From 16dc419ff05d75e6ee27653c23a9023b24820358 Mon Sep 17 00:00:00 2001
From: Denny Biasiolli <dennybiasiolli@users.noreply.github.com>
Date: Sat, 19 Oct 2024 22:23:33 +0200
Subject: [PATCH] Pagination: allowing negative page numbers and offsets

---
 rest_framework/pagination.py | 15 ++++++++
 tests/test_pagination.py     | 70 ++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/rest_framework/pagination.py b/rest_framework/pagination.py
index a543ceeb5..c62212d1c 100644
--- a/rest_framework/pagination.py
+++ b/rest_framework/pagination.py
@@ -191,6 +191,7 @@ class PageNumberPagination(BasePagination):
     last_page_strings = ('last',)
 
     template = 'rest_framework/pagination/numbers.html'
+    allow_negative_page_numbers = False
 
     invalid_page_message = _('Invalid page.')
 
@@ -225,6 +226,14 @@ class PageNumberPagination(BasePagination):
         page_number = request.query_params.get(self.page_query_param) or 1
         if page_number in self.last_page_strings:
             page_number = paginator.num_pages
+        if self.allow_negative_page_numbers:
+            try:
+                page_number = int(page_number)
+                if page_number < 0:
+                    page_number = paginator.num_pages + page_number
+                return max(page_number, 0)
+            except ValueError:
+                return page_number
         return page_number
 
     def get_paginated_response(self, data):
@@ -384,6 +393,7 @@ class LimitOffsetPagination(BasePagination):
     offset_query_description = _('The initial index from which to return the results.')
     max_limit = None
     template = 'rest_framework/pagination/numbers.html'
+    allow_negative_offsets = False
 
     def paginate_queryset(self, queryset, request, view=None):
         self.request = request
@@ -447,6 +457,11 @@ class LimitOffsetPagination(BasePagination):
 
     def get_offset(self, request):
         try:
+            if self.allow_negative_offsets:
+                offset = int(request.query_params[self.offset_query_param])
+                if offset < 0:
+                    offset = self.count + offset
+                return max(offset, 0)
             return _positive_int(
                 request.query_params[self.offset_query_param],
             )
diff --git a/tests/test_pagination.py b/tests/test_pagination.py
index 02d443ade..f5fdedf2c 100644
--- a/tests/test_pagination.py
+++ b/tests/test_pagination.py
@@ -260,6 +260,40 @@ class TestPageNumberPagination:
         with pytest.raises(exceptions.NotFound):
             self.paginate_queryset(request)
 
+    def test_negative_page(self):
+        request = Request(factory.get('/', {'page': -1}))
+        print(request)
+        with pytest.raises(exceptions.NotFound):
+            self.paginate_queryset(request)
+
+    def test_allowed_negative_page(self):
+        self.pagination.allow_negative_page_numbers = True
+        request = Request(factory.get('/', {'page': -2}))
+        queryset = self.paginate_queryset(request)
+        content = self.get_paginated_content(queryset)
+        context = self.get_html_context()
+        assert queryset == [86, 87, 88, 89, 90]
+        assert content == {
+            'results': [86, 87, 88, 89, 90],
+            'previous': 'http://testserver/?page=17',
+            'next': 'http://testserver/?page=19',
+            'count': 100
+        }
+        assert context == {
+            'previous_url': 'http://testserver/?page=17',
+            'next_url': 'http://testserver/?page=19',
+            'page_links': [
+                PageLink('http://testserver/', 1, False, False),
+                PAGE_BREAK,
+                PageLink('http://testserver/?page=17', 17, False, False),
+                PageLink('http://testserver/?page=18', 18, True, False),
+                PageLink('http://testserver/?page=19', 19, False, False),
+                PageLink('http://testserver/?page=20', 20, False, False),
+            ]
+        }
+        assert self.pagination.display_page_controls
+        assert isinstance(self.pagination.to_html(), str)
+
     def test_get_paginated_response_schema(self):
         unpaginated_schema = {
             'type': 'object',
@@ -527,6 +561,42 @@ class TestLimitOffset:
         queryset = self.paginate_queryset(request)
         assert queryset == [1, 2, 3, 4, 5]
 
+    def test_negative_offset(self):
+        """
+        A negative offset query param should be treated as 0.
+        """
+        request = Request(factory.get('/', {'limit': 5, 'offset': -5}))
+        queryset = self.paginate_queryset(request)
+        assert queryset == [1, 2, 3, 4, 5]
+
+    def test_allowed_negative_offset(self):
+        """
+        A negative offset query param should be treated as `count - offset`.
+        """
+        self.pagination.allow_negative_offsets = True
+        request = Request(factory.get('/', {'limit': 5, 'offset': -10}))
+        queryset = self.paginate_queryset(request)
+        content = self.get_paginated_content(queryset)
+        context = self.get_html_context()
+        assert queryset == [91, 92, 93, 94, 95]
+        assert content == {
+            'results': [91, 92, 93, 94, 95],
+            'previous': 'http://testserver/?limit=5&offset=85',
+            'next': 'http://testserver/?limit=5&offset=95',
+            'count': 100
+        }
+        assert context == {
+            'previous_url': 'http://testserver/?limit=5&offset=85',
+            'next_url': 'http://testserver/?limit=5&offset=95',
+            'page_links': [
+                PageLink('http://testserver/?limit=5', 1, False, False),
+                PAGE_BREAK,
+                PageLink('http://testserver/?limit=5&offset=85', 18, False, False),
+                PageLink('http://testserver/?limit=5&offset=90', 19, True, False),
+                PageLink('http://testserver/?limit=5&offset=95', 20, False, False),
+            ]
+        }
+
     def test_invalid_limit(self):
         """
         An invalid limit query param should be ignored in favor of the default.