duplicate `get_page_size` and related properties from PageNumberPagination

rest_framework/pagination.py

@@ -491,13 +491,26 @@ class CursorPagination(BasePagination):
     http://cramer.io/2011/03/08/building-cursors-for-the-disqus-api/
     """
     cursor_query_param = 'cursor'
+
+    # The default page size.
+    # Defaults to `None`, meaning pagination is disabled.
     page_size = api_settings.PAGE_SIZE
+
+    # Client can control the page size using this query parameter.
+    # Default is 'None'. Set to eg 'page_size' to enable usage.
+    page_size_query_param = None
+
+    # Set to an integer to limit the maximum page size the client may request.
+    # Only relevant if 'page_size_query_param' has also been set.
+    max_page_size = None
+
     invalid_cursor_message = _('Invalid cursor')
     ordering = '-created'
     template = 'rest_framework/pagination/previous_and_next.html'
 
     def paginate_queryset(self, queryset, request, view=None):
-        if self.page_size is None:
+        self.page_size = self.get_page_size(request)
+        if not self.page_size:
             return None
 
         self.base_url = request.build_absolute_uri()
@@ -577,6 +590,19 @@ class CursorPagination(BasePagination):
 
         return self.page
 
+    def get_page_size(self, request):
+        if self.page_size_query_param:
+            try:
+                return _positive_int(
+                    request.query_params[self.page_size_query_param],
+                    strict=True,
+                    cutoff=self.max_page_size
+                )
+            except (KeyError, ValueError):
+                pass
+
+        return self.page_size
+
     def get_next_link(self):
         if not self.has_next:
             return None