_writer_unref           (SysprofCaptureWriter              *self);

src/tests/test-capture.c

@@ -36,6 +36,7 @@ test_reader_basic (void)
 
   writer = sysprof_capture_writer_new ("capture-file", 0);
   g_assert (writer != NULL);
+  g_assert_cmpint (sysprof_capture_writer_get_buffer_size (writer), ==, 4096*64);
 
   sysprof_capture_writer_flush (writer);