Merge branch 'tc-git-tower-pagination-links' into 'master'

API: do not set rel="next" pagination header when no records found

Closes #36618

See merge request !13629

changelogs/unreleased/tc-git-tower-pagination-links.yml

+---
+title: Improve API pagination headers when no record found
+merge_request: 13629
+author: Jordan Patterson
+type: fixed

lib/api/helpers/pagination.rb

@@ -11,7 +11,7 @@ module API
 
       def add_pagination_headers(paginated_data)
         header 'X-Total',       paginated_data.total_count.to_s
-        header 'X-Total-Pages', paginated_data.total_pages.to_s
+        header 'X-Total-Pages', total_pages(paginated_data).to_s
         header 'X-Per-Page',    paginated_data.limit_value.to_s
         header 'X-Page',        paginated_data.current_page.to_s
         header 'X-Next-Page',   paginated_data.next_page.to_s
@@ -26,20 +26,25 @@ module API
 
         links = []
 
-        request_params[:page] = paginated_data.current_page - 1
-        links << %(<#{request_url}?#{request_params.to_query}>; rel="prev") unless paginated_data.first_page?
+        request_params[:page] = paginated_data.prev_page
+        links << %(<#{request_url}?#{request_params.to_query}>; rel="prev") if request_params[:page]
 
-        request_params[:page] = paginated_data.current_page + 1
-        links << %(<#{request_url}?#{request_params.to_query}>; rel="next") unless paginated_data.last_page?
+        request_params[:page] = paginated_data.next_page
+        links << %(<#{request_url}?#{request_params.to_query}>; rel="next") if request_params[:page]
 
         request_params[:page] = 1
         links << %(<#{request_url}?#{request_params.to_query}>; rel="first")
 
-        request_params[:page] = paginated_data.total_pages
+        request_params[:page] = total_pages(paginated_data)
         links << %(<#{request_url}?#{request_params.to_query}>; rel="last")
 
         links.join(', ')
       end
+
+      def total_pages(paginated_data)
+        # Ensure there is in total at least 1 page
+        [paginated_data.total_pages, 1].max
+      end
     end
   end
 end

spec/lib/api/helpers/pagination_spec.rb

@@ -52,7 +52,13 @@ describe API::Helpers::Pagination do
           expect_header('X-Page', '1')
           expect_header('X-Next-Page', '2')
           expect_header('X-Prev-Page', '')
-          expect_header('Link', any_args)
+
+          expect_header('Link', anything) do |_key, val|
+            expect(val).to include('rel="first"')
+            expect(val).to include('rel="last"')
+            expect(val).to include('rel="next"')
+            expect(val).not_to include('rel="prev"')
+          end
 
           subject.paginate(resource)
         end
@@ -75,15 +81,53 @@ describe API::Helpers::Pagination do
           expect_header('X-Page', '2')
           expect_header('X-Next-Page', '')
           expect_header('X-Prev-Page', '1')
-          expect_header('Link', any_args)
+
+          expect_header('Link', anything) do |_key, val|
+            expect(val).to include('rel="first"')
+            expect(val).to include('rel="last"')
+            expect(val).to include('rel="prev"')
+            expect(val).not_to include('rel="next"')
+          end
+
+          subject.paginate(resource)
+        end
+      end
+    end
+
+    context 'when resource empty' do
+      describe 'first page' do
+        before do
+          allow(subject).to receive(:params)
+            .and_return({ page: 1, per_page: 2 })
+        end
+
+        it 'returns appropriate amount of resources' do
+          expect(subject.paginate(resource).count).to eq 0
+        end
+
+        it 'adds appropriate headers' do
+          expect_header('X-Total', '0')
+          expect_header('X-Total-Pages', '1')
+          expect_header('X-Per-Page', '2')
+          expect_header('X-Page', '1')
+          expect_header('X-Next-Page', '')
+          expect_header('X-Prev-Page', '')
+
+          expect_header('Link', anything) do |_key, val|
+            expect(val).to include('rel="first"')
+            expect(val).to include('rel="last"')
+            expect(val).not_to include('rel="prev"')
+            expect(val).not_to include('rel="next"')
+            expect(val).not_to include('page=0')
+          end
 
           subject.paginate(resource)
         end
       end
     end
 
-    def expect_header(name, value)
-      expect(subject).to receive(:header).with(name, value)
+    def expect_header(*args, &block)
+      expect(subject).to receive(:header).with(*args, &block)
     end
 
     def expect_message(method)